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Old 09-05-2013, 21:03   #1
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AC will not run off generator

Howdy,
I'm new to this forum and wanted to start by saying hello to everyone from sunny phoenix, az.

Now to my issue:

I have an airrr ac system on my 1998 maxum 3200SCR. It works like a champ when it's powered from the shore but the compressor will not start when it's powered off of the generator. The generator is a westebeke 4.5gca (pretty sure). That came factory installed with the boat and ac setup. The generator was tested recently and is putting out clean power ~120v @60hz. The ac capacitors have been removed and tested by ac technicians and found to be working properly. Compressor on the ac unit was changed last year. Didn't solve the problem. Refrigerant pressures are normal. When you turn the unit on it starts its power up sequence normally but "greys out" when the start relay closes. Voltage drops to about 108. Thought that it may help to add a hard start to it but that aggravated the problem and caused it to not work on shore or generator power. Marine techs are stumped, two electrical engineers whom I know well are stumped and the ac techs are stumped. Anyone have any ideas? I have been on multiple forums searching down an answer to this but have yet to find much help. Thanks in advance for any ideas



DL
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Old 09-05-2013, 21:12   #2
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Re: AC will not run off generator

Seems like you have already tried most of the easy and obvious solutions.

My first thought is that the problem must be with the generator OR the wiring from the generator to the AC or panel. If the AC works on shore power just fine and not on the generator then I would say with 99% certainty that the problem is not directly with the AC.

You say the generator was tested. How? Did someone just put a meter on it and see proper volts and frequency or was it tested with a load? Was it tested with a plain resistive load or a capacitive load like you would see with the AC startup?

Could be that the generator looks good static but can't put out full power.
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Old 09-05-2013, 21:43   #3
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Re: AC will not run off generator

The generator was tested static with a true RMS voltmeter and with a small load (microwave). We didnt notice much of drop but that may not have been a good enough test. How would you go about testing the generator to determine if it is putting out its rated current? I think you may be on to something here... thank you in advance.


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Old 09-05-2013, 21:45   #4
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I agree with Skip. Make sure wire size from generator is correct gauge and all connections are good to the AC panel. Next I would find someone with a load bank to confirm the generator is putting out full power. I would also see what the amp draw is on the AC unit at startup with an ammeter and find someone to confirm your generator size.
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Old 09-05-2013, 21:52   #5
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Re: AC will not run off generator

First, what rubikoop said. Make sure all wires and connections are good, tight, clean, etc.

Then a quick and dirty load test, hook up an electric space heater or two to load down the generator. These will be straight resistive loads so will not be a complete test but it will give an initial indication if the generator can produce full output. If running about 4000 watts of space heaters doesn't show a voltage drop then you need to rig up some kind of capacitive load like an AC motor. See if you can borrow a AC powered portable compressor of appropriate power demand and see if the generator will start that up.
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Old 09-05-2013, 21:54   #6
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Re: AC will not run off generator

By the way, is this boat new or old? Did the air con ever run off the generator or is this a new problem? A full medical history on your ailment might help in the diagnosis.
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Old 09-05-2013, 21:58   #7
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Are you trying to start air conditioner with all other 120v breakers off? No water heater, battery charger etc. running, correct?
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Old 09-05-2013, 23:11   #8
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Re: AC will not run off generator

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Originally Posted by skipmac View Post
You say the generator was tested. How? Did someone just put a meter on it and see proper volts and frequency or was it tested with a load? Was it tested with a plain resistive load or a capacitive load like you would see with the AC startup?

Could be that the generator looks good static but can't put out full power.
That was my first thought.... have seen similar problems with faulty voltage regulator on gen
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Old 10-05-2013, 00:45   #9
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Re: AC will not run off generator

very few people have AC on their boats. There is no reason you should. You can achieve the exact same thing using far less energy, much more reliable and simple.

