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Old 16-06-2011, 15:46   #16
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Re: A/C Start Up on Generator

I agree with installing a hard start capacitor. I like the solid state ones, but you'll need the right one for your specific compressor motor. Make sure you test the voltage - amperage at the compressor terminals with the genset running and shore power off to see if it's an electrical problem first; IE wrong wire size or connection corrosion.
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Old 17-06-2011, 07:00   #17
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Re: A/C Start Up on Generator

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Originally Posted by Seahunter View Post
I agree with installing a hard start capacitor. I like the solid state ones, but you'll need the right one for your specific compressor motor. Make sure you test the voltage - amperage at the compressor terminals with the genset running and shore power off to see if it's an electrical problem first; IE wrong wire size or connection corrosion.
I don't know if I understand you well
But we tested also with the shore power and there is almost no drop in voltage and the compressor start without problem
The unit is old (was an option originally in the boat- 1984) but is working perfectly and I don't want to change it for something newer.
But the start up with the gen is the problem
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Old 17-06-2011, 07:20   #18
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Re: A/C Start Up on Generator

So, if there is no drop in voltage when starting the A/C from shore power, and a 30 volt drop when starting from the generator, where is that voltage being dropped? Perhaps the generator wiring, perhaps a connection.
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Old 17-06-2011, 07:34   #19
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Re: A/C Start Up on Generator

You can't compare AC voltage drop from shorepower and voltage drop from a genset.

Shorepower voltage drop is mostly dependent on the size of the wire going back to the shorepower outlet and the wiring size upstream from there. The grid has effectively unlimited current supply capability.

But a genset in addition to the wire voltage drop has additional voltage drop in its windings and as the genset speed drops due to the engine not having enough torque.

But having said all of the above, if you have installed Dometic's Smart Start system which significantly reduces inrush current and your A/C still won't start, then you most likely have a problem with the wiring to your genset or the genset itself.

One test that you can do that isn't very expensive: Disconnect the A/C supply from the genset downstream from the breaker protecting the genset. You should have a breaker within sight distance of the genset to meet NEC. Go to Home Depot or Lowes and buy enough #10 2 conductor plus ground Romex cable to go from that breaker to the A/C. Wire it to your A/C and try starting it. #10 is bigger than it needs to be but will completely eliminate wiring, connections and other breakers as a cause.

If it still won't start then the problem lies in your genset.

David
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Old 17-06-2011, 07:56   #20
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Re: A/C Start Up on Generator

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Originally Posted by djmarchand View Post
One test that you can do that isn't very expensive: Disconnect the A/C supply from the genset downstream from the breaker protecting the genset. You should have a breaker within sight distance of the genset to meet NEC. Go to Home Depot or Lowes and buy enough #10 2 conductor plus ground Romex cable to go from that breaker to the A/C. Wire it to your A/C and try starting it. #10 is bigger than it needs to be but will completely eliminate wiring, connections and other breakers as a cause.

If it still won't start then the problem lies in your genset.

David
WOUAW
you've lost me there
can you explain in lay terms please so that I can understand it
Thank you
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Old 17-06-2011, 07:59   #21
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Re: A/C Start Up on Generator

Quote:
Originally Posted by djmarchand View Post
You can't compare AC voltage drop from shorepower and voltage drop from a genset.

Shorepower voltage drop is mostly dependent on the size of the wire going back to the shorepower outlet and the wiring size upstream from there. The grid has effectively unlimited current supply capability.

But a genset in addition to the wire voltage drop has additional voltage drop in its windings and as the genset speed drops due to the engine not having enough torque.

But having said all of the above, if you have installed Dometic's Smart Start system which significantly reduces inrush current and your A/C still won't start, then you most likely have a problem with the wiring to your genset or the genset itself.

One test that you can do that isn't very expensive: Disconnect the A/C supply from the genset downstream from the breaker protecting the genset. You should have a breaker within sight distance of the genset to meet NEC. Go to Home Depot or Lowes and buy enough #10 2 conductor plus ground Romex cable to go from that breaker to the A/C. Wire it to your A/C and try starting it. #10 is bigger than it needs to be but will completely eliminate wiring, connections and other breakers as a cause.

If it still won't start then the problem lies in your genset.

