Saturday, February 4, 2023


How long can my RV’s residential fridge run before generator takes over to recharge?

Dear Dave,
I installed a residential fridge in my RV. I have a four 6-volt golf battery setup and 300-watt solar panels with a 3000-watt AIMS inverter. When fully charged, how long should it run before gen power should take over?  —Jimmie, 1984 Vogue II

Dear Jimmie,
We get this question quite often and it is a difficult one to answer as there are many variables that factor into the equation. First, if you have four 6-volt deep cycle batteries they have two connected in series, a positive to negative, which creates a 12-volt bank and the other two are connected in the same manner. Your batteries are most likely close to 120 amp hours, but connecting them in series does not double the amp hours, just the voltage. Then, these two 12-volt battery banks are connected parallel, which is positive to positive and negative to negative. This does double the amp hours, which will give you 260 amp hours from all four batteries. However, with lead-acid batteries you can only use 50 percent, so that means you have only 120 amp hours available.

What condition are the batteries in

The next factor is what condition these batteries are in, as lead-acid batteries are prone to sulfation, which coats the plates and reduces the storage capacity. If you do not have a multistage charger, your batteries have not been maintained properly and have sulfation. The only way to tell is to charge them and put a load tester on to verify the amp hours, which most service centers cannot do.

Even if you have batteries that are in great condition, you have to factor in other 12-volt components that will be using battery power such as the lights, water pump, roof vents and any LP appliance. These also draw 12-volt power. Here is a chart of the amp draw of some common 12-volt components.

The 300-watt solar panels are a good addition, but the next factor is how much time are they exposed to the sun, as most roof-mounted panels only get about 4-5 hours of direct exposure. If you are parked in a shaded area, it is even less. That is why I recommend supplementing your roof-mounted panels with portables that can be moved out past the trees for direct exposure.

As you can see, there are several variables. With the typical system setup as yours with your residential fridge, I would doubt you will get much more than a day or two, if that, before needing to recharge the batteries with a generator or shoreline power.

 You might also enjoy this from Dave 

How long will 100 W solar panel and two batteries run residential fridge?

Dear Dave, 
When I purchased my RV from Camping World they never told me anything about the solar panel on the roof and the inverter. I know now that the residential refrigerator runs off the two batteries that are charged from the solar panel or shore power, but the inverter is in the off position and has to be turned on manually, I assume. I would think that if we lost shore power it would automatically switch on the inverter. I’m trying to understand the solar system and the RV, and if I should upgrade the 100 W panel to a bigger panel. I heard that there’s a 300 W or 350 W panel available now. —Joseph, Cedar Creek 38ftk 43’

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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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11 days ago

On my 2017 Forest River 34QS, we have a Magnum MS2012 2K inverter/charger. You can use the generator auto start feature & can set it to start when the battery voltage gets to a certain point. To be honest I’ve not set it up!

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