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Old 06-14-2014, 06:07 PM   #20
ksanders
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City: SEWARD ALASKA
Vessel Name: DOS PECES
Vessel Model: BAYLINER 4788
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Quote:
Originally Posted by djmarchand View Post
We haven't talked about size, much. One poster said buy big. I totally disagree.

David
I dont know David

From the engine prospective...Its the same argument about having engines in a boat capable of semi displacement speeds and running the boat at displacement speeds. Or the engine in my F-350, yet I almost never tow anything anymore. I've not seen any real data indicating lightly loading a modern engine is harmful, especially with the bursts of higher loading inherent in power production. Remember that every backup generator in this country is very much oversized due to NEC requirements. There is some fuel savings but not as much as people think. Especially when you consider how much you really run your boats generator.


From the generator end prospective I can say that its better to run a lighter load on a generator end. Oversized generator ends last longer. Here's why...

A generator end is rated by the manufacturer at a certain KW at a certain temperature rise. It can produce and is rated at a higher KW at a higher temperature rise. Once enough KW of load is applied then the manufacurer derates the generator to standby only service.

Generator packagers have a strong financial incentive to use the smallest generator end they can get away with. That means that at their rated output they are running the highest internal temperature RISE that the manufacturer recommends. Manufacturers use temperature RISE as their measurement because they cannot control the ambient temperature the generator will be operated in. Think of how hot it is in your generators sound shield, in your lazerette, on a hot day in the heat of summer. Then consider that you are loading the heck out of that generator. Bigger is cooler running, increasing lifespan.

There's also another issue that makes larger better. That is the ability to handle a sudden load. When a large load is applied the engine decreases RPM. This also makes voltage fall off because voltage regulation is not a perfect science, it is frequency dependent. The governor senses the decreased frequency and increases the throttle setting. The engine increases in RPM and the governor senses that and decreases the throttle. These processes take time. Time to sense the falling frequency. Time to move the throttle, time to deliver more fuel. A larger engine and generator end create more rotating mass, making them inherently more frequency stable.

Because of the engine issues being arguable at best, and the generator end issues favoring a larger generator, and the inherent frequency stability of a larger generator set, I'd recommend on the larger generator given a choice.


Quote:
Originally Posted by psneeld View Post
Kevin...

What's the deal with inverter type gensets like the little Hondas?

Someone asked awhile back and can't remember if you jumped in and explained why we don't see more versions of the type in permanently mounted sets.
I love the little hondas. Great little generators. Reliable, inexpensive. I cant think of anything wrong with them except they are not built in.

As to why there are not more generators like that I have no clue. Probably as was suggested R&D money.
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