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Old 07-31-2014, 02:04 PM   #1
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Generator Loading Requirements

The "new genset" thread made me realize how ignorant I am in this area. I often hear about how important it is to run the gen under a proper load, but I don't really understand why. Is it to extend the life of the engine side of the power generation side? And if it's for the engine, is it true for gas gennys or just diesel?

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BD
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Old 07-31-2014, 02:56 PM   #2
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The "new genset" thread made me realize how ignorant I am in this area. I often hear about how important it is to run the gen under a proper load, but I don't really understand why. Is it to extend the life of the engine side of the power generation side? And if it's for the engine, is it true for gas gennys or just diesel?

Thanks,
BD
Yes it's to extend the life of the diesel engine. Can't speak to the gas versions. But they may be more forgiving. With light loads you get cylinder wall glazing and other issues that can shorten the life of the prime mover.

That said, while it's best to properly load a Genset, as few hour as most non-commercial users but on them, relatively speaking, most pleasure craft owners are not going to have to deal with the effects of light loading unless it's very, very low all the time, they run the Genset a lot and they own the Genset a long time.

Now the second or third owners, that might be a different story.
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Old 07-31-2014, 04:30 PM   #3
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Now the second or third owners, that might be a different story.
Yeah that would be me. I'm the second owner. When I bought the boat the engine had 121 hours on it. The generator had 208! Of course I have no idea how he used it, but the boat in general seemed well maintained. Neither seem like very many hours though.

Thanks for the input. I'm hoping that gas engines are a little more tolerant of low loads.

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Old 07-31-2014, 04:46 PM   #4
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Yeah that would be me. I'm the second owner. When I bought the boat the engine had 121 hours on it. The generator had 208! Of course I have no idea how he used it, but the boat in general seemed well maintained. Neither seem like very many hours though.

Thanks for the input. I'm hoping that gas engines are a little more tolerant of low loads.

BD
208 hours is nothing.
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Old 07-31-2014, 04:48 PM   #5
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BDofMSP,

Engine hours vs. generator hours are meaningless. As an example, if I travel two hours to our favorite anchorage, stay 3 days and run my generator 3 hours a day, then travel home, I will have put 4 hours on the engines and 9 hours on the genset. Howard
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Old 08-01-2014, 06:21 AM   #6
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>I'm hoping that gas engines are a little more tolerant of low loads.<

Another area where gas is far better than diesel is gas suffers almost not at all from underloading.

Most diesel noisemakers are happy with 50% load on up , and operating at 95% makes them even more happy.

IF and when the expensive diesel noisemaker assemblers copy the Honda operating style , create DC , invert it to AC and allow the engine to operate at low RPM, but high load , sizing noisemakers for long life will be less of a Black Art.
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Old 08-01-2014, 07:36 AM   #7
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Thanks FF,

Once again this forum has taught me something very useful. For me that's like 330 days in a row!

BD
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Old 08-01-2014, 08:04 AM   #8
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Read the owner's manual! This is another area of much dockside urban legend. It is usually just a matter of having "some load" vs "no load".

Take my 23 year old Onan with a little Cummins 4 cylinder on it. The only thing any of the manuals... service or operating mention about load is running it with NO load at all.
Prior to my ownership it was the only AC source on board away from the dock so, according to the POs was run at very low loads almost all the time for 2000 hours. It surveyed beautifully, and has run beautifully for another 5000 hours, most of that at around 25% load (20 amps @240). Surveyed great again at that point, no soot, runs smooth, picks up loads quickly. As a couple of techs have said " keep running it like that and it will last forever".

So, read the manual, talk to the manufacturer. Size, run and maintain accordingly.
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Old 08-01-2014, 08:15 AM   #9
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IF and when the expensive diesel noisemaker assemblers copy the Honda operating style , create DC , invert it to AC and allow the engine to operate at low RPM, but high load , sizing noisemakers for long life will be less of a Black Art.
Ahh, the Tesla vs Edison debate again. If the genset owner is not experienced enough to know importance of loading the diesel, DC to AC conversion pitfalls will elude him as well.

AC to DC conversion on a multi thousand KW scale occurs in mine hoisting systems. Great application and one to keep both Nicolas and Thomas Alva happy.

But FF is correct, if most of the time you're at 50% load on up, it should cause no harm and is easy to do
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Old 08-01-2014, 11:09 AM   #10
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Read the owner's manual! This is another area of much dockside urban legend. It is usually just a matter of having "some load" vs "no load".

Take my 23 year old Onan with a little Cummins 4 cylinder on it. The only thing any of the manuals... service or operating mention about load is running it with NO load at all.
Prior to my ownership it was the only AC source on board away from the dock so, according to the POs was run at very low loads almost all the time for 2000 hours. It surveyed beautifully, and has run beautifully for another 5000 hours, most of that at around 25% load (20 amps @240). Surveyed great again at that point, no soot, runs smooth, picks up loads quickly. As a couple of techs have said " keep running it like that and it will last forever".

