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Old 28-07-2017, 15:17   #1
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How big a generator for A/C

I have a Webasto 16K BTU aboard. How big a gen do I need to run this on the hook?
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Old 28-07-2017, 15:28   #2
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How big a generator for A/C

Larger than a Honda 2KW, it will run it easy enough, but will not start it, even with a soft start capacitor.
However there is an expensive smart start, Dometic I think that will start it with a Honda 2 KW.

The cheap Supco hard start will not work with a Honda, it helps with my built in Diesel gen set, but isn't enough for the Honda. Supposedly the Dometic will, but it's over $400 I think.
I know as I have a Webasto 16K and used to have Honda's, it took both of them connected together to do it, one would not.
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Old 30-07-2017, 06:24   #3
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Re: How big a generator for A/C

Quote:
Originally Posted by SqPeg View Post
I have a Webasto 16K BTU aboard. How big a gen do I need to run this on the hook?
You will need a generator that will provide sufficient power as needed by the A/C unit at about 80% of the generator's rated capacity. For example, in our case we also have a 16K BTU A/C unit. We sized our generator to handle that and have sufficient additional capacity to charge our batteries or run our water heater at the same time. Hence, for us, about 4.2KW. Note that buying and installing a generator is not an inexpensive proposition; and, a generator can be costly to maintain and repair unless one is very rigorous about one's maintenance regime.

FWIW...
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Old 30-07-2017, 06:39   #4
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Re: How big a generator for A/C

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I have a Webasto 16K BTU aboard. How big a gen do I need to run this on the hook?
4kW or larger.

Air Conditioners are called "generator eaters" for a reason. Be sure to have plenty of other AC appliances to keep the generator at work.
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Old 30-07-2017, 07:51   #5
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Re: How big a generator for A/C

This BIG.
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Old 30-07-2017, 11:24   #6
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How big a generator for A/C

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4kW or larger.

Air Conditioners are called "generator eaters" for a reason. Be sure to have plenty of other AC appliances to keep the generator at work.


My generator is a 3.5 KW, it runs a Webasto 16k and a Webasto 6K simultaneously and also charges batteries with the 60 amp charger.
If I want to heat water, or run the toaster then I have to turn off the little AC.
At 110 VAC 3.5 kw can make 31.8 amps. My boat only has a 30 amp electrical system. I think a 3.5 KW gen is a good match for a 30 amp boat, now if you have a 50 amp system maybe you want a bigger generator.
I don't understand why someone would put an 8KW generator on a 30 amp boat?
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Old 30-07-2017, 11:48   #7
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Re: How big a generator for A/C

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My generator is a 3.5 KW, it runs a Webasto 16k and a Webasto 6K simultaneously and also charges batteries with the 60 amp charger.
If I want to heat water, or run the toaster then I have to turn off the little AC.
At 110 VAC 3.5 kw can make 31.8 amps. My boat only has a 30 amp electrical system. I think a 3.5 KW gen is a good match for a 30 amp boat, now if you have a 50 amp system maybe you want a bigger generator.
I don't understand why someone would put an 8KW generator on a 30 amp boat?
We have a 10kw generator.
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Old 30-07-2017, 12:18   #8
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Re: How big a generator for A/C

Many people buy a generator that is too big "they might want more power". Those generators run at full rpm with a light load and can glaze the cylinders in 1000 hours or less. My boat came with 2 1800 rpm generators, both 14kw and both with glazed cylinders.
Small 60hz generators usually run at 3600 rpm. Bigger ones at 1800 and big diesels at 1200 w/o a glazing problem (20 kw+ depending on engine).
What I think is a better solution for 24/7 AC power is a good inverter and battery bank.
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Old 30-07-2017, 14:58   #9
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How big a generator for A/C

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We have a 10kw generator.


Your maybe a 50 amp 220 V boat? In other words maybe your boats electrical system can support it?

Just I see no logic in having a generator that can supply twice the power that a boats electrical system can handle, however I see it a lot.
Excess expense and weight, and loss of storage.
I think most often it's boats that come from the factory with a generator, cause everyone knows an 8 is better than a 5 and a 10 is even better.
I struggled with it when buying and installing the generator I have, whether to go with a 5.5 or a 3.5. I'm glad I went with the small one and saved the weight.

Just me, but I doubt many small boat gensets ever make it to 20,000 hours.
If your a generator only boat, no Solar, and full time on the boat. I'd expect 1,000 hours a year or more?

I have a Magnum 2800W inverter, and it stays on all the time, I don't bother turning it off when we go to bed. We have gotten used to always having AC power
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Old 31-07-2017, 03:33   #10
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Re: How big a generator for A/C

Consider a smaller generator and an inverter/charger with a battery assist feature for peak/start up loads (Victron, Magnum, etc.). This way the generator will run at load while running the AC.

I haven't tried this with my Honda 2k, my Victron and a 16k AC, but I bet it would work. I can handle nearly twice the rated output of the Honda for 10+ minutes easily.
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Old 31-07-2017, 05:23   #11
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Re: How big a generator for A/C

Just tested the starting and running load on my 14K BTU A/C.

120V system

21 Amps for less than one second to start ( 2.5 Kw)

9 Amps to run ( 1.1 Kw)

Used a good amp meter with a high hold function
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Old 31-07-2017, 05:27   #12
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Re: How big a generator for A/C

Once you get past the startup, a 2k generator is usually still pretty marginal. Your Honda/Yamaha 2k generators are only rated for 1.6k watts continous. A 16k BTU air/con is going to be pulling pretty close to 1.6k watts once running.

That means you get to run nothing else and if used frequently, it will likely live a short life.

3k would be a good starting number. Should be able to start the air/con without getting exotic. It's got enough excess to not wear out the generator too quickly but enough to get the generator up to temp and exercise it well. Plus if you want to run the TV and some lights in the evening, you have enough excess to do it.
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Old 31-07-2017, 05:57   #13
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Re: How big a generator for A/C

never found a need for a gen set... can't stand the noise... another waste of fuel.
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Old 31-07-2017, 06:09   #14
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Re: How big a generator for A/C

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never found a need for a gen set... can't stand the noise... another waste of fuel.
So how do you propose to run the air/con (which was the original question not if you like generators)
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Old 31-07-2017, 06:17   #15
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Re: How big a generator for A/C

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I have a Webasto 16K BTU aboard. How big a gen do I need to run this on the hook?
SqPeg, a few people have mentioned it but allow me to simplify for you in case you're not aware. A 3kw or a 3.5kw genset will happily run a 16K BTU air con. The problem is the start-up load. When an air con compressor kicks in, it bumps up the amps to four or five times the running amps. It's only momentarily but it's enough to pop the fuse on your genset. I have a 3.5kw genset and the start up load on my 16k air con pops the fuse. It seems that other people with similar setups don't have any issues. Maybe my air con is getting old. You can buy a soft start (Google or Youtube them). What these do is to slowly wind up the air con until its gets rolling rather than bang it into life.

Hope this helps.
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