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hugues asked

Battery voltage dropping down to 3V when switching on Multiplus II inverter

All brand new equipment and battery here.

Multiplus II 24 / 3000 / 70

Acconic lithium battery 200 Ah 25.6V nominal

Just connected my inverter for the first time today through the Lynx distributor.

Made sure the battery + and - are set properly on the inverter.

Inverter is grounded to the vehicle chassis and ground connected to negative bus of Lynx distributor.

Inverter switch is in off position.

As soon as I turn on my main circuit switch, battery voltage drops down to 2-3 volts, I then turn off immediately the switch, voltage comes back to normal (26.2V) right away.

If I disconnect the battery plus cable on the inverter, then turn on main switch, battery voltage remains stable.

I disconnected all cables from the inverter and measured the resistance between battery plus and minus, i get a slowly climbing reading of 35 kohm after 10-15 minutes, climbing very slowly from this point, starts at around 1 kohm.

I connected the inverter to shore power (AC IN), and managed to connect my laptop to it with the MK3.USB dongle. Made sure all the battery parameters are ok. Upgraded firmware, restarted.

When inverter is powered by AC-IN, i can switch on my battery connection and voltage does not drop. I can charge the battery from the inverter. Voltage is currently around 26.2 V when no load, I would think the battery SOC is around 50%, but it's new so difficult to tell. BMS discharge cutoff is 20.8V according to battery spec.


Any idea what is going on ? Could it be that my battery SOC is close to 0% and when the inverter capacitor is charging it trips the battery BMS ?

I'm currently charging the battery.



batterymultiple inverters
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2 Answers
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hugues answered ·

Just realised today that if i turn on my MPPT solar charger first then I can turn on my main switch and battery voltage keeps steady. I guess the MPPT gets most of the inverter capacitor inrush current. I will still install a pre-charge resistor with a push button accross my main switch though, in case the MPPT trick does not work.

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nickdb avatar image nickdb ♦♦ commented ·
This is why it is the easiest and preferred precharge method. As long as the sun is shining.
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hugues answered ·

Update:

I charged my battery using shore power and inverter/charger.

I don't think the battery was close to 0% SOC, it did not take much time to charge.

But in any case, now that it is almost full (90% SOC, voltage was close to 29 V),

I still have the same problem: when the inverter is switched off, when i connect my battery to it, battery voltage drops right away to 2-3 V, probably BMS tripping.

I can only start the inverter from shore power, then I'm able to connect the battery.

Not sure if the problem is with the battery or inverter.

Tomorrow I'll install my 220 V breaker box and connect a load to the inverter, without shore power, to see if the battery can follow without tripping.

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kevgermany avatar image kevgermany ♦♦ commented ·
Might be that the battery can't handle the inrush current for the capacitors in the Multiplus. BMS cuts out.
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