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Old 01-06-2012, 13:50   #1
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Cruisair A/C Starting Amperage Demand

I have two Cruisair A/C units on Jamu (2003 L-42), and used them extensively during this cruising season in Mexico. One is a model FX-16P and the other is model SXE-16.
After our GOM transit to Pascagoula, MS in mid-May (540 nm in 82 hrs), the
mosquitos on our first evening anchorage at Petit Bois in Gulf Islands Nat'l
Seashore convinced me that a portable generator to run one A/C unit would be worth the trouble. The 115v current draw for each unit at full load is 11-13
amps, well within the operating range of a Honda or Yamaha 2000. I bought the Yamaha and tried it out dockside on one 30A shore power circuit with the fwd A/C. The A/C (which had been running for some time) re-started and ran just fine. A couple of days later we sailed to spend another night at the island, and I rigged the generator to run for a couple of hours in the evening. The A/C seawater pump started, but when the compressor tried to start, the amps surged for an instant to over 30A, and the A/C unit switched off. I switched to the other circuit and got the same result with the aft A/C.

Back at the marina on shore power and the units do show an instantaneous high amperage draw upon startup. I've not tried the A/C on generator again, for fear of damaging either the A/C or generator.

Has anyone experienced this with Cruisair units? Is this a 'hard-start'
capacitor issue? Is a 'soft-start' kit available? I can't figure why the A/C
worked with the generator at dockside and then failed to do so at anchor, unless it has something to do with the fact that the A/C had been running at dockside and was 'warm'. Any advice appreciated.

Safe Sailing,
Joe Donnaway
s/v Jamu
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Old 01-06-2012, 13:57   #2
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Re: Cruisair A/C Starting Amperage Demand

FWIW, I purchased a Fluke meter capable of measure in-rush to size my generator properly. My Marine-Air 16kbtu units measure 57a of in-rush at startup and ~13a normal running.
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Old 01-06-2012, 14:39   #3
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Re: Cruisair A/C Starting Amperage Demand

An old "rule of thumb" about starting current says it is about 5 times normal running current for a typical motor. Applying that rule to DodDun's case, gives results (5x13=65) in the same ball park as his empirical values.
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Old 01-06-2012, 15:26   #4
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Re: Cruisair A/C Starting Amperage Demand

Hi Joe
I have a Marine Air 16000 BTU unit and I run a Honda 2000 invertor generator. I had simular problem. A couple of things, Are you sure all other AC items are off? such as battery chargers etc. I also found I could not get it to start/run in eco mode.
In answer to your question regarding soft start device yes there are Frequency soft start devices, I found on the Marine air website. You could probably find one in the Grainger catolouge as well. Hope this helps.
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Old 01-06-2012, 16:03   #5
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Re: Cruisair A/C Starting Amperage Demand

Quote:
Originally Posted by JamuJoe View Post
Has anyone experienced this with Cruisair units? Is this a 'hard-start'capacitor issue? Is a 'soft-start' kit available? I can't figure why the A/Cworked with the generator at dockside and then failed to do so at anchor, unless it has something to do with the fact that the A/C had been running at dockside and was 'warm'. Any advice appreciated.

Safe Sailing,
Joe Donnaway
s/v Jamu
I recommend you check out this:

SmartStart Reduces Startup Surge - Dometic

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Old 01-06-2012, 16:07   #6
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Re: Cruisair A/C Starting Amperage Demand

In-rush current to start a motor can easily go to 10X normal running current. And starting a compressor is always a problem, as they also take a lot of oomph to get going. An air-con compressor can easily take 5hp out of an engine until it gets everything running happily. Since this can take several minutes, I suspect a "soft-start" device won't really help (though I must admit that I haven't tried one). This is also why it was easier to get running once it had been running a while - the "freon" takes a while to get back to its rest state, so it's easier to restart after it's been running.

Most of the issues involved are thermal. Circuit breakers are (usually) thermal devices, & the overload specs on generators are usually thermal as well. Heat takes a while to build up to damaging levels, & most generators will say how long they can handle an overload (but that's just one point on what is really a curve).

The problem you're seeing is that motor startup is high, & your motor is driving a compressor, which also has high startup loads (& those loads will take longer to settle down than the startup current on your motor). So you're trying to start a double whammy.

So you really need a bigger generator, even though it will be loafing a bit under normal running conditions. There may be shortcuts that might work for a while, but to really solve the problem, get a bigger hammer.
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Old 01-06-2012, 16:21   #7
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Re: Cruisair A/C Starting Amperage Demand

Wow, a lot of opinions and some mis-information. So here is mine:

A Honda or Yamaha EU2000i generator is marginal with a 16,000 btu unit. Such a unit will draw 12-15 amps continuously and the Honda is only rated to 13 amps continuously.

Cruisaire (Dometic) gives the locked rotor amps (LRA) on their spec sheeet. I think it is about 40 amps for the 16K btu unit. But that doesn't mean that a 2,000 watt (about 17 amps) generator won't start it. It all depends on how heavy are its windings and how much extra torque its engine can deliver. The high starting current lasts for less than a second, not minutes as opined above.

There are several things that may be keeping your A/C from starting:

1. Other connected loads. Take them all offline.
2. It is in Eco mode. Most, maybe all 16,000 btu units will not start in this mode.
3. It was recently (within a minute or so) running. When a compressor runs it builds up head pressure that is ok to carry on a running basis. But until the pressure leaks down it will make it much harder to restart. I think Cruisaire has a time delay to avoid this.

If nothing will work, then Dometic's Smart Start device will almost certainly work. It is a sophisticated capacitor bank that is engaged for just the few miliseconds that it takes to start the compressor.

David
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Old 01-06-2012, 16:56   #8
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Re: Cruisair A/C Starting Amperage Demand

Quote:
Originally Posted by djmarchand View Post
Wow, a lot of opinions and some mis-information. So here is mine:

A Honda or Yamaha EU2000i generator is marginal with a 16,000 btu unit. Such a unit will draw 12-15 amps continuously and the Honda is only rated to 13 amps continuously.

Cruisaire (Dometic) gives the locked rotor amps (LRA) on their spec sheeet. I think it is about 40 amps for the 16K btu unit. But that doesn't mean that a 2,000 watt (about 17 amps) generator won't start it. It all depends on how heavy are its windings and how much extra torque its engine can deliver. The high starting current lasts for less than a second, not minutes as opined above.

There are several things that may be keeping your A/C from starting:

1. Other connected loads. Take them all offline.
2. It is in Eco mode. Most, maybe all 16,000 btu units will not start in this mode.
3. It was recently (within a minute or so) running. When a compressor runs it builds up head pressure that is ok to carry on a running basis. But until the pressure leaks down it will make it much harder to restart. I think Cruisaire has a time delay to avoid this.

If nothing will work, then Dometic's Smart Start device will almost certainly work. It is a sophisticated capacitor bank that is engaged for just the few miliseconds that it takes to start the compressor.

David
FWIW, The current Dometic model (Vector) 16k btu unit has a LRA of 62a @ 120v.
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