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Old 31-07-2017, 06:26   #16
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Re: How big a generator for A/C

My dock neighbor showed up one day with his Honda 2000 to run his AC. I asked what size AC...16k, said he's run it a number of times with the Honda. I was shocked and asked if I could plug my boat into it to try to run my 16k unit.
Plugged it in, started it up and let it run a minute or two to warm up, turned on the AC fan only and then hit the compressor.
The Honda bogged down a little for a second or two, then came back up and ran like a champ. Couldn't believe it.
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Old 31-07-2017, 07:46   #17
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Re: How big a generator for A/C

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Originally Posted by fallingeggs View Post
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.


Had a friend with this same setup and it worked.
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Old 31-07-2017, 09:35   #18
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Re: How big a generator for A/C

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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'll admit to being on shaky ground here, but is it not possible, perhaps even desirable, in this scenerio, to tweak the electrical system just a little bit in order to use all the power?
Say, run separate wires from the generator to whatever appliance is the main power hog ... Battery charger perhaps. Then let everything else stay as it was. I'd guess a good electrician can help set this up safely somehow.

Free-standing generators often have two or more sockets, and so are entirely ready for this. Your favourite power tool goes into one socket, and the rest of the boat into the other , right?
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Old 31-07-2017, 09:58   #19
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Re: How big a generator for A/C

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I'll admit to being on shaky ground here, but is it not possible, perhaps even desirable, in this scenerio, to tweak the electrical system just a little bit in order to use all the power?
Say, run separate wires from the generator to whatever appliance is the main power hog ... Battery charger perhaps. Then let everything else stay as it was. I'd guess a good electrician can help set this up safely somehow.

Free-standing generators often have two or more sockets, and so are entirely ready for this. Your favourite power tool goes into one socket, and the rest of the boat into the other , right?


That's commonly done in boats that have two shore power cords.

Most often seen with twin 30 amp cords. 1 or 2 air conditioners on one cord and everything else on the other.

However now you're on a boat that requires 60 amps to function, not 30.

So generator size follows suit. 4kw to 8 kw.
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Old 31-07-2017, 10:08   #20
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Re: How big a generator for A/C

So if you are planning to cruise in the tropics, where extra capacity to run A/C can come in really handy ... it makes sense to install a super-size generator if you're getting one in the first place.
Even if you don't need all the power initially.
The same would apply if someone is pondering trips to the Arctic, probably (i.e. heating) ...
Mystery solved :-)
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Old 31-07-2017, 13:47   #21
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Re: How big a generator for A/C

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So if you are planning to cruise in the tropics, where extra capacity to run A/C can come in really handy ... it makes sense to install a super-size generator if you're getting one in the first place.
Even if you don't need all the power initially.
The same would apply if someone is pondering trips to the Arctic, probably (i.e. heating) ...
Mystery solved :-)


Not so fast.

The problem with air-conditioning on boats in the tropics is at night it cools off and the air-conditioner doesn't run very often often. What this leads to is a large generator with no load on it. During the day with the heat load from the sun it may take all of the air conditioning running all of the time to keep the boat cool. Once the sun goes down you may only need less than a third of the total air conditioning capacity. The problem is now you have a large under-loaded generator that leads to cylinder bore glazing.
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Old 31-07-2017, 14:47   #22
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Re: How big a generator for A/C

I have a 5 KW Northern Lights with 16k MarineAirr water to air heat pump and run other loads too. You need to turn on the HWH too and that will help level the load. I agree that in SW Florida and the tropics the load may be light at night. I have heard that the new inverters (mine is 2kw and 2003 model) have the ability to load share and could be a solution to a smaller more balanced to the load generator.
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Old 31-07-2017, 14:51   #23
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Re: How big a generator for A/C

I don't have boat experience but in the RV world, 4k AC generator runs at 3600 rpm and works great for 30 amp service. It powers one 14-16k btu AC and one 5k btu AC plus normal house loads. Have to turn off the 5k btu AC to run the microwave or a hair dryer, etc.
I have tried running the 14k btu AC from a Honda 2k and it revs to the moon, struggles for a min, then drops out due to overload. I tried it a couple times and same result.
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Old 31-07-2017, 15:56   #24
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How big a generator for A/C

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Originally Posted by FlyingScot View Post
I have tried running the 14k btu AC from a Honda 2k and it revs to the moon, struggles for a min, then drops out due to overload. I tried it a couple times and same result.

Depends on the unit, my old AC the Honda would start it, but the new Webasto forget it, same thing you had. However once running the Webasto pulls less power than the old one, just is harder to start.
Now unless I'm mistaken the 24k Webasto comes from the factory with a hard start kit and is easier to start than the 16K, but I'd bet a Honda would be busting a gut to run it if it could start it.
My 16K Webasto pulls about 11 amps running I think and my 6K about 5. A Honda is good for 13 continuous if memory serves, so 11 is awful hard.

When I was trying to make things work with a Honda that is what the small 6K Webasto in the forward Stateroom was for, a Honda could run it easily in Eco mode and start it too.

Awfully sure with the Dometic hard start kit that your 14K will start with a Honda.
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Old 04-08-2017, 19:09   #25
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Re: How big a generator for A/C

I have a Honda 2000i generator to power my Marvair 16000 BTU unit on my Catalina 375 sailboat. The startup surge amperage on the Marvair is 42.8 amps and running is 12.67 amps. I have tried both the Supco SSP7 and the Dometic Smartstart both of which work when the Honda runs at high RPM (ECO mode off) but will not work when ECO mode is on.
I then purchased online the Micro-Air Easy start 364 ($300). The Micro-Air works much better using a 5 minute delay between compressor startup cycles from the A/C thermostat. The Honda smoothly starts the compressor even on low RPM Eco mode for less noise and better fuel economy.
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