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Old 09-05-2014, 12:29   #16
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Re: Northern Lights v Westerbeke?

I don't think you want to run your generator for long periods of time at rated power. It's like running your main engine at full throttle. They are rated for it and can do it but they will age much quicker. I would spec the gen size to about double your average operating load so that you are running mostly at half throttle. Clearly, you have to make peak load also when you spec it.

Also, make sure that the wet exhaust is installed correctly. Account for extreme heel. Water can jet up the exhaust and trickle to the head and valves. This scenario will cause ruin to your valves, valve seats, head, pistons, and block.

Ask me how I know.
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Old 09-05-2014, 13:23   #17
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Re: Northern Lights v Westerbeke?

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Originally Posted by LakeSuperior View Post
I don't think you want to run your generator for long periods of time at rated power. It's like running your main engine at full throttle. They are rated for it and can do it but they will age much quicker. I would spec the gen size to about double your average operating load so that you are running mostly at half throttle. Clearly, you have to make peak load also when you spec it.

Also, make sure that the wet exhaust is installed correctly. Account for extreme heel. Water can jet up the exhaust and trickle to the head and valves. This scenario will cause ruin to your valves, valve seats, head, pistons, and block.

Ask me how I know.

I would question this blanket statement. It's my opinion that properly sizing an auxiliary generator is rather complicated.

If the application is in a motor yacht where all systems are AC powered, and the load remains relatively constant, perhaps selecting a generator which typically operates at 60-70% of total capacity might be acceptable. This would allow some cushion for start-up loads (in-rush current), as well as added electrical loads,but would also likely be in the most energy efficient range of generator operation. Selecting for lesser capacity percentages (such as the 50% quoted above) results in the diesel engine portion of the generator being outside of the "sweet spot" of typical diesels. It also results in the selection of a larger, more expensive and heavier generator. Note that these "assumptions" may vary based on the manufacturer's choices of the power head and the accompanying engine, and where on the operating curves of both devices the assembled generator typically operates.

For those of us, especially sailors, who use generators, the primary (though not sole) use is the recharging of the batteries with modest incidental and/or occasional additional loads - vacuum, electric drill, coffee maker, etc. For such usage, how would you size this generator - 50% of the battery charger demand???

I admit to making some broad generalizations, but the point is that an underloaded generator is no better than overloaded one. Perhaps selecting a unit that will operate at 85-90% of capacity during the typical "worst case" situation. I also believe that while the engine will be happy at 85% of design rpm, the generator on light duty units may be overstressed at a continuous demand of this capacity.

The case I am trying to make is that generator selection is not easy and is really best done on a case by case basis, subject to the actual or anticipated demands of the user.
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Old 09-05-2014, 14:01   #18
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Re: Northern Lights v Westerbeke?

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Originally Posted by redsky49 View Post
I would question this blanket statement. It's my opinion that properly sizing an auxiliary generator is rather complicated.

If the application is in a motor yacht where all systems are AC powered, and the load remains relatively constant, perhaps selecting a generator which typically operates at 60-70% of total capacity might be acceptable. This would allow some cushion for start-up loads (in-rush current), as well as added electrical loads,but would also likely be in the most energy efficient range of generator operation. Selecting for lesser capacity percentages (such as the 50% quoted above) results in the diesel engine portion of the generator being outside of the "sweet spot" of typical diesels. It also results in the selection of a larger, more expensive and heavier generator. Note that these "assumptions" may vary based on the manufacturer's choices of the power head and the accompanying engine, and where on the operating curves of both devices the assembled generator typically operates.

For those of us, especially sailors, who use generators, the primary (though not sole) use is the recharging of the batteries with modest incidental and/or occasional additional loads - vacuum, electric drill, coffee maker, etc. For such usage, how would you size this generator - 50% of the battery charger demand???

I admit to making some broad generalizations, but the point is that an underloaded generator is no better than overloaded one. Perhaps selecting a unit that will operate at 85-90% of capacity during the typical "worst case" situation. I also believe that while the engine will be happy at 85% of design rpm, the generator on light duty units may be overstressed at a continuous demand of this capacity.

The case I am trying to make is that generator selection is not easy and is really best done on a case by case basis, subject to the actual or anticipated demands of the user.
Redsky, you are almost spot-on. I was trying to motivate not designing a system to operate at the margins. I did not want to get into the details for the many use cases. A diesel operates well at various loads, think of an automotive application.

Note also that the generator engines run at a fixed RPM. Also note that I specified that peak demand must be accommodated in specifying the size.

You meant to ask, "how would I size this generator, at twice the battery charger load." This means that the generator operates at 50% of rated max load.

If it were me would look at the break specific fuel consumption specification, BSFC, for the engine and find where peak efficiency load is for the operating RPM. I would then begin to spec the system from there.

Just a side note, it has been my experience that yacht power management is not well integrated. One example, I would have a huge battery charger that can charge the AGM batteries at close to rated current. I have not personally observed one system that is set up to charge AGMs. This would allow a cruiser to run the generator for a much shorter duration per day.
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Old 09-05-2014, 14:03   #19
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Re: Northern Lights v Westerbeke?

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Originally Posted by LakeSuperior View Post
I don't think you want to run your generator for long periods of time at rated power. It's like running your main engine at full throttle. They are rated for it and can do it but they will age much quicker. I would spec the gen size to about double your average operating load so that you are running mostly at half throttle. Clearly, you have to make peak load also when you spec it.

