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Rob Mitchell avatar image
Rob Mitchell asked

What happens to onboard 12v accessories when I replace charger/converter with multiplus?

I'm about to replace my onboard charger/converter (12v) with a Multiplus 12/3000/120. I will be disconnecting the charger/converter and wiring the multiplus into the breaker panel 120v circuits.

Since the 12v converter will be disconnected as it's an all-in-one Parallax 7345 unit I assume I will loose the ability to operate all my motorhome 12v accessories that we connected to the DC circuit branch of the breaker panel.

Is my assumption sound? If so what have others done to get the 12v line operational? I'm thinking the 12v lights, radio, etc.

dc system
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6 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

You can to leave the DC connection from your battery bank to the converter as-is. (Your Multi will connect to the battery also.) You can disable the power panel's internal charger on it's AC input side. The DC output side of the charger will remain across the battery but that's OK.

Disconnect your RV from AC shore power and turn off the Multi so there's no shock/spark hazard.

Remove the cover from your power panel and locate a wire that runs from one of the AC breakers to the charger input below. Remove that wire from the breaker and tape over the end to prevent it from contacting anything.

Replace the cover, reconnect to shore power and turn your Multi back on.


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Rob Mitchell avatar image Rob Mitchell commented ·

Hi Kevin, I have a Paralax 7345 converter charger all-in-one unit. I don't believe there is a way to disconnect the power coming into the charger/converter and still have the converter provide 12v to my accessories. Maybe I'm missing something in the details of how the charger/converter works.

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Kevin Windrem avatar image Kevin Windrem Rob Mitchell commented ·

You are correct. After the Multi is installed, the converter will not supply DC power (because it's disabled). But the battery will as always. The Multi takes the place of the converter, charging the battery and providing power to the RV's DC loads.

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Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @Rob Mitchell

I've moved your question to the general section.

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Rob Mitchell avatar image
Rob Mitchell answered ·

Hi Kevin, but how does your suggested approach still allow the onboard 12v circuits for lights, radio, water pump, etc. to still function if the converter is disconnected from the panel? That is the part I don't understand. Maybe I'm missing some fundamental wiring information here.

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Kevin Windrem avatar image Kevin Windrem commented ·

The power panel consists of three parts: AC distribution (breakers), DC distribution (fuses), and converter. AC and DC distribution systems are completely independent. The converter output, DC distribution system and battery are all in parallel. This parallel connection forms a "DC bus". You do NOT want to disconnect the DC distribution from the battery when incorporating the Multi. Rather, you will connect the Multi to this DC bus as well. (A solar charger would also connect to the DC bus if you had one.)

The converter takes AC input off the AC distribution system and makes DC to charge the battery and feed the RV's DC loads.

In reality, the Multi and converter could both charge the battery assuming the battery could take that much charging current. We want to REPLACE the converter with the Multi's charger to avoid overcharging the battery.

There's another reason to disable the converter: If you connect the Multi's AC output to the AC distribution system, the converter will get AC power from the Multi and attempt to charge the battery. This sounds like perpetual motion, but losses result in this loop simply draining the battery.

The easiest way to disable the converter is to disconnect it's AC input. It's normally connected to one of the AC distribution branch circuits, making it simple to disconnect. With the AC input to the converter disconnected, only the battery is available to supply power to the DC loads. This is what happens when you run your RV without a shore power connection.

When you add the Multi to the DC bus, it takes the place of the converter, charging the battery and supplying power to the DC loads when shore power is present. Of course it can only do that when connected to shore power and turned on or to charge only.


Inserting the Multi's AC in/out connection between shore power and the AC power distribution panel means all your AC loads will also receive power either from shore power if present or from the battery via the Multi in inverter mode. You'll always have AC power in your RV, however you need to manage the loads to avoid draining the battery bank when shore power isn't present. I even turn off the inverter at night when not on shore power to avoid the idle draw of the inverter.

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Kevin Windrem avatar image
Kevin Windrem answered ·

Because the Multi draws a lot of current from the battery, that connection path needs to be short and heavy duty. The most logical connection point for the panel is the battery.

The thing to keep in mind is, disregarding wire resistance, the Multi, battery and Panel are all connected in parallel.

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sglad avatar image
sglad answered ·

"I don't believe there is a way to disconnect the power coming into the charger/converter and still have the converter provide 12v to my accessories."

You can disconnect the 120Vac supply wires going to the converter section and it will not operate. These wires would be connected to one of the ac breakers. Battery charging will now be from the inverter. Everything else stays the same with regard to the Parallax. It will still provide 12Vdc distribution to the loads.

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babyrocket avatar image
babyrocket answered ·

Reviving this thread - I have a 2022 Grand Design 5th wheel and recently installed a new Victron Multiplus inverter/converter in the front compartment with 4 lithium batteries. I thought I needed to disconnect the old converter at the AC panel to prevent it from trying to charge the batteries along with the Multiplus, but when I unplugged it the whole DC panel lost power. Plugging the converter back into the AC panel restored 12v power.

Should I just leave the converter plugged in, or is there another way to disconnect it without losing all 12v power?

Thanks in advance for any help!

Patrick

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Kevin Windrem avatar image Kevin Windrem commented ·
You may have disconnected the main 12 volt feed to the distribution panel.

The easiest way to disable the converter is to find the AC input to the converter module and disconnect that from the breaker. The DC output of the converter would still be connected to the DC bus but that should not cause any problems.

To disconnect the converter from the DC bus, you'd need to open it up and disconnect the wires from the converter module to the DC distribution board.

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