Average voltage?
11-01-2021, 09:47 PM
#1
Average voltage?
Average voltage?So this will be a question for old-timers:
Backin the old nickel days when we bought matched packs, stick racers were always concerned about average voltage. You were always looking for those magic turbomatcher numbers for average voltage at a certain discharge rate.
o obviously, our lipos will never display those numbers now- since there"s no commercial matches now, and dealers can just "claim" a high C rating that cant be verified.
So my question is: would testing a lipo battery for average voltage at a set discharge rate be worthwhile? With my 308 and the software I could do it- but is it wortwhile?
Backin the old nickel days when we bought matched packs, stick racers were always concerned about average voltage. You were always looking for those magic turbomatcher numbers for average voltage at a certain discharge rate.
o obviously, our lipos will never display those numbers now- since there"s no commercial matches now, and dealers can just "claim" a high C rating that cant be verified.
So my question is: would testing a lipo battery for average voltage at a set discharge rate be worthwhile? With my 308 and the software I could do it- but is it wortwhile?
11-01-2021, 10:19 PM
#2
Average voltage?So this will be a question for old-timers:
Backin the old nickel days when we bought matched packs, stick racers were always concerned about average voltage. You were always looking for those magic turbomatcher numbers for average voltage at a certain discharge rate.
o obviously, our lipos will never display those numbers now- since there"s no commercial matches now, and dealers can just "claim" a high C rating that cant be verified.
So my question is: would testing a lipo battery for average voltage at a set discharge rate be worthwhile? With my 308 and the software I could do it- but is it wortwhile?
Backin the old nickel days when we bought matched packs, stick racers were always concerned about average voltage. You were always looking for those magic turbomatcher numbers for average voltage at a certain discharge rate.
o obviously, our lipos will never display those numbers now- since there"s no commercial matches now, and dealers can just "claim" a high C rating that cant be verified.
So my question is: would testing a lipo battery for average voltage at a set discharge rate be worthwhile? With my 308 and the software I could do it- but is it wortwhile?
11-01-2021, 11:26 PM
#3
That was important back when there was no such thing as boost and turbo and when your battery might not even last a 4 minute race if you had your gearing too tall. There’s also no such thing as “peaking” a LiPo pack. None of that stuff applies anymore - and neither does discharging your packs after a race. Forget everything you’ve learnt from your NiCad days - they no longer apply.
11-02-2021, 03:38 AM
#4
I'm not sure it is relevant... First there are only two elements... Then the IR is way more relevant for LiPO.
11-02-2021, 03:53 AM
#5
Small sample size, but towards the end of the round-cell era I was running NiMHs straight from bulk packaging and comparing them with matched packs on my own test equipment. The "unmatched" cells were better.
Matching may have mattered with 80s cell manufacturing technology, but in the 00s the manufacturing was so consistent, all the matchers were doing were putting a few extra-heavy load cycles on the cells before the customer got to use them.
You'd think there was money to be made in "matching" LiPos, I wouldn't be surprised if someone has tried it but found that the numbers you get wouldn't make a persuasive sales pitch.
Matching may have mattered with 80s cell manufacturing technology, but in the 00s the manufacturing was so consistent, all the matchers were doing were putting a few extra-heavy load cycles on the cells before the customer got to use them.
You'd think there was money to be made in "matching" LiPos, I wouldn't be surprised if someone has tried it but found that the numbers you get wouldn't make a persuasive sales pitch.
11-02-2021, 05:55 AM
#6
To shed some additional light on this topic. IR (internal resistance) is the most important factor of a lipo battery in terms of performance, until it reaches 2.0 per cell. Then the discharge curve (fade) of the battery becomes the most important. Most "quality" batteries you purchase from but not limited to: Fantom, R1 wurks, EA Motorsports, Team Scream, etc, should have an IR of 2.0 per cell or lower after a couple of runs, or right out of the box. Testing batteries is another added element to racing, and its not necessary but may be something you find interesting like myself.
You can graph this with your icharger and a computer or do it over time. Ideally you need a 15-20 amp discharge capability(about what we draw in stock on average) and the stock icharger cannot do that, but it will discharge a 2s at about 12 amps which is close enough for the test to see which pack is the best. If you don't want to do this with your computer you can do it with your phone, and note pad.
So what you would do is charge the battery to full, then set a discharge down to the voltage you come off the track at (likely about 3.7v per cell). Writing the voltage down every 30 seconds, and the IR would be a great way to easily see which pack is better. You can then see which battery had a high voltage over a specific period of time, a high voltage means more power and less fade. Likely the pack with the best IR is not the best pack for fade. You may give up .1 IR for a lot less fade.
In terms of MAH for your application. The highest MAH battery is likely not the way to go, it has extra weight which can make your car hard to balance, as well as a decreases COG performance making the car less forgiving to drive. Again, this is highly specific to an application for example you may want a heavier battery in 2wd buggy for the extra weight transfer, but for a class like stock touring car, a 5800 super low profile may provide a better car feel. I personally have tried an 8000 mah full height stick pack, a 6000 mah low profile stick pack, and a 5800 super low profile stick pack, and found the numbers to be very similar for all of the batteries for MY APPLICATION (which is stock touring car, on indoor carpet track). I personally like how the 5800 super low profile stick packs feel, because of this the last minute of the run I do give up a little bit more time (about .05 to .1 seconds per lap). Which would be about .3 to .4 seconds overall from the last minute. For me the marginal loss in time was worth the added handling performance of the lower profile battery. Not only was I able to lower the COG, but I was also able to put 40 grams of that weight i lost into the center of the car (near the motor mount), which is an added bonus. The other weight I was able to place near the center of the car, just not as perfect as the motor mount. This created a better handling car for me, and one that was easier to drive resulting in better average lap times, but overall the same fast lap, but I was able to get a couple of "fast" laps.