So, read the manual, talk to the manufacturer. Size, run and maintain accordingly.
Thank you!

There is no magic number for generator loading. Just dont run them unloaded for long periods of time.
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Old 08-01-2014, 01:22 PM   #11
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I too would not worry too much about gennie loading. I make my living dealing with engines and gennies and in nearly 20yrs have seen only a couple where cylinders were glazed, causing either low compression or high oil consumption.

I have seen many with manifolds and mixers clogged with carbon. That is usually not a big deal to clean.

On my personal boat, the 5kW NL clogged with carbon after 1600hrs of my use (had about 3600 on it when I installed it). And I was fairly good at keeping a load on it. If it was running it was usually around 1.5 to 3kW of load, only rarely run below that (sleeping, with airs cycling off). Sometimes I would run it near 5kW, taking it right to the smoke limit for like 1/2hr now and then. And still it clogged up. Noticed that it started smoking at lower and lower loads, then got hard to start.

Pulled head, manifold and mixer and chipped out the packed carbon, and replaced the valves, lapped them in. Runs fine now. Never has had a blowby or oil use problem, still does not.

So even with what I considered judicious use, it clogged. But the fix is not a real big deal.
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Old 08-01-2014, 10:26 PM   #12
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I would suggest checking with the manufacturer and reading the manuals.

We did so with Northern Lights (Lugger) and their statements are as follows. The break in period of the first 100 hours is very important. That includes watching oil pressure and engine temperature closely as well as keeping check on oil fill. They recommend change of oil and filters at 50 hours. For the first 100 hours they recommend 75% load, but a minimum of 50% load for proper seating of the piston rings. They also recommend varying the loads. Basically what they'd recommend for the Lugger engine period. On larger generators (99 for instance) then the load factor isn't as critical. Now, that said, the stress over and over proper break in but once past that period they said that load (as long as not 0 load) was of very little concern and that there were many many far more important factors.
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Old 08-02-2014, 11:49 AM   #13
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Thanks to all for the input. I certainly have read the owners manual but it does not specify anything about load other than a) exercise it once a week "under load" and b) run it at no load for 5 minutes to cool it down. That's it.

Being gasoline powered, it seems like one less thing for me to worry about. I'll run it when I need it and then shut it off.

Thanks,
BD
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Old 08-02-2014, 12:02 PM   #14
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Not to hijack this thread, and the MODS can move it if judged a hijack but I'm real curious as to how forum members feel about running a genset for A/C during sleeping hours. I'm looking for safety issues, not "be kind to your neighbors," as I would never use my genset at night if other boats are in propinquity. Thanks, Howard
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Old 08-02-2014, 12:07 PM   #15
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Not to hijack this thread, and the MODS can move it if judged a hijack but I'm real curious as to how forum members feel about running a genset for A/C during sleeping hours. I'm looking for safety issues, not "be kind to your neighbors," as I would never use my genset at night if other boats are in propinquity. Thanks, Howard
Diesel or gas?
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Old 08-02-2014, 12:08 PM   #16
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Great question, my bad. It's a diesel genny. 8KW Onan. Thanks for asking.
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Old 08-02-2014, 12:13 PM   #17
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Thanks to all for the input. I certainly have read the owners manual but it does not specify anything about load other than a) exercise it once a week "under load" and b) run it at no load for 5 minutes to cool it down. That's it.

Being gasoline powered, it seems like one less thing for me to worry about. I'll run it when I need it and then shut it off.

Thanks,
BD
Yes also at no load for start up.

I would bet your system also had some load recommendations for break in. Which is all our diesel have. Once fully broken in, our manufacturer does not feel load, or lack of load, is a big issue. So many other things in taking care of your generator that are more important.

I've heard the precautionary warnings but from my experience they aren't coming from the manufacturers beyond what is in the manual.
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Old 08-02-2014, 12:16 PM   #18
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Not to hijack this thread, and the MODS can move it if judged a hijack but I'm real curious as to how forum members feel about running a genset for A/C during sleeping hours. I'm looking for safety issues, not "be kind to your neighbors," as I would never use my genset at night if other boats are in propinquity. Thanks, Howard
Diesel, I don't think a thing about it. Gasoline, I would probably be more reluctant, but with proper precautions and knowing my set up I'd do that as well.

We boat in places where air conditioning is essential. We also have other electric needs on board. Therefore, we either have shore power or generator at night.
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Old 08-02-2014, 12:40 PM   #19
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Diesel, I don't think a thing about it. Gasoline, I would probably be more reluctant, but with proper precautions and knowing my set up I'd do that as well.

We boat in places where air conditioning is essential. We also have other electric needs on board. Therefore, we either have shore power or generator at night.
What he said.
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Old 08-02-2014, 05:17 PM   #20
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What he said.
Ditto
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