question

jbakuwel avatar image
jbakuwel asked

Multi in float, battery SOC 39%

Hi all,

I've got an off grid client with a Multi, PV inverter (SMA Sunny Boy) and DC coupled charge controller combined with battery monitor (Midnite Classic). for which I've written a script to integrate it with Venus. The PV inverter's wireless link fails at times when it rains hence it doesn't show in Venus (you only see the DC coupled charge controller) but it of course still does the job. Multi is running firmware v2624474 with PV assistant and has been updated not so long ago.

As you can see the Multi is in Float:

multi-in-float.pngwhile the batteries are just being recharged after a couple of dark days. The charging parameters for the LFP batteries are:

veconfig-charger.png

Any ideas?

Jan

MultiPlus Quattro Inverter Chargerbattery chargingVRM
multi-in-float.png (27.5 KiB)
veconfig-charger.png (34.5 KiB)
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3 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

Where are you getting the SOC information? If it is from the Multi, then it WILL be incorrect as it does not see the charging current from the DC coupled solar controllers. The battery monitor calculating SOC needs to see ALL of the charge and discharge current.


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jbakuwel avatar image jbakuwel commented ·

Hi @Kevin Windrem,

Thanks for replying.

Yes, I know :-)

The DC coupled charge controller is equipped with a shunt and has a battery monitoring function. This battery monitor script reads the SOC calculated by the DC coupled charge controller, not the Multi and that battery monitor (not the Multi) has been selected in Venus as the battery monitor to use.

As far as I understand, the SOC is not part of the charging algorithms in the Multi; these are driven by V and current accepted by the battery. With a battery sitting at 53V (while being charged and at a known low SOC), and the Multi programmed as shown, I'd expect the Multi to be in Absorp, not Float.

cheers,
Jan

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Harold Lopez avatar image
Harold Lopez answered ·

Have you tried to measure the battery bank voltage with an external multimeter? Only to check if the voltage displayed is the actual system voltage. This measurement should be done with the solar charger turned off. In addition, you should check if the open circuit battery voltage drops abnormally below 13.2V.

In addition, you should try to measure the internal resistance of each battery, to check that all batteries are OK.

If everything seems to be OK, you should try adjusting your charge coefficient (peukert) in the Smarshunt and check if your settings match the battery supplier's specifications.

Best of luck.

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reenie-h avatar image
reenie-h answered ·

I have a similar problem. MPPT 150 70 is showing 42% but is in float mode.
I'm very new to this so please use simple terms and language that a clever 5 year old could cope with.

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