34LikesWARNING - LiPo "C" Discharge Ratings are INVALID!
01-30-2018, 02:55 PM
#1
WARNING - LiPo "C" Discharge Ratings are INVALID!
(If a moderator is available, this thread may prove useful as a "Sticky")
QUICK REFERENCE GUIDE:
In this thread, you will learn why there is no such thing as an accurate "C Rating" on ANY battery that is manufactured today. However, here is a quick summary: If you want more amperage from a LiPo battery, buy a larger mAH capacity pack. Its almost an accurate way of choosing batteries.
TRUE LiPo Amperage Rating = Highest Internal Resistance of a given LiPo battery pack, when measured CORRECTLY, plugged into this LiPo Performance calculator along with its capacity in mAh: Lipoly Objective Performance Calculation Tool REV5.xlsx
TRUE C Rating = TRUE LiPo Amperage Rating divided by 1/1000 of given LiPo's capacity (mAh), or divided by given LiPo's Ah.
CORRECT method of measuring Internal Resistance is discussed in this thread. Guidelines for choosing wiring and connectors for various setups are included in 02/04/2018 update towards bottom of post.
NOW ON TO THE TREAD, EXPLANATION, AND DISCUSSION:
Spoiler ALERT - This is a LONG thread, but it is important for your safety that you know this information, so please take the time to read the entire thread carefully, and use the included links to further your knowledge.
Hobby Grade RC - It is fast, thrilling, action-packed, and is a ton of fun. The hobby is a blast, and I recommend it to everyone that I know. However, the hobby is also very technical, and can be dangerous at times as well.
Today we are here to talk about the most dangerous part of the RC hobby: Lithium-Polymer batteries. These batteries are so dangerous because their chemical and Lithium Metal composition makes them incredibly volatile.
A simple puncture, overcharging, over-discharging, or even just throwing the thing hard enough at a wall can cause the battery to internally short, creating extreme heat that can cause an explosion, fire, or release deadly chloride fumes. See short video example:
However, we aren't here to discuss LiPo safety. Oh wait, we are, but not that side of it. You see, for years, the standard advertising practice used by companies who make Lithium-Polymer batteries is to display the discharge and amperage rating as a term called "C". Simply put, C equals one thousandth of a battery's capacity in mAH or simply one times its Ah. Lets take this Two-Cell (2S) 7.4V, 7200mAh/60C/120C SMC Racing LiPo that I own and use it as an example throughout this thread. So, 1C of this battery equals 7.2 amps of electrical current. 7200mAH divided by 1000 or 7.2Ah divided by 1.
The smaller 60C rating is the rating for continuous amperage draw, while the higher 120C rating is the burst amperage rating. So the standard practice by us consumers has been to take the lower number, in this case "60C" discharge rating and multiply it by 7.2, or one thousandth of the chosen LiPo's capacity, and use the result to determine weather or not a battery is suitable for use with our chosen ESC and motor. In my case, my battery is rated to handle 432 amps of continuous discharge according to the manufacturers C rating. I drive a full-size Volkswagen GTI, and the battery used to start it is a fairly high-grade, expensive automotive battery rated at 450 amps. Wow, that little 2S LiPo sure looks quite impressive, doesn't it?
Well here is the thing... Marketing departments of companies are given the task of making their product sell, using whatever means necessary. These companies exaggerate the ratings of their products so their products will sell when competing with other companies. In this thread, you will find out just how exaggerated these ratings are, and you will also learn how to determine the TRUE, SAFE amount of current you can load on your battery. To give you a hint before we begin going over the facts, my SMC Racing 2S/7200mAh/60C/120C battery was ACTUALLY only capable of dealing with a continuous load of 137 amps when it was brand new. Curious to see why? Then continue on reading.
To explain why my battery and indeed ALL LiPo batteries on the market are incapable of performing to their advertised "C" ratings, we have to go back a few years. At this time, a curious man (who shall remain nameless) decided to take a 2S 5000mAh/40C/80C LiPo and perform a few tests on it (battery manufacturer was never reviled in his findings). The very first test was to charge the battery to its maximum 8.4V and then simulate a 190 amp load using a custom-made regenerative/resistance discharger (VERY DANGEROUS, DO NOT ATTEMPT!). He plugged his device into his laptop via USB and used custom software to create a 190 amp load on his battery. This should be perfectly acceptable according to the manufacturer as the C rating would indicate that his battery is capable of handling a 200 amp continuous load.
To explain what happened, I must first explain that in order for an amperage rating to be valid, the battery MUST be able to safely take a load equal to that rating while ALSO delivering the battery's full rated capacity. So what did the man find? Well luckily the battery didn't explode, but it did "puff up", a problem commonly found in LiPo's when they experience over-charging or a load they simply can not handle. The stress causes the LiPo cells to swell and bust out of their casing. NEVER attempt to use a LiPo that has busted out of its case. The curious man found that the battery had only put out a mere 842mAh before becoming completely discharged down to 6.01V. Due to the trauma the battery had experienced throughout his test, combined with the swelling of the battery, the the battery was no longer safe for use, and had to be discarded.
This event started getting RC hobby enthusiasts to look into the nature of C ratings. They began running tests on batteries from many different manufacturers, using a new type of testing methodology that until then was only used by battery manufacturers themselves, to determine the correct amperage ratings of their batteries. This will be discussed and their testing will be linked later on. For now we must learn why C ratings even are listed on battery packs if they are untrue. Well, they are true, in a way, but not true in the way you would imagine.
A manufacturers posted "Continuous C" rate is ACTUALLY the absolute maximum amperage that it's battery can deliver, regardless of the outcome or consequences. To put this in perspective, my SMC Racing LiPo is capable of delivering the 432 amps that it is rated for, however loading the battery with that amperage continuously would completely destroy the cells, and the battery would need to be replaced. Also, this load could cause a fire, explosion, or the release of chlorine gasses, so DO NOT EVER ATTEMPT IT! In fact, according to the USA Military, no Lithium-Polymer battery pack is capable of more than a TRUE 50 C rating using materials, technologies, and manufacturing processes available today.
So now that we know why C ratings are completely invalid, lets look at the correct way of determining your LiPo's SAFE continuous discharge amperage rating. The RC enthusiasts who began data logging LiPo performance, have a Lithium-Polymer performance tool here:Lipoly Objective Performance Calculation Tool REV5.xlsx This tool uses the same exact values for calculating LiPo amperage as testing engineers do at actual LiPo factories themselves, so it is very accurate! However, to most enthusiasts it just looks like a bunch of incomprehensible gibberish.
So how do we use this performance tool? How do we find the values they are looking for? Well there is only one value that you need to find, and unfortunately it requires a high grade, modern charger as a lot of chargers do not feature this tool and so cannot determine the required value. This value is the Internal Resistance (IR) of a battery. Higher-Grade chargers have a tool used for measuring IR in their menu choices.
To measure IR correctly, you must first determine if your pack is ready for accurate testing. If your pack has been in storage for more than two weeks, you will need to fully discharge the battery down to 3.1V per cell and then fully recharge and balance the battery to 4.2V per cell. Discharging and then re-charging your battery is referred to as a "Full Cycle". For batteries that have been in storage over 2 months, 2 Full Cycles will be required for accurate testing. For batteries that have been in storage for a year or longer, 3 Full Cycles will be required for accurate testing.
