why generators need to run under load

I've been told to run my generator under load and I do.  But why under load?  What makes the difference if i just let it run versus turning on the a/c or heat too?  And run it monthly?

I'm not an electrician.

I don't run mine monthly in the winter or summer for that matter.
I do run it going down the road if needed or if no shore power is available.
I have run it from time to time but I have no set schedule for running it.

I do run it under load when I do run it.
My guess is it's better to run voltage through the coils - maybe it dries any moisture out of them.
Maybe it's better for the engine too - most people wouldn't start their car and just let it idle and never drive it.
I would think running the coolant through it would be better for it too. IF no load was ever put on it, would it ever use the
coolant for it's purpose?  IDK.

My generator has about 270hrs on it - when I bought it, it had about 230 - so I put about 40 hrs on it in the year I have owned it.
When I'm home, most of the time it's plugged in, so for me it's more for on the road use or at rest stops I'll run it if I'm going to be there
for more than 20-30 minutes.

I know that someone with way more knowledge will be able to tell you better then I can answer your question.

winona said:

I've been told to run my generator under load and I do.  But why under load?  What makes the difference if i just let it run versus turning on the a/c or heat too?  And run it monthly?

Click to expand...

The problem is you need to load the "generator" part to heat it up and remove moisture. Running with no load doesn't load the windings.
Bill

I've heard that if it isn't run for a long time, a generator will loos its residual magnetism, and won't produce any voltage. The way to maintain magnetism is to put a load on the generator.

I don't know how long it takes for a generator to lose its magnetism, but I had a cheap 3000 watt generator that I used only for rare home power outages. I'd occasionally (every 3 years or so) remember that I hadn't run it. It always started right up and generated fine every time.

I wouldn't worry about having a load on the entire time you have your generator running. I assume that you'd be putting a load on it sometime while it's running, or you wouldn't have turned it on!

BTW, I respectfully disagree about idling being hard on a car engine. It's not great for the environment, but it the cooling system is able to keep up fine with an idling engine. If idling were hard on an engine, I doubt that truckers would keep theirs running all night at truck stops.

Running a generator under load on some time based Preventative Maint. schedule mostly comes from good practices for preventing issues with the diesel engine more than the generator itself.  Drying out any moisture that has accumulated in the generator windings by loading them up with some amount of current (current flow will produce some heat), will certainly dry out some of the moisture that is on the windings, but as soon as you shut the generator down and things start to cool off and return to ambient air temperature, if there is a high relative humidity, the windings cooling off will cause moisture to condense back on the windings.  It would be a never ending cycle of on/off, on/off, and so on.  And the thing to remember, the windings themselves are coated with a varnish that insulates them and protects them from shorting out the coils.  That same insulation/varnish also protects the windings from moisture, which if the windings were left unprotected, would short out.  As I recall, the load testing of diesel generators is more for preventing a condition that is called "wet stacking".  Wet-stacking occurs when the generator does not reach designed operating temperature, allowing carbon and un-burned fuel to build up in the exhaust system.....so again, it's more about the diesel engine than the generator itself.

Another advantage, and probably one that is most relevant to most of us that have gasoline powered generators is that when starting and running the generator under a load, it simulates an actual "working" condition.  It proves that the generator will in fact start up, it also tests your transfer switch for proper operation, and it also serves to heat the engine sufficiently to get rid of any moisture in the engine oil that may have accumulated there......kind of like using your car for very short trips and never fully warming the engine up.

jdonhowe said:

BTW, I respectfully disagree about idling being hard on a car engine. It's not great for the environment, but it the cooling system is able to keep up fine with an idling engine. If idling were hard on an engine, I doubt that truckers would keep theirs running all night at truck stops.

Click to expand...

most people wouldn't start their car and just let it idle and never drive it.

Click to expand...

The point I was trying to make was about a total car.

So idling would NOT move any of the suspension or ball joints or springs or flat spots on the tires or charge the battery too much etc.

Truckers run their engines for the AC or heat.  I also assume that if they have an inverter or generator for their microwave it works
better with the engine running - also diesels use very little fuel when idling - probably less then a gas unit of the same size.

I wasn't trying to imply that just idling an engine is bad for it, but that it wouldn't be too good for a car to never be run down the road.
In the same way a generator idling with no load would not be the best thing for it either.

Sorry if I was clear.  And again IT's just my opinion - doesn't mean I right all the time and it's fine to disagree. 

jdonhowe said:

I've heard that if it isn't run for a long time, a generator will loos its residual magnetism, and won't produce any voltage. The way to maintain magnetism is to put a load on the generator.

I don't know how long it takes for a generator to lose its magnetism, but I had a cheap 3000 watt generator that I used only for rare home power outages. I'd occasionally (every 3 years or so) remember that I hadn't run it. It always started right up and generated fine every time.

I wouldn't worry about having a load on the entire time you have your generator running. I assume that you'd be putting a load on it sometime while it's running, or you wouldn't have turned it on!

