8s 24v BMS settings

OnTheFlyPDX

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Putting a 8s 24v 230ah battery together. Right now I’m doing the quick charge with a 10 amp bench supply and the cells in series with the jiabaida 100a bms (same as overkill) hooked up and set to shut off once any cell hits 3.65v. Then I’ll put them in parallel to do a top balance before reassembling in series with the bms. Wondering if anyone could take a look at my bms settings to let me know if I have set it up correctly for when I actually start using the battery in the rv? I will be using a lv2424 hybrid as my inverter/charge controller. Please let me know if there’s any other details needed. Thanks!
 

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Horsefly

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A few quick things:
  1. You almost certainly don't want the cycle capacity to be 80Ah on a 230Ah pack. That number is supposed to be how much of the total 230Ah available you expect to use each cycle. I would think 200Ah to 220Ah would be fine. If you stay "between the knees" (3.4V to 3.0V) you will probably get 215Ah or more.
  2. You have the over-voltage set to 3.6V. There's really no reason to have it anything other than 3.65V. It won't change much, but it will slow down the inadvertent high-voltage disconnect (HVD) a little bit.
  3. I personally would set the charge under-temp a little higher, like maybe 3° - 5°C. The reason is that if it doesn't trip under-temp until the sensors say 1°C, the sensors could be wrong. In addition, at low temps above 0°C you can charge, but at a lower rate. Better to raise the under-temp setting (and the release by the same amount).
 

Horsefly

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Ooops. I hit post before I meant to. :unsure:

The only other thing is the 80%, 60%, 40%, and 20% voltages. I don't really know that it matters much, and I'd like to think that the BMS is using some Coulomb counting to determine what the real SoC is. I have two JBD BMS's: One from Overkill, and one directly from JBD. On the Overkill one, I changed the numbers to mostly match the discharge curve that has been posted here lots of times. That one is set to 3.325,3.275, 3.25, and 3.2V. The one directly from JBD I haven't changed yet, but it has some crazy number: 3.329, 3.322, 3.291, and 3.266. I haven't messed with this second one enough yet to know how it works. I do know that the Overkill version with my settings seems to pretty closely match the SoC reported by my Victron Smart Shunt. But - as I said - I'm not completely sure how these voltages are used.
 

OnTheFlyPDX

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  1. You almost certainly don't want the cycle capacity to be 80Ah on a 230Ah pack. That number is supposed to be how much of the total 230Ah available you expect to use each cycle. I would think 200Ah to 220Ah would be fine. If you stay "between the knees" (3.4V to 3.0V) you will probably get 215Ah or more.

Thanks for explaining that Horsefly. I didn’t know what that parameter meant. Set to 215Ah. Also followed your advice on high voltage and temp cutoffs.

Ooops. I hit post before I meant to. :unsure:

The only other thing is the 80%, 60%, 40%, and 20% voltages.

I don’t understand what those values do either. Hopefully someone will chime in and explain.
 

Horsefly

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I just reviewed the Overkill manual, and they suggest 3.4V, 3.3V, 3.2V, and 3.1V. That doesn't sound like a scientifically analyzed set of numbers, but more of a "good enough" set. I think my first set are probably better.

Like you said, maybe someone will chime in with some knowledge of what exactly these are used for. I do hope it isn't for the SoC display.
 
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