Shipping back.

[prestonbill]

Yup it was too good to be true. I ordered 8 300ah batteries from esare and thry came in approximately on time. The shipping voltage was between 3.299 and 3.30 with one bei g at 3.4. I paralleled them and charged to 3.64. Put them in series and hooked up overkill bms. Hooked up to inverter with electric 1500 watts and as soon as i turned the heater on the voltage dropped from a settled 3.52 to 3.3 and within 2 minutes or less 1 cell dropped to 2.5, cut off, and another one dropped to 2.9 with the other 2 just over 3.2. Am i doing something wrong and showing my ignorance? The other 4 did almost the same thing. So the final question is who to ship with to get them back so i can get a refund.
Bill

 

[time2roll]

Did you verify voltage on the cell terminals directly with a voltmeter to compare with the BMS? Would not be the first to have an issue with the sensor wire connections giving a false reading.

Can you test capacity of the cells that dropped to 2.5 volts? If they are flat dead they should take 30 hours individually at 10 amps back to 3.650 volts. If they go 2.500 to 3.650 in a couple hours they are DOA.

 

[Bob B]

Could also be a problem with the bus bar connections to the cells. You need to know how to use a DVM to troubleshoot.

 

[MisterSandals]

So the final question is who to ship with to get them back so i can get a refund.

Who did you order from?
If you ordered from an unknown seller in China, or even AliExpress, I am pretty sure there is a LOT more to it than just shipping them back.
Did you contact the seller and get a return authorisation?
Then, when you are told to pound sand, hopefully you can dispute with your credit card company.

 

[Bud Martin]

" I paralleled them and charged to 3.64."
What was the charging current and how long did it take to get to 3.64V?
Eight 300Ah in parallel (2400Ah), if charging from 50% SOC, that will be about 1200Ah, so charging at 10A rate that will be take about 120 Hours (5 days) to full charge.

 

[Dzl]

I think you need to do a bit more testing / verification before attempting a refund. You may well have received bad cells and you may well be making a measurement error or have some other issue on your end.

 

[Brett V]

“ Hooked up to inverter with electric 1500 watts and as soon as i turned the heater on the voltage dropped from a settled 3.52 to 3.3 and within 2 minutes or less 1 cell dropped to 2.5, cut off, and another one dropped to 2.9 with the other 2 just over 3.2. Am i doing something wrong and showing my ignorance? The other 4 did”

so you’re pushing 1500 watts on a 4s battery? Conservative ball park figure is 150 amps minimum. How well did you clean and prepare the bus bar connections? At that load, good…no, REALLY good connections are critical.

 

[prestonbill]

Well i will start over and clean all connections. Hopefully it will help and things will line up. After doing 1500watts (125amp) i lowered it to 1350 watts because i have overkill BMSs that are 120 amp. Still dropped down. Time to get busy. Thanks guys

 

[Dzl]

Well i will start over and clean all connections. Hopefully it will help and things will line up. After doing 1500watts (125amp) i lowered it to 1350 watts because i have overkill BMSs that are 120 amp. Still dropped down. Time to get busy. Thanks guys

Even 1350W may be well be exceeding your BMS limits after accounting for inverter inefficiency (for example an inverter @85% efficiency supplying 1350W would be pulling 1350 / .85 / 12V = 140A). I dont know if this could account for your problem, but its not something you want to do regularly. I think the JBD BMS has self protection features, but exceeded the BMS current rating, or even running near 100% for a prolonged period of time, is best avoided.

As to the problem, independently verifying the cell voltages with a multimeter as @Bob B alluded to, and rechecking/cleaning/fastening all connections as you are planning to do seem like good first troubleshooting steps.

 

[prestonbill]

Thanks Dzl. I did not put the inverter in the loop.

 

[Dzl]

Thanks Dzl. I did not put the inverter in the loop.

Gotcha, sorry, I misunderstood

 

[prestonbill]

Gotcha, sorry, I misunderstood

I meant that i didnt figure it in.