Small Lipo Puff Testing...
10-20-2015, 10:45 AM
#1
Small Lipo Puff Testing...
A few weeks ago I was wandering the pits and decided about 2/3 of the guys' batteries were puffed, maybe more. They were using them, but that's something to avoid. I talked to a couple and they said it was from too high an amp draw, which makes sense and I've read about it, too.
I've been playing around with little voltage meters for quite awhile and started using the alarm system instead of relying on my speedo's LVC. Except for letting some sit around hot and fully charged one weekend, I've had no problems. If the battery's balance lead isn't long enough, I just use an extension cable. At the track, I've started putting a single layer of some kind of tape over the mouths of the buzzers because they're LOUD.
So, I took some of the smaller ones I've collected and punished them in heavy trucks. Of course, they only lasted literally a few minutes and read from 100-120F at the casing when done. The wiring, connectors - all of it was really warm.
Each of the following, and it's sibling currently stored in the fridge - 6 total, have an additional 5-6 death runs on them. BUT, I stopped momentarily a few times at the end of the runs when my 3.7v alarm went off. I didn't rely on the LVC to protect them.
The smaller batteries have more "pump" or oscillation from duress to static voltage than their larger counterparts. So, several brief restarts leave them at storage voltage and ready for charging after cooling or the fridge when I let them lay around. The larger ones only need a couple restarts to reach storage voltage because they're operating at a more appropriate load and don't dip as much; so they have a flatter descent to the threshold.
The results? Here you see NO puffing at all. They all have some foam around them, but that'll pooch, too, if swollen. I laid a ruler firmly against them to compress the foam and it settled flat. They balance as they always did and now I know that I can relax my cycling routine. Imagine how much even more stable the higher quality batteries will be with just a little higher LVC than what's available in the speedo?
So, I'm assuming the problem here is not only too much current as discussed, but also finalized as damage if the dip is too low and lasts too long. Comments are welcome.
I was afraid to use the smaller ones (1600 to 2200's) in my T4 or eMaxx (in pairs), for examples. Not any more: just stop at 3.7v. How cool is that? Not a lot of runtime, but I don't always have a half hour to play.
I can still get a couple warm up laps and finish a heat using that much capacity from a right sized battery. At the park, it doesn't matter so much how long they last.
My next test will be if using the alarm at 3.4-3.5v will also protect them, like maybe it would respond faster. If I stop once at that point, the no-load rise might leave them at storage voltage, too.
Thanks to wrongchannel for the pic placement tip!
Gene
I've been playing around with little voltage meters for quite awhile and started using the alarm system instead of relying on my speedo's LVC. Except for letting some sit around hot and fully charged one weekend, I've had no problems. If the battery's balance lead isn't long enough, I just use an extension cable. At the track, I've started putting a single layer of some kind of tape over the mouths of the buzzers because they're LOUD.
So, I took some of the smaller ones I've collected and punished them in heavy trucks. Of course, they only lasted literally a few minutes and read from 100-120F at the casing when done. The wiring, connectors - all of it was really warm.
Each of the following, and it's sibling currently stored in the fridge - 6 total, have an additional 5-6 death runs on them. BUT, I stopped momentarily a few times at the end of the runs when my 3.7v alarm went off. I didn't rely on the LVC to protect them.
The smaller batteries have more "pump" or oscillation from duress to static voltage than their larger counterparts. So, several brief restarts leave them at storage voltage and ready for charging after cooling or the fridge when I let them lay around. The larger ones only need a couple restarts to reach storage voltage because they're operating at a more appropriate load and don't dip as much; so they have a flatter descent to the threshold.
The results? Here you see NO puffing at all. They all have some foam around them, but that'll pooch, too, if swollen. I laid a ruler firmly against them to compress the foam and it settled flat. They balance as they always did and now I know that I can relax my cycling routine. Imagine how much even more stable the higher quality batteries will be with just a little higher LVC than what's available in the speedo?
So, I'm assuming the problem here is not only too much current as discussed, but also finalized as damage if the dip is too low and lasts too long. Comments are welcome.
I was afraid to use the smaller ones (1600 to 2200's) in my T4 or eMaxx (in pairs), for examples. Not any more: just stop at 3.7v. How cool is that? Not a lot of runtime, but I don't always have a half hour to play.
I can still get a couple warm up laps and finish a heat using that much capacity from a right sized battery. At the park, it doesn't matter so much how long they last.
