BMV 702 SOC incorrectly reading 100% when charging via solar

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bluerover asked Jul 8, '19

BMV 702 SOC incorrectly reading 100% when charging via solar

I have a battery bank on a norrowbaot, charged by an alternator and mppt solar. Monitored using a BMV702.

bMV settings are

Charged voltage 13.2 as recommended in the manual for a 12v system

Tail current 1.5%

When charging via th alternator everything works fine. SOC reads 100 once the current going in drops below the tail current. This is usually when the “current consumed” is displaying at close to 0AH.

However, when the battery is being charged by solar and the engin is not running, the SOC will jump to 100% even when the “current consumed is still way off 0 (maybe at-20AH. If you then start the engine the current going into the batteries will be way above the tail current suggesting the bats are not fully charged.

The issue I think is that the MPPT controller regularly outputs less than the tail current into the batteries ( we only have. Single 160w panel, thus making the monitor believe that the tail current has been reached and the battery fully charged.

2 questions

1.does my assessment of the situation seem reasonable

2. Is there a way to prevent this (maybe by changing the charged voltage or tail current?) would there be an issue changing the BMV charged voltage to 14.4 to match the adsorption voltage set in the mppt controller?

Thanks in advance for any advice

BMV Battery Monitor solar

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Answer 1 · 2019-07-08T23:23:38Z

Mark answered · Jul 08, 2019 at 11:23 PM

Yes your assessment sounds correct and reasonable.

I would firstly start by increasing the 'charged voltage' to about 0.2 to 0.4v below the MPPT absorption voltage. BUT as you are also using the alternator to charge then ideally it should also be set below the alternator charge voltage so that it can sync from BOTH sources. If the alternator is charging at a significantly lower voltage than the MPPT then you may need to compromise and only set it up to sync from the MPPT.

I wouldn't go any lower with the 'tail current %', but you could try increasing the 'charged detection time'.

To better 'track' the battery SOC % without having to constantly sync you can also play with the 'charge efficiency' as required.

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Answer 2 · 2019-07-09T08:45:38Z

bluerover answered · Jul 09, 2019 at 08:45 AM

Thanks, I will give those suggestions a go and let you know how I get on

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