BTW, I respectfully disagree about idling being hard on a car engine. It's not great for the environment, but it the cooling system is able to keep up fine with an idling engine. If idling were hard on an engine, I doubt that truckers would keep theirs running all night at truck stops.

Click to expand...

Welcome to the forum.
Well actually this comes direct from Cummins/Onan. The proper way is to start it let it warm up then apply load.  Then when ready to shut down, step down the load and let run with no load for 5-10 min before shutting off. You should follow this last part any time you have ben running under load.
As far as truckers idling engines all night that is a buy gone thing. Now they have strict time limits on idling in rest areas and fuel stops.
Bill

Bill

WILDEBILL308 said:

As far as truckers idling engines all night that is a buy gone thing. Now they have strict time limits on idling in rest areas and fuel stops.
Bill

Click to expand...

Well I guess no one told the truckers because I was in a rest stop in September for the night and both truckers on either side of me
were idling all night long and I assume most of the other truckers were idling too.  I had to start my generator to muffle some of the
sound coming from their engines.

So if it's "buy gone" it's not enforced that I can tell.

I suggest reading the Onan RV Generator Handbook - lots of solid advice there for RV owners.
https://power.cummins.com/sites/default/files/literature/rv/F-1123-EN.pdf

With respect to exercise, Onan says:

Regular ?exercise? is
an important part of keeping your generator healthy. Lack of exercise can cause
moisture build-up and fuel system degradation that make it run poorly. In fact,
in as little as 30 days, the fuel in gasoline-powered generators can begin to gum
and varnish the fuel system. Fuel varnishing results in hard starting and surging. (A
surging generator never settles at a stable operating speed

Click to expand...

RedandSilver said:

Well I guess no one told the truckers because I was in a rest stop in September for the night and both truckers on either side of me
were idling all night long and I assume most of the other truckers were idling too.  I had to start my generator to muffle some of the
sound coming from their engines.

So if it's "buy gone" it's not enforced that I can tell.

Click to expand...

Are you sure it was idling engines you were hearing, and not the auxiliary power units many OTR trucks run these days so they don't get ticketed under the excess idling laws in many states? Refrigeration units sometimes run pretty continuously as well.

I just wish I could remember to run my genny once in a while.  The MH sits on my driveway, I walk past it ATLEAST 5 times a day, and I never can remember "oh, I ought to run the generator". But, it hasn't failed me yet.

malexander said:

I just wish I could remember to run my genny once in a while.  The MH sits on my driveway, I walk past it ATLEAST 5 times a day, and I never can remember "oh, I ought to run the generator". But, it hasn't failed me yet.

Click to expand...

Yes the diesel generator is  more forgiving but they still need to be run under load to warm the windings. 
Bill 

Gary RV_Wizard said:

I suggest reading the Onan RV Generator Handbook - lots of solid advice there for RV owners.
https://power.cummins.com/sites/default/files/literature/rv/F-1123-EN.pdf

With respect to exercise, Onan says:

Click to expand...

Thanks for the link to the manual  --- read the parts that pertained to mine.  And now I'm trying to figure out what to run that fulfills the 50% to 70% load for time frame.  Can't make that much coffee nor run a hair dryer that long.    So the air conditioner when it's already 20 degrees this winter?

My generator is gas, and I've added Stabil and run the engine and generator for while, hopefully to get it where it needs to be.

Sometimes this tryin' to do right for my rv makes my brow wrinkle.....

I run electric space heaters to load the genny when too cold for the A/C.

Gary RV_Wizard said:

I suggest reading the Onan RV Generator Handbook - lots of solid advice there for RV owners.
https://power.cummins.com/sites/default/files/literature/rv/F-1123-EN.pdf

With respect to exercise, Onan says:

Click to expand...

StaBil treated fuel in the tank for the generator should take care of those issues.

It's an easy routine to keep. It's also a good opportunity to poke around and look for leaks, critters or any other problem that might pop up.

Heli_av8tor said:

I run electric space heaters to load the genny when too cold for the A/C.

Click to expand...

In some mild weather conditions, I run both a space heater and an A/C at the same time to exercise the genny...

There are in fact several reasons for running under load

I have heard the "Residual Magnetism" thing but am not convinced of it.. read on

When I got my first PORTABLE the waveform was a bit.. nasty.. Even though it was a quality unit with a rated Harmonic Distortion of less than 3% it was nasty.. There are some electronic parts in the generator circuit that had.. Well.. Gotten lazy is the best way to say it.. After the first tank of gas (I powered a light system with it, Nasty waveform does not matter) it was nice and clean, the parts and been Re-Conditioned.

And the big one

Oil collects impurities. Many of these "Burn off" when the engine reaches proper operating temp.
IT WILL NOT GET HOT ENOUGH if running no load.

Needed to run the generator under load for a bit.

Needed to blow the leaves and acorns off the driveway with the electric leaf blower.

Hmmmm...

All done!

[Residual Magnetism]  is not an issue with generators in the onan and generac, designed for RV use. They both rely on exciting voltage each time they are started up. The exciting voltage magnetizes the rotor through the slip rings.