My next test will be if using the alarm at 3.4-3.5v will also protect them, like maybe it would respond faster. If I stop once at that point, the no-load rise might leave them at storage voltage, too.
Thanks to wrongchannel for the pic placement tip!
Gene
10-20-2015, 01:02 PM
#2
I use that exact low voltage alarm when I use my 2S. I don't have any puffing on my Lipo's (I have like 12 of them in different shapes and sizes).
What I do is set the alarm to sound at 3.7v and only run the battery down to 3.80-3.82v, meaning the alarm do not sound. I use a count-down timer on my radio.
By the time you take it out of the car the voltage will rise to around 3.83-3.85v which is my storage voltage.
What I do is set the alarm to sound at 3.7v and only run the battery down to 3.80-3.82v, meaning the alarm do not sound. I use a count-down timer on my radio.
By the time you take it out of the car the voltage will rise to around 3.83-3.85v which is my storage voltage.
10-29-2015, 04:16 PM
#4
I've spent a ton of time thinking about lipo puffing in the about 8 years and countless batteries I've had.
Here are some interesting things I've noticed, keep in mind all the batteries I've ever had were turnigy or zippy LiPo's so it'll vary a little from manufacture to manufacture.
High C ratings prevent puffing. I used to get only a year out of any battery before they would puff up a fair amount running 20-45C batteries and none of my 65C+ batteries have started puffing.
I am almost certain that the C rating is a function of the batteries internal resistance. If the battery has a high resistance, the voltage drops lower but it also gets hotter. My 90C 7500mah LiPo's are 2-3mOhms per cell. My 5000mah 25C packs are 15-20mOhms per cell. My 65C 4600mah LiPo's are 5-8mOhms per cell. If you draw the same amount of current through all of them, then the 25C's will produce around 7-8 times the amount of heat of the 90C's and around 2-4 times the amount of heat as the 65C's internally. I've had my 90C 7500mah (675A) packs for over a year now and they show no signs of puffing at all while racing and bashing a truggy (120A system) with enough power to wheelie at the end of the front stretch. My 10,000mah 25C (250A) batteries in my bicycle (35A system) have all puffed a little in a year, with the same amount of use. The big difference here is that the bike continuously draws 20-35A for extended periods while the truggy is in bursts.
The resistance (C rating) changes with age/puffing. I check the internal resistance of my batteries every couple months. Over the past year the internal resistance of all my batteries has gone up, especially in those that start puffing.
A cell that's acting up always has a higher internal resistance. Every time a friend has had a problem with there pack being balanced or charging, the misballanced and misbehaved cell usually has 2+ times the resistance as the others in the pack. It also seems like when you see a cell growing in resistance, it's the one that starts giving you trouble later on. Weirdly though, new cells seem to be able to flip flop around until they get a few cycles on them.
Being fully charged. This one I've just started noticing. My bicycle's batteries are a tight squeeze when they are fully charged installing into the bike (the label has been ripped because of this) but they have 2-3mm clearance when I take them out (always 3.8-3.95v/c at the end of the day), even when they are warm from a wide open 1 mile trip. I charge them at 1C (rated for 2C) while my 90C packed are usually charged at 1.33C (rated for 2 again) and still never puff. One big difference here is my charger for my 2s batteries starts slowing down around 4.05-4.1v/c and only charges to 4.16-4.18v/c while my 10s charger doesn't start slowing down until 4.2v/c.
Overcharging. My friend is the most docile RC driver you'll ever meet except for rock crawlers yet he had his batteries puff up after 15 runs. Later on I plugged up one of his fresh off the charger packs (5000mah 35C in a slash) and my voltmeter showed 4.28 for the highest cell. I also have a good friend who races and all his packs puff after a month, even the new 90C 7500mah's I run. Found his battery at 4.25v/c plus he drives supper hard. The entire reason he got the 7500's is so he can last a 10min main.
Just a couple things I've noticed if anyone is interested.
Here are some interesting things I've noticed, keep in mind all the batteries I've ever had were turnigy or zippy LiPo's so it'll vary a little from manufacture to manufacture.
High C ratings prevent puffing. I used to get only a year out of any battery before they would puff up a fair amount running 20-45C batteries and none of my 65C+ batteries have started puffing.