Once your battery is ready for testing, select the "Balance Charge" option on your charger and allow the battery to fully charge to it's 4.20V per cell nominal fully charged state. To get the best IR reading (lower is better), the battery's temperature has to be nominal as well. So after fully charging the battery, UNPLUG the battery (IMPORTANT) and allow it to sit, cool, and settle at room temperature for a period of AT LEAST 60 minutes, 90-120 minutes is preferable. According to the testers, 72 degrees F is the best temperature for both the internals of the battery as well as the external air temperature. Take note that after resting and stabilizing, the battery's temperature is very sensitive. If you pick up the battery, the heat transferred from your hand is enough to alter the results, so be careful! After your LiPo has settled and cooled for the minimum period, you can then reconnect you battery to your charger (balance connection is REQUIRED), and head to your charger's IR meter. (IMPORTANT - If you attempt to use the IR meter at a voltage other than 4.20V per cell, or if the battery has not been allowed to cool and stabilize, you will get EXTREMELY inaccurate readings, so follow the instructions CAREFULLY!)
Once at the IR meter, record the IR of each individual cell in the LiPo pack. The highest IR of all the cells is what you will use to plug into the LiPo performance tool for accurate calculation. Additionally, you can optionally choose to record the individual voltage of each cell given within a battery pack using the "battery meter" tool located in most chargers' menu options. This data may be optional but is relevant and will help determine even more accurate results. Voltage tends to drop in batteries that sit fully charged for long periods of time, possibly changing the accuracy of your results.
Now it is time to head to the LiPo performance tool and calculate your results. Enter your IR and LiPo capacity into the performance tool. You will notice that the third value: "Figure of Merit" will be automatically calculated. This calculation may be slightly incorrect as the number was generated by a database containing data from other tests used to determine an average for batteries with certain IR and capacities. However, do not be concerned. If there is any miscalculation, it will be minuscule. The FOM term is extremely complex, but there is a link at the bottom of the LiPo Performance Tool page if you wish to research it. TAKE NOTE: IR tends to increase as a battery ages and is subjected to more cycles, I recommend that you record the IR of your batteries annually and use the results in the LiPo performance tool to determine if they are still suitable for use in your setup. To make this convenient, take the measurement before heading out to run your vehicle. Simply plan a running day and charge you batteries earlier so you can allow them to cool and stabilize, and take a reading before you head out.
Well, there you go! The number displayed in the final, bottom box is your battery's TRUE, SAFE rating for continuous amperage! As for me, the IR of my SMC LiPos was 2.3 back when they were brand new, so plug that into the calculator along with it's 7200 mAh capacity and you will see that my batteries were capable of 137 amps continuous load/discharge when they were new. So what do our findings mean? What batteries are safe to use in what applications?
Well, when it comes to electric motors, there are 3 states of amperage pull that should be considered when choosing a Lithium-Polymer battery pack for purchasing. I will use my owned Tekin T8 Gen 2 4038 2250Kv 4S brushless truggy motor as an example. The three different ratings to be considered are continuous amperage draw, amperage draw under acceleration, and burst amperage.
Lets go ahead and dismiss burst amperage right away. Batteries and ESC's alike are designed with burst amperage in mind and so if your ESC and battery are rated to handle the motor's continuous amperage, then they will surely deal with its bursts as well. Amperage bursting occurs only in certain situations and only lasts for 1/10-1/4 of a second. Say your vehicle is at a stand still, and you are about to punch the throttle straight to 100%. If your ESC has "launch" or "punch" settings and this setting is set to maximum, then only at this point of slamming from a stop to 100% throttle will you ever see an amperage burst. It is the draw created when a motor is under absolute MAXIMUM stress, just starting up to move the vehicle and experiences a draw spike to get the vehicle moving. The T8 4038 motors can generate spikes/bursts up to 150 amps, and regularly hit 120 amps!
So which draw is more important then? Continuous draw or draw under acceleration? The answer is draw under acceleration. Continuous draw is the draw created by the motor once the vehicle has already reached its target speed. It is the draw created to maintain that speed, under NO acceleration, and is therefore a quite lower draw than acceleration or burst amperage. Continuous motor draw is a minor issue. T8 4038 Motors tend to draw around 50-60 Amps in this state.
So, draw under acceleration. Why is it so important? Well, because you will use it every day, and alot. Every time you accelerate your vehicle you can experience close to the maximum acceleration draw after the burst and for those few seconds you are getting your vehicle up to speed if you are at 100% throttle. This draw occurs so often while driving that it could be considered a secondary type of continuous draw, rather than a separate category. When determining the TRUE, Safe amperage of your battery, you want that result to be equal to or greater than the acceleration draw of your chosen motor.
The T8 4038 motors draw around 85-100 amps under acceleration. Therefore, to be safe using a Tekin T8 4038 powered system, you MUST use a battery capable of a TRUE rating of at least 100 continuous amps.
Now this is assuming that you are using 4S LiPo power to run this motor. As you decrease voltage (3S,2S,1S), the required amperage to perform the same task increases in a fairly linear way. So on 2S, you will be required to use a battery capable of 200 continuous amps to power a Tekin T8 4038 motor safely. Trust me, the only batteries currently on the market that are TRULY capable of 200 continuous amps are ones that will completely empty your wallet. Running your vehicle on anything other than its intended voltage range is NOT RECOMMENDED! (1/8th: 4-6S, 1:10th: 2-3S, ect.)
This thread will update as new, related information becomes available.
If you want to further research the topic of fake C ratings versus true amperage ratings, then I invite you to type "LiPo Fake C Rating" into Google. Enjoy the research!
USEFUL LINKS:
LiPo Performance Tool (TRUE Amperage found HERE): Lipoly Objective Performance Calculation Tool REV5.xlsx
LiPo Performance testing database: https://www.rcgroups.com/forums/show...e#post20484169
LiPo Performance tool explanation (how it was created): https://www.rcgroups.com/forums/show...rformance-tool
Video Explaining Wiring Connectors and their amperage ratings:
RC Wiring amperage limitations information: https://www.rcgroups.com/forums/show...10&postcount=7
If you have tested your batteries CORRECTLY and have results to share, please post them in the comments below! You can also share your findings in the LiPo testing performance database. HOWEVER, TAKE NOTE that the database thread is STRICTLY a database thread and is NOT to be used for discussions! They also require that you use specific equipment for posting in the database. If you want to discuss your results, please see the LiPo performance tool explanation thread, or simply discuss your results here. ALSO NOTE, for results to be valid for use in the official database then specific details such as age, and number of cycles must be EXACTLY ACCURATE and available for posting.
I hoped this thread explained true amperage ratings, and I hope it means we can all be safer enjoying the best hobby on the planet!
UPDATE 02/01/2018:
Testing Completed! All 4 of my SMC Racing 2S/7200mAh/60C/120C pack results are fairly good!
