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Old 13-06-2010, 10:06   #1
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8Kw Marine AC Generators ?

Dear Forum,
Looking for recommendations on a trusty marine generator in the 8Kw range for new build boat project. I am trying to cut through the salesmanship and find some reliable third party recommendations.

Thanks,
Shack
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Old 13-06-2010, 10:34   #2
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You might want to PM Neelie (see Cruisers & Sailing Forums - View Profile: neelie ) He ans his wife just replaced their generator and I believe he can off some good information.

We have a Panda that we have been very satisified with but they do demand rigerous maintenance. Unfortunately, I suspect many here with disagree with the suggestion as there were some issues with the vendor many years ago but ownership has since changed and the Company has become quite reliable. Unfortunately, poor reputations once earned are difficult to overcome.

FWIW...
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Old 13-06-2010, 11:29   #3
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Dear Forum,
Looking for recommendations on a trusty marine generator in the 8Kw range for new build boat project. I am trying to cut through the salesmanship and find some reliable third party recommendations.

Thanks,
Shack
Just a couple of tips:

1. Why do you need such a big one? 8kW is an awfully big genset for a sailboat. A genset too big for your needs will not be sufficiently loaded to run well and you may have premature wear.

2. If you are sizing the genset to handle the startup loads on an AC system, consider instead putting in a charger/inverter that will draw on battery power automatically to deal with the brief inrush loads. Then you can use a smaller genset which will be easier to load up. We have a 6.5kW Kohler on our 54 foot boat and we have difficulting keeping an adequate load on it. A European shore power connection is 15 amps or about 3.6kW; our 6.5kW genset is almost like two shore power connections. Even running the washing machine and with the battery charger in bulk mode, and the electric water heater going, it is hard to keep a 50% load on it.

3. A 1500 or 1800 RPM genset from a company Northern Lights, Kohler, or Onan will be more expensive and heavier than a 3000 or 3600 RPM model or, God forbid, a Fischer-Panda, but will run in a much more relaxed, understressed, quiet way, last longer, and give you less trouble. Highly recommended.

4. Three-cylinder, low speed gensets have a far more pleasant sound and motion than two-cylinder or four-cylinder ones. Like a horse cantering rather than trotting, if that makes any sense to you. Our Kohler, with its 1000cc (!) three-cylinder Yanmar, is completely inaudible to neighbors at anchor, and is not loud enough below to be even very noticeable, much less disturbing anyone. This has a big effect on how you use the genset, by the way. It means that in a pinch, on a particularly sultry night, you could run it all night, in order to run air conditioning. High speed or two cylinder gensets could not be used in that way without disturbing neighbors and/or interrupting your own sleep.

5. Run, don't walk, in the opposite direction from any Fischer-Panda, with all due respect to the previous poster. Customer service may be better but these devices are the worst conceived things, from an engineering point of view, for the intended purpose that you could ever imagine. They are museums of shockingly awful engineering solutions. The statistics, showing trouble rate of something like 10x higher than the next worst genset, bears this out. The most common model of this uses a single-cylinder (!) engine screaming away at the redline in a sealed compartment, just to name the most obvious wrong-headed feature out of dozens. This is not the way you want to generate power on board.
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Old 13-06-2010, 11:37   #4
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I have liked the 8kw Onan that I've had for 13 years. The only maintenance issue has been the water pump">raw water pump. It is made by Sherwood. They die quickly if you start them with the sea-cock closed. Replacing the impellers is somewhat of a difficult task, but it is easy to change the whole pump, and much less likely to result in saltwater dripping from them onto electrical ground connectionss below it.
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Old 13-06-2010, 11:52   #5
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I have liked the 8kw Onan that I've had for 13 years. The only maintenance issue has been the raw water pump. It is made by Sherwood. They die quickly if you start them with the sea-cock closed. Replacing the impellers is somewhat of a difficult task, but it is easy to change the whole pump, and much less likely to result in saltwater dripping from them onto electrical ground connectionss below it.
Onan, Northern Lights, and Kohler of that type are all similar and good. I forgot which one of them (I think Onan) was best in the ARC survey ("The Great Atlantic Gear Test"). In that size range, the low speed ones all use derated three-cylinder engines. Kohler uses Yanmar, Northern Lights uses Lugger, and Onan uses Cummins, all excellent engines.

Look for automatic shutoffs in case of not just oil pressure and coolant temperature, but also exhaust temperature and alternator windings temperature. I don't know about Northern Lights and Onan, but our Kohler has all of those. Also useful would be some kind of on-board diagnostics which can tell you what fault led to a shutdown. Our Kohler does NOT have that, to our regret (although we have never had an automatic shutdown -- knocking on wood -- so the desire is theoretical). Maybe the newer ones do.

I don't think you can kill any genset with a shut seacock; I think they all have at least a temperature shut-down.
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Old 13-06-2010, 12:34   #6
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1. Why do you need such a big one? 8kW is an awfully big genset...
Dockhead,
There will be small work shop aboard with a requirement for some AC power tools. We're still doing the amp math, but I'd rather estimate big then pair down during refinement and final selection. I won't need anything larger than 8Kw. The bottom line is that 30A with a 4Kw gen is likely to be on the verge of being too small. I'll probobly end up somewhere in the middle.

