Skipping cell testing on small build?

[BongoPete]

I'm building a small 230a 12v battery for a van setup using supposedly EVE cells (Docan) and a 200a JBD BMS. I don't have a power supply unit to top balance, and I don't have a capacity tester. I do have a basic multimeter. I don't plan on building any other batteries in the foreseeable future.

I'm debating whether or not it's worth it to spend $40 on a PSU to top balance and/or some more $ on a tool to capacity test. A Google didn't reveal anywhere near me (Portland, OR) that offers this type of service or rental of these tools.

I'm thinking about just building the battery and using it and keeping an eye on the BMS stats and the shunt (probably victron but TBD). This would make a dispute harder to succeed at with Docan but I think that would be an uphill battle anyway (maybe credit card company would step up). Am I a fool for skipping these steps?

 

[Rocketman]

Probably a fool for skipping… but I did the same…

I made two batteries a small 12v 50ah with eight 25ah 2p4s Fortune cells. Then I got eight 272ah Lishen cells and made a 12v battery 2p4s 544ah. For the big battery I made the box so the cells would just fit in when at the shipping charge (40%???) automatic compression when filled to 100% - so I did not top balance them - nor try to match a high & low cell. It has worked for me - but your mileage may vary.

After it was in I filled the battery, then did a useable test - turned off charging to the MotorHome, and ran everything until my Victron inverter stopped - which was when I called the test. The bms had not shutdown yet. (I figure there was another 8% or more in it).

I think I got about 530 Ah for useable - used the batteries for 1-1/2 years in the MotorHome, did another useable test and it stopped at 525Ah. I am very happy with the batteries.

 

[42OhmsPA]

I've been running 32 230ah EVE cells from Docan since October 2022 in 48v packs, 8 of them were used in a 24v pack for months before I converted to 48v, I didn't capacity test any of them.... I see over 440ah measuring with my shunt, I haven't taken them below 3.125v per cell. I have zero concerns they don't meet / exceed specs.

 

[LakeHouse]

I'm building a small 230a 12v battery for a van setup using supposedly EVE cells (Docan) and a 200a JBD BMS. I don't have a power supply unit to top balance, and I don't have a capacity tester. I do have a basic multimeter. I don't plan on building any other batteries in the foreseeable future.

I'm debating whether or not it's worth it to spend $40 on a PSU to top balance and/or some more $ on a tool to capacity test. A Google didn't reveal anywhere near me (Portland, OR) that offers this type of service or rental of these tools.

I'm thinking about just building the battery and using it and keeping an eye on the BMS stats and the shunt (probably victron but TBD). This would make a dispute harder to succeed at with Docan but I think that would be an uphill battle anyway (maybe credit card company would step up). Am I a fool for skipping these steps?

You’re not doing anything wrong by not capacity testing.
I bought a truck a few years ago and the manufacturer claims it has a 420 Horsepower engine and that the gas tank holds 136L of fuel.
I’ve not tested either of these claims directly.
Dynamometers are expensive.
I’ll grant that I could probably measure the fuel tank capacity with minimal effort, but I know that in the past I’ve put more than 120 liters in when the fuel has been low. So if it’s only 130L instead of 136, would it really matter much? I think not.
My point is: if your testing costs more than it’s worth, don’t feel bad about skipping it. And if your 230’s turned out to be 228’s, you’d feel like you got cheated but in reality you’d be short less than 1% of your promised capacity. Build your battery and use it, and soon enough you’ll get a decent idea of how much capacity it has.

 

[Rednecktek]

I had similar thoughts when I built my first battery and sprung for the DC power supply but not the tester. When I built my second battery I was glad to have the power supply. I've built 4 now and not only use it to top balance but have used it at times to fake solar input to various MPPT controllers since sun and the Pacific Northwest tend to be mutually exclusive most of the year.

As for the load tester, the various shunts and field tests have been "on paper" for what's expected so good enough for me. If I only get 276ah out of a 280ah battery, it's usually the BMS that's cutting out anyways, so close enough.

 

[BongoPete]

Thanks for the feedback. I'll probably skip it from the outset and if I have any problems with cell voltages matching I'll rethink it.

 

[Rednecktek]

A few charge/discharge cycles, doesn't have to be too deep, will also allow the BMS to get some balancing time.

 

[Ellcon123]

I never tested my 3 packs. Just built and started using. The BMS and balancers keep things sorted.

 

[JJJJ]

Capacity testing was very popular a few years ago when buyers would attempt to authenticate the cells they purchased. I personally found top balancing invaluable in my case. One of my battery sets came from a EV breakdown and individual and then top balancing woke up the electrolyte in the cells. An active balancer has kept them very well maintained since then.

 

[Skypower]

Your bms may give you a “ballpark” idea of the overall capacity once you get a few cycles on it. Take it down to 10% and note kWh. You should probably have a good battery meter in your van and it’ll give you a better idea of what the whole battery is worth. Charge-Discharge Multi Tester, DROK 0-120V 400A DC Voltmeter Coulometer, Battery Monitor https://a.co/d/c0Eeanu

 

[sunshine_eggo]

Thanks for the feedback. I'll probably skip it from the outset and if I have any problems with cell voltages matching I'll rethink it.

You probably will. Even if the as-received voltages are identical, that won't mean anything meaningful in terms of balance. Worth noting that "balance" refers to state of charge - NOT voltage. Voltage only represents balance when all cells are above 3.40V.

My 9 cells came in with about 30Ah difference in their as-received SoC. That would take about 1-2 months for a JBD to balance assuming it's above 3.40V/cell 24/7.

If you find you can charge to the desired voltage without triggering BMS charge protection, balance is good enough.