Battery Information: 4X SMC Racing 7.4V (2S) LiPo - 7400mAh/60C/120C Rated - 4mm Inboard connectors - 10AWG wire
Battery Age: Approx. 36 Months
# of cycles on battery: Approx. 250 - 300 FULL cycles (High of 4.2V per cell and Low of 3.1V per cell)
Estimated Battery condition: Nearing end of Life Cycle, will be disposed soon
Testing Equipment: Hitec X2 AC Plus Smart Charger (Not capable of decimal places in IR readings)
Methodology: Batteries cycled down to 6.4V (3.2V per Cell) and back up to 8.4V (4.2V per cell) twice. All batteries sat to cool and stabilize for 120 minutes after charging, ambient temperature 68 degrees F. All batteries achieved a voltage of either 8.39 or 8.40V after the charge.
Values were recorded using the "BATTERY RESISTANCE" and "BATTERY METER" options on the X2 AC Plus charger.
RESULTS AFTER 120 MINUTES OF STABILIZATION:
Battery 1: Cell 1 - 4.06V, IR is 11; Cell 2 - 4.18V, IR is 2; calculated safe amperage is 63 continuous amps
Battery 2: Cell 1 - 4.19V, IR is 4; Cell 2 - 4.11V, IR is 2; calculated safe amperage is 104 continuous amps
Battery 3: Cell 1 - 4.09V, IR is 6; Cell 2 - 4.16V, IR is 3; calculated safe amperage is 85 continuous amps
Battery 4: Cell 1 - 4.17V, IR is 5; Cell 2 - 4.13V, IR is 5; calculated safe amperage is 93 continuous amps
Highest Calculated TRUE C Rating: 14.444C (104 continuous amps divided by 7.2 capacity) (19.028 C rating when batteries were new)
Are results valid for use in the official database: No, batteries are too old, Battery 1 may have a damaged cell, and testing equipment is not substantial enough.
Summary: While I do not own equipment capable of a truly accurate reading, these results do show how age has affected my packs. When they were new, they were all capable of 137 amps of continuous current. Notice how the IR tends to favor Cell 2 in each of the packs, Cell 1 seems to always have the higher IR for me. These batteries may just be suitable for use in my 1/8th truggy considering my readings were probably not all that accurate due to equipment limitations. However, they will not be suitable for long. I have yet to decide weather or not I will be running these batteries again at all. If so, Battery 1 has been marked as potentially damaged and will be run with battery 2 to help pick up the slack. Thankfully over-drawing current by a few amps is generally accepted as not being dangerous. It will probably destroy the cells completely over time, but should not explode or cause a fire in any way, so I am comfortable using them on a 100 amp draw system considering they need replacing anyways, might as well finish them off with some fun. All batteries took about 6500mAh input when charging from 6.4V to 8.4V, none of the batteries are "puffed" at all and will be disposed of immediately if puffing ever occurs during use.
What have I learned: SMC Racing LiPos are incredible, they are the only company currently posting TRUE IR-based amperage ratings in the titles of their Lithium-Polymer batteries pages as well as under the "specifications" tab. I highly encourage you to check out their selection! The easiest way of navigating their website is to hover your mouse over the "Batteries" tab in the upper-left hand corner of the page, and selecting batteries via your desired voltage [I.E. 7.4V (2S), 11.1V (3S), ect.] You may be saying "but your batteries performed quite badly!" but keep in mind that they are 3 years old and have been subjected to hundreds of cycles. At this age, ANY LiPo would struggle to give a good reading. In fact I would say these batteries have outperformed any other LiPos I have ever owned, and yes that does include my old Maxamps battery. I never tested the Maxamps because it failed after about 14 months. SMC Racing: https://www.smc-racing.net/
BONUS LESSON - EXTENDING THE LIFE OF YOUR LITHIUM-BASED BATTERIES:
Because of the composition of Lithium-Polymer batteries, the cells do not like being subjected to full cycles. Much the same as smart phone batteries that loose the ability to hold a charge over its lifetime of being repeatedly charged, Lithium-Polymer batteries also loose their ability to hold a charge and their ability to put out good amperage over time and as more cycles are performed. If a LiPo had its own way, it would probably choose to sit at 3.8V per cell (Storage Mode) and never perform a cycle.
You can slow down the aging process by not charging or discharging your batteries fully. Discharging fully does the most damage, so to have your batteries last for years and get hundreds of cycles more than the life cycle rating, then set your ESC cutoff voltage to 3.3V per cell or more, and then if possible, set your charger's maximum charge target voltage to 4.0-4.1V per cell. As you lower the percentage of full cycles you are subjecting your batteries to, the damage done to the lifespan of the battery is also reduced, so go as high on cut-off voltage as possible, and as low on charging voltage as possible. ONLY charge or discharge your batteries completely when necessary, such as championship race days.
Yes, you will see a drop in run time, however your batteries will have a much longer life span overall and will perform consistently throughout that lifetime. Plus, a smaller cycle also means a lower amount of time required to recharge the battery, so it should "level out". Allowing your batteries to cool after a run, before putting them on a charger is important for prolonging life as well. The same rule is applied to letting your batteries cool after a charge before running them. The 60-120 minutes stabilization time is unnecessary in this scenario. A decent 10-15 minutes or until cool-to-the-touch is adequate. 800-1000 cycle lives of Lithium-Polymer batteries is technically possible, however this would require ridiculously small cycles and short run times combined with EXTREME attention to detail, so I wouldn't bother attempting this feat.
Keeping your batteries as cool as possible while running and charging will also prolong the life of the batteries. Battery temperature increases as they are put under more and more stress. So, to keep your batteries as cool as possible while charging, charge at the minimum rate you are comfortable with (Less than 1C charging rate is highly recommended, around 0.8C seems to work perfectly for me - 6.0 Amps charge rate for my 7200mAh SMC Lipos). To keep your batteries as cool as possible during running, avoid running your vehicle on extremely hot days if possible, and select batteries that are considered overkill for your setup. A battery that can handle 150 amps of continuous load will stay much cooler while running a T8 motor than a battery that is only capable of 100 continuous amps. As a general rule of thumb, purchasing the highest mAh capacity batteries that you can afford and will fit into your vehicle is a good rule to go by.
SMC Racing offers very high capacity and amperage batteries for very reasonable prices and most of these batteries are ROAR approved. They currently offer a 4S 7400mAh/149 Amp/90C battery for just $80, even less expensive than a comparable Gens Ace. This is the battery I will be purchasing to run my 1/8th scale racing truggy and all of my 1/8th scale bashing rigs. The power of this battery is simply IMMENSE and is capable of powering any 1/8th scale vehicle designed for 4S-6S operation under just about any circumstances without breaking a sweat. The only exception would be speed runs. Due to higher gearing and high-traction asphalt, speed running causes a brushless motor to draw an IMMENSE amount of amperage. For this situation, SMC Racing offers a 4S EXTREME EDITION 6000mAh/190 Amp/150C Lipo battery for $90 that is a good choice. Take note that in their product description they specifically state that the extreme edition batteries are not intended for daily use, and are to be used only when necessary.
