BMV 700 not synchronising

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linkshouse asked Aug 5, '22

BMV 700 not synchronising

Good morning.

My BMV700 never synchronises even though it regulalry registers 100% charge.

I have included screenshots from this morning taken just now (around 07:00). As you can see the current status is 99% by mid morning the solar panels will have taken this back up to 100%. I never thought to include screenshots of the solar controller history but this is going into float every day too.

My question therefore is why does the BMV never show any synchronisations, and does this matter?

Many Thanks

Phill

BMV Battery Monitor

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Alexandra ♦ commented · Aug 05, 2022 at 06:23 AM

@linkshouse

What batteries do you have? Lead acid?

What are the charge voltages on the mppt?

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linkshouse Alexandra ♦ commented · Aug 05, 2022 at 06:26 AM

2 x 100Ah Lead Carbon (110Ah - 100Ah at C20)

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linkshouse Alexandra ♦ commented · Aug 05, 2022 at 06:31 AM

Rather than try and remember off the top of my head I just popped out to check the mppt settings -

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kevgermany answered · Aug 05, 2022 at 11:44 AM

Somewhere on the manual it says that synchronisation count is only after a discharge to xx%. I think it was 80%, but no time to check now. Your numbers show little discharge, so looks really good to me.

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linkshouse commented · Aug 05, 2022 at 02:15 PM

I suspect that’s it, thanks. I hadn’t spotted that. A related question for me was that there were no charge counts either and it’s the same problem.

I see in the manual now I knew where to look that it needs to drop below 65% for a charge cycle and 90% for a synchronisation.

At the moment the van has been parked on the drive since I upgraded the batteries so I don’t think they’ve ever been below 95%.

Thanks

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Answer 1 · 2022-08-05T13:23:15Z

JohnC answered · Aug 05, 2022 at 01:23 PM

Hi @linkshouse

It won't sync if the SOC has already reached 100.0%. You'll have to read that last decimal point from the settings page.

With such light loads and the settings you're using, that's likely to be a very common occurrence. The high Peukert will be underestimating the Ah drawn (get your batt specs and put them through Victron's Peukert Calculator, ideally C20 vs C100), and then consider reducing the Charge Efficiency Factor (different batts, but I use 90-91%). Both these things contribute to reaching the 100% prematurely.

Then to actually have a sync occur, it needs to meet the necessary conditions. You have Charged V set up just below Absorb, so if it's already dropped to Float by the time the Amps get lower than 3% it won't sync either. You need to decide whether to sync in Absorb or Float and set the Tail Accordingly (3% will be too high at a Float V, I use 0.7% in winter and 0.6% in summer).

You really need to understand how this all works, and tune it to suit.

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