David
The genset is a external portable set
It is connected to the same marine plug as the shore power would.
So from there the wiring is exactly the same. Going to the AC power panel etc...
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Old 17-06-2011, 09:02   #22
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Re: A/C Start Up on Generator

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I don't know if I understand you well
But we tested also with the shore power and there is almost no drop in voltage and the compressor start without problem
The unit is old (was an option originally in the boat- 1984) but is working perfectly and I don't want to change it for something newer.
But the start up with the gen is the problem
I guess this was a test. I assumed, probably wrongly that someone has tested the amperage rating of the genset. If the AC works with shorepower, but not with the genset, the genset is probably too small. If the genset is dropping voltage at startup, it's because it's trading votlage for amperage it doesn't have. What is the brand, make and model of the genset?
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Old 17-06-2011, 09:11   #23
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Re: A/C Start Up on Generator

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Originally Posted by Seahunter View Post
I guess this was a test. I assumed, probably wrongly that someone has tested the amperage rating of the genset. If the AC works with shorepower, but not with the genset, the genset is probably too small. If the genset is dropping voltage at startup, it's because it's trading votlage for amperage it doesn't have. What is the brand, make and model of the genset?
As stated in this thread in anterior posting the gen is a 3600 w
should be enough
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Old 17-06-2011, 09:21   #24
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Re: A/C Start Up on Generator

It's really starting to sound like the generator isn't putting out what it is rated for.
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Old 17-06-2011, 09:36   #25
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Re: A/C Start Up on Generator

The generator people are very helpful: they just send me the way to solve the problem.
There is a tuning to do on the generator to solve this drop in voltage.
I put in attachement what they send me right now.
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Old 17-06-2011, 09:37   #26
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Re: A/C Start Up on Generator

You've got a big air conditioner (15K BTU) on a small genset (3.6KW). And they're old. New technology compressors are easier starting than old but a current Cruiseair 16kBTU unit draws 10.4 amps running and has a "locked rotor" draw of 62 amps.

It wouldn't surprise me if your air conditioner briefly draws over 40 amps when starting. Even today, gensets have "optimistic" capacities. Once you're over 80% load, voltage and even frequency can start to vary.

The Victron inverter/charger (Mastervold makes a similar unit I believe) isn't cheap - about $2300 - but it will solve this problem, as well as take great care of your batteries, and give you high quality sine wave 110v power.

Another advantage is that they can be set to not overload your genset which can really shorten its life. I have mine set to never draw more than 80% of the max capacity. The Victron uses the batteries to make up any short term shortage. Same with shore power. I never pop a shore power breaker because I set the Victron to limit the draw on a 30amp service to 27 amps.

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Old 17-06-2011, 09:38   #27
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Re: A/C Start Up on Generator

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Originally Posted by Alecadi View Post
As stated in this thread in anterior posting the gen is a 3600 w
should be enough
Yes I read that. I asked what make, model it was. But as you previously stated it is 3600 peak. The genset's probably too small to get through all the wiring you have and even if you wired it directly to the AC unit it might start as unlike fridges, AC units start under load. Adjusting the voltage peak on idle won't fix the problem; only a bigger genset. A genset's amperage is like a bottle of water, it can hold only so much and this adjustment isn't going to allow you to add more water.
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Old 17-06-2011, 10:37   #28
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Re: A/C Start Up on Generator

Sorry, didn't realize that it wasn't a permanently installed genset.

Reading between the lines of the attachment you posted, I think you have a Chinese made generator/inverter, like the Honda EU series. For maximum power and voltage output, set the econo switch to off. This lets the engine run at maximum rpm and power.

David
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Old 17-06-2011, 11:33   #29
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Re: A/C Start Up on Generator

To David: YES the econo was off all the time.. :-)
To CarlF: a bigger genset would be too much, I would not even be able to put it on desk!!
To all: have you seen what the gen people send me to solve the problem (see post#25) ? Any comments or recommendation?
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Old 17-06-2011, 11:52   #30
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Re: A/C Start Up on Generator

My experience is with a Frigidare 5000 BTU AC and Honda 1000 is:
normal amp draw when running is ~5amps (it starts around 4.8 and slowly climbs to 5.2 for some reason).
When set on low, Fan draws about .5 amps, but when compressor kicks in it goes up to 14 amps, the gen has a 4 second delay before disconnecting, with eco-throttle on, sometimes it recovers in 4 seconds and sometimes it doesn't.
One thing I can't explain, when set to high, the draw is the same, I'm using kill-a-watt to measure the amps.
Tom
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