SMC 4S 7400mAh/149 Amp/90C LiPo: https://www.smc-racing.net/index.php...product_id=491
SMC 4S 6000mAh/190 Amp/150C EXTREME LiPo: https://www.smc-racing.net/index.php...product_id=395
SMC also offers high capacity and extreme edition batteries in other voltages.
Battery University - How to Prolong the life of Lithium-Based Batteries: How to Prolong Lithium-based Batteries - Battery University
(The topic is Lithium-Ion cellular batteries, however the same principle does apply to Lithium-Polymer)
UPDATE 02/04/2018:
YouTube Video found with accurate testing of several popular LiPo battery packs! Check it out here:
CHOOSING CORRECT WIRING AND CONNECTORS FOR YOUR SETUP:
It can often be confusing to decide just how large in diameter you need your wires to be to run a certain application. The same can said for connectors. Most RC enthusiasts assume that 12AWG and Deans connectors are suitable for just about any application. In fact, this is a DANGEROUS assumption and can lead to electrical fires that are sure to ruin your day.
12AWG wiring is capable of 50-60 continuous amps and can handle bursts up to 100 amps. Deans Ultra connectors and any other connectors based off the same plug style and size are also only capable of 50-60 continuous amps and bursts up to 100 amps. This makes 12AWG wiring and Deans Ultra connectors very suited for one another, but they are only suitable for use in models running 1/10 scale motors or smaller.
1/8th scale vehicles tend to draw more than 12AWG wire or Deans connectors are SAFELY capable of handling. In 1/8th scale applications it is recommended to use 10AWG wire and connectors capable of 90 continuous amps or higher. The two-digit number next to a connectors name represents its amperage rating in MOST cases. For example, an XT90 connector is capable of 90 continuous amps and is acceptable for use in 1/8th scale applications.
Sparking is another issue when it comes to connectors. After your ESC has been disconnected for a few seconds, the capacitors inside the ESC are drained of their electrical charge. When you connect a battery to your ESC, the capacitors draw a massive spike of electrical power to charge up, even if your ESC is switched off. This sudden draw is what causes the "connection spark" commonly found in most electronics setups.
The power and size of a spark increases as the amount of Voltage being supplied increases. While 1S and 2S LiPo users won't experience much of an issue, 3S and 4S users will begin to notice issues such as degrading/burning/corroding connectors over time. As you approach very high voltages such as 6S-10S for large scale cars and helicopters, the spark gets quite dangerous and can easily start fires. This is why I recommend AS 150 connectors for all applications up to 1/8th scale vehicles. With a continuous amperage limit of 150 amps, combined with a spark-arresting female tip, they are the safest possible choice for 1/10 and 1/8th scale vehicles. There are also spark-arresting versions of the XT90 connectors available on the market.
It is VERY IMPORTANT that ALL THREE areas of main wiring are rated to handle the acceleration current of your motor. For example, if you have 10AWG wiring on your ESC input leads but only have 12AWG leads coming out of the battery and are running a Tekin T8 motor, you are at SERIOUS RISK of electrical fire. Larger wires leading into smaller wires creates a choke point in the electrical system that means increased heat and electrical resistance. Now if you have overkill wires on the ESC (8AWG for a Tekin T8 motor) and 10AWG battery leads you may think this is okay. Technically it is, but it is still a choke point and is not recommended. Wiring between ESC, Motor, and Battery should be IDENTICAL for best results.
This can create some problems for users who purchase LiPos with smaller gauge leads but need larger gauge wires for their application. LiPo battery packs are NOT RECOMMENDED to be disassembled or modified in any way as they are extremely dangerous to work with. If you have no other choice, proceed with EXTREME CAUTION! Alternatively, next time you purchase batteries and need different wiring, I would recommend contacting the manufacturer and discussing the possibility of a custom order.
I am personally not comfortable with disassembling a LiPo battery pack. Therefore, if a LiPo does not include the correct gauge leads for my purposes, I will simply not purchase the battery.
So what is the right choice for your setup? Well here are some guidelines that should help you decide (use acceleration amperage draw from motor to decide):
150-200 Amp Draw (1/5 Scale): 8AWG Wire Minimum; 8mm Bullet connectors rated for 200+ amps minimum; Spark Arrest REQUIRED
80-100 Amp Draw (1/8 Scale): 10AWG Wire Minimum; XT90, 6mm Bullet, or 90+ continuous amp rated connector minimum; Spark Arrest highly recommended
40-60 Amp Draw (1/10 - 1/12 Scale): 12AWG Wire Minimum; Deans Ultra, 5mm Bullet or 60+ continuous amp rated connector minimum; Spark Arrest optional but recommended
39 Amp Draw and below (1/14 and smaller Scale): 14AWG Wire Minimum, Deans, 4mm Bullet or 40+ continuous amp rated connector minimum; Spark Arrest unnecessary but recommended
DISCLAIMER: Although EXTREMELY unlikely, I am not responsible for any damage or harm done by using this information. I am also not affiliated with SMC racing or any of its partners. I simply enjoy and appreciate the honesty and integrity of SMC and I choose to support them by purchasing their products.
QUICK REFERENCE GUIDE:
In this thread, you will learn why there is no such thing as an accurate "C Rating" on ANY battery that is manufactured today. However, here is a quick summary: If you want more amperage from a LiPo battery, buy a larger mAH capacity pack. Its almost an accurate way of choosing batteries.
TRUE LiPo Amperage Rating = Highest Internal Resistance of a given LiPo battery pack, when measured CORRECTLY, plugged into this LiPo Performance calculator along with its capacity in mAh: Lipoly Objective Performance Calculation Tool REV5.xlsx
TRUE C Rating = TRUE LiPo Amperage Rating divided by 1/1000 of given LiPo's capacity (mAh), or divided by given LiPo's Ah.
CORRECT method of measuring Internal Resistance is discussed in this thread. Guidelines for choosing wiring and connectors for various setups are included in 02/04/2018 update towards bottom of post.
NOW ON TO THE TREAD, EXPLANATION, AND DISCUSSION:
Spoiler ALERT - This is a LONG thread, but it is important for your safety that you know this information, so please take the time to read the entire thread carefully, and use the included links to further your knowledge.
Hobby Grade RC - It is fast, thrilling, action-packed, and is a ton of fun. The hobby is a blast, and I recommend it to everyone that I know. However, the hobby is also very technical, and can be dangerous at times as well.
Today we are here to talk about the most dangerous part of the RC hobby: Lithium-Polymer batteries. These batteries are so dangerous because their chemical and Lithium Metal composition makes them incredibly volatile.
A simple puncture, overcharging, over-discharging, or even just throwing the thing hard enough at a wall can cause the battery to internally short, creating extreme heat that can cause an explosion, fire, or release deadly chloride fumes. See short video example:
However, we aren't here to discuss LiPo safety. Oh wait, we are, but not that side of it. You see, for years, the standard advertising practice used by companies who make Lithium-Polymer batteries is to display the discharge and amperage rating as a term called "C". Simply put, C equals one thousandth of a battery's capacity in mAH or simply one times its Ah. Lets take this Two-Cell (2S) 7.4V, 7200mAh/60C/120C SMC Racing LiPo that I own and use it as an example throughout this thread. So, 1C of this battery equals 7.2 amps of electrical current. 7200mAH divided by 1000 or 7.2Ah divided by 1.
