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Old 03-02-2015, 09:22 PM   #1
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2.5 KW Diesel gen too small?

I have a 32 Island Gypsy, single screw. The inverter is no working and I want to be able to run air and lights while anchored.

There used to be a generator on the boat as there is an extra sea cock in the hull. I'm not a limited budget and am wondering if a 2.5 KW DIESEL generator would be a good fit for my Ford Lehman diesel powered trawler.

My AC runs 12,000 BTUs. I want to be able to run a few lights and the AC with the 2.5 KW generator. Do you think it will produce enough power?
It's priced right at $3k and is relatively small.

I would assume I would want diesel rather than gasoline to run off my two main diesel tanks, right?

Any thoughts?
Thanks,
Rick
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Old 03-02-2015, 09:34 PM   #2
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It depends partly on your ac unit. Older models used a piston compressor that draws more running amps and has a significantly higher starting amp requirement. Rotary compressors draw less amps and the start up load can be significantly smaller. Starting the compressor will be the issue. There should be enough amps to run it. If you can post the amperage requirement from the manufacturers label on the unit, that would be very helpful.

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Old 03-02-2015, 09:38 PM   #3
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Well, 12000 btu is 3.2kW. So you're not gonna make it with 2.5KW genny. If the ac has 'soft start' then you might get away with a 4 kW unit, but better would be a 5kW. Even then, I would borrow or rent a genny on wheels of that size, walk it along the dock and plug in your ac. Test it will start the ac before buying and plumbing one into your boat. And yes, diesel is best. Boat gennies are not cheap though.
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Old 03-02-2015, 09:46 PM   #4
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Our phasor 3.5Kw in our camano would run our 16k BTU and nothing else.
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Old 03-02-2015, 09:46 PM   #5
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You might need to add a SmartStart soft starter or something like it to the A/C unit to reduce the start up load.
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Old 03-02-2015, 09:52 PM   #6
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Well, 12000 btu is 3.2kW. So you're not gonna make it with 2.5KW genny. If the ac has 'soft start' then you might get away with a 4 kW unit, but better would be a 5kW. Even then, I would borrow or rent a genny on wheels of that size, walk it along the dock and plug in your ac. Test it will start the ac before buying and plumbing one into your boat. And yes, diesel is best. Boat gennies are not cheap though.

Your using the wrong formula. A Webasto 12K btu ac unit draws 8.5 amps at 115 volts. 115 x 8.5 = 977.5 watts (slightly less than 1 KW). There is more than enough power to run it, the question is does the genset have enough muscle to start it.

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Old 03-02-2015, 10:01 PM   #7
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Yes, I was converting to cooling capacity. It seems that input power is a lot less. So based on your calc and Oliver's actual numbers then the OP might be OK with his 2.5kW unit if the ac is soft start. Personally I'd still test it out first before buying....
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Old 03-02-2015, 10:04 PM   #8
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Can you tell us a little more about this 2.5 KW genset. If it is that small then it probably has a Farymann diesel. Even though they are used on the small Fishcher-Panda gensets, I consider them a toy.

Whether a generator will start a 12,000 but A/C depends on the starting current of the A/C and the generator's ability to supply it. Some small gensets like the NextGen 3.5 KW unit and maybe the Phasor 3.5 KW mentioned above have 5 KW generator ends. These will supply enough starting current for a 12 or even 16,000 btu A/C unit.

And as others have said, you can install a soft start kit on the A/C compressor. Supco makes one and Dometic makes a better one.

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Old 03-02-2015, 10:10 PM   #9
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Rick,

It will be tight, but a modern Cruiseair 12K BTU AC unit draws 8.7A cooling and 10.9A heating. It draws 58A locked rotor on startup.

Dometec makes a SmartStart Soft Starter which reduces the start amperage by up to 65%, or in the case of the above unit, a little over 20A or 2.3KW. Theoretically, it should work.

I've heard of other TF members that have successfully run some 16K BTU marine air conditioners using Honda EU2000 portable generators.

Good luck with your project.
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Old 03-02-2015, 10:11 PM   #10
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Start amps = 1.8 X run amps. So according to Ted's numbers 8.5 x 1.8 = 15.3 amps for start up. Or 1.836k watts. All this in theory, you have additional resistance in the wiring. Then there is the RPM factor, high RPM gensets will drive Ya nuts.
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Old 03-02-2015, 10:18 PM   #11
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My 12000btu Mermaid draws about 8-10A depending on temps. A 2.5kW might or might not start it.

What gennie brand/model is the 2.5?
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Old 03-03-2015, 07:47 AM   #12
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A better question might be why NOT the Honda?

It will run the AC , is almost silent , cheap, and can be used at home at times.

With no install time the only hassle is the rotten gas required to be sold today.

A steel old style 6 gal OB tank would make a good easy to fill tank .

IF you operate infrequently , simply run the unit out of gas , and dump the gas into your car.
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Old 03-03-2015, 07:50 AM   #13
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Quote:
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A better question might be why NOT the Honda?

It will run the AC , is almost silent , cheap, and can be used at home at times.

With no install time the only hassle is the rotten gas required to be sold today.

A steel old 6 gal OB tank would make a good easy to fill tank .

IF you operate infrequently , simply run the unit out of gas , and dump the gas into your car.

This is what I was thinking. Way cheaper and they have been known to start good size AC units with the help of a start capacitor.
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Old 03-03-2015, 08:38 AM   #14
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Again I find myself in complete agreement with FF. Honda has a heck of a warranty also as an upsize.
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Old 03-03-2015, 08:47 AM   #15
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Good article here on running a 16K BTU unit off a Honda EU2000.... Using various soft start methods (Supco and Dometic).
The Supco start capacitors are only $12 on Amazon, so simple and cheap enough to try out. I'm going to and test with my 2K watt portable gen. It should be all I need to run the 12K BTU Mermaid on my boat..

Honda eu2000i and air conditioning - Page 3 - SailNet Community
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Old 03-03-2015, 08:54 AM   #16
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Buy at least a 3 1/2 kw gen. You never know what you may add. It would be expensive to upgrade.
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Old 03-03-2015, 09:38 AM   #17
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The Honda generator might be a viable option for infrequent use. OP lives in FL and may plan on using it a fair amount. The honda is quiet under modest loads, but gets noisier at half or more capacity. There have been a couple of theads on the forum about building sound shields for them. Not sure I would feel comfortable going to bed at night at anchor with one running in the cockpit or up on the cabin roof. Think a properly installed and maintained diesel marine generator has a significantly lower risk factor. Don't forget about the carbon monoxide exhaust which is extremely dangerous.

Ted
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Old 03-03-2015, 09:39 AM   #18
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You seem to have enough info on the required size of the gen set, I would add you need to check into the sound levels as well, have a friend with small 3.5 diesel gen and boy does that put out a racket, no way you would be leaving it running for AC needs.
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Old 03-03-2015, 09:55 AM   #19
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The Nestgen is powered with a Kubota engine, belt drive geared to 60 cycles, and runs at 2800 rpm. Not a screamer or terrible vibration. I had a 5kw and was very happy with it. Built in Jacksonville. They are very helpful.

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Old 03-03-2015, 12:12 PM   #20
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I had a mastervolt 3kw generator (Kubota motor). Ran my 16000 btu air conditioner ok, but surged when the compressor started. I added the dometic smart start and it worked much better. Downside to a lot of small single cylinder gensets is the high rpm (3600 for the one I had). A lot of noise and vibration. One suggestion, install the exhaust water separator option if available, it makes it quieter.

The Honda is a great generator, CO is a killer. I would go with the diesel.
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