AC will not run off generator

[rwidman]

Again, did it work when powered by the genset at some time in the past? This is key. Without this information, there can only be speculation.

[rwidman]

Originally Posted by hellosailor

.......... 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. .

That's highly unlikely.

[hellosailor]

skip-
" However, if he has had several engineers and techs working on the boat "
I'm betting they were all alleged professionals. Come on now, how many pros have you had try to fix things, and totally miss the problem? Plumbers, electricians, mechanics...you name it. Heck, the first time I brought a "new" car in for the first warranty service, the highly certified, uniformed, trained, dealer-employed mechanic couldn't find the damned idle screw on the engine, I had to show him where it was. And more recently, I've had a full-time franchised oil change guy unable to figure out where the oil filter was in my car. I had to point it out AND lend him the right cap wrench, too. (A job I almost always do myself, yes, but there was two feet of snow on the ground at the time and I wanted their bay more than their services.)

If they were really pros, they wouldn't be stumped, now would they?

[Dennis.G]

Originally Posted by Dflatimer

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. ..

If 108 VAC at panel, likely under 100 VAC at compressor, and way under that for first few cycles at startup. AC compressors have huge inrush currents as they startup under a full mechanical load. Can make a 4.5 kW generator seem too small, even when running load is well under that capacity.

Air conditioned boats carry 8, 10 or 15 kW generators (or larger) mostly for this reason (to handle motor inrush current loads while running loads are a fraction of generator capacity).

[hellosailor]

Might also note that nominal "110/120" in the US is normally spec'd by the power companies as 117VAC plus or minus something like five percent. From the wikipedia "In the United States[3] and Canada,[4] national standards specify that the nominal voltage at the source should be 120 V and allow a range of 114 to 126 V (RMS) (−5% to +5%)."

So 108 volts at the panel is already less than a normal AC compressor will be happy to run on. Way less. (I'd still make the phone calls, phone calls are simple, cheap, and easy compared to mechanical work.)

[Sailmonkey]

Originally Posted by Dennis.G

Air conditioned boats carry 8, 10 or 15 kW generators (or larger) mostly for this reason (to handle motor inrush current loads while running loads are a fraction of generator capacity).

I have personally installed several small generators on boat for the express purpose of running an AC. Several of those have been 4kw westerbekes and panda's, those both were able to start and run 16k units without a problem.

[Dennis.G]

Originally Posted by Sailmonkey

I have personally installed several small generators on boat for the express purpose of running an AC. Several of those have been 4kw westerbekes and panda's, those both were able to start and run 16k units without a problem.

Depends.
Some 10 kBTU AC units have starting loads of 4.5 kW and running load of 1.5 kW. Many are much better, but can't count on it. You obviously chose correct combinations in your work.

[J Clark H356]

A 4.5 KW generator will run the AC just fine if everything is in working order. I suggest you check voltage at the genset, then at the electrical panel, then at the HVAC unit and compare. Somewhere, you are losing power, or if it is there, the problem lies with the HVAC unit. Most likel, it is a bad connection somewhere that is causing a large voltage drop if the generator itself is putting out the proper voltage and the HVAC is running off shore power.

[Dflatimer]

Wow. Thank you for all of the information.

To answer some of the questions that were brought up

This is the original factory installed ac unit and genset

The wiring going to and from these units is sufficient

The air conditioning worked fine for years on the generator

I have tried turning all other ac items off. Doesn't change the problem for better or worse

The 108 volt drop that I mentioned earlier was taken from the supply terminal on the ac unit control board.

I have checked the wires, switches, etc rather thoroughly for continuity and it seems to all be fine.

I think I am going to run, at least for now with the theory that the generator is not outputting full power. I may be able to source a load bank and test this. But ill likely just round up 4000 watts of space heaters. Now for a moment, lets just assume that the problem is that the generator is not putting out rated power. What would likely be the culprit? Is it something that can be repaired without pulling the generator out and sending it to westebeke?