The smaller 60C rating is the rating for continuous amperage draw, while the higher 120C rating is the burst amperage rating. So the standard practice by us consumers has been to take the lower number, in this case "60C" discharge rating and multiply it by 7.2, or one thousandth of the chosen LiPo's capacity, and use the result to determine weather or not a battery is suitable for use with our chosen ESC and motor. In my case, my battery is rated to handle 432 amps of continuous discharge according to the manufacturers C rating. I drive a full-size Volkswagen GTI, and the battery used to start it is a fairly high-grade, expensive automotive battery rated at 450 amps. Wow, that little 2S LiPo sure looks quite impressive, doesn't it?
Well here is the thing... Marketing departments of companies are given the task of making their product sell, using whatever means necessary. These companies exaggerate the ratings of their products so their products will sell when competing with other companies. In this thread, you will find out just how exaggerated these ratings are, and you will also learn how to determine the TRUE, SAFE amount of current you can load on your battery. To give you a hint before we begin going over the facts, my SMC Racing 2S/7200mAh/60C/120C battery was ACTUALLY only capable of dealing with a continuous load of 137 amps when it was brand new. Curious to see why? Then continue on reading.
To explain why my battery and indeed ALL LiPo batteries on the market are incapable of performing to their advertised "C" ratings, we have to go back a few years. At this time, a curious man (who shall remain nameless) decided to take a 2S 5000mAh/40C/80C LiPo and perform a few tests on it (battery manufacturer was never reviled in his findings). The very first test was to charge the battery to its maximum 8.4V and then simulate a 190 amp load using a custom-made regenerative/resistance discharger (VERY DANGEROUS, DO NOT ATTEMPT!). He plugged his device into his laptop via USB and used custom software to create a 190 amp load on his battery. This should be perfectly acceptable according to the manufacturer as the C rating would indicate that his battery is capable of handling a 200 amp continuous load.
To explain what happened, I must first explain that in order for an amperage rating to be valid, the battery MUST be able to safely take a load equal to that rating while ALSO delivering the battery's full rated capacity. So what did the man find? Well luckily the battery didn't explode, but it did "puff up", a problem commonly found in LiPo's when they experience over-charging or a load they simply can not handle. The stress causes the LiPo cells to swell and bust out of their casing. NEVER attempt to use a LiPo that has busted out of its case. The curious man found that the battery had only put out a mere 842mAh before becoming completely discharged down to 6.01V. Due to the trauma the battery had experienced throughout his test, combined with the swelling of the battery, the the battery was no longer safe for use, and had to be discarded.
This event started getting RC hobby enthusiasts to look into the nature of C ratings. They began running tests on batteries from many different manufacturers, using a new type of testing methodology that until then was only used by battery manufacturers themselves, to determine the correct amperage ratings of their batteries. This will be discussed and their testing will be linked later on. For now we must learn why C ratings even are listed on battery packs if they are untrue. Well, they are true, in a way, but not true in the way you would imagine.
A manufacturers posted "Continuous C" rate is ACTUALLY the absolute maximum amperage that it's battery can deliver, regardless of the outcome or consequences. To put this in perspective, my SMC Racing LiPo is capable of delivering the 432 amps that it is rated for, however loading the battery with that amperage continuously would completely destroy the cells, and the battery would need to be replaced. Also, this load could cause a fire, explosion, or the release of chlorine gasses, so DO NOT EVER ATTEMPT IT! In fact, according to the USA Military, no Lithium-Polymer battery pack is capable of more than a TRUE 50 C rating using materials, technologies, and manufacturing processes available today.
So now that we know why C ratings are completely invalid, lets look at the correct way of determining your LiPo's SAFE continuous discharge amperage rating. The RC enthusiasts who began data logging LiPo performance, have a Lithium-Polymer performance tool here:Lipoly Objective Performance Calculation Tool REV5.xlsx This tool uses the same exact values for calculating LiPo amperage as testing engineers do at actual LiPo factories themselves, so it is very accurate! However, to most enthusiasts it just looks like a bunch of incomprehensible gibberish.
So how do we use this performance tool? How do we find the values they are looking for? Well there is only one value that you need to find, and unfortunately it requires a high grade, modern charger as a lot of chargers do not feature this tool and so cannot determine the required value. This value is the Internal Resistance (IR) of a battery. Higher-Grade chargers have a tool used for measuring IR in their menu choices.
To measure IR correctly, you must first determine if your pack is ready for accurate testing. If your pack has been in storage for more than two weeks, you will need to fully discharge the battery down to 3.1V per cell and then fully recharge and balance the battery to 4.2V per cell. Discharging and then re-charging your battery is referred to as a "Full Cycle". For batteries that have been in storage over 2 months, 2 Full Cycles will be required for accurate testing. For batteries that have been in storage for a year or longer, 3 Full Cycles will be required for accurate testing.
Once your battery is ready for testing, select the "Balance Charge" option on your charger and allow the battery to fully charge to it's 4.20V per cell nominal fully charged state. To get the best IR reading (lower is better), the battery's temperature has to be nominal as well. So after fully charging the battery, UNPLUG the battery (IMPORTANT) and allow it to sit, cool, and settle at room temperature for a period of AT LEAST 60 minutes, 90-120 minutes is preferable. According to the testers, 72 degrees F is the best temperature for both the internals of the battery as well as the external air temperature. Take note that after resting and stabilizing, the battery's temperature is very sensitive. If you pick up the battery, the heat transferred from your hand is enough to alter the results, so be careful! After your LiPo has settled and cooled for the minimum period, you can then reconnect you battery to your charger (balance connection is REQUIRED), and head to your charger's IR meter. (IMPORTANT - If you attempt to use the IR meter at a voltage other than 4.20V per cell, or if the battery has not been allowed to cool and stabilize, you will get EXTREMELY inaccurate readings, so follow the instructions CAREFULLY!)
Once at the IR meter, record the IR of each individual cell in the LiPo pack. The highest IR of all the cells is what you will use to plug into the LiPo performance tool for accurate calculation. Additionally, you can optionally choose to record the individual voltage of each cell given within a battery pack using the "battery meter" tool located in most chargers' menu options. This data may be optional but is relevant and will help determine even more accurate results. Voltage tends to drop in batteries that sit fully charged for long periods of time, possibly changing the accuracy of your results.
Now it is time to head to the LiPo performance tool and calculate your results. Enter your IR and LiPo capacity into the performance tool. You will notice that the third value: "Figure of Merit" will be automatically calculated. This calculation may be slightly incorrect as the number was generated by a database containing data from other tests used to determine an average for batteries with certain IR and capacities. However, do not be concerned. If there is any miscalculation, it will be minuscule. The FOM term is extremely complex, but there is a link at the bottom of the LiPo Performance Tool page if you wish to research it. TAKE NOTE: IR tends to increase as a battery ages and is subjected to more cycles, I recommend that you record the IR of your batteries annually and use the results in the LiPo performance tool to determine if they are still suitable for use in your setup. To make this convenient, take the measurement before heading out to run your vehicle. Simply plan a running day and charge you batteries earlier so you can allow them to cool and stabilize, and take a reading before you head out.
