MultiPlus Compact 12/1600/70-16 doens't charge to 100% goes into decharging float

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lsi asked Sep 19, '22

MultiPlus Compact 12/1600/70-16 doens't charge to 100% goes into decharging float

I have 2 Victron AGM Supercycle 170 batteries in parallel and my Multiplus doesn't seem to charge them to 100% but comes in a float stage, slowly discharging.

I restarted the Multiplus. It goes into bulk for about 30 seconds, then to absorbtion for 15 minutes with only 1,8A of charging and then to float with 0,3A

As this system has some small users while idle, it actually is decharging slowly.

I would expect that when the BVM712 is at 84% the Multiplus would go into bulk and then absorbtion until almost full and the to float where the float charge is equal or higher than drain from small users.

The system looks like this;

MultiPlus Compact 12/1600/70-16 running firmware 497
Color control GX running firmware 2.89
BMV712-F running firmware 4.08
3x SmartSolar Charger MPPT 75/15 running firmware 1.59
2x Victron AGM supercycle 170 in parallel
Victron Cyrix which charges the starter battery

The multiplus, BMV and smart solars are all connected to the color control using the VE bus.
The smart solars and BMV 712 also are connected in their bluetooth network
Interesting enough the smart solar shows in their configuration (in the color control) that they are not networked.

Multiplus-II float

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Answer 1 · 2022-09-19T12:22:36Z

JohnC answered · Sep 19, 2022 at 12:22 PM

Hi @LSI

On the face of it, it appears that your batteries are fully charged and the BMV is showing an incorrect SOC. Don't use the SOC from the Multi, turn that off if it isn't already. Grab a copy of the BMV manual from the Victron website and get familiar with it. There's also tutorials to help with setting it up correctly. Come back if you need more specific help with this. A couple of other little things..

The Amps from the BMV aren't adjustable, so if it's wired up correctly it will show/contain your "drain from small users", so no need to guess.

Best turn off your BT networking. That's mainly for systems without a GX, and you don't want it interfering anyway. Take a look at the DVCC section in your CCGX manual for similar functionality.

And oh, VE.Bus is only between the Multi and the GX. The BMV and mppts are likely using VE.Direct. (Just for pedantics).

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lsi commented · Sep 19, 2022 at 01:27 PM

Thanks @JohnC

I changed from a BMV702 to 712 and must have made a mistake with the battery full voltage.

Still the Ah drainage is a mystery sometimes. First in negative line from the batteries there is a Victron 500 shult connected to the BMV712 which is connected to the color control.
Behind the Victron shunt there is another shunt from Simarine (which came with their Pico tank monitor). Interesting enough the BMV712 shows more Ah drained than the Simarine.

Regardless of the SOC, I would assume that when the BMV712 has a status of 70 Ah used, it should charge with more than 70Ah to get back to 100%

Thanks for pointing to the DVCC function. Ignored that because of the warning but will turn it on now. Will see than if the MPPT's are seen as part of the network. They are individually connected with VE.direct to the color control (but I was told that they would not work together with the Multiplus with regards to coordination of going into bulk, absorbtion or float mode).

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JohnC ♦ lsi commented · Sep 19, 2022 at 02:10 PM

@LSI

Indeed it will need more than 70Ah to get back to 100%, because of the Charge Efficiency. But you won't see that reported anywhere, only the Discharge since the last sync. It will count back, but that's an adjusted figure.

You won't see DVCC reported as 'networked', but the wires and the selections you've made within it are gospel. You can use the Tail function in the mppts to terminate Absorb, using the SCS part, but the Multi doesn't do that. And it probably shouldn't either, as using both the mppts and Multi together need special considerations. And you'd need to think over why you would want to put your batts through another full charge cycle when solar may have already done it on a particular day.

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Answer 2 · 2022-09-19T12:28:49Z

lsi answered · Sep 19, 2022 at 12:28 PM

Turned our that somehow the fylly charged voltage of the BMV712 was set to 14,4

Reduced it to 13,4 (float voltage at 13,6)

Aborbtion charging remained now for about 1 hour, starting at SOC 84,7% up to 87%

After an hour it reset to 100%

Still curious about whether the batteries are really full or not.
I believe the Ah used was about 70Ah while 84,7% suggest only 52Ah used and when charging for an hour at 5A it could never recover from -52Ah....

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JohnC ♦ commented · Sep 19, 2022 at 12:52 PM

@LSI

The batteries are full when they can't accept (much) charge. And the BMV can be set to act on this (good you found the CV setting). Your BMV had drifted and the SOC reading wasn't correct.

Ah Discharged wont match SOC anyway if you're using a Peukert Exponent above unity, so take care with this. And Charge Efficiency adjustment can help prevent future drift, you just need to apply yourself to getting it right.. :)

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