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Discussion Starter · #1 · (Edited)
I've been doing the occasional look on alibaba for batteries, found another one that is very affordable, well without knowing shipping costs. Would like advice on using these batteries and my analysis. Alibaba is a freaky website, they always want me to download an app, here's a search that got me here on alibaba. "lipefo4 battery 3.7v 135ah oumeida". Here's the link:
3.7v Lithium Ion Battery 3.7v 135ah Rechargeable Battery For Electric Vehicles 3.7v135ah 3.7v Battery - Buy Ternary Lithium Battery 3.7v135ah,3.7v Battery,3.7v Lithium Ion Battery Product on Alibaba.com

Editing my mistakes (milliohm, not microohm)

Specs
  • 3.7v nom, 4.2V cut-off, 4.2V charge voltage, 3C-5C max discharge, 3C charge, 0.4mohm resistance, 20C-60C operating temp
  • dimensions: 50mm x 175mm x 140mm
  • 135ah x 3.7v => 0.5 kWh
  • 2.25kg

The inverter is 480V max, 480V/4.2= 114 batteries. 421V nominal.
114 batteries => 57 kWhr
228 batteries => 114 kWhr
$29 ea at 228 volume, $6,612 plus shipping and plates, etc.

3C discharge for 135ah battery means 3x135=405A. 5C=>675A
Two in parallel gives 810A, the motor looks like 730A peak, 300A continuous.
At peak current, 730A, 365A per string.
365A * (0.4 milliohm) * 114 = 16.7 V drop per string at peak.
(365A^2) * ( 0.4 / 1000) *114*2 = 12 kW generated at peak
(150A^2) * ( 0.4 / 1000) *114*2 = 2 kW generated continuous max

That's a lot of watts!

2.25kg x 228 => 518 kg, 1130lbs.

The temp specs, -20C to 60C, haha, i have eye dr appt in a week because these glasses are way off... :)

What do you suggest for heat/cool? Cold plates inbetween on the 140x175 end? Would plates on the 50x140 surface work or the 175x50 surface?

If these are something I can really make work, it's much more economical than the used tesla batteries I've seen, but also very heavy.

Thanks!
Mark

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Interesting. At $30 apiece (shipping might double that?), might be worth getting a few to take apart (how can they be cooled?) and to test to see what their real specs are.

Used cells for this range of capacity shoupd be in the $30 range by now but the grid storage and solar people are propping up prices because they're happy to not pay deep cycle Pb pricing. Ironically, they could care less about weight, whereas for us it's fatal to the project.
 

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Those voltages do not look right to me for LFP cells. Isnt the charge voltage generally 3.65, and nominal 3.20 per cell for LiFePO4?

And on your calculation you are dividing milliohms by a million - so your I^2 R calculation is off by 1000. Should be 12000watts at peak, and 2000 watts continuous. Even at 12000 watts, it will take a long time to heat up 1100lbs of batteries. Didnt old-school prismatic batteries like this generally just air-cool the packs?
 

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Discussion Starter · #6 ·
Those voltages do not look right to me for LFP cells. Isnt the charge voltage generally 3.65, and nominal 3.20 per cell for LiFePO4?

And on your calculation you are dividing milliohms by a million - so your I^2 R calculation is off by 1000. Should be 12000watts at peak, and 2000 watts continuous. Even at 12000 watts, it will take a long time to heat up 1100lbs of batteries. Didnt old-school prismatic batteries like this generally just air-cool the packs?
Doh! What was i thinking? Thanks! I've corrected the original post.

These are old-school? when I'm looking at batteries, what would i look for "new school"? :) Thx!
 

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These are old-school? when I'm looking at batteries, what would i look for "new school"? :) Thx!
Well, 10 years ago this was basically the only way to get lithium cells for a conversion. Now, with as many production EVs as are out there, most people try and track down a pack from a wrecked car and repurpose it. That is what I did for my truck, with a tesla-made pack from a Mercedes. I think both routes have merit, honestly, and probably plenty of pitfalls. You are taking a risk with a pack from a crashed car, but honestly, you are also gambling that the prismatics are not a lesser battery grade being passed off as top quality (which you will need for a traction pack for a car). Plenty of debate each way. In general, you should be able to get a used EV pack for around 150$/kwh. New "Grade A" LFP prismatics that are shipping from a US warehouse are easily twice that. Once you add shipping and customs fees, I am not sure what your price point will be on these particular cells. I would do plenty of reading about making sure you were getting what you paid for.