Well, there you go! The number displayed in the final, bottom box is your battery's TRUE, SAFE rating for continuous amperage! As for me, the IR of my SMC LiPos was 2.3 back when they were brand new, so plug that into the calculator along with it's 7200 mAh capacity and you will see that my batteries were capable of 137 amps continuous load/discharge when they were new. So what do our findings mean? What batteries are safe to use in what applications?
Well, when it comes to electric motors, there are 3 states of amperage pull that should be considered when choosing a Lithium-Polymer battery pack for purchasing. I will use my owned Tekin T8 Gen 2 4038 2250Kv 4S brushless truggy motor as an example. The three different ratings to be considered are continuous amperage draw, amperage draw under acceleration, and burst amperage.
Lets go ahead and dismiss burst amperage right away. Batteries and ESC's alike are designed with burst amperage in mind and so if your ESC and battery are rated to handle the motor's continuous amperage, then they will surely deal with its bursts as well. Amperage bursting occurs only in certain situations and only lasts for 1/10-1/4 of a second. Say your vehicle is at a stand still, and you are about to punch the throttle straight to 100%. If your ESC has "launch" or "punch" settings and this setting is set to maximum, then only at this point of slamming from a stop to 100% throttle will you ever see an amperage burst. It is the draw created when a motor is under absolute MAXIMUM stress, just starting up to move the vehicle and experiences a draw spike to get the vehicle moving. The T8 4038 motors can generate spikes/bursts up to 150 amps, and regularly hit 120 amps!
So which draw is more important then? Continuous draw or draw under acceleration? The answer is draw under acceleration. Continuous draw is the draw created by the motor once the vehicle has already reached its target speed. It is the draw created to maintain that speed, under NO acceleration, and is therefore a quite lower draw than acceleration or burst amperage. Continuous motor draw is a minor issue. T8 4038 Motors tend to draw around 50-60 Amps in this state.
So, draw under acceleration. Why is it so important? Well, because you will use it every day, and alot. Every time you accelerate your vehicle you can experience close to the maximum acceleration draw after the burst and for those few seconds you are getting your vehicle up to speed if you are at 100% throttle. This draw occurs so often while driving that it could be considered a secondary type of continuous draw, rather than a separate category. When determining the TRUE, Safe amperage of your battery, you want that result to be equal to or greater than the acceleration draw of your chosen motor.
The T8 4038 motors draw around 85-100 amps under acceleration. Therefore, to be safe using a Tekin T8 4038 powered system, you MUST use a battery capable of a TRUE rating of at least 100 continuous amps.
Now this is assuming that you are using 4S LiPo power to run this motor. As you decrease voltage (3S,2S,1S), the required amperage to perform the same task increases in a fairly linear way. So on 2S, you will be required to use a battery capable of 200 continuous amps to power a Tekin T8 4038 motor safely. Trust me, the only batteries currently on the market that are TRULY capable of 200 continuous amps are ones that will completely empty your wallet. Running your vehicle on anything other than its intended voltage range is NOT RECOMMENDED! (1/8th: 4-6S, 1:10th: 2-3S, ect.)
This thread will update as new, related information becomes available.
If you want to further research the topic of fake C ratings versus true amperage ratings, then I invite you to type "LiPo Fake C Rating" into Google. Enjoy the research!
USEFUL LINKS:
LiPo Performance Tool (TRUE Amperage found HERE): Lipoly Objective Performance Calculation Tool REV5.xlsx
LiPo Performance testing database: https://www.rcgroups.com/forums/show...e#post20484169
LiPo Performance tool explanation (how it was created): https://www.rcgroups.com/forums/show...rformance-tool
Video Explaining Wiring Connectors and their amperage ratings:
RC Wiring amperage limitations information: https://www.rcgroups.com/forums/show...10&postcount=7
If you have tested your batteries CORRECTLY and have results to share, please post them in the comments below! You can also share your findings in the LiPo testing performance database. HOWEVER, TAKE NOTE that the database thread is STRICTLY a database thread and is NOT to be used for discussions! They also require that you use specific equipment for posting in the database. If you want to discuss your results, please see the LiPo performance tool explanation thread, or simply discuss your results here. ALSO NOTE, for results to be valid for use in the official database then specific details such as age, and number of cycles must be EXACTLY ACCURATE and available for posting.
I hoped this thread explained true amperage ratings, and I hope it means we can all be safer enjoying the best hobby on the planet!
UPDATE 02/01/2018:
Testing Completed! All 4 of my SMC Racing 2S/7200mAh/60C/120C pack results are fairly good!
Battery Information: 4X SMC Racing 7.4V (2S) LiPo - 7400mAh/60C/120C Rated - 4mm Inboard connectors - 10AWG wire
Battery Age: Approx. 36 Months
# of cycles on battery: Approx. 250 - 300 FULL cycles (High of 4.2V per cell and Low of 3.1V per cell)
Estimated Battery condition: Nearing end of Life Cycle, will be disposed soon
Testing Equipment: Hitec X2 AC Plus Smart Charger (Not capable of decimal places in IR readings)
Methodology: Batteries cycled down to 6.4V (3.2V per Cell) and back up to 8.4V (4.2V per cell) twice. All batteries sat to cool and stabilize for 120 minutes after charging, ambient temperature 68 degrees F. All batteries achieved a voltage of either 8.39 or 8.40V after the charge.
Values were recorded using the "BATTERY RESISTANCE" and "BATTERY METER" options on the X2 AC Plus charger.
RESULTS AFTER 120 MINUTES OF STABILIZATION:
Battery 1: Cell 1 - 4.06V, IR is 11; Cell 2 - 4.18V, IR is 2; calculated safe amperage is 63 continuous amps
Battery 2: Cell 1 - 4.19V, IR is 4; Cell 2 - 4.11V, IR is 2; calculated safe amperage is 104 continuous amps
Battery 3: Cell 1 - 4.09V, IR is 6; Cell 2 - 4.16V, IR is 3; calculated safe amperage is 85 continuous amps
Battery 4: Cell 1 - 4.17V, IR is 5; Cell 2 - 4.13V, IR is 5; calculated safe amperage is 93 continuous amps
Highest Calculated TRUE C Rating: 14.444C (104 continuous amps divided by 7.2 capacity) (19.028 C rating when batteries were new)
Are results valid for use in the official database: No, batteries are too old, Battery 1 may have a damaged cell, and testing equipment is not substantial enough.
Summary: While I do not own equipment capable of a truly accurate reading, these results do show how age has affected my packs. When they were new, they were all capable of 137 amps of continuous current. Notice how the IR tends to favor Cell 2 in each of the packs, Cell 1 seems to always have the higher IR for me. These batteries may just be suitable for use in my 1/8th truggy considering my readings were probably not all that accurate due to equipment limitations. However, they will not be suitable for long. I have yet to decide weather or not I will be running these batteries again at all. If so, Battery 1 has been marked as potentially damaged and will be run with battery 2 to help pick up the slack. Thankfully over-drawing current by a few amps is generally accepted as not being dangerous. It will probably destroy the cells completely over time, but should not explode or cause a fire in any way, so I am comfortable using them on a 100 amp draw system considering they need replacing anyways, might as well finish them off with some fun. All batteries took about 6500mAh input when charging from 6.4V to 8.4V, none of the batteries are "puffed" at all and will be disposed of immediately if puffing ever occurs during use.
