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Author Topic: why generators need to run under load  (Read 1249 times)

winona

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why generators need to run under load
« on: November 18, 2017, 02:47:00 PM »
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?
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RedandSilver

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Re: why generators need to run under load
« Reply #1 on: November 18, 2017, 03:19:19 PM »
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.
2002 Rexhall Rose Air  Cummins 8.3  350hp

WILDEBILL308

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Re: why generators need to run under load
« Reply #2 on: November 18, 2017, 03:19:50 PM »
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?

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
2003 Bounder 38N
300 HP 5.9 Cummins
Allison 3000MH Trans.
Towing 2014 Honda CRV
Home base Fort Worth, Texas
A man who carries a cat by the tail learns something he can learn in no other way.
-Mark Twain-

jdonhowe

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Re: why generators need to run under load
« Reply #3 on: November 18, 2017, 04:09:38 PM »
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.
John
2018 Safari Condo Alto 1723
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xrated

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Re: why generators need to run under load
« Reply #4 on: November 18, 2017, 04:46:32 PM »
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.
« Last Edit: November 18, 2017, 05:13:06 PM by xrated »
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RedandSilver

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Re: why generators need to run under load
« Reply #5 on: November 18, 2017, 05:06:14 PM »
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.

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

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. 
2002 Rexhall Rose Air  Cummins 8.3  350hp

WILDEBILL308

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Re: why generators need to run under load
« Reply #6 on: November 18, 2017, 07:06:18 PM »
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.
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

 
2003 Bounder 38N
300 HP 5.9 Cummins
Allison 3000MH Trans.
Towing 2014 Honda CRV
Home base Fort Worth, Texas
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RedandSilver

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Re: why generators need to run under load
« Reply #7 on: November 18, 2017, 07:23:10 PM »
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

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.
2002 Rexhall Rose Air  Cummins 8.3  350hp

Gary RV_Wizard

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Re: why generators need to run under load
« Reply #8 on: November 18, 2017, 07:51:14 PM »
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:

 
Quote
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
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

NY_Dutch

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Re: why generators need to run under load
« Reply #9 on: November 18, 2017, 07:57:42 PM »
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.

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.
Dutch
2001 GBM Landau 34' Class A
F53 Chassis, Triton V10, TST TPMS
2011 Toyota RAV4 4WD/Remco pump
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malexander

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Re: why generators need to run under load
« Reply #10 on: November 18, 2017, 08:02:34 PM »
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.
Marshall Alexander
2007 Fleetwood Bounder 38N DP, 2008 GL 1800 Goldwing, 2007 VTX 1300, Cessna 150 & 172, Rans S19 Venterra

WILDEBILL308

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Re: why generators need to run under load
« Reply #11 on: November 18, 2017, 08:15:49 PM »
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.
Yes the diesel generator is  more forgiving but they still need to be run under load to warm the windings.  ;)
Bill 
2003 Bounder 38N
300 HP 5.9 Cummins
Allison 3000MH Trans.
Towing 2014 Honda CRV
Home base Fort Worth, Texas
A man who carries a cat by the tail learns something he can learn in no other way.
-Mark Twain-

winona

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Re: why generators need to run under load
« Reply #12 on: November 18, 2017, 08:56:25 PM »
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:

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.   :D  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.....
Winnebago Trend
Dorothy and Bailey, my big loveable lab

Heli_av8tor

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Re: why generators need to run under load
« Reply #13 on: November 18, 2017, 09:06:45 PM »
I run electric space heaters to load the genny when too cold for the A/C.
Tom & Theresa
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xrated

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Re: why generators need to run under load
« Reply #14 on: November 18, 2017, 09:12:47 PM »
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:

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

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Re: why generators need to run under load
« Reply #15 on: November 18, 2017, 09:17:22 PM »
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.
I don't have gray hair. I have wisdom highlights.

NY_Dutch

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Re: why generators need to run under load
« Reply #16 on: November 18, 2017, 10:04:59 PM »
I run electric space heaters to load the genny when too cold for the A/C.

In some mild weather conditions, I run both a space heater and an A/C at the same time to exercise the genny... ;)
Dutch
2001 GBM Landau 34' Class A
F53 Chassis, Triton V10, TST TPMS
2011 Toyota RAV4 4WD/Remco pump
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John From Detroit

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Re: why generators need to run under load
« Reply #17 on: November 19, 2017, 06:59:36 AM »
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.
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Re: why generators need to run under load
« Reply #18 on: November 19, 2017, 05:52:43 PM »
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! ;)
Stephen S.
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'99 Winnebago Chalet
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Charlie 5320

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Re: why generators need to run under load
« Reply #19 on: November 19, 2017, 07:34:13 PM »
[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.
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skydivemark

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Re: why generators need to run under load
« Reply #20 on: November 19, 2017, 08:51:11 PM »
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.   :D  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 don't think 50%-70% is absolutely necessary, just a significant load. Maybe turning on the water heater, holding tank warmers(as long as there's a few gallons or more in them) and fridge would be enough (if it's not cold enough to run air conditioner).
Also, the coffee maker uses a good load when on without brewing coffee, just be sure there's sufficient  water in the carafe as to not overheat the glass.
Just my opinion.
2015 Thor Four Winds 31L
Clermont, FL

HappyWanderer

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Re: why generators need to run under load
« Reply #21 on: November 19, 2017, 09:27:59 PM »
I don't think 50%-70% is absolutely necessary, just a significant load. Maybe turning on the water heater, holding tank warmers(as long as there's a few gallons or more in them) and fridge would be enough (if it's not cold enough to run air conditioner).
Also, the coffee maker uses a good load when on without brewing coffee, just be sure there's sufficient  water in the carafe as to not overheat the glass.
Just my opinion.