Why would you think prices on quality LI batteries would be dropping?

Not going to happen...
Do an image search for "price per kwh for lithium batteries 2010 to present" and you will come up with a lot of graphs like this one:



The curve is starting to flatten out, but I suspect it will keep improving for a bit. I suspect the scale of production is going to grow by leaps and bounds, which should lend itself to economies of scale. I am curious what makes you think the price will stop dropping?
 

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If these are LiFePO4, then the advertised voltages are way too high. That chemistry has a full voltage of about 3.34 and is generally considered a nominal 3.2V cell. So there is some confusion about what they are selling versus the advertising versus what you would actually get.

Ask to see a copy of some cell test data and the certifications package. What sort of warranty do they offer? Get it in writing before sending any money. Be a smart buyer and don't get scammed. i would get a sample from them first and do some bench testing before commit for such a large order.

example datasheet:
 

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Do not make the mistake of charging these in freezing temps.
 

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Discussion Starter · #12 ·
Wow, I'd like to really thank you all for the information, it's great! And you've helped me to avoid some sort of misrepresented battery!

I found an updated chart on lithium battery pricing.
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My initial costs from parts houses ($/kwhr)
Used Tesla: $299
New Leaf (Alibaba): $234
LG Chem Super Cell: $310
CALB 72ah: $603 (super duper high amperage)
These batteries and some from the same vendor: $53-$68 ==> too good to be true

It looks like buying batteries from local houses are a premium. Hybrid and racing batteries, high current, are definitely at a premium.
 

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Discussion Starter · #14 ·

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If they're too cheap, they may be inspection/test rejects that went out the back door on the night shift.

Shipping costs these days is a killer - a couple of years ago it wasn't, so you need to compare landed costs, including adding in Trump's China tax (VAT disguised as duty fees) that you'll get dinged for.
 

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The picture says ternary lithium, comparison here, The difference between Ternary Lithium battery and LiFePo4 battery | Shenzhen A&S Power battery

The text says LTO , lithium-titanate, a lower voltage low density battery, https://en.wikipedia.org/wiki/Lithium-titanate_battery

Text also talks about LiFePo4, which looks like a generic statement.
...
The LiFePO4 and LTO references in that listing only appear in the section about the company; I agree that this is likely generic text used for all of their product listings, even when not applicable to the specific product. Within the product information the nominal voltage and description as "ternary" are consistent.
 

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Discussion Starter · #17 ·
Toshiba has nice modules. They don't sell to individuals, but they're in Mitsubishi EV and apparently Nissan now.

This summer, I'll buy a 2012 Nissan Leaf that gets only 75 miles on a charge. It drives, but the passenger side is crunched in and you cannot use those doors. I'll salvage it eventually, great price.

The 2012 is the 24kWhr battery. Maybe I can get a replacement before i salvage it with one of the higher capacities and then use the batteries for salvage. anyways, discovered MyNissanLeaf.com for more info.
 

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The Toshiba module uses a pair of 23Ah cells and runs 160A continuous....what spec gives you wood with these? The Bolt EV cells are triple the current rating, for example.

75 miles of range is good enough to get you started....the price is right - free.
 

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Discussion Starter · #19 ·
75 miles of range is good enough to get you started....the price is right - free.
That’s some sage advice. Battery won’t affect the fun much and provides a learning tool. There will be newer cheaper batteries a few years later.

I could save more cash by using the leaf drive unit. A quick look, I haven’t seen anything about new gears that would get really big gear ratios. With 200lb-ft torque, I’d need some pretty big gear swap to feel happy with it. FYI, the leaf has more performance than the original ICE (100 hp, 173 lbs-ft), but that only went 50 mph.


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These batteries are of a similar type to those being used in off grid home power solutions. I am currently monitoring the Lifepo4 market at the moment for that reason. I can tell you that as each new battery model comes out, the older ones drop significantly in price. It is a fast moving market.

For example, the release of the latest 304ah Lifepo4 batteries instantly caused the superseded 280ah models to drop in price. Currently you can save around 25 to 33% in value by choosing the 280ah model. So older models like the ones mentioned in the op can be bought for very low prices.

Also, the latest models are all being set up extremely successfully to charge to 3.45v and working down to 2.8v... with very little degradation. If you want to operate between 2.5 and 3.7v as the specs say, they will work, and you might drain another 5ahrs out of each pack, but your expected battery life will plummet 100s if not 1000s of cycles.
 
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