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scott asked

MPPT 150/85 magic smoke

Hi all, so...magic smoke.

My charge controller happily charging (48V) batteries on an "equalize" setting. No problems so far. I switch on my MultiPlus 48/5000/70-100, with no load - just switch on the battery isolator. Suddenly smoke from the CC. Switch all off instantly.

Both had happily coexisted and functioned together the previous day.

No visible popped capacitors after removing the cover, and all connections are good. Panel voltage within specs (110V), and battery too. One battery (of the 4) suss, though still at 12V. I connect the CC with a good 12V battery, and switch on battery isolator. Sparks! Switch off quickly.

Inspect, and nothing out of the ordinary. Check battery and panel voltages, and all good.

Have beer, and curse unit.

Next day, reconnect 48V battery and switch on CC.

Lights come up, and accepts 48V battery bank - no sparks or smoke.

Check voltages before switching on panels, and solar panel "voltage in" terminals reading 47V???

Should be 0V - no?

No shorts, and panel voltage isolated. 47 v is coming from within charge controller.

Suggestions please!


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wkirby avatar image
wkirby answered ·

Smells like MOSFETs to me. I've not had the lid off a MPPT, but I imagine that you would not see the MOSFETs as they would be underneath the PCB.

Whenever you connect the battery to a MultiPlus there is a high inrush current as the capacitors inside charge up. This inrush current could have pulled the battery Voltage down significantly if you have a suspect battery. The sudden unexpected Voltage drop could have caused excessive current to flow through the MPPT which in turn allowed the smoke to be released from the MOSFETs.

The 47V you see on the PV terminals is the battery Voltage (with some Voltage drop) as the semiconductors in the MPPT are short circuit.

Using the switch on the front of the Multiplus to turn it on and off mitigates the massive inrush current to it.

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scott avatar image scott commented ·

Thanks WKirby, sounds like you have it.

The sparks seemed to come from under the circuit board, but as the unit is under warranty I dont want to start dismantling.

Have only had the lid off to make connections to the battery/panels.

I like the Victron units, but surely this scenario could have been protected against?!


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