The water heater is drained in the winter, so that's out. My tank heaters are 12 volts, so that won't work. Refrigerator is only a couple of amps.

I'll stick with the space heaters.
I don't have gray hair. I have wisdom highlights.

WILDEBILL308

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Re: why generators need to run under load
« Reply #22 on: November 19, 2017, 09:36:34 PM »
I have run the block heater, both AC units and turned on the Convection oven to pre heat. I think I was at about 42 amps.
I would run over 50% load as a minimum. It is pretty easy to do and will save you money in the long run.
Bill
2003 Bounder 38N
300 HP 5.9 Cummins
Allison 3000MH Trans.
Towing 2014 Honda CRV
Home base Fort Worth, Texas
A man who carries a cat by the tail learns something he can learn in no other way.
-Mark Twain-

Gary RV_Wizard

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Re: why generators need to run under load
« Reply #23 on: November 20, 2017, 11:20:36 AM »
I feel the 50%-70% load is an engineers ideal "wish list", as is the 2 hour run time and every 4 week interval.  Undoubtedly "goodness", but well beyond a minimum requirement.  I notice they give an example of one a/c unit on a 4000W genset, yet one a/c is about a 1400 watt load, not the 2000-2800 that the percentage would suggest.  1400/4000 is only about 35%.   I think you can take some liberties, as long as you actually do it. Similarly, 30-40 minutes is probably adequate in all but the dampest climates and 6 weeks instead of 4 isn't going to be a killer either.

The 4 week interval is driven primarily by the potential for gasoline evaporation is warm, dry climates.  Diesels can go longer between exercises, since they have no carburetor to worry about and the fuel evaporates slowly as well. Moisture is the primary concern with diesel gensets, and northern winters and western climates in general are dry enough that moisture build-up is slow. Spring and fall, however, often have the warm/cold cycles that produce a lot of condensation in machinery of all kinds.

For what it's worth, Onan used to recommend 50% load for 30-45 minutes.

With my Onan QD 7500, I would run one or both heat pumps (1400 watts each) for about 45 minutes a couple times each winter in Florida. That's about a 33% load. Space heaters work well to, at 1500 watts each.
« Last Edit: November 20, 2017, 11:27:06 AM by Gary RV_Wizard »
Gary
--------------
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

winona

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Re: why generators need to run under load
« Reply #24 on: November 20, 2017, 02:02:03 PM »
With some of our storms here in Northwest Indiana, I like the thought of being able to run a cord from Winona to power a lamp or something in the house when I lose electricity.  One year I shoveled a path through the snow to the outlet and ran the cord into the house.

Mine is winterized so nothing is in the tanks nor water heater.  Suppose I could always pop my popcorn out there?

Thanks, and I have appreciated all the input!
Winnebago Trend
Dorothy and Bailey, my big loveable lab

HappyWanderer

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Re: why generators need to run under load
« Reply #25 on: November 20, 2017, 02:46:07 PM »
During Irene and Sandy, the motorhome became our source of power and refrigeration for several days. It's nice to have it sitting out in the driveway.
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yolo

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Re: why generators need to run under load
« Reply #26 on: November 20, 2017, 02:49:19 PM »
On a diesel generator you need to run at half load or more to keep the carbon from collecting on the pistons, head and valves.  Back before I knew this I used to run our diesel generator on our sailboat about 3 or 4 hours a day with only the battery charger as a load which was probably a 5% load.  After a couple of years of this practice the generator refused to run.   After about $1500 to remove the head, clean and de-coke the head, valves and exhaust manifolds, the diesel mechanic told me to run a load on the engine when charging.  After that I would air-condition or heat the great outdoors to load the engine and had no further problems.


When I graduated to RVing I always would always put a load on the generator when running the monthly runs or when camping.
Bill Bell -- SW Florida
Sailboat -> Powerboat -> Motorhome -> Rest Home -> Funeral Home
Presently between Motorhome and Rest Home

boatbuilder

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Re: why generators need to run under load
« Reply #27 on: November 20, 2017, 02:54:21 PM »
The other reason to run the generator under load besides warming up the oil and windings is that most engines at idle move very little fuel, so if the fuel system is compromised it may not be noticed. By loading them up you move more fuel through the system and will know if you have a fuel system issue.
Charlie

John From Detroit

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Re: why generators need to run under load
« Reply #28 on: November 20, 2017, 04:03:52 PM »
I try to run mine between campgrounds once a year.

Space heaters.. I do not like plugging space heaters into Standard RV type Quick-Box or Speed-Box outlets.. They tend to give my noise a sence of Overheated Romex.. That is an aroma that frightens me as it were because it is often followed by a "Company" that makes house calls.. A Fire company.

(Political question, DO NOT ANSWER THIS, Why are a group of firefighters called a Company?)

I have special heavy duty outlets (12 ga wire wrapped around a properly tightened screw) in 3 places.. No problem with those outlets.

During and following Hurricane Matthew My Generator got a good workout  (2 RVs)   And a couple of weeks ago I was preped to use it.. but wound up only running on battery power for a few hours.
Nothing adds excitement like something that is none of your business
My Home is where I park it.

skydivemark

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Re: why generators need to run under load
« Reply #29 on: November 20, 2017, 06:01:47 PM »
The water heater is drained in the winter, so that's out. My tank heaters are 12 volts, so that won't work. Refrigerator is only a couple of amps.

I'll stick with the space heaters.

OOPS For  missing the part about freezing winter weather, I'm in FLA so freezing weather isn't something I pay a lot of attention to.
2015 Thor Four Winds 31L
Clermont, FL

 

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