What size portable gen do I need to rent to test AC?

Henry Boyd

Henry Boyd

Well-Known Member
Apr 24, 2007
6,014
Newburyport, on the peaceful and serene Merrimack
Boat Info
‘09 Sabre 38 Hardtop Express “Serenity”
Engines
Volvo D6 w/IPS450 Pods
OK, Before everybody gets their undies in an uproar, I need to rent a generator to test my air conditioning. We are on a mooring, and our dock does not have electricity. I want to make sure the AC is working before we go off in July to a rented slip for a weekend. In the past the boatyard that stored the boat for the winter would put us in a temporary slip that had power and I could test the AC. It did not work out that way this spring. So in order to prevent a weekend disaster with no AC, I need to test it now.

What size portable generator will sufficiently power up the single unit 13,000 BTU AC?

Henry
 
I've got one 16K and one 10K...the 16K draws 45A when starting; the 10K draws 32Astarting. I'd guess a 13K is going to draw 35-38 amps when starting. At 120V that gets you near 32kw.

But you may have a problem with wiring a portable generator to the boat. All portables I've seen have fixed 120V outlets, usually at 15A ea.......I've got a 10kw portable on a trailer that has 20A outlets. Even if you split on of the 30A-240V outlet into 2 120's you stlll wouldn't have enough amps to start the A/C unit. But, I may be missing something......maybe one of the CSR electrical whiz kids will solve this one for you.

As an alternative, run over to the marina where you buy fuel and ask the dockmaster for permission to tie up long enough to test your a/c.......unless he's either covered up with transients or a jackass, most will help out since they know you'll likely be back for fuel, beer, diet coke, ice, etc.
 
Is there a boat in your marina that has a genny? If agreeable with the owner, you can plug a shore power plug into a 110 outlet in his cockpit using a cheater. I used to do this when we rafted off a Viking during hot weather in a boat that had AC but no genny. Obviously you don't want to have the water heater, stove, etc. on but just an AC will be fine for a while.
 
You should be OK with a 5 Kw unit, as this is what they put in the 280. I can run A/C Microwave and water heater without an issue while on hook and I have a 5 KW unit.
30 amps at 120 volts = 3.6 Kw.
 
66pony said:
You should be OK with a 5 Kw unit, as this is what they put in the 280. I can run A/C Microwave and water heater without an issue while on hook and I have a 5 KW unit.
30 amps at 120 volts = 3.6 Kw.
Click to expand...

Right, but not if he is plugged into some guy's 110 cockpit outlet.
 
Then bring in the boat when the dock is usable and plug it in.....or am I missing something?
 
Capacity is not the problem...wiring it is. I think sbw1's approach is the easist if you have a friend with a generator equipped boat.

The problem with any portable is going to be tapping the generator for the 35-38A starting load. My portable is a Miller welder and all the outlets are fused at 15A for 120v and 30A for 240V. The only way I could power your boat with it is to rewire the output panel to eliminate it from the circuit, and t hat might be a problem for the rental company.
 
I guess I'm back to Frank's original suggestion, i.e. go visit a marina with power. Although I'm surprised at the current ratings on the generator side of the welder.

OSD9 - Dock is 250 ft from the house, a little too far to run an extension cord. :smt043

Henry
 
fwebster said:
The problem with any portable is going to be tapping the generator for the 35-38A starting load.
Click to expand...


It is typical for an appliance like an air conditioner to draw a starting load nearly 2x the running load, as this high load is very brief in duration, wiring and breakers are typically sized for the running load.

In example, here are the specs from a 12KW marine AC unit from wrightmarine.com

Running amperage: Cool = 9.4 amps,
Add one amp for the standard seawater pump.
Start up amperage is calculated by running amperage multiplied by 1.8.

I think your estimates are a bit high, the example above only draws 18.7A at start up, this is only a 12K unit, but the OP should check the specs on his to find out what he needs
 
Start up amps are not a big deal. Watch your panel. You only hit it for less than a second before things settle down. Bumps up again when the compressor runs but not by much. I would have guessed 10-12 amps to run it on cool.
 
My numbers come directly from the CruiseAir site for the unit in the original poster's boat. CruisAir's giudance is that starting loads should be sized for 3X the running load.

I understand the difference between running and starting load, but his qquestion is about using a portable generator for powering the boat A/C. Its not the breaker on the boat that is a concern, but the 15A circuit protection on the generator is not going to pass the 38A starting load demand without tripping.
 
Lots of unknowns here.

I don't see the make/model info for the actual AC unit is question. Sea Ray archives show the AC unit in the 02 280 to be a 10K unit.

The critical number in this case will be the surge capacity of the generator in question. A high starting load (in excess of the generators surge capacity) is more likely to bog the generator and cause the engine to shut down, than to trip the breaker.
 
Irrespective of what SR archives say, Henry asked about powering up a 13K btu unit......

It doesn't matter if the generator engine bogs down or the breaker trips........this most likely is not going to be as simple as Henry thought.
 
Frank,

I have a lot of respect for the knowledge you bring to the board, and I'm not trying to get into a petty argument.

My position is that its not as complicated as you make it sound, the actual power requirements are likely far less than you state. The only way to know for sure is to get the details for the unit in question.

You said you provided specs for Henry's particular AC unit, however the make & model info is no where to be found in this thread, I checked the archive, thinking that might have been where you got the details. This is obviously not the case as Sea Ray lists a 10K unit as the AC they put in that boat.

Again, its not my intention to pick a fight, merely trying to help out.
 
I have a one ton unit aboard Just Ducky with a 4.5 kW genset. I also have a 4kW "portable" genset at home with 15A@120, 30A@120, and 30A@240 outlets. Should be fine to run the boat's AC for a test.

Best regards,
Frank
 
I have an adapter that lets me plug the 30 amp round twist lock into a standard 15 amp receptacle.

Using this I have run the air conditioning pluged into a standard receptacle without issue.

If at start up the load briefly exceeds 15 amps a breaker will not trip.

Not sure how many people here understand breaker time current trip curves but if you have a 15 amp circuit breaker and you apply a 20 amp load it takes about ½ hour for the breaker to trip.

This would be a thermal overload not a magnetic overload like a short circuit, which will trip in as little as 1 cycle (1/60th of a second)
 
Paddled out to the boat at lunchtime. It is a 10k BTU machine, my mistake and apologies. According to Cruiseair manual, it (and everything from 10 to 16k BTU) requires a 20 amp circuit. Astonishingly the tag states 10.7 amps running and 47, (yes forty seven) amps max.

Since we are supposed to have rain for the next several days, this is on hold. When the sun comes back out, I'm off to HD to see what they have to rent.

I also have the Marinco adapter cord Doug mentioned. Its become invaluable for winter projects at the boatyard.

Thanks everyone

Henry
 
Be sure you also have your breaker off for the battery charger. When you first plug the boat in it goes to a heavy mode for 10 min or so for a quick charge.
I used to run my AC with my portable Honda 2000.
 
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