Can we talk about Prismatic LiFePo4 Cells?

[Kaly]

I’m late to this conversation but this can give an idea to the first question

Ben Hur Deck / Matrix Pro 2 Truck/ MBS 8 in Wheels/ Dual TB 6350 Motor/ Dual...

[leroy]

one of things I’m told by battery people is that the cylindrical cell is not as efficient of a shape for batteries as is the flat pouches. That’s just what I hear,

[leroy]

My battery guy is using Panasonic !0Ah pouches for my battery packs, and they are cheaper than comparable lithium ion cell packs

[Pantologist]

Well, a box will easily fit a box’s shape more efficiently while a cylinder will not. Makes sense.

[leroy]

The pouches are a bit more compact

[leroy]

I keep forgetting that when I order them, 3.2 not 3.7 , those .5 volts add up quickly.

[leroy]

I think the pricing is getting better. I ordered a 19.2v 11,000mAh pack for $170, I also got a 11s pack, but I don’t remember what I paid or sold it for to be honest. I can get them assembled as I want, I can specify “three rows of three” , which is really nice.

[localredhead]

Hook us up with your battery guy

[tomtom13]

@leroy

The other day, some cat on here said he was planning to put a 10s5p on a board,that’s fifty batteries, the cell count alone complicates the whole build process. There has got to be a better way. I’ve been checking out LiFePo4, and it seems to be good tech. The battery folks love LiFePo4. They tell me, the flat prismatic cells are a more efficient shape for a battery than an 118650 cylinder. but the cylinders seem way more popular. They tell me, LiFePo4 cells can have very high capacity, and I see 3.2.v 20Ah cells everywhere. They tell me LiFePo4 packs don’t need a BMS, but I see LiFePo4 BMS being sold. They tell me LiFePo4 batteries are less expensive, and they sell them for less. So why aren’t you using LiFePo4 prismatic cells?

Just to debunk few myths about prismatic cells:

1. they “can be more efficient” but realistically they are not that much more than pack formed with 18650
2. prismatic cells require compression !!! so your box has to stop expanding (swelling) cell. Cylindrical cell are perfectly self contained
3. prismatic cells are more problematic to cool because you pack them flat. Reality of lifepo cells:
4. main advantage of using lifepo cells is that those are inherently safer to use, they will have a thermal run away but it’s harder to achieve and resulting fire is not as bad as cobalt cells and definitely much better than lipo.
5. secondary advantage of using lifepo is that operational voltage curve is very flat between 90%-20% making a control system much more simple.
6. third reason is that lifepo is actually lighter than cobalt cell (things tend to blur recently) but if you make a car than packaging is number 1 and weight is number 2, when you make a truck then weight is number 1 problem and packaging is number 2 so lifepo cell are chosen almost elusively in heavy weight vechiles (trucks, busses, tanks)
7. fourth reason for using lifepo is that those tent to have less impedance on low drainage (up to 5C) than Cobalt. so you will loose less to heat - tends to matter if range is main problem.
8. lifepo is not using coblat which is rare metal (makes it expensive) and is very toxic … (so when you see EV car with cobalt cells on fire don’t go near without respirator !!!)

Any, absolutely ANY lithium cell REQUIRES bms … without it you are asking for it … if you will discharge any lithium cell (lipo, cobalt, ferrite) below critical minimum voltage you are in danger of fire !!!

and yes I design and make EV’s :* so got few suckers like that kicking about for fun

ps. I would not advice to touch synopoly cells - those have 30% failure rate from our experience (compared to 5% for calb) they lie in data sheet (it quotes capacity for voltage drops that would literally destroy the cell) … and price vise work out more expensive than calb (even tho calb charges more per Ah but hey charge for realistic capacity !)

[longhairedboy]

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That’s 12S/8ah worth of prismatics above, and 12S/10Ah worth of 18650s below.

I guess density depends on the specific pouches you use. Those pouches are older, but i may have found some that will give me the 12S/10Ah i’m looking for and will still fit in my box.

But don’t ever be confused about which cell format is more flexible for building. 18650s win there. I can get pretty much any shape i want out of them, even weird ones that allow odd counts like 13S. Pouches have to be worked around a little more when it comes to cell layout.

*please excuse the messy 18650 pack, it was freshly re-packed.