What have I learned: SMC Racing LiPos are incredible, they are the only company currently posting TRUE IR-based amperage ratings in the titles of their Lithium-Polymer batteries pages as well as under the "specifications" tab. I highly encourage you to check out their selection! The easiest way of navigating their website is to hover your mouse over the "Batteries" tab in the upper-left hand corner of the page, and selecting batteries via your desired voltage [I.E. 7.4V (2S), 11.1V (3S), ect.] You may be saying "but your batteries performed quite badly!" but keep in mind that they are 3 years old and have been subjected to hundreds of cycles. At this age, ANY LiPo would struggle to give a good reading. In fact I would say these batteries have outperformed any other LiPos I have ever owned, and yes that does include my old Maxamps battery. I never tested the Maxamps because it failed after about 14 months. SMC Racing: https://www.smc-racing.net/
BONUS LESSON - EXTENDING THE LIFE OF YOUR LITHIUM-BASED BATTERIES:
Because of the composition of Lithium-Polymer batteries, the cells do not like being subjected to full cycles. Much the same as smart phone batteries that loose the ability to hold a charge over its lifetime of being repeatedly charged, Lithium-Polymer batteries also loose their ability to hold a charge and their ability to put out good amperage over time and as more cycles are performed. If a LiPo had its own way, it would probably choose to sit at 3.8V per cell (Storage Mode) and never perform a cycle.
You can slow down the aging process by not charging or discharging your batteries fully. Discharging fully does the most damage, so to have your batteries last for years and get hundreds of cycles more than the life cycle rating, then set your ESC cutoff voltage to 3.3V per cell or more, and then if possible, set your charger's maximum charge target voltage to 4.0-4.1V per cell. As you lower the percentage of full cycles you are subjecting your batteries to, the damage done to the lifespan of the battery is also reduced, so go as high on cut-off voltage as possible, and as low on charging voltage as possible. ONLY charge or discharge your batteries completely when necessary, such as championship race days.
Yes, you will see a drop in run time, however your batteries will have a much longer life span overall and will perform consistently throughout that lifetime. Plus, a smaller cycle also means a lower amount of time required to recharge the battery, so it should "level out". Allowing your batteries to cool after a run, before putting them on a charger is important for prolonging life as well. The same rule is applied to letting your batteries cool after a charge before running them. The 60-120 minutes stabilization time is unnecessary in this scenario. A decent 10-15 minutes or until cool-to-the-touch is adequate. 800-1000 cycle lives of Lithium-Polymer batteries is technically possible, however this would require ridiculously small cycles and short run times combined with EXTREME attention to detail, so I wouldn't bother attempting this feat.
Keeping your batteries as cool as possible while running and charging will also prolong the life of the batteries. Battery temperature increases as they are put under more and more stress. So, to keep your batteries as cool as possible while charging, charge at the minimum rate you are comfortable with (Less than 1C charging rate is highly recommended, around 0.8C seems to work perfectly for me - 6.0 Amps charge rate for my 7200mAh SMC Lipos). To keep your batteries as cool as possible during running, avoid running your vehicle on extremely hot days if possible, and select batteries that are considered overkill for your setup. A battery that can handle 150 amps of continuous load will stay much cooler while running a T8 motor than a battery that is only capable of 100 continuous amps. As a general rule of thumb, purchasing the highest mAh capacity batteries that you can afford and will fit into your vehicle is a good rule to go by.
SMC Racing offers very high capacity and amperage batteries for very reasonable prices and most of these batteries are ROAR approved. They currently offer a 4S 7400mAh/149 Amp/90C battery for just $80, even less expensive than a comparable Gens Ace. This is the battery I will be purchasing to run my 1/8th scale racing truggy and all of my 1/8th scale bashing rigs. The power of this battery is simply IMMENSE and is capable of powering any 1/8th scale vehicle designed for 4S-6S operation under just about any circumstances without breaking a sweat. The only exception would be speed runs. Due to higher gearing and high-traction asphalt, speed running causes a brushless motor to draw an IMMENSE amount of amperage. For this situation, SMC Racing offers a 4S EXTREME EDITION 6000mAh/190 Amp/150C Lipo battery for $90 that is a good choice. Take note that in their product description they specifically state that the extreme edition batteries are not intended for daily use, and are to be used only when necessary.
SMC 4S 7400mAh/149 Amp/90C LiPo: https://www.smc-racing.net/index.php...product_id=491
SMC 4S 6000mAh/190 Amp/150C EXTREME LiPo: https://www.smc-racing.net/index.php...product_id=395
SMC also offers high capacity and extreme edition batteries in other voltages.
Battery University - How to Prolong the life of Lithium-Based Batteries: How to Prolong Lithium-based Batteries - Battery University
(The topic is Lithium-Ion cellular batteries, however the same principle does apply to Lithium-Polymer)
UPDATE 02/04/2018:
YouTube Video found with accurate testing of several popular LiPo battery packs! Check it out here:
CHOOSING CORRECT WIRING AND CONNECTORS FOR YOUR SETUP:
It can often be confusing to decide just how large in diameter you need your wires to be to run a certain application. The same can said for connectors. Most RC enthusiasts assume that 12AWG and Deans connectors are suitable for just about any application. In fact, this is a DANGEROUS assumption and can lead to electrical fires that are sure to ruin your day.
12AWG wiring is capable of 50-60 continuous amps and can handle bursts up to 100 amps. Deans Ultra connectors and any other connectors based off the same plug style and size are also only capable of 50-60 continuous amps and bursts up to 100 amps. This makes 12AWG wiring and Deans Ultra connectors very suited for one another, but they are only suitable for use in models running 1/10 scale motors or smaller.
1/8th scale vehicles tend to draw more than 12AWG wire or Deans connectors are SAFELY capable of handling. In 1/8th scale applications it is recommended to use 10AWG wire and connectors capable of 90 continuous amps or higher. The two-digit number next to a connectors name represents its amperage rating in MOST cases. For example, an XT90 connector is capable of 90 continuous amps and is acceptable for use in 1/8th scale applications.
Sparking is another issue when it comes to connectors. After your ESC has been disconnected for a few seconds, the capacitors inside the ESC are drained of their electrical charge. When you connect a battery to your ESC, the capacitors draw a massive spike of electrical power to charge up, even if your ESC is switched off. This sudden draw is what causes the "connection spark" commonly found in most electronics setups.
The power and size of a spark increases as the amount of Voltage being supplied increases. While 1S and 2S LiPo users won't experience much of an issue, 3S and 4S users will begin to notice issues such as degrading/burning/corroding connectors over time. As you approach very high voltages such as 6S-10S for large scale cars and helicopters, the spark gets quite dangerous and can easily start fires. This is why I recommend AS 150 connectors for all applications up to 1/8th scale vehicles. With a continuous amperage limit of 150 amps, combined with a spark-arresting female tip, they are the safest possible choice for 1/10 and 1/8th scale vehicles. There are also spark-arresting versions of the XT90 connectors available on the market.
