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philb avatar image
philb asked

Connecting a Victron MPPT to a Multiplus inverter - charger disabled.

I have a Multiplus 48/5000/70 operating as a UPS connected to a 48 battery bank. I have dissabled the charger of the Multiplus in VE Configure.

I have recently purchased a SmartSolar charge controller MPPT 250/60 to charge the batteries/supply the inverter. When connecting the the charge controller to the DC bus (with the batteries isolated) there was considerable arcing. I was expecting no voltage to be present as the Multi's charger was off. However there is 39Vdc from the Multi present on the DC bus.

Is this voltage normal with the charger is off? Is it safe to connect the Multi and the charge controller to the bus or can either of them be damaged?

MultiPlus Quattro Inverter Charger
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Murray van Graan avatar image
Murray van Graan answered ·

Hi @PhilB. You most likely measured the charge held by the large capacitor bank inside the multi which was charged when the batteries was connected.

It is safe to connect both the multi and MPPT to the DC Bus, obviously each device should be fused correctly.

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solardude avatar image
solardude answered ·

I always recommend a switch or contactor between the battery and each component. Turning the switch or contactor OFF will eliminate the big arc when connecting components. It also gives you options when servicing individual components without having to disconnect the whole system.

The spark is normal, but I don’t like it, so I put a switch or contactor on every battery system I install.

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

If you don't see the spark (because it's in a switch or contactor), doesn't mean it is not there.

These arcs can destroy a switch or contactor really fast, always pre-charge, or for a one time connection: live with the spark.

On my test systems, I always make sure voltages are almost equal to prevent sparks.

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