Monday, December 5, 2022


Ask Dave: Why don’t RV’s house batteries charge when motorhome is plugged into outlet?


Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. Today he discusses charging an RV’s house batteries from a house outlet.

Happy Holidays, Dave.
I have a 2019 Gulfstream BT Cruiser 5230B. My two 12-volt house batteries will charge with an onboard Onan 4000 generator or with my 6.8 V-10 engine running. However, the batteries don’t charge up when my MH is plugged into a standard house 110 outlet. Inverters/converters are off, as with any/all appliances. Is my outlet insufficient to keep these batteries charged? Thanks for the assist. —Karl

Happy Holidays to you, too, Karl.
The short answer is there may not be enough power available from your residential source to run everything in the rig and provide a charge to the battery from the converter.

First, let’s look at the residential source you are plugging into. If it’s a typical 20-amp outlet in the garage or side of the house, it is probably not a dedicated outlet. It’s probably rather “ganged” to other outlets in the garage that might have power-drawing components plugged in such as a freezer, refrigerator, air compressor, etc. So, you may not be getting a full 20 amps available to the rig and the distribution center.

The size of electical cord is important

Another consideration is the size of electrical cord. The cord in this photo is a “heavy duty” cord from a hardware store. However, it is only rated at 10 amps, which is not sized for plugging in an RV but, unfortunately, happens quite often.

When you plug into a power source, the shoreline cord goes to the distribution center which has circuit breakers for 120-volt appliances inside the rig as well as the converter, which is your battery charger. If you are running the refrigerator or any other appliance, it will draw amps as shown in the chart below.

Although the refrigerator doesn’t draw a lot of amp power, if you have anything else on in the rig, there will not be sufficient power available to the converter to charge the batteries.

Test charge coming in at the batteries

One test you can conduct is to plug the unit in to the 120-volt source and use a multimeter to test the charge coming in at the batteries. Set it to the 12-volt DC setting and place the red probe on a positive post and the black on negative. If your batteries are lower than 12.6 volts, the converter should be applying a 13.6 volt charge or higher if it’s a multi-stage or desulfation charger. Then it should go to a 13.2 volt maintenance charge.

Here is how the typical converter operates, when the batteries are lower than 12.6 volts. The charger applies a 13.6-volt charge until the batteries get to 12.6 volts. Then the charger goes into a maintenance state of 13.2 volts. A typical battery fully charged at 12.6 volts will not accept a charge lower than 13.2 volts, so it stays there as a maintenance charge. If your multi-meter shows 13.2 volts, then I would shut off the converter at the distribution center and disconnect the battery cables and test the battery as it sits. If it is lower than 12.6 volts, there is a problem.

Read more from Dave here


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Billy Lafreniere
11 months ago

Since you stated that the converter is off… If you want the house batteries to charge while plugged in you must turn the converter on. That is what the converter does… 120v to 12v (nominal voltages) As there not being enough power available at the receptacle that you plugged the rv into. They don’t work like that. 120v circuits don’t work the same as water in your pipes meaning that they don’t share the available current between everything that wants it. The circuit will draw all the current it wants up until it goes over the breaker/fuse rating which will then pop/blow and shut the power to that circuit off. If the circuit feeding the rv couldn’t handle the load it would pop, not slow down the charge.

Dick and Sandy near Buffalo, NY
11 months ago

In any RV that has an inverter/charger, that device must be on to charge the house and chassis battery(s). Most if not all RV’s with an inverter operate on at least 30 AMP service and require that amount of power to charge and operate the RV. Dave found out that a standard house outlet will not provide enough power to operate his RV. I will assume that he has a 30 AMP electrical cord for his RV. If he wants to plug his RV into his home electrical system properly, he will need a dedicated 30 AMP outdoor receptacle on his home. He can do it himself if he is qualified and it usually requires inspection by a qualified electrician. We have a larger DP coach and I put a 50 AMP box on the outside of our garage and had it inspected. Parts are available at many local or on line sources. If you are having it done by an electrician, be absolutely positive that the electrician is familiar with your RV’s electrical requirements and the proper plug receptacle and wiring required.

Billy Lafreniere
11 months ago

A 12v 50 amp converter at full load (at 100% efficiency) would draw 5 amps @ 120v… (in truth 6-7 amps) The 30 amp rating or 50 amp rating of the panel/service have nothing to do with the charging of the battery. That is the total combined load that the rv panel/cord set can handle. Will you have problems using the a/c and microwave at the same time? Yes… Can it run the lights and the converter with no issues? Yes. The O.P. stated that everything else was off. and the batteries were not charging. Not that they were popping breakers in their house.

The Saint!
11 months ago

^^^^Bill LaFreniere has your answer^^^^

11 months ago

I wonder if the OP shuts off the “salesman” switch which cuts off all power. I know on my rig it does.

11 months ago

What he said ^^

Rock & Tina
11 months ago

Dave, he states in his question that his, “Inverters/converters are off,…” His batteries will never charge with his converter off.

11 months ago
Reply to  Rock & Tina

Yep. Caught that right away. Don’t know why Dave didn’t

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