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Building a battery out of cells. Does this sound correct?

Gene G

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A company in China will send me eight 3.2 volt 202 amp cells for 1197 including shipping. And sell a BMS for the system for 74.00 So The company is Shenzhen RJ Energy Co. Ltd .
Question - anybody heard of it?
I'm thinking it would be better to buy a BMS here and pay a bit more for a known quanity. (I did not see a temputure limiter for charging on their BMS.)
So I'd need one BMS for each four cell 12 volt battery? I'm guessing it would be a system comprised of two 202 amp batteries? Seems like a deal to me - any thoughts. Files attached are the cells and the BMS. Thanks, Gene
 

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  • RJ-3.2V202AH-R09[3377].pdf
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He's discounting the 200amp cells to 110 after talking a bit. He said they have several thousand and gives a 3 year warranty - except for damage by customer. I need to look for Wills page with the BMS's he recommends and total up the costs. Sure would be nice to swap out two lead acid 100 amp batteries for two 200Ah LiFePO4 batteries.
 
That's $0.172/kWh; which is about the price of Liitokala 32700 cells that would need to do a lot of DIY to make into a pack, so might be a bargain.
Let's see... 202 Ah at 3.2V = 640Wh/cell
  • >6000 cycles at 100% DoD? Doubt that's true.
  • For the 32700s it's 5.6g/w and their weight is 4100g, so it's plenty heavy enough.
  • Max discharge rate is 2C? Lithium cells can do better than this, my guess is the wiring internally is skimpy.
  • Standard charging is 0.2C? That seems really low. If the BMS is charging at 80 amps, it could be a problem.
With the skimpy wiring, assuming you assembled them as two 12V batteries in parallel, would give you a max draw of ~100 amps at 2C. Seems low.

The standard charging of .2C means they would take forever to recharge (10 amps).

The BMS over current protection is 100 amps, but each pack maxes at 50 amps.

So nice price at $110, but I'd have concerns.

Update: Crossed out some stuff I had wrong... thanks Will!
 
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That 6000 cycles at 100% dod is a red flag in my book. Maybe at 90%, but 100%? Doesnt seem right

The lowest quality lifepo4 are 1c discharge rate, and high quality does 3c. 2c is not bad, but yeah, you will need a bms to match it. Daly has some awesome bms's available that I love. I have 5 of them for lifepo4 and they work great.

Oh .2c is standard on the data sheets. it says 1c max. and the battery studies say .4-.5c for lifepo4.

These actually seem like good cells for the price. People are buying these aluminum case ones and they work well. They are not a sinopoly, but they should work well regardless. I would buy an extra cell in case you need it later down the line, or if one is not matched properly when you get the set. Hard to beat for the price
 
That's $0.172/kWh; which is about the price of Liitokala 32700 cells that would need to do a lot of DIY to make into a pack, so might be a bargain.
Let's see... 202 Ah at 3.2V = 640Wh/cell
  • >6000 cycles at 100% DoD? Doubt that's true.
  • For the 32700s it's 5.6g/w and their weight is 4100g, so it's plenty heavy enough.
  • Max discharge rate is 2C? Lithium cells can do better than this, my guess is the wiring internally is skimpy.
  • Standard charging is 0.2C? That seems really low. If the BMS is charging at 80 amps, it could be a problem.
With the skimpy wiring, assuming you assembled them as two 12V batteries in parallel, would give you a max draw of ~100 amps at 2C. Seems low.

The standard charging of .2C means they would take forever to recharge (10 amps).

The BMS over current protection is 100 amps, but each pack maxes at 50 amps.

So nice price at $110, but I'd have concerns.

Oh these are raw cells. No internal wiring inside. The discharge rate is dependent on electrolyte and cell design with lifepo4. Sinopoly has the best at 3c. There are no wires inside, they are raw cells
 
have seen quality control issues with the vents and people complain that the support from the company is horrible. Their distribution is pretty bad too, why are they not sold at marine stores? But yes, amazing stats. I like them, on paper
 
I guess I'm stuck with lead acid until I save some money up.

I keep hearing all the great cheap stuff is right around the corner.

At 70 years old, right around the corner sounds a lot like right around the coroner.

Thanks for the help!
 
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