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Generator Question?

nickthehunter
Nomad II
Nomad II
How big of a generator do I need to run my 15K BTU air conditioner? Assuming I may also be running a coffee pot or microwave at the same time.
14 REPLIES 14

patchelect
Explorer
Explorer
You could be right about the 2800KW, but if you made a mistake and it wasn't large enough you'll find ways to double joint your knees to kick yourself in the tail!

And the inrush (starting) current on any electric motor is generally THREE times the rated running amperage. It may only be for a nano second, but that could be the difference between "Ahhh" and "Ah CXXP"
Paul
1969-1970 University of Viet Nam 11B. I was drafted. Agent Orange is still killing and maiming in Viet Nam.

tatest
Explorer II
Explorer II
If it is the Coleman Mach series, the manufacturer recommends 3.6/4 KW, for the protection of the A/C from low starting voltages. Yes, the 15K goes on a 20 amp branch circuit, draws 14-17 amps running, but might double or triple that briefly while starting the compressor.

Hooked up to power, this is a surge and brief voltage drop. Hooked up to a conventional genset, this surge is handled by trading rotational energy for extra power, slowing the generator briefly. Inverter gensets, if large enough, might not even sag the voltage (if not running in economy mode). Some will overspeed to briefly supply more than the rated power. In either type, the protective circuitry in the generator has to allow the surge, and if sized too small the surge will prolonged and the generator more likely to disconnect or even shut down.

I know campers who have gotten away with using the Yamaha EF3000ISEB for a 15K A/C, while the EF2400IS (nominally 20 amps) couldn't handle an A/C that large. One brand might work while another might not, and within brands, different models of the same nominal size have different surge capabilities. In the smaller sizes, it is best to look for something offering a "boost" feature.
Tom Test
Itasca Spirit 29B

nickthehunter
Nomad II
Nomad II
moresmoke wrote:
According to Champion a 3100i will handle a 13.5K and a 3400i will run a 15K A/C. So for those two models of generator, I would be tempted to follow the manufacturer's advice.
The only problem with that theory is that I am pretty sure that AC is on a 20 amp breaker or less; it may be on a 15 amp breaker. If the TT wasn't in the storage yard all wrapped for safe keeping for the winter I would go check it out. But I'd be willing to bet dollars to donuts the breaker ain't more than 20 amps.
I think the 3100 may do it and turn off the AC before starting the microwave.
On paper, a 2800W could even work. I could be tempted to try that out.

moresmoke
Explorer
Explorer
According to Champion a 3100i will handle a 13.5K and a 3400i will run a 15K A/C. So for those two models of generator, I would be tempted to follow the manufacturer's advice.

SoundGuy
Explorer
Explorer
tatest wrote:
When my women start running their morning grooming and breakfast appliances it is usually a tossup whether the 30 amp breaker in the RV or the 30 amp breaker at the power post is the first to go. They blow breakers in my house too, usually too much on a branch circuit, as in trying to blow dry under the heat lamps.


Time for a little "edumacation" on the subject of power management. :W
2012 Silverado 1500 Crew Cab
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2003 Fleetwood Yuma * 2008 K-Z Spree 240BH-LX
2007 TrailCruiser C21RBH * 2000 Fleetwood Santa Fe
1998 Jayco 10UD * 1969 Coleman CT380

tatest
Explorer II
Explorer II
4KW. It can run with a coffee pot, toaster, small RV microwave assuming the A/C is running and not trying to start. It might not run a blow dryer and curling iron at the same time as the A/C is running, that combo can be a heavier load than RV microwave (and coffee maker loads depend on what point in the brewing cycle).

With 4KW of genset, the 30 amp main for the whole RV is likely to pop before you overload the generator. Your house limit is usually 3.6 KW.

When my women start running their morning grooming and breakfast appliances it is usually a tossup whether the 30 amp breaker in the RV or the 30 amp breaker at the power post is the first to go. They blow breakers in my house too, usually too much on a branch circuit, as in trying to blow dry under the heat lamps.

For the A/C alone, Coleman sets 30 amp service, 4KW genset, as minimum for their 15K BTU/hour A/Cs and heat pumps. Brief starting loads go 2-4 times that capacity, and only the larger gensets have enough spare rotational energy to handle the overload.
Tom Test
Itasca Spirit 29B

theoldwizard1
Explorer
Explorer
nickthehunter wrote:
How big of a generator do I need to run my 15K BTU air conditioner? Assuming I may also be running a coffee pot or microwave at the same time.

If you insist on running all 3, you are going to need a >3,500W !

2gypsies1
Explorer
Explorer
Turn off the air if using the microwave or coffee pot. Also... there are excellent stove-top coffee pots. They make great coffee.
Full-Timed for 16 Years
.... Back in S&B Again
Traveled 8 yr in a 40' 2004 Newmar Dutch Star Motorhome
& 8 yr in a 33' Travel Supreme 5th Wheel

Isaac-1
Explorer
Explorer
There are a lot of it depends,but I can tell you the 4000 watt Onan Micro-quiet (yeah right) in mine will power the 13,500 btu air conditioner and the mircowave / convection oven either in microwave or convection mode at the same time. Can't help on the coffee pot though as I rarely drink the stuff.

The_real_wild1
Explorer
Explorer
Go with a 4k or bigger.

DrewE
Explorer
Explorer
wing_zealot wrote:
hbillsmith wrote:
Champion 3100 or similar. Turn off A/C while running Microwave then just turn the A/C back on. For such a short period you'll be cool enough. Otherwise you need a 5500 or similar and those weigh around 200#.
would it make a difference if it was a coffee pot that he was using and it was on for like an hour or so?


It depends on the coffee maker. Some use about as much power as a microwave (or close enough), and some small single serving coffee makers are only 300W. (Obviously a stovetop percolator uses no electricity on a gas stovetop.) I think most coffee makers with a hot plate to keep the coffee warm don't use a huge amount of power for the warmer, but do use considerably more during the brew cycle, so it shouldn't be a problem to turn the air conditioner back on once the brewing is complete.

I think the Onan 4K in my motorhome will run the air conditioner and microwave simultaneously, though I am not sure I've actually tried that combination. It does do a 1500W electric heater and the microwave (and converter/fridge) together, though it sounds a bit strained in the process. It might well benefit from a bit of tuning up/maintenance.

wing_zealot
Explorer
Explorer
hbillsmith wrote:
Champion 3100 or similar. Turn off A/C while running Microwave then just turn the A/C back on. For such a short period you'll be cool enough. Otherwise you need a 5500 or similar and those weigh around 200#.
would it make a difference if it was a coffee pot that he was using and it was on for like an hour or so?

hbillsmith
Explorer
Explorer
Champion 3100 or similar. Turn off A/C while running Microwave then just turn the A/C back on. For such a short period you'll be cool enough. Otherwise you need a 5500 or similar and those weigh around 200#.
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2oldman
Explorer
Explorer
What size gen do i need? 2011
What size.. 2013
Which gen.. 12/2013
"If I'm wearing long pants, I'm too far north" - 2oldman