200 Amp Super Cell

moderator007 · 2019-09-28T19:38:27.000Z

MtnDon:

There are a variety of sizes, up to 30 to 40 AH capacity. Charging in series can present issues if individual cell voltages vary in use. I have some 30 AH ones and use a BMS to keep the cell voltages matched.

How does your friend charge his?

His implementing a BMS, he reached out to me to help with it.
My first experience seeing these cells in hand. They’re massive compared to a 18650 .

The_Last_Katun · 2019-09-28T19:47:06.000Z

Maybe you want to get to do this

48Volt 10Ah

Agro · 2019-09-28T20:08:30.000Z

Brings this to my mind.
Some LEDs could be driven linearly with it. E21A, Luxeon MZ come to my mind…

will34 · 2019-09-28T20:20:05.000Z

I bought 8 of these from alarmhookup on eBay to build a DIY car starter with real amps, unlike those cheap LiPo “1000A” powerbank/starters with a measly 8awg wiring. Planning to do 4S2P setup with a 650A rated battery switch. I think 400A real amps is enough to start pretty much any gas engine.

moderator007 · 2019-09-29T01:36:41.000Z

4 in series will start a car.

.
I thought this video was interesting, the wrench actually melts about the 5 minute mark with a few more cells added.

grin · 2019-09-29T21:27:51.000Z

They also have 15ah 40150

amishbill · 2019-09-29T23:15:35.000Z

I can see Ham Radio folks liking these for a 4s pack.

I’m guessing you’d need a special BMS to handle the charge current?

Couchmaster · 2019-09-29T23:55:40.000Z

Thank you for sharing, that’s damned impressive. Looks like a mistake would be deadly?

moderator007 · 2019-09-30T01:14:43.000Z

That’s one benefit to these cells, they dont catch fire and explode. Lifepo4 just smoke with heat.

will34 · 2019-09-30T07:42:56.000Z

amishbill:

I can see Ham Radio folks liking these for a 4s pack.

I’m guessing you’d need a special BMS to handle the charge current?

Sometimes there are good bms taken out of used or discarded lifepo4 racing or solar batteries for sale on eBay. Some people make their own using starter motor or winch solenoids. The generic Chinese ones cannot be trusted for high amps tasks.

ggf31416 · 2019-09-30T20:03:35.000Z

The Last Katun:

They 8000mAh batteries. 200A refers to “spurt” capacity and can discharge at 25C (maybe they thought that 8000mAh X 25C = 200A?).
At 3.2 volts, 8Ah are 25 watts, a little just for one car, although model racing.
Specifications are conflicting, I do not trust

25C for an 8000mAh battery is 200A, (8Ah / (1/25)h) = 25*8 A = 200A by definition. Whether the 25C rating is real or not (i.e. is it safe to discharge the battery from 100% to 0 in just 144 seconds?) is another matter.

It won’t be 3.2V at 200A because of internal resistance, but at 2.5V (just a guess) it would be 500W.

amishbill · 2019-09-30T20:10:56.000Z

OK - Someone call DBSAR and tell him to put the LT1 on hold until it can be reworked to hold several of these….

klrman · 2019-09-30T20:15:46.000Z

moderator007:

That’s one benefit to these cells, they dont catch fire and explode. Lifepo4 just smoke with heat.

Is that true, even if you short circuit them? It would be fun to build a 1600 amp one for starting pickups in Winter up here with dead batteries.

BlueSwordM · 2019-09-30T20:55:45.000Z

They can catch on fire, just at a higher temperature.

Anyway, it would be better to put 4 of these in parallel and 4 in series for absolute maximum current capability.

25C seems perfectly adequate for such a large cell that has such low capacity.

ggf31416 · 2019-09-30T21:03:50.000Z

OTOH if you can put 8 Samsung 18650s 20S (30A) in parallel the volume would be the same as a single 38120 (they are ~2x in every dimension), the result would be 16Ah and 240A, or if you use Molicel P26A, 20.8Ah and 200A according to Mooch’s 25A rating. Of course to put many cells in parallel (and series) you need a more complex design.

BlueSwordM · 2019-09-30T21:04:18.000Z

Well, here’s the problem.

You need to put them in series for 12V operation.

The power density on this is insane.

ggf31416 · 2019-09-30T21:32:44.000Z

You can do 4S32P with 18650s for 14.4V or 14.8V (nominal), that would be the equivalent of 4S4P 38120s. However you need a good BMS for that and you really need to know what are you doing or risk blowing yourself, which I don’t. I guess that LiFePo4 may be safer, and indeed all the 18650s metal cans add weight.

amishbill · 2019-09-30T21:35:38.000Z

ggf31416:

You can do 4S32P with 18650s for 14.4V, . ….

… and therein lies the rub. 4x 18650 hits a max of 16.8v at a full charge.

Some of us run gear that tends to get squirrely with it’s ‘magic smoke containment’ at that value. LiFePO4 is a godsend in this case.

The_Last_Katun · 2019-09-30T22:08:42.000Z

ggf31416:

The Last Katun:

They 8000mAh batteries. 200A refers to “spurt” capacity and can discharge at 25C (maybe they thought that 8000mAh X 25C = 200A?).
At 3.2 volts, 8Ah are 25 watts, a little just for one car, although model racing.
Specifications are conflicting, I do not trust

25C for an 8000mAh battery is 200A, (8Ah / (1/25)h) = 25*8 A = 200A by definition. Whether the 25C rating is real or not (i.e. is it safe to discharge the battery from 100% to 0 in just 144 seconds?) is another matter.

It won’t be 3.2V at 200A because of internal resistance, but at 2.5V (just a guess) it would be 500W.

At a first reading I had not classified them as reliable because the chinese sometimes shoot amazing characteristics but then it is not true; but then I read the tests and comments, and I changed my mind.

moderator007 · 2019-09-30T22:20:45.000Z

I haven’t tried this myself but according to all that I have read is they do not catch fire except in very rare instances, which I only find one video after the fire. But I read it can happen in rare instances.
This video shows one catching fire, when these guys throw it in a fire.

This one, they shoot a nail in it.

They have a pretty flat discharge curve even at high current loads.
This is a Lifepo4 chemistry not a Lipo, they are the safest of all lithium cells.