[LithiumaniacsEVRacing]

Comparing discharge 3000 amps @ total weight.

A123 26650 cells (70g each)
120 burst amps each
25P = 1750g cells only (Note: 3000amps)
____________________________

LifeBatt P20AH (610g each)
500 burst amps each
6P = 3660g cells only (Note: 3000amps)
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K2 26650 (82g each)
150 burst amps each
20P = 1640g cells only (Note: 3000amps)
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A123 AMP20 Pouch (495g each)
450 burst amps each
7P = 3465g cells only (Note: 3150amps)
____________________________

Headway LifePO4 38120P (330g each)
160 burst amps each
19P = 6270g cells only (Note: 3040amps)
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Gaia 45AH HP (1500g each)
1250 burst amps each
3P = 4500g cells only (Note: 3750amps)
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Haiyin P68100120F (170g each)
400 burst amps each
8P = 1360g cells only (Note: 3200amps)
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[Jordysport]

http://www.mavizen.com/A123.html

A123 AMP20 Pouch Cells (495g)
750A Peak
4P = 1980g (Note: 3000Amps)

thats the peak values for them, says on your first post your using burst figures which are normally higher than Peak values/maximum values. I would be inclined to tend towards contin figures

[LithiumaniacsEVRacing]

Originally Posted by Jordysport

http://www.mavizen.com/A123.html

A123 AMP20 Pouch Cells (495g)
750A Peak
4P = 1980g (Note: 3000Amps)

thats the peak values for them, says on your first post your using burst figures which are normally higher than Peak values/maximum values. I would be inclined to tend towards contin figures

This information is for EV drag racers, so the burst rating is the more important number. As for Mavizen claims, I was in contact with the owner which directed me to someone for battery sales, he stated the numbers on the pouch cell were "fudged" and they do not put out 750 burst amps. He recommend I buy the Nanophosphate® ANR26650M1-B.

Until I see factory specs showing a burst rating of 750amps, then she stands. Trust me, if they do push 750amps I might consider building a pack.

[Jordysport]

Originally Posted by LithiumaniacsEVRacing

This information is for EV drag racers, so the burst rating is the more important number. As for Mavizen claims, I was in contact with the owner which directed me to someone for battery sales, he stated the numbers on the pouch cell were "fudged" and they do not put out 750 burst amps. He recommend I buy the Nanophosphate® ANR26650M1-B.

Until I see factory specs showing a burst rating of 750amps, then she stands. Trust me, if they do push 750amps I might consider building a pack.

Correct me if i am wrong but whenever i see "burst" ratings they normally say less than 1/2 seconds and your going to be running more than that on a 1/4 mile. i am using cont figures anyway for mine, so got a nice safety factor.

[rwaudio]

Comparing cells based on the spec sheet is useless given your application. Voltage sag is as big a consideration if not more important than peak current.

Buy 10 of each cell and test them with real equipment and you'll have some data to make an informed decision.

[LithiumaniacsEVRacing]

Originally Posted by Jordysport

Correct me if i am wrong but whenever i see "burst" ratings they normally say less than 1/2 seconds and your going to be running more than that on a 1/4 mile. i am using cont figures anyway for mine, so got a nice safety factor.

You are wrong, burst ratings range from 1S to 5S. In drag racing the first 3 to 5 seconds in very very important.

[LithiumaniacsEVRacing]

Originally Posted by rwaudio

Comparing cells based on the spec sheet is useless given your application. Voltage sag is as big a consideration if not more important than peak current.

Buy 10 of each cell and test them with real equipment and you'll have some data to make an informed decision.

I trust most reputable companies to publish the correct data, all the companies I posted have data graphs on voltage sags. I agree, some cells will sag more than others. This does not change the burst ratings we need when launching an electric drag racing car. Last year we launched with a 220V pack, it's the amps that gave us the great punch off the line. Our pack produced enough burst amps to supply two Zilla's with 4000BA. I understand what your saying, but believe stronger push off the line (burst amps) produces a better 1/4 ET.

[PStechPaul]

I'd like to get some experience with Lithium cells, and I'd like to build a cell tester capable of as high as 500 or even 750 amps for very short bursts (like 100 mSec) which would characterize the cell. Such a short burst would probably be a lot safer and more accurate than trying to use a carbon pile tester as you have used in your videos.

If you can send me a few cells, even those that are "weak", I could put together a simple tester to see if it is of use to you, and maybe we can trade. I'd like some lithium cells for some much less demanding applications, so your rejects and discards might be fine for me. And if you don't mind a prototype sort of tester, you'd be able to get much better data. From that point, we could discuss further possibilities.

You can PM me or correspond via my paul@enginuitysystems.com email.

[Jordysport]

Originally Posted by LithiumaniacsEVRacing

You are wrong, burst ratings range from 1S to 5S. In drag racing the first 3 to 5 seconds in very very important.

Last time i checked "less than 1/2 seconds was within 1-5 seconds" , Peak Figures are more like 1 min ratings from looking at published data, thus unless your doing under 5 second 1/4 mile i see a serious pack reliability issue over the whole 1/4 mile run.

[PStechPaul]

Has anyone run a datalogger to see actual battery current vs time for a drag race? For a series wound motor, I would think it would be maximum at the start, and then maybe stay constant until the motor speed BEMF (and brush inefficiency) does not allow any more current even at full pack voltage so the current goes down.

For an optimal race, I think, the torque should be tightly controlled and maximized, so that any slippage of either drive wheel would result in a lower PWM to regain traction. I assume that is already done, but if not it seems like a good idea. And there may always be better ways to implement it, and there may be other factors such as the higher tire temperature caused by friction might result in better traction.

The other thing that might limit a dragster's ability to accelerate would be the lifting of the front end off the ground, resulting in loss of steering. One way to compensate might be to steer using differential control to the two separate rear drive wheels, so you could alctually steer the entire way on those two wheels. It works on a Segway... (BTW, what's the world record for a 1/4 mile on a hot-rod Segway?)

I suppose it has already been observed that the acceleration of the motor itself is transferred to the wheels. A motor which spins axially along the direction of motion will torque more pressure on the side opposite the direction of motor rotation. For a dual drive, they could spin in opposite directions. But for a transverse mounted motor, the acceleration and change of force is from front to back. One way will transfer more pressure to the drive wheels but will tend to lift the front. The other way will keep the front down but maybe lose some traction on the rear...

I know this has drifted off-topic. Mostly I think the actual battery discharge profile is needed to determine the overload safert factors and actual capability.