SmartSolar 100/50 appears to short out battery - is this normal?

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frankvw asked Jun 7, '24

SmartSolar 100/50 appears to short out battery - is this normal?

I've got a Multiplus 24/100/16 connected to a BlueNova 26V 108Ah 2.8kWh LiFePO4 battery. This works fine. Now I'm adding a SmartSolar 100/50 which will charge the battery when there's sunlight, while the Multiplus will charge it from the mains at night and on cloudy days. I have also added a separate Phoenix inverter fed from the same battery.

Since the MPPT and the SmartSolar both charge the same battery (in parallel) they should have the same charging profile. The instructions for the Multiplus state that one should connect it to just the battery, set it up properly and only then connect it to the mains. So I did the same with the SmartSolar: I connected it to the battery with the expectation that that would allow me to set it up before connecting the PV array.

However, the SmartSolar appears to short out the battery: as soon as I connect it the battery clamping voltage drops to 2-3V. There's no arcing and the battery fuses don't blow, so my guess is that the BMS throttles everything down to prevent overloads. Disconnecting the SmartSolar restores normal battery voltage and the Multiplus works normally again, as does the Phoenix inverter.

Is shorting out the battery normal behavior for the Multiplus if there is no PV array connected? Is there a way for me to set the SmartSolar to work with the proper charging profile first before connecting the PV array? Connecting the PV array would mean that the SmartSolar will begin to charge the battery before I've had the opportunity to set the proper charging profile. But maybe I'm wrong and going about this the wrong way.

Any advice would be helpful. Tnx!

// FvW

battery charging MPPT SmartSolar setup

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Answer 1 · 2024-06-07T21:09:02Z

delf67 answered · Jun 07 at 09:09 PM

No, that doesn't sound normal at all. You should be able to connect the smartsolar to the battery and program it before you connect the PV. Do you have a different battery you could connect the MPPT to and see if it exhibits the same behaviour? A 12V lead acid would do to see if the MPPT has a fault.

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Answer 2 · 2024-06-08T09:48:50Z

frankvw answered · Jun 08 at 09:48 AM

I tried two SLA batteries. That worked. Then I reconnected the LiFePO4 battery again and now that works, too! My guess is that because out-of-the-box all capacitors are still entirely discharged the rush-in current makes the BMS nervous. But then, BlueNova batteries are known for having a somewhat temperamental BMS, as I understand it.

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delf67 commented · Jun 08 at 10:04 AM

Glad you sorted it.

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frankvw delf67 commented · Jun 11 at 12:00 PM

It's a bit of a pain since it's a matter of timing: I have to disconnect the battery, then reconnect it before the capacitors in the inverter and solar charger have discharged too far. Of course the battery will not be disconnected often, so once it's working it's working, and I guess I can live with it now that I know the nature of the beast.

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