Thanks All for the quick repsonses,
I'll check out your recommendations for their specs and watch for more replies.

Shack
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Old 13-06-2010, 12:37   #7
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Just a couple of tips:

5. Run, don't walk, in the opposite direction from any Fischer-Panda. They are museums of shockingly awful engineering solutions. .
Sometimes it nice to have a yacht so small that stuff like this just can't be accommodated even if we wanted to and its one less nightmare we need worry about. Instead we will keep our little Honda 20i which suits us fine for the occasional charging we may need

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Old 13-06-2010, 12:46   #8
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Definitely get a 1500/1800 rpm unit - much quieter and smoother.

Get the sound shield and also consider a water separating muffler

Consider ease of maintenance in your planned mounting location. My Onan has all regular maintenance items on the same side of the unit. Obviously, that side should be easy to reach.

I chose between Northern Light, Onan, and Kohler - any would be a good choice. Onan seemed to have the largest service network according to their web sites and and greatest familiarity among mechanics according to my unscientific local poll. I never like to hear a boat yard mechanic say "Never seen one of these before...". I'm pretty sure Onan was the top unit in the ARC poll.

Here is a really detailed report by Victron Energy testing gensets with their inverters. They all do pretty well so it's not clear this will help a purchase decision.

http://www.victronenergy.com/upload/...7-jan-2008.pdf

Carl
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Old 13-06-2010, 12:47   #9
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Dockhead,
There will be small work shop aboard with a requirement for some AC power tools. We're still doing the amp math, but I'd rather estimate big then pair down during refinement and final selection. I won't need anything larger than 8Kw. The bottom line is that 30A with a 4Kw gen is likely to be on the verge of being too small. I'll probobly end up somewhere in the middle.

Thanks All for the quick repsonses,
I'll check out your recommendations for their specs and watch for more replies.

Shack
Good luck. Don't forget about startup loads, and managing them with an inverter like those Victrons. That will give you different amps to use when doing your calculations -- average continuous loads, instead of peak loads, which can be a huge difference.

The other great thing about those charger/inverters is that they will shed certain loads (water heaters) when amps are tight, and will automatically cut down the charging current when the amps are needed for something else.

This can really help solve the very serious, classical problem of generator sizing -- if you size the thing to handle the maximum currents, then in normal operation you will not have enough load on it to keep from screwing up the engine.

Here's one very sweet looking genset:

http://www.northern-lights.com/marine/M673L3.html
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Old 13-06-2010, 14:14   #10
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Here is a really detailed report by Victron Energy testing gensets with their inverters. They all do pretty well so it's not clear this will help a purchase decision.

http://www.victronenergy.com/upload/...7-jan-2008.pdf

Carl
Carl,
Great link!! Thanks. Great point was made about about a hybrid system of inverters and genet.

Thanks
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Old 13-06-2010, 15:03   #11
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Inverter/chargers like the Victron's are also a great way to keep the gensets below their maximum power as you can set the maximum genset draw at the inverter. A knowledgeable friend has told me that he's never actually seen a genset damaged by light loading - although it couldn't be good - but that that he has seen plenty wrecked by sustained overloading. I set my max draw at 75% of rated genset amps (as mentioned, the inverter will use battery power to cover any starting surge or brief overage).

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Old 13-06-2010, 15:09   #12
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Inverter/chargers like the Victron's are also a great way to keep the gensets below their maximum power as you can set the maximum genset draw at the inverter. A knowledgeable friend has told me that he's never actually seen a genset damaged by light loading - although it couldn't be good - but that that he has seen plenty wrecked by sustained overloading. I set my max draw at 75% of rated genset amps (as mentioned, the inverter will use battery power to cover any starting surge or brief overage).

Carl

That's very interesting indeed.

I wonder how a genset can be wrecked by overloading. Surely the breaker should trip if you overload them, and surely a good genset should be designed to put out its maximum output on a continuous basis?

And besides that, you have exhaust temperature shut-down (on Kohler, and also Northern Lights as I see, at the very least).

What kinds of gensets did he see wrecked from overloading, I wonder? Surely not any good quality ones.
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Old 13-06-2010, 15:12   #13
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One thing to consider with generator sizing is the load. Most genset engines like an 80%+ load or problems can occur. Some gensets have a peak load that may help your sizing decision.
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Old 13-06-2010, 15:34   #14
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Dockhead,

The overload is not the wiring (the breakers) but the diesel. My friend's complaint was that genset kw ratings from even top name manufactureres are not for "continuous" operation - just like many marine propulsion diesels. Overheating, seal problems, and inadequate lubrication all can appear.

The Victron report also mentions that running at less than 30% load badly reduces fuel efficiency - whether or not it hurts the engine.

So my "takeaway" is to try to keep the genset loaded at between 30% and 75%. This is actually a pretty wide range.

Carl
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Old 13-06-2010, 15:52   #15
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I just downloaded an Onan 9kw operators manual. Under the "Loading the Generator Set" section it reads:

"It is best to run the generator set at 1/4 to 3/4 load."

They explain that less than 25% is bad because of carbon buildup. They are silent as to why it is best to not run above 75%.

Carl
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