Amp hours drawn not even close to what SOC is reporting.

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neoneddy asked Apr 14, '19

Amp hours drawn not even close to what SOC is reporting.

I've got a fresh 600ah @24v Telecom battery bank.

2x Multiplus 3kva

2x 100/50 mppt

BMV 702

Raspberry pi Venus OS device (latest beta 2.3~40)

I'm 3-4 days into a run here where we've had no sun , only snow and clouds. I'm 230 ah drawn, but SOC from the BMV says 80% or so , on average I'm pulling 2.4 amps. Being that's it's cold here still, I'm not using much power for the fridge in my RV, no AC, or anything else.

Battery temp is around 5.5 C 30-40F

Battery voltage is around 24.4. Under load

I have set the capacity of my bank at 600ah in the BMV as well as resetting the cycles and history when I changed battery banks.

Only thing I can think of is because the draw is so slow, the effective capacity has increased. The 600ah is at a 20 hour rate across 6 batteries in a 3x2 configuration, I think that's 30a per hour draw, I'm at 2.4a per hour.

battery charging monitoring battery capacity

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Answer 1 · 2019-04-14T18:18:47Z

Ole Saether answered · Apr 14, 2019 at 06:18 PM

If you want the SOC to follow Ah discharge you need to disable Peukert compensation. See section 4.2 05. Peukert exponent in the manual.

Also please search for "Peukert" in the manual and read and you will undestand why the BMV works like this.

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Answer 2 · 2019-04-14T18:44:32Z

neoneddy answered · Apr 14, 2019 at 06:44 PM

I understand Peukert's Law, sorry I didn't mention it. I guess I hadn't done the math on it.

I wonder if my Peukert's number is wrong for my battery bank, I think I'm using the default. I had to do custom charge parameters for these AGM batteries, the stock victron options all seemed to bulk charge at too high a voltage. 14.6 or 14.8 for some. I wanted 14.4 per 12v battery, I bring all this up to wonder if all my custom settings are messing up the automatic Peukert compensation, or I guess this is just how the long tail plays out.

Thanks for the insight.

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