Switching from shore power to inverter in an RV


Old 10-14-17, 02:41 PM
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Question Switching from shore power to inverter in an RV

We have a 2003 Roadtrek Rv which has a converter equipped with an automatic AC switch which switches from shore power to generator power. It also functions as a power distribution center for both 12VDC and 110VAC.

We want to replace the existing small coach battery (which is charged by the converter) to three large deep-cell batteries, and then connect those batteries to a 1000w inverter to power two small 110v refrigerators.

These refrigerators would normally run from 110VAC coming from the converter but need to be plugged into the inverter when neither shore power or generator is available.

I would like to leave the refrigerators plugged into 110v outlets and switch the input with a manual double-throw switch. What I do not know is whether I can connect the white (neutral) wires coming from both sources together, or whether they need to be switch as well, using either a DPDT switch or a DPDT relay. A better alternative would be to get a device that would do that switch automatically. Looking for your advise.
Old 10-14-17, 03:19 PM
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Welcome to the forums.

Two 120v fridges and 3 batteries in a Roadtrek Rv.

That's a modified 1 ton van chassis.... correct ?
Are these dorm type small fridges ?
How are you going to charge the 3 batteries ?

If you don't have anything yet.... consider something like the Xantrex prosine charger/inverter.
Power Inverter, Pure Sine Wave Inverter

The normal transfer switches used in RV's don't switch the grounds.
Old 10-18-17, 06:52 PM
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I'm brand new to the forum, but I'll throw in my .02 here. I recently did a very similar job to this on my travel trailer.

I purchased an inverter that has a transfer switch built in:

This type of inverter requires you to run the shore power to it, and then back out. That allows it to know if you're plugged in, or running on batteries. I used a 12 gauge extension cord for this, cut in half with the plugs cut off.

In my trailer's power panel (battery charger/breakers/12V supply), there is a single breaker that supplies power to all of the outlets (my fridge is on this circuit). Another breaker supplies power to the charger, and another goes to the air conditioner.

I disconnected the black wire from the outlet's breaker and replaced it with the black wire from the extension cord. The extension cord runs to the inverter/transfer switch and back. The black wire returning from the inverter is then wire-nutted to that original black wire you pulled off the breaker. I wired the inverter/transfer inline before all of the outlets.

I had the exact same question as you did about the Neutrals. Turns out, you just wire them together in the breaker panel. I had extra spaces in the neutral bar that I used for this. Same for the grounds, in the ground bar. When I did this though, I found out that the inverter/transfer switch was labeled wrong. The hot and neutral were switched. To fix this, I simply swapped the hot and neutral inside the inverter.

My trailer does not have a generator, but I assume that any generator would be on its own transfer switch before the breaker panel, so that would be irrelevant.

So now, if there is shore power on the main umbilical cord, the entire system (including the fridge and the air conditioner) will run off shore power (same goes if the umbilical was plugged into a running genny). As soon as that power goes away, the transfer switch in the inverter flips and supplies only the outlets with power from the batteries.

My batteries are charged in three different ways. Shore power, 190 watt solar system, truck alternator. All three ways are parallel.

With all that said, Pete has some great questions. What sort of fridges do you have, and do you know the actual power consumption? Mine is a standard propane/AC RV fridge which draws 2.3 amps (or maybe 3.2?) fairly continuously. I have about 220Amp-hours of battery capacity and I have since learned that my fridge will draw down my batteries somewhere around 6-7 hours.

A great tool to have in your box is a device called a "kill-a-watt" meter. They're about $20. You plug it into your outlet, and then plug your device into it. Let your fridge run for about 12 hours and then see exactly how much power it used. Then you can determine if your batteries and (more importantly), your charging system will be up to the task for running the two fridges.


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