Exercising your generator with a load

Exercising your generator with a load

Hey Mike, about this tip…

Don’t just exercise the pooch, exercise the generator, too. Fire it up and run it at half-load (or more) for two hours each month.

I just read this Quick Tip in the RV Daily Tips Newsletter, but I wonder just how to run a generator at half-load? And why do I have to run it for two hours? That’s a lot of gasoline and gas costs money. Can’t I just run it for 5 or 10 minutes every month to make sure it’s working? –Joey D.

Hey Joey,
Let’s cover this as a two-part answer. So how and why do you load a generator at 50% power? It’s difficult to turn on enough LED lights to load even half of what a small Honda EU2000 generator can produce, and if you have a 3kW to 6kW genny that’s even more difficult to get enough load.

What we need is something that draws continuous power, can be adjusted to between 750 and 1,500 watts, and doesn’t break the bank. Lucky for us that exactly describes a portable electric space heater you can purchase anywhere for $25 to $40. Here’s a link to a good one on Amazon. I like the ceramic space heaters a lot since they’re compact and have a tip-over safety switch. And many of them have dual-heat settings for 750 or 1,500 watts, which is just perfect for a 1kW, 2kW or even 3kW generator. This one on the left is a 750/1,500-watt version.

So if you have a little 1kW generator like I use for just charging batteries and running my electric hedge trimmer out in the woods, select the 750-watt setting. If you have a 2kW genny, then the 1,500-watt setting would be fine since that would be a 75% load. If you have a 3kW genney, then the 1,500-watt setting on the heater would provide a 50% load. And if you have a 6kW generator with 240-volt output (actually 120/120-volts), then buy a second 1,500-watt space heater and load each 3,000-watt side of the generator to 1,500 watts. Pretty easy, really…

So why is a load really needed and how long do we need to run the generator? Well, what we’re trying to do is get the generator up to full operating temp in order to burn off any water vapor and the resultant acids that build up in the oil. And to do that you need at least an hour of running with the generator producing enough current to make the engine work hard and produce heat. Just idling it doesn’t work really well since it probably won’t come up to full temperature. And the worse thing you can do is run it for 5 or 10 minutes and shut it off, which is just enough time to build up a bunch of corrosive acids in the engine which will eventually rot out the exhaust system and internal oil seals. Nope, if you’re going to start up an engine, then you really should run it for at least an hour. And while running it once a month is the gold standard, I admit to being a little lazy and maybe only starting and running them every couple of months over the summer. But pick your times and put it on your maintenance calendar. 

In any event, follow all safety precautions when running a generator. Don’t do it in an enclosed space to avoid carbon monoxide poisoning. Don’t place the space heater next to anything flammable since it’s surprisingly easy to set things on fire. And don’t run it unattended because if something does go wrong, you want to be close by to deal with it. Pull up a lawn chair with a good book (maybe my book RV Electrical Safetyshameless plug), start up the genny and turn on the heater load. And don’t forget to always check your generator’s engine oil first before ANY startup. Yes, I  know they have low-oil shutoff systems, but generators are expensive and you can keep them running for decades with just a little preventive maintenance. 

At the end of the camping season it’s really best to drain out all the gasoline you can, and run the fuel tank dry. This helps prevent varnish buildup in the carburetor or fuel injector. But if you’re full-timing or otherwise can’t guarantee your generator will be shut down for the entire winter, then add an appropriate amount of a fuel additive such as STA-BIL® Fuel Stabilizer. I’ve used this in my chainsaws and snow blowers for decades since I don’t want to drain out the chainsaw gas over the winter (I live in the woods), and I might not need to use my snow blower all winter after fueling it up in the fall (I live in Maryland). And I regularly use STA-BIL® Fuel Stabilizer in both my 1kW and 3kW Honda generators, which I generally don’t run dry unless they’re very close to empty. But I do run a space heater load on them a few times a year even if I don’t need generator power for anything in particular. That way if there’s a power outage or I need AC power in the woods I can guarantee a quick start … and that always works for me.

Let’s play safe out there….


Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.




12 thoughts on “Exercising your generator with a load

  1. Mike Sokol

    Note that I said “gold standard” is a monthly run, which is what home backup generators are often set up to do. The key is that if you have a portable generator and it’s not run for a year or more, then the chances it will start when you need it goes down.

  2. Steven Scheinin

    Is the same true for propane powered generators?

    1. Mike Sokol

      Propane doesn’t create any varnish in the carburetor since there’s no liquid, so there’s no need to drain any fuel. And propane is supposed to be cleaner burning with less acids produced in the oil, so perhaps you don’t need to run it as long. However, it’s still a good idea to run them periodically under load to keep all the seals in good shape and confirm everything is working.

  3. Debby Clark

    In a Class A motorhome with a 8KW generator, wouldn’t running both air conditioners while the generator was on create sufficient load, vs me going out and buying space heaters? I’m assuming that testing the generator each month for an hour at a time under load applies here also?

    1. Mike Sokol

      Yes, you could run the air conditioners to load the generator. The key is to get some kind of load on it.

  4. Barry

    Additional, the windings inside the generator portion will develop rust over time. Running a generator until fully warmed with a 50% or greater load will assist in keeping the electrical windings free of moisture and therefore rust.

    1. Dave

      I have heard this same story for years but I have never done what is recommended here and have never had a problem. I worked on this kind of stuff all my adult life and I have multiple large gasoline generators and a Honda eu2000. They have sat for years without being used and when I do use them they start right up and work perfectly. The only thing I do is make sure the float bowls are empty and they have good oil which also sits in them for years on end. They are also stored indoors. If I had to start them every month and run them for 2 hours I think I wouldn’t own them and this procedure would do more harm than good. This is truly an old techs tale. Run it once a year to make sure it is ready for camping and don’t worry about beating yourself to death exercising your generator!
      I have had and used generators for decades. I have never had to exercise any of them. I may run them with a heater load once every 2-3 years to make sure they work properly and have never had a problem. Make sure you drain or run the carbs dry and use Sta-Bil in the tank. I also use Mobil1 syn oil in them. The windings in a gen are made of copper which will not rust. The parts inside are usually coated on all modern gens. I really have to laugh at all the people wasting time and gas every month thinking their genset will go bad if they don’t run it.

    2. Mike Sokol

      I’ve seen rust in the air gap a few times from the iron in the stator and rotor, but the copper windings themselves should not be able to rust due to the insulation.

  5. Frank

    For full timers, who do not boondock, this monthly exercise regimen is not doable, as most campgrounds prohibit generator use.

    1. Fred

      You could run the gens while travelling down the road & running heaters or air conditioner, while travelling between rv parks

      1. Norm

        This is only true if you are driving a motorhome, not pulling a trailer.

    2. Mike Sokol

      If you’re using the generator all the time then this isn’t necessary. I’m mostly talking about portable generators that are left in storage.

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