It is VERY IMPORTANT that ALL THREE areas of main wiring are rated to handle the acceleration current of your motor. For example, if you have 10AWG wiring on your ESC input leads but only have 12AWG leads coming out of the battery and are running a Tekin T8 motor, you are at SERIOUS RISK of electrical fire. Larger wires leading into smaller wires creates a choke point in the electrical system that means increased heat and electrical resistance. Now if you have overkill wires on the ESC (8AWG for a Tekin T8 motor) and 10AWG battery leads you may think this is okay. Technically it is, but it is still a choke point and is not recommended. Wiring between ESC, Motor, and Battery should be IDENTICAL for best results.
This can create some problems for users who purchase LiPos with smaller gauge leads but need larger gauge wires for their application. LiPo battery packs are NOT RECOMMENDED to be disassembled or modified in any way as they are extremely dangerous to work with. If you have no other choice, proceed with EXTREME CAUTION! Alternatively, next time you purchase batteries and need different wiring, I would recommend contacting the manufacturer and discussing the possibility of a custom order.
I am personally not comfortable with disassembling a LiPo battery pack. Therefore, if a LiPo does not include the correct gauge leads for my purposes, I will simply not purchase the battery.
So what is the right choice for your setup? Well here are some guidelines that should help you decide (use acceleration amperage draw from motor to decide):
150-200 Amp Draw (1/5 Scale): 8AWG Wire Minimum; 8mm Bullet connectors rated for 200+ amps minimum; Spark Arrest REQUIRED
80-100 Amp Draw (1/8 Scale): 10AWG Wire Minimum; XT90, 6mm Bullet, or 90+ continuous amp rated connector minimum; Spark Arrest highly recommended
40-60 Amp Draw (1/10 - 1/12 Scale): 12AWG Wire Minimum; Deans Ultra, 5mm Bullet or 60+ continuous amp rated connector minimum; Spark Arrest optional but recommended
39 Amp Draw and below (1/14 and smaller Scale): 14AWG Wire Minimum, Deans, 4mm Bullet or 40+ continuous amp rated connector minimum; Spark Arrest unnecessary but recommended
DISCLAIMER: Although EXTREMELY unlikely, I am not responsible for any damage or harm done by using this information. I am also not affiliated with SMC racing or any of its partners. I simply enjoy and appreciate the honesty and integrity of SMC and I choose to support them by purchasing their products.
Last edited by wallacengineeri; 12-18-2018 at 07:38 AM.
01-30-2018, 07:04 PM
#3
EDIT: What I mean specifically is that most people are aware that C ratings are inaccurate, but then they have no idea how to determine the actual safe amperage for their batteries
Last edited by wallacengineeri; 01-30-2018 at 07:15 PM.
01-30-2018, 07:24 PM
#4
I use one of these to determine a batteries true C rating
To date the best I have seen is 24C
Universal ESR Analysis Meter - ProgressiveRC
To date the best I have seen is 24C
Universal ESR Analysis Meter - ProgressiveRC
01-30-2018, 07:29 PM
#5
I use one of these to determine a batteries true C rating
To date the best I have seen is 24C
Universal ESR Analysis Meter - ProgressiveRC
To date the best I have seen is 24C
Universal ESR Analysis Meter - ProgressiveRC
01-30-2018, 07:39 PM
#7
Yes I am aware, it is posted in the thread as a part of the instructions. But the best known testing methodology is to charge the pack and fully balance, then allow to settle for 60-120 minutes, then take IR readings.
Last edited by wallacengineeri; 01-30-2018 at 07:50 PM.
01-31-2018, 05:31 AM
#11
Thanks for the tutorial on how to calculate C ratings, though I would prefer you move the formula to the top of the OP so folks can quickly reference the method later instead of having to scroll down through a wall of text to get to the formula.
Is this really true? Trying not to get sarcastic here ( I am a fan of SMC) but this really sounds like a fan boy elitism comment that could turn many people away. I'm sure there are other brands who post accurate C ratings, but without personally testing every single brand on the planet, I just don't see how this statement can be anything but false 
What have I learned: SMC Racing LiPos are incredible, they are the only company currently posting TRUE IR-based amperage ratings
01-31-2018, 06:09 AM
#12
Thanks for the tutorial on how to calculate C ratings, though I would prefer you move the formula to the top of the OP so folks can quickly reference the method later instead of having to scroll down through a wall of text to get to the formula.
Is this really true? Trying not to get sarcastic here ( I am a fan of SMC) but this really sounds like a fan boy elitism comment that could turn many people away. I'm sure there are other brands who post accurate C ratings, but without personally testing every single brand on the planet, I just don't see how this statement can be anything but false
Is this really true? Trying not to get sarcastic here ( I am a fan of SMC) but this really sounds like a fan boy elitism comment that could turn many people away. I'm sure there are other brands who post accurate C ratings, but without personally testing every single brand on the planet, I just don't see how this statement can be anything but false
A while ago, SMC attempted to sell a "TRUE C" rated pack, but because the number was so low, nobody bought it, and it really hurt the reputation of the company. Now, they include the TRUE IR-Based amperage alongside the "Doomsday C Rating" so they can advertise high C ratings while retaining their honesty and integrity. They even have an article on their OWN website explaining that their OWN C ratings are bogus and to pay attention to the amperage instead. THAT is how honest they are.
I will NEVER, EVER buy another brand of LiPo so long as SMC is around to sell me theirs.
I appreciate the owners will to sacrifice the reputation of his company in order to ensure that consumers are provided with SAFE, correct information that will help them avoid electrical fires and explosions. I also appreciate the sheer value of the product you get for the money spent. I mean come on, you can spend $80 for a 4S LiPo that performs JUST AS WELL, IF NOT BETTER than a comparable $150-$200 4S LiPo on the market today. How can I say no to that?
SMC Racing C Rates and other information article: https://www.smc-racing.net/index.php...egory&path=163
On another note, how do I move my results post up to just under the OP? Or should I copy-paste the test into the OP and just delete the post?
Last edited by wallacengineeri; 01-31-2018 at 06:27 AM.
01-31-2018, 06:35 AM
#13
Thanks for the tutorial on how to calculate C ratings, though I would prefer you move the formula to the top of the OP so folks can quickly reference the method later instead of having to scroll down through a wall of text to get to the formula.
Is this really true? Trying not to get sarcastic here ( I am a fan of SMC) but this really sounds like a fan boy elitism comment that could turn many people away. I'm sure there are other brands who post accurate C ratings, but without personally testing every single brand on the planet, I just don't see how this statement can be anything but false
Is this really true? Trying not to get sarcastic here ( I am a fan of SMC) but this really sounds like a fan boy elitism comment that could turn many people away. I'm sure there are other brands who post accurate C ratings, but without personally testing every single brand on the planet, I just don't see how this statement can be anything but false