1. wind sock
2. electric fan
3. Put tarps above deck to prevent direct sunlight from hitting the deck.
4. salt/fresh/salt spray incoming air in a duct, to dry/cool/dry it
5. pump cool deep water (5-10 meters) up hose through heat exchanger in boat.
6. Insulate boat properly and have very large tanks of water which circulate through radiators outside to cool at night, and keep the boat very cool all day. Also you can drip water onto radiators to make them cooler. Same system can be adapted to keep the boat warm in winter.
7. Drink ice water
8. Sweat

I can think of many more, but maybe you can try some of those or come up with your own.
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Old 10-05-2013, 09:42   #10
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Re: AC will not run off generator

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Originally Posted by skipmac View Post
By the way, is this boat new or old? Did the air con ever run off the generator or is this a new problem? .
That's the key question here. If it used to work but now it doesn't, any talk of wire sizes being too small or things being connected wrong is irrelevant.

The other thing - if you have had technicians working on this but they can't figure it out, I don't know how people on a web forum are going to figure it out. I suspect you need better technicians.

A competent technician (marine electrician) can determine if the genset is capable of supplying the needed current at the needed voltage. It's not that difficult.

If, as you say, the genset output voltage is dropping to 108 volts when you try to start the AC unit, that could be your problem right there. Check with the AC unit's manufacturer to find the minimum startup voltage for the unit.
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Old 10-05-2013, 09:42   #11
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Re: AC will not run off generator

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Originally Posted by boat_alexandra View Post
very few people have AC on their boats. There is no reason you should. You can achieve the exact same thing using far less energy, much more reliable and simple.

1. wind sock
2. electric fan
3. Put tarps above deck to prevent direct sunlight from hitting the deck.
4. salt/fresh/salt spray incoming air in a duct, to dry/cool/dry it
5. pump cool deep water (5-10 meters) up hose through heat exchanger in boat.
6. Insulate boat properly and have very large tanks of water which circulate through radiators outside to cool at night, and keep the boat very cool all day. Also you can drip water onto radiators to make them cooler. Same system can be adapted to keep the boat warm in winter.
7. Drink ice water
8. Sweat

I can think of many more, but maybe you can try some of those or come up with your own.
That helps a lot.
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Old 10-05-2013, 09:58   #12
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Re: AC will not run off generator

If Maxum are still in business I would suggest calling them. It is possible that the AC and genset were sized so that the AC was designed to run on shorepower only, in which case you may need a larger genset if you want to run the AC from it.

Also find out who made the AC, or at least, find a nameplate on the compressor motor, and ask them how big a genset it needs, how much load it will draw on startup.

This will tell you IF there's something wrong, before you go any further.
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Old 10-05-2013, 10:04   #13
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Re: AC will not run off generator

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If, as you say, the genset output voltage is dropping to 108 volts when you try to start the AC unit, that could be your problem right there. Check with the AC unit's manufacturer to find the minimum startup voltage for the unit.
OP thinks the genset is a 4.5 KW model. If correct it would take a pretty serious compressor to overload that, even on a startup.
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Old 10-05-2013, 10:07   #14
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Re: AC will not run off generator

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Originally Posted by hellosailor View Post
If Maxum are still in business I would suggest calling them. It is possible that the AC and genset were sized so that the AC was designed to run on shorepower only, in which case you may need a larger genset if you want to run the AC from it.

Also find out who made the AC, or at least, find a nameplate on the compressor motor, and ask them how big a genset it needs, how much load it will draw on startup.

This will tell you IF there's something wrong, before you go any further.
Verifying the model and capacity of the genset definitely important. However, if he has had several engineers and techs working on the boat and they all overlooked such an obvious issue as the genset being too small then the OP is in serious trouble and needs to find some new engineers.

He did speculate the gen is model 45 something which indicates to me a 4.5 kW. Should be plenty if operating correctly.
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Old 10-05-2013, 10:16   #15
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Re: AC will not run off generator

Quote:
Originally Posted by hellosailor View Post
If Maxum are still in business I would suggest calling them. It is possible that the AC and genset were sized so that the AC was designed to run on shorepower only, in which case you may need a larger genset if you want to run the AC from it.

Also find out who made the AC, or at least, find a nameplate on the compressor motor, and ask them how big a genset it needs, how much load it will draw on startup.

This will tell you IF there's something wrong, before you go any further.
^^+1 The AC compressor will pull about 2 times the rated amps for a second at startup. Sounds like the genny is a bit small. So turn everything else AC off and try starting the A/C on the generator. Could be bad wiring or bad contacts on the A/C relay too. But probably the genny is too small. Might be possible to install a soft start device for the AC. See Link

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