Thanks again for all the replies



DL

[um saudade]

Electric motors (and this is an electric motor driving a compressor) are INDUCTIVE loads! There are capacitors to start it by providing an out of phase condition and capacitors to cause it to look more like a resistive load when running and thus improve the power factor, but it is not a capacitive load.
KW is a true output of a generator as opposed to KVA which assume an in phase (pure resistive) condition. The closer to a 0 degree phase angle a prime mover can operate the better the performance in terms of true power vs. apparent power which is power not realized.
How hard does the engine on the generator work when it tries to start? It should try its little heart out and the rpm and thus the voltage should take a great dip if the starting load is too big for the prime mover. Some generators will even stall if the load does not drop out in some way. If it does not grunt pretty hard then I would suspect something in the regulation on the generator or a bad wiring connection causing the voltage to the device to drop off severely at inrush current.
It could be the governor is not allowing the genset to run at full throttle and thus it does not produce its full torque potential.
To insure a good start the voltage at the AC should not drop below 90 volts or so and only for less than a half second.
I think this genset should start this AC.

Good Luck

[DotDun]

Originally Posted by Dennis.G

Depends.
Some 10 kBTU AC units have starting loads of 4.5 kW and running load of 1.5 kW. Many are much better, but can't count on it. You obviously chose correct combinations in your work.

Also, just because a unit pulls 4.5 kW starting on shorepower doesn't mean it won't start on less (ex. 3.5 kW), it'll just take longer (1/2 second?).

[rwidman]

Originally Posted by Dflatimer

Wow. Thank you for all of the information.

To answer some of the questions that were brought up

This is the original factory installed ac unit and genset

The wiring going to and from these units is sufficient

The air conditioning worked fine for years on the generator

I have tried turning all other ac items off. Doesn't change the problem for better or worse

The 108 volt drop that I mentioned earlier was taken from the supply terminal on the ac unit control board.

I have checked the wires, switches, etc rather thoroughly for continuity and it seems to all be fine.

I think I am going to run, at least for now with the theory that the generator is not outputting full power. I may be able to source a load bank and test this. But ill likely just round up 4000 watts of space heaters. Now for a moment, lets just assume that the problem is that the generator is not putting out rated power. What would likely be the culprit? Is it something that can be repaired without pulling the generator out and sending it to westebeke?

Thanks again for all the replies



DL

It's possible that there is a loose or corroded connection in the wiring from the genset that is causing a voltage drop under load. You don't really need space heaters, your AC unit itself is a test load. Check the voltage at the genset and compare it to the voltage at the AC when you are trying to start it. If there's more than a volt or two difference, look for a wiring problem.

As for repairing the genset, you shouldn't have to return it to the manufacturer. Contact them for an authorized repair center in your area.

[hellosailor]

"To answer some of the questions that were brought up"
Anything else you're holding back? <G>

There is often a large electrolytic capacitor used to help in starting, which may be internal to the AC assembly. Electrolytics are known to age and fail, and in that case the failure of a starting capacitor would explain the change. You're probably looking for a "tin can" probably an inch or two wide and 3-5" long with two wires coming out of it. If there is black goo oozing out one end as well--that's a failed capacitor.

An electrician would disconnect it and test it with a meter to be sure.

That still leaves the 108 volts in question. As rw suggests, if the compressor is seeing 117 from shore power but 108 from the genset, you probably have a genset or wiring problem.

[rwidman]

Want a quick test of the boat's wiring? Measure the distance from the genset output to the AC input. Not through the boat, but in as direct a line as possible. Add a couple feet to this measurement and go to the home center and buy that length of #10 romex cable. Disconnect the wires at the genset output and connect the romex. Disconnect the wires at the AC input and connect the romex. Fire up the genset, then try to start the AC. If it starts, your problem is most likely in the boat's wiring. If not, you're back to either the AC or the genset. Since the AC works on shore power, it pretty much has to be a problem with the genset.

[Greggegner]

Make sure the wiring is good then I would try a starting capacitor between the ac panel and the unit. This lowers the initial power that is required from the generator. Besides peak power requirements to start the compressor the generator may not be able to ramp up it's output quick enough. Keep us informed, with your generator you should be able to run the air.