I am almost certain that the C rating is a function of the batteries internal resistance. If the battery has a high resistance, the voltage drops lower but it also gets hotter. My 90C 7500mah LiPo's are 2-3mOhms per cell. My 5000mah 25C packs are 15-20mOhms per cell. My 65C 4600mah LiPo's are 5-8mOhms per cell. If you draw the same amount of current through all of them, then the 25C's will produce around 7-8 times the amount of heat of the 90C's and around 2-4 times the amount of heat as the 65C's internally. I've had my 90C 7500mah (675A) packs for over a year now and they show no signs of puffing at all while racing and bashing a truggy (120A system) with enough power to wheelie at the end of the front stretch. My 10,000mah 25C (250A) batteries in my bicycle (35A system) have all puffed a little in a year, with the same amount of use. The big difference here is that the bike continuously draws 20-35A for extended periods while the truggy is in bursts.
The resistance (C rating) changes with age/puffing. I check the internal resistance of my batteries every couple months. Over the past year the internal resistance of all my batteries has gone up, especially in those that start puffing.
A cell that's acting up always has a higher internal resistance. Every time a friend has had a problem with there pack being balanced or charging, the misballanced and misbehaved cell usually has 2+ times the resistance as the others in the pack. It also seems like when you see a cell growing in resistance, it's the one that starts giving you trouble later on. Weirdly though, new cells seem to be able to flip flop around until they get a few cycles on them.
Being fully charged. This one I've just started noticing. My bicycle's batteries are a tight squeeze when they are fully charged installing into the bike (the label has been ripped because of this) but they have 2-3mm clearance when I take them out (always 3.8-3.95v/c at the end of the day), even when they are warm from a wide open 1 mile trip. I charge them at 1C (rated for 2C) while my 90C packed are usually charged at 1.33C (rated for 2 again) and still never puff. One big difference here is my charger for my 2s batteries starts slowing down around 4.05-4.1v/c and only charges to 4.16-4.18v/c while my 10s charger doesn't start slowing down until 4.2v/c.
Overcharging. My friend is the most docile RC driver you'll ever meet except for rock crawlers yet he had his batteries puff up after 15 runs. Later on I plugged up one of his fresh off the charger packs (5000mah 35C in a slash) and my voltmeter showed 4.28 for the highest cell. I also have a good friend who races and all his packs puff after a month, even the new 90C 7500mah's I run. Found his battery at 4.25v/c plus he drives supper hard. The entire reason he got the 7500's is so he can last a 10min main.
Just a couple things I've noticed if anyone is interested.
10-30-2015, 07:35 AM
#5
Hey, Rc_Dude, that's what I need to know about!
IR was always a big deal with NiCd's & NiMh's; so, although the performance is much greater, it looks like the same rules mostly apply.
I can make some basic rules from your full & over-voltage observations and I need to find my good DVM and verify my chargers' readings.
About your chargers, are they both advertised as "intelligent?" I've read about fast charge curves being in some chargers' chips with an ending 15-20% descent into voltage dominance vs. current. Sounds like the bike charger has a faster descent, if any.
Do you use a manual loading/reading and hand calculate IR or do your chargers have it built in?
Thanks a bunch,
Gene
IR was always a big deal with NiCd's & NiMh's; so, although the performance is much greater, it looks like the same rules mostly apply.
I can make some basic rules from your full & over-voltage observations and I need to find my good DVM and verify my chargers' readings.
About your chargers, are they both advertised as "intelligent?" I've read about fast charge curves being in some chargers' chips with an ending 15-20% descent into voltage dominance vs. current. Sounds like the bike charger has a faster descent, if any.
Do you use a manual loading/reading and hand calculate IR or do your chargers have it built in?
Thanks a bunch,
Gene
10-30-2015, 08:29 AM
#7
About your chargers, are they both advertised as "intelligent?" I've read about fast charge curves being in some chargers' chips with an ending 15-20% descent into voltage dominance vs. current. Sounds like the bike charger has a faster descent, if any.
Do you use a manual loading/reading and hand calculate IR or do your chargers have it built in?
Do you use a manual loading/reading and hand calculate IR or do your chargers have it built in?
This is why I like the iCharger brand chargers a lot better than HiTec, problem is iCharger doesn't make a duo 10A charger and sometimes has problems with surge current running off a car battery or LiPo...
Another thing is my HiTec charger's LCD display misspells works/characters all the time. Turn it on and it reads chargerer or dischchar or storge instead of charge, discharge, and storage. Change the mode and come back and they will usually fix themselves. The thing just doesn't feel sturdy at all.
And lastly, this is my second Ultima x2 after the first was returned due to an OBSESSIVE C term (slowing down at 3.8v/c and only charging to 4.05 or so) in that equation above.
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