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don-b asked

Defective Multiplus Compnact?

The Multiplus is installed in a motorhome. Before the electric water heater turned on, the DC buss was at 13.60V (the float voltage), and current in/out of the battery was 0.0. But when the electric water heater turned on, the AC voltage dropped from 120V to 115V and the DC output of the Multiplus Compact dropped from 13.60V to 13.55V and the current draw from the battery went to -4.5A (there are 12V DC loads always present). The Multiplus DC voltage slowly climbed back to 13.60V, and the battery discharging slowly went back to 0.0V, but this affects my battery monitor’s SOC readout (slowly dropping over time while on shore power). And this behavior needlessly discharges my battery. Why isn’t the output of the Multiplus more stable with varying AC input voltages? Did I get a defective Multiplus Compact?

MultiPlus Quattro Inverter Charger
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2 Answers
ejrossouw avatar image
ejrossouw answered ·

Hi @Don B. Is the multiplus configured to power assist? What is the current version of the installed firmware? How stable is the shore power? If the multi struggles to sync it may well have stepped in to ensure you still have a hot shower. Has this been happening at other shore power connections? And finally, when there is a load applied to a battery, it is normal for the voltage to drop and then recover when the load is removed. Maybe if you can provide more insight on the setting and actual model, this could be better explained and possibly be remidied. You mention DC output on the multi? The only DC output is the charging of the battery to my knowledge or am I missing something? I'm no expert, but this is where I personally will start looking.

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don-b avatar image don-b commented ·
ejrossouw, thanks for replying. I'm not using the Multiplus's inverter, only as a charger, and to provide DC voltage to the 12V DC buss in the motorhome for the 12VDC appliances. And the Multiplus AC Input Current Limit is set to 50A and I'm on a 30A breaker, so its power assist feature is not being used.

Using VEConfig, I see that the "Software Version" is 2708430. I'm assuming this is the Multiplus's firmware version and not VEConfig's. I don't know how to see if this is the latest firmware for my Multiplus. It is a brand new unit, and I did ask the dealer to make sure it had the latest firmware.

You mentioned that it is normal for the voltage to drop and then recover when the load is removed, and I agree when we're talking about the AC input to the motorhome. But since I've had bench power supplies that could maintain a rock solid DC output voltage regardless of a small variance of their AC input voltage (especially when their DC output current was low), this is what makes me think that a high quality DC power supply such as the Multiplus should be able to maintain a rock solid DC output voltage regardless of a small variance of AC input voltage, because this small discharging/charging of the house battery messes with the BMV-712's SOC algorithm, which didn't happen with my old lead acid AGM battery and old Battery Monitor... it stayed at 100% SOC when plugged into shore power with the same electric water heater and air conditioner. Which makes me think that maybe I got a defective Multiplus? I really wish I could hash this out with Victron tech support, but it appears there is none. And the tech support of the dealer I bought the equipment from isn't helping, which is why I'm here. - Thanks!


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Kevin Windrem avatar image Kevin Windrem don-b commented ·

The Multi is not a power supply. It's a battery charger and as such it backs out of the way when the battery reaches it's float voltage. It won't kick back in until the battery voltage has fallen back down to the absorption threshold voltage.

If your AC loads are connected to the Multi's output then it may kick into assist mode on heavy loads for a little while. When this happens, the inverter/charger core is no longer functioning as a charger, but rather as an inverter taking power from the battery. This can quickly bleed off the float charge. If you put the Multi in CHARGE ONLY mode then it won't do this which would be a good test.

Are you saying that the SOC is dropping significantly over time? E.g, down to 80%. Or is it just dropping a couple percent then back up again?

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Kevin Windrem avatar image
Kevin Windrem answered ·

You maybe exceeding the input current limit programmed for the Multi. The Multi would then be working in assist mode and drawing power from the battery to supplement limited incoming AC power. The default input current limit is the maximum for the inverter model but can be changed in configuration during install OR via the power control panel or GX device (CCGX, Cerbo GX, etc.).

The GX device will tell you what mode the Multi is operating in but you can also read the status via the lights on the front of the Multi. Refer to the manual for a description. (Power assist is indicated by MAINS ON solid on and INVERTER ON flashing.)

It's possible the incoming AC is falling below the minimum acceptable voltage under heavy load and is being rejected. The default is 94 volts so unless this was changed during install and configuration 115 volts should be OK.

When the Multi is in the ON mode and AC input is present (and accepted by the Multi), the Multi's output voltage will track the input since they are essentially tied together. The inverter/charger core can "assist" incoming power if the input current limit is exceeded or use excess incoming power to charge the batteries. But the AC output voltage can't be different than the AC input voltage in this condition. If AC input is not present, the Multi will produce 120 volts at its output.

It will help us diagnose your problem if you list all components in your system including inverter/charger model, any GX device battery monitor, solar, etc.

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don-b avatar image don-b commented ·
Kevin, thanks for replying. The Multi's input current limit is set to 50A, so it's not working in assist mode here in my tiny motorhome (I'm on a 30A breaker). And as I mentioned, the drop in the Multi's DC output is only temporary... it slowly returns to the set voltage of 13.60V within about 10 seconds. But during this time, the battery is discharging. And when the air conditioner's compressor or the AC electric water heater engages, the motorhome's AC voltage will dip from 124VAC to 120VAC, so still within the Multi's range of operation. But it is this small dip in AC voltage which appears to be causing the proportionally small dip in the Multi's DC output voltage... which is what I feel should not occur. I've had bench power supplies that had a rock steady DC output when the AC input would vary like mine is varying. This is what makes me think I might have gotten a defective Multiplus.


Multiplus Compact 12/2000 (in charger mode only, I don't use the inverter portion)
Victron BMV-712
No solar
Battle Born 100AH battery



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