Tuesday, September 26, 2023


RVelectricity – Just Ask Mike (J.A.M.): Predator powering a 5th wheel RV

Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM. Today I discuss inverter generators.


Dear Mike,
I would like to leave my small Predator inverter generator in my pickup bed and use my fifth wheel pigtail to at least keep the batteries charged and using lights. Is this possible? Thanks. —Ron M.

Dear Ron,
Yes, that should work very well, especially if you get the right kind of adapter and extension cord. Let’s explore why…

Amps needed at 12 volts vs. 120 volts

Okay, let’s assume you have a converter that can charge your RV house batteries at 80 amps. That’s pretty common nowadays with lithium batteries.

So does that mean that your generator needs to supply 80 amps of current? Nope… it’s more like 1/10th of that, which is 8 amps or so (maybe 10 amps, adding in all the various inefficiencies). That’s because there’s roughly a 10:1 ratio of voltage to current needed. It’s all about the power (watts) needed.

It’s all about the watts, baby!

So a 12-volt battery that’s charging at 80 amps is using around 960 watts of power or so. That’s because 12 volts x 80 amps = 980 watts. To figure out the amps needed to be supplied by a 120-volt generator all we have to do is divide 980 watts / 120 volts = 8 amps.

Voila! Since there’s a 10:1 ratio between the 120-volts AC from the generator and the 12-volt DC needed by the batteries, there’s an inverse 1:10 ratio of amperage needed to convert from 120-volts AC to 120-volts DC.

The following ad was auto-inserted by Google

Can your little Predator supply 8 amps at 120 volts?

You bet your sweet bippy it can. Let’s look at a typical 2,000-watt Predator (or any other brand) inverter generator.

  • Runtime: 12 hours @ 25% load
  • Quiet, only 66 dB
  • Electronic overload protection
  • 79.7cc air-cooled OHV gas engine
  • 2000 starting watts, 1600 running watts

So let’s convert 1600 running watts to how many amps of current would be available at 120-volts AC. We just have to divide watts by volts to find amps. That’s 1600 watts / 120 volts = 13.3 amps.

That means that a 2000-watt Predator inverter generator can easily supply 13 amps of current at 120 volts continuously. And since your converter/charger only needs around 8 amps of current at 120 volts, there’s another 4 amps at 120 volts left over for powering lights and such. And that 4 amps at 120-volts AC is around 40 amps at 12-volts DC. Easy peasy!

The hookup

This also hints that you really don’t need to run a heavy 50-amp shore power cord over to the generator in the bed of your truck since it’s limited to 16 amps of output current. I would suggest you get a 15-to-50 amp dogbone adapter and a heavy-duty 12-gauge extension cord, maybe 25 feet in length.

With that setup you should be able to keep your batteries charged while powering lights and possibly even your refrigerator at the same time. And if you pull too much current for your generator to supply, it will just shut itself down.

OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play safe out there….

Send your questions to me at my new RVelectricity forum here.

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

You don’t want to miss Mike’s webcasts on his YouTube channel.

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  1. Mike, Along the same train on thought, wouldn’t it make even more sense to power an inverter in the tow vehicle with a high output alternator and send 120VAC back to the fifth wheel while in motion?

  2. I carry a nice long 30amp cord from a previous 5th wheel I used to own. I carry it in my Class A basement along with dogbones, etc to go up or down from 15 to 50 Amp etc no matter what source is available. The 30 Amp is just as easy to handle as heavy duty extension cord (which I have also, haha) .

  3. I run my Predator 3500 inverter/generator from the back of my truck and it makes it very convenient not to have to unload the generator whenever I need to use it. There are a few things to keep in mind if you are going to do this.

    Generator exhaust under load is HOT. It will melt any spray in or plastic truck bed liner. (Don’t ask me how I know this). If you Google generator exhaust extensions you will find a number of suppliers on Amazon and E-Bay that make kits that will route your exhaust overboard. If you don’t want to go to this much trouble make sure there is nothing around the exhaust that could be damaged by the heat.

    Speaking of heat also make sure that there is nothing blocking the air flow around, under and over the generator. These things run hot and anything that blocks the airflow will seriously shorten the life of your generator.

  4. If the pickup has a cap over the bed, It’s a good idea to make sure that the windows are left open, when running the generator. Most new generators have a built in CO2 detector that will shut it down, if it detects any CO2.

  5. With the generator in the truck bed is there any danger of carbon monoxide accumulation because of poor air flow? This could migrate into the 5th wheel.

  6. I found out how people in Texas used the F150 hybrid truck with the Pro Power Onboard Generator to power their home. After the hurricane. They ran extension cords from the F150 to the homes appliances. It was not ran thru the electric panel.


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