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Old 30-12-2006, 20:03   #1
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generators and ac motors

i ahve been looking at 2 kw electric motors to run a watermaker i was looking at using a 3kw kipor generator to run as this will apparently just handle the startup current required of the motor, an electrical engineer friend of mine who works on the mines abd deals exclusively with generators reckons i need at least 4.5kww and reckons that while 3kw may work it will kill my motor quickly, now i dont want or have the money for a generator this larg has anyone got any ideas or real world info on this one
sean
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Old 30-12-2006, 20:11   #2
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Startup multiplier is usualy 3-5 times run current. Look into adding a capacitor to the motor to aid in startup.
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Old 30-12-2006, 20:12   #3
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is this a simple process?
can you elaboarte a little for this electrical moron
sean
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Old 30-12-2006, 21:23   #4
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Northern Cat:

am buying a 3.5kw generator that has a very high startup capacity. NEXTGEN ULTRA COMPACT MARINE GENERATORS
Got a good price from Never Monday. Don't know about sending it to Aussie though. I have heard it is a very good model and uses the Kubota 7hp.
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Old 30-12-2006, 22:10   #5
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it looks nice but i am trying to stay lightweight so i can outsail bad weather 8-) hence a petrol genny.
sean
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Old 30-12-2006, 22:35   #6
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Pretty darn lite for a diesel gnerator. 160 lbs (about 73 kg) and a hell of alot safer.
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Old 30-12-2006, 22:59   #7
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but i am trying to stay under 40kilos
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Old 31-12-2006, 04:21   #8
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Starting current should be determined from the specific motor nameplate.
The current drawn by a motor during across the line starting is specified on the motor nameplate as Locked Rotor Amps (LRA).
This current is typically five to six times the Full Load Amps (FLA) of the motor, and as high as ten times FLA for high efficiency motors.
This inrush current lasts only until the motor shaft has reached its rated speed, so it is typically of very short duration, perhaps less than one second.
The addition of an electrolytic capacitor (start capacitor) provides a more ideal phase relation (voltage & current) and results in greater starting torque with much less power input.
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Old 31-12-2006, 06:15   #9
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Thanks Gord!

Northerncat,
I'm not aware of a marinized petrol genny in the weight you are looking for. The two smallest are the Kohler 5E
http://www.kohlerpowersystems.com/pdfs/g2058.pdf
and the Westerbeke 3.0BPMG
http://westerbeke.com/brochures/GASG...%2E0BPMG%2Epdf
Both are nearly double your weight requirement.
If you are looking to use a portable petrol genny, please don't. There is a whole nother thread around here regarding that.

Here is a thread from a SeRay board fI requent. It's about using a Honda Portable generator.
Club Sea Ray Home :: View topic - Honda Generator
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Old 31-12-2006, 07:08   #10
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If you are looking to use a portable petrol genny, please don't. There is a whole nother thread around here regarding that.
i read the thread and i dont quite get why not they did mention co poisoning but as these are usually run in the open that isnt a problem so why else not???, there are quite a few people on cats who have these portable genny's and just stick them up the front of the boat when they use them, i was looking at the kipor 3000 as it does 2600kwmax and can apparently handle a surge current of 3500 for 1-3 seconds, this would hopefully be enough to run a watermaker and also could be handy for aircon and battery charging
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Old 31-12-2006, 07:10   #11
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also i have looked for any threads on the subject but have found very little, oh and the weight of the genny 26kilos which is a good 50 kilos lightewr than the diesel
sean
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Old 31-12-2006, 08:48   #12
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I'm going to have to agree with Sean (the other Sean) on this one. If he's looking to be lightweight and economize, the petrol genset isn't so bad, with the exception of it being less reliable.

Like everything with sailing, it would be about risk management. He should:

*Keep the genset outside and in a locker similar to a propane/LPG locker
*Use caution as it gets hot
*Don't let any CO inside the vessel or sit downwind breathing in CO
*Store all petrol carefully and properly (we all have it aboard for our ourboards, don't we??)
*Locate it near the stern, since sailboats face into the wind 99% of the time or when you are underway. This keeps CO and exhaust falling over the stern and not collecting in the cockpit (assuming center cockpit)

While I doubt the smaller petrol genset will work for his application (2KW electric motor), I'm sure it's a reasonable solution for more modest power requirements. I wouldn't count on it performing well for more than 6 mos, and wouldn't stake my watermaking or refrigeration on it (owing to the fact that petrol engines are more maintenace intensive and don't last as long). However, it would work.

When our old diesel genset died this summer, I bought a 3.5KW petrol and used it up on deck for 2 weeks, running it each day. Now, I have a new "portable" genset mounted on deck permanently. It's a 5KW Yanmar diesel, but it is air cooled and deck mounted. It has the same issues as Sean's would have, with the exception of being a more reliable diesel unit. Weighing in at 200lbs, it's much more heavy than Sean wants though. I used it every single day for 6 mos without incident. It provided all power for our charter guests, 120VAC refer, computers, lights - everything since we didn't tie to a dock the whole time.

If all cautions are taken, I don't see why a "portable" (meaning air cooled) genset can't be made to work for marine use.
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Old 09-01-2007, 17:05   #13
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generators and AC

Have a look at this DIY desalination system designed by a Yachtie.
I am building one like this very soon based around powering with a Honda motor which will also be used with a 100amp alternator and a freezer compressor.
basics
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Old 09-01-2007, 17:23   #14
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NextGen 3.5KW Generator

Charlie,

I've got one, 2.5 years old. In the sound shield. Love it. Been very reliable.

Only downside: inspecting or changing the raw water impeller is a real bitch. The designers of this model are absolute masochists. Think 2-3 hours, for what should be a 20-minute job!

Bill
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Old 09-01-2007, 18:33   #15
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Like some of the guy's here I dont have a huge amount of knowledge on generating electrickery on boat's apart from solar and the alternator on the motor.

I too don't want a diesel gen [ a $$$ thing] and would probably go for the Kipor like Sean[NC], but I do have the engine and control's, starter etc for a Yammy 9.9 4 stroke O/B down in the shed and always wondered what could be done to get a large spinny thing onto that to generate power.

Being electric start, watercooled and 4 stroke, it could live in the well ventilated back step area and being close on 10 hp should pump out the Amps and would be nice and quiet.

Any comment's

Dave
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