Help with Battery capacity on BMV 712

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cplus asked Aug 8, '22

Help with Battery capacity on BMV 712

I'm converting the lead acid battery to LiFePO4 on my rv right now, just hooked up the Victron mppt 100/50 solar charger, Victron BMS 712 and a 2000w inverter connect to a brand new 200ah LiFePO4 battery for testing, all other chargers and loads are disconnected. I did few discharge tests with a hair dryer through the inverter, in 10 mins it used about 20ah battery, and it shows 80% battery remaining, I charged up again did the same test and got the same result. According to this the battery is only 100ah not 200ah, a 1700w device can only last 45mins, is there something wrong with the settings or the battery?

Thanks in advance.

BMV Battery Monitor

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cplus commented · Aug 08, 2022 at 09:24 PM

Thanks for the reply, sorry I didn't make my self clear, I have a 200ah battery, does it looks right? The battery has a 200a BMS, so I hope that's ok for the drain

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kevgermany ♦♦ cplus commented · Aug 09, 2022 at 03:20 AM

Sorry, brain fade on my part. You were clear.

All I've done is show the 712 is working off a 100Ah base, not 200Ah.

Try setting the 712 to a 100Ah battery and repeat the test. If the numbers don't change, try setting it to a 400Ah battery and repeat. Looks like there's a problem with the 712, might be software.

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cplus kevgermany ♦♦ commented · Aug 09, 2022 at 04:04 AM

I did changed it to 100ah and run the same test, it shows 19 mins time remaining about 1 min into the test. I'll try set to 400ah tomorrow. thanks

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Matthias Lange - DE answered · Aug 09, 2022 at 03:38 AM

Set the Peukert to the recommend 1.05 and test again.

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cplus commented · Aug 09, 2022 at 04:05 AM

I will give a shot tomorrow and report, thanks

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JohnC ♦ cplus commented · Aug 09, 2022 at 07:48 AM

The Peukert is your problem for sure. When you have a fair amount of Ah registered, you can actually change it and it will recalculate the Ah. And you can change it back at will.

If you think your batteries are perfect, then you could set it to 1.0 and see the actual Ah measured, not corrected. But they won't be perfect in practice.

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Answer 1 · 2022-08-08T17:16:21Z

kevgermany answered · Aug 08, 2022 at 05:16 PM

Your 1700W load is pulling about 134A, so expected life of the battery is about 100/134*60minutes, assuming you empty it completely. About 45minutes.

20% of 45mins is 9 minutes. So the 80% after 10 minutes is correct (rounded)

80% of 100Ah is 80Ah or 20Ah used.

So meter/settings/readings correct.

However draining the battery this quickly will give lower real capacity than 100Ah. And unless the battery is rated for this discharge rate, will cause premature failure of the battery.

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Answer 2 · 2022-08-09T04:50:59Z

cplus answered · Aug 09, 2022 at 04:50 AM

Sorry I lied can't wait till tomorrow knowing I might have a wrong setting, changed the peukert to 1.05 and solved the problem.
Thanks!

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