Also, make sure that the wet exhaust is installed correctly. Account for extreme heel. Water can jet up the exhaust and trickle to the head and valves. This scenario will cause ruin to your valves, valve seats, head, pistons, and block.

Ask me how I know.
While I agree not to undersize your generator, Northern Lights are powered by Lugger engines and generally are made for continuous use and turn less rpm's than comparable engines. Still sizing should be for peak load, which means on average it will require much less. I find typical 1/4 to 1/2 load on unit.
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Old 09-05-2014, 14:19   #20
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Re: Northern Lights v Westerbeke?

[QUOTE=Note also that the generator engines run at a fixed RPM. Also note that I specified that peak demand must be accommodated in specifying the size.[/QUOTE]

You are right, of course. Fingers got in the way of brain while typing.

Although there are a few generators that do vary the engine rpm according to load, I meant to say rated load, not rpm, as most generators run at the typical 1800 or 3600 rpm speed.

In any case, you got my drift
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Old 09-05-2014, 15:36   #21
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Re: Northern Lights v Westerbeke?

Quote:
Originally Posted by LakeSuperior View Post
I don't think you want to run your generator for long periods of time at rated power. It's like running your main engine at full throttle. They are rated for it and can do it but they will age much quicker. I would spec the gen size to about double your average operating load so that you are running mostly at half throttle. Clearly, you have to make peak load also when you spec it.

Also, make sure that the wet exhaust is installed correctly. Account for extreme heel. Water can jet up the exhaust and trickle to the head and valves. This scenario will cause ruin to your valves, valve seats, head, pistons, and block.

Ask me how I know.
Good advice about exhaust, and about heeling

As far as running at rated power is concerned -- it depends on the type of generator. A light duty, intermittent use generator should really not be run for long periods at full rated output. A heavy duty, continuous duty generator can be run at full rated output with much less trepidation. That is largely because of how they are rated. My Kohler has a 1000cc Yanmar three-cylinder engine with cast iron block and head, an engine which develops 24 horsepower in intermittent duty form, at 3000 rpm. In my generator, the same engine is rated for only 6.5kW, which requires only about 12 horsepower, running at 1500 rpm. So you can truly run that generator all day and night long at 1500 rpm asking it to produce only 12 horsepower. I wouldn't do that with my Honda suitcase generator, nor would I do it with any of the many marine generators driven by one-cylinder Kubota rototiller engines.
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Old 09-05-2014, 19:25   #22
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Re: Northern Lights v Westerbeke?

A key element in choosing a generator on a new build is deciding on your AC Electrical configuration.

For Superyachts, I worked with Dick Gee, the Founding technical director of Northern Lights to analyse the MTBF on their GENS continously running at either 1200, 1500, or 1800 RPM.

It became obvious from their many repair-spares records that 1500rpm had the least problems.

So I always recommended that Owners specified equipment for 50hz unless they planned on being US based.

Load Analysis and design criteria for Gens was calculated to run at optimum 80% in the tropics with full hotel loads.
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Old 09-05-2014, 21:29   #23
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Re: Northern Lights v Westerbeke?

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No the phasor genset in the 6KW is not a single cylinder. Its 3, and 1800 rpm. Only the 3500 watt and the 2500 watt are 1 cylinder. Kubota is a great engine. I have never has an issue in the excavation field. We run the #$@%@ out of them, and they keep on ticking. A typical day for us results in us stalling then engine 3-10 times a day as we push it far beyond what it is designed to do. I have seen one with over 14,000 hours, and other then leaking its fine.
I didn't realize you were talking about the big Phasor -- sorry. Of course nothing in the world wrong with those. And of course there is nothing wrong with Kubota engines, either. One of those marinized by Beta or Nanni would be high on my list if I ever repower. The problem is the one cylinder ones (designed for rototillers) used by FP, Phasor and others in the smaller gensets, which are not designed for long-term use and which give a lot of cruisers a lot of problems when run harder than they were designed for. There's actually nothing wrong with the one-cylinder Kubota, either -- in a role it was designed for. The worst abuse of this poor engine is in certain FP gensets which have them running at redline in a sealed box with delicate electronics surrounded by a lot of salt water. Not a recipe for reliability!
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Old 10-05-2014, 09:53   #24
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Re: Northern Lights v Westerbeke?

Hi Folks

Many thanks for all the sound input, much appreciated! We will go for the NL. For what its worth, we will be installing it unshielded in an insulated engine room, probably with the additional cushion mounts.

Good sailing
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Old 10-05-2014, 10:06   #25
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Re: Northern Lights v Westerbeke?

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Hi Folks

Many thanks for all the sound input, much appreciated! We will go for the NL. For what its worth, we will be installing it unshielded in an insulated engine room, probably with the additional cushion mounts.

Good sailing
FWIW, I have an older, 3-cyl., 8kw Westerbeke genset in an insulated engine compartment, but with no sound shield (probably not enough room for one). It's extremely quiet above decks, but somewhat uncomfortably loud down below. I generally don't run it for more than a few hours at a time (at most) and never overnight while anchored, so not a huge deal. Just thought I'd mention it in the event you may want to plan your installation for an add'l sound shield down the road. I'm assuming the new ones are quieter, but don't know for sure.

Best of luck with the upgrade.
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