If you're using this in an outdoor track (larger than most carpet tracks) a higher MAH battery may be more useful to you, because once you get below 3.7v per cell the batteries fade will start to increase noticeably. My batteries come off of a 50x100 track after a 6 minute run at 3.82v per cell, this is the 5800 super low profile, the 6000 comes off at 3.85v per cell, and so does the 8000 mah.
You can graph this with your icharger and a computer or do it over time. Ideally you need a 15-20 amp discharge capability(about what we draw in stock on average) and the stock icharger cannot do that, but it will discharge a 2s at about 12 amps which is close enough for the test to see which pack is the best. If you don't want to do this with your computer you can do it with your phone, and note pad.
So what you would do is charge the battery to full, then set a discharge down to the voltage you come off the track at (likely about 3.7v per cell). Writing the voltage down every 30 seconds, and the IR would be a great way to easily see which pack is better. You can then see which battery had a high voltage over a specific period of time, a high voltage means more power and less fade. Likely the pack with the best IR is not the best pack for fade. You may give up .1 IR for a lot less fade.
In terms of MAH for your application. The highest MAH battery is likely not the way to go, it has extra weight which can make your car hard to balance, as well as a decreases COG performance making the car less forgiving to drive. Again, this is highly specific to an application for example you may want a heavier battery in 2wd buggy for the extra weight transfer, but for a class like stock touring car, a 5800 super low profile may provide a better car feel. I personally have tried an 8000 mah full height stick pack, a 6000 mah low profile stick pack, and a 5800 super low profile stick pack, and found the numbers to be very similar for all of the batteries for MY APPLICATION (which is stock touring car, on indoor carpet track). I personally like how the 5800 super low profile stick packs feel, because of this the last minute of the run I do give up a little bit more time (about .05 to .1 seconds per lap). Which would be about .3 to .4 seconds overall from the last minute. For me the marginal loss in time was worth the added handling performance of the lower profile battery. Not only was I able to lower the COG, but I was also able to put 40 grams of that weight i lost into the center of the car (near the motor mount), which is an added bonus. The other weight I was able to place near the center of the car, just not as perfect as the motor mount. This created a better handling car for me, and one that was easier to drive resulting in better average lap times, but overall the same fast lap, but I was able to get a couple of "fast" laps.
If you're using this in an outdoor track (larger than most carpet tracks) a higher MAH battery may be more useful to you, because once you get below 3.7v per cell the batteries fade will start to increase noticeably. My batteries come off of a 50x100 track after a 6 minute run at 3.82v per cell, this is the 5800 super low profile, the 6000 comes off at 3.85v per cell, and so does the 8000 mah.
11-02-2021, 07:48 AM
#8
Id would not worry about Nixx voltages with lipos. the only thing that matters is ir and that can vary alot..i would not run a 8000 mah pack unless It was a longer than 12 minute race. Id either ask how many mah races at yor track put back into there used batteries or find that info out myself then run a pack with 2x that mah rate used lighter is better as in weight of battery..
11-06-2021, 09:07 AM
#9
I use 2 different measurements to test my batteries. I have lots of lipos of different capacities, age, brands, etc. I also sometimes race up to 6 classes in one day, so knowing which batteries to put in which vehicles is important to me.
I've always heard, lipo with lowest IR will provide best performance. I think IR is a useful tool, but it's only helpful when comparing batteries of the same capacity. My problem was how does a 5000mah with a lower IR compare to a 6500mah with higher IR.
I use a 20amp discharge cycle, where I discharge the batteries for 5 minutes (typical race duration) and take the average voltage at 1 minute intervals. I guess you could do it at 30 second intervals, but I haven't found any differences that would have me change battery rankings. You can pretty easily do this with the icharger duos and an SD card. Just tell it to log and set the log interval to 30 or 60 seconds.
The other test I do is a punch test, where I measure the difference in pack voltage from resting voltage and 2 seconds into a 65 amp discharge. I'm sort of limited to 65A with my current testing rig. I'd like to get closer to 100a.
I do both of my tests with a Arduino that's measuring the cell voltages off the balance port. I had tried manually recording the cell voltages with my punch test, but didn't like the inaccuracy of manually timing.
I've always heard, lipo with lowest IR will provide best performance. I think IR is a useful tool, but it's only helpful when comparing batteries of the same capacity. My problem was how does a 5000mah with a lower IR compare to a 6500mah with higher IR.
I use a 20amp discharge cycle, where I discharge the batteries for 5 minutes (typical race duration) and take the average voltage at 1 minute intervals. I guess you could do it at 30 second intervals, but I haven't found any differences that would have me change battery rankings. You can pretty easily do this with the icharger duos and an SD card. Just tell it to log and set the log interval to 30 or 60 seconds.
The other test I do is a punch test, where I measure the difference in pack voltage from resting voltage and 2 seconds into a 65 amp discharge. I'm sort of limited to 65A with my current testing rig. I'd like to get closer to 100a.
I do both of my tests with a Arduino that's measuring the cell voltages off the balance port. I had tried manually recording the cell voltages with my punch test, but didn't like the inaccuracy of manually timing.
11-06-2021, 03:29 PM
#10
Lipos discharge differently than NimH Nicads are different than Nimh. Lipos are more about the discharge rate. High Capacity cells have lower IR and better Quality cells will as well.
a 5000Mah pack has a different Discharge than a 6500Mah or 8000mah. bigger capacity is better in most cases. But then the physical size and weight of the pack then comes into play.
a 5000Mah pack has a different Discharge than a 6500Mah or 8000mah. bigger capacity is better in most cases. But then the physical size and weight of the pack then comes into play.
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