what wattage

upnover

upnover

Grumpy, decrepit Old Man
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Mar 20, 2005
Location
Morganton NC
Need help from a number cruncher
What size generator is needed to run a 13,500BTU AC unit? What wattage?

Need to know numbers, not what you have seen used
Thanks
 
Any idea what the amp load and voltage is on the A/C unit?

Assuming a Dometic 13,500... you're about 15 amps at 120V, that's 1800W. I'd look for at least double that for a gen set.
 
found when googled, that 1 watt = 3.41 BTU per hour,
No sure if a 2000w generator would pull a 13,500 watt Camper AC unit
the "per hour" thing is what gets me

His camper paperwork does not have the info we need, we are assuming it's a 13,500, it may only be a 11K or 11.5K

I do know that my Honda eu3000is will run his whole camper, All lights, AC, heater fan(yes he had it all going) and even the microwave

Found a 2000w inverter style generator(quiet) and was wondering if it would run the AC and nothing else.
 
BTU is a measure of energy. Watt is a measurement of power. Power is energy over time. That's where the hours come from.

I wouldn't rely on a conversion constant to go from BTU to watts. That won't account for inefficiencies in the device... it's just doing the straight math to convert X units into Y units. Need to look at the watt or amp requirements on the specific device.

If it's a 1800 watt load, you could run it on a 2000 watt inverter. How long depends on the quality of the inverter (overheating, etc) and the size of your batteries. You wouldn't do it for long w/o running the batteries down.
 
Chip becareful, your Honda gen at 3000 watts is like 4500 with the cheaper gens. I found this out when I bought mine. My gen runs 3 campers with 13000 btu ac units and its a 6500 watt cont rating.
 
don't forget to account for added draw when the compressor kicks in and out, that in some cases will almost double the amp draw for a few seconds. if you over draw the rated capacity too many times, it'll cook the inverter.

use of long extension cords and wrong size cords also have quite an effect on amp draw as well. ( 12ga wire MINIMUM, no more than 50ft, shorter is better )
 
saf-t scissors said:
BTU is a measure of energy. Watt is a measurement of power. Power is energy over time. That's where the hours come from.

I wouldn't rely on a conversion constant to go from BTU to watts. That won't account for inefficiencies in the device... it's just doing the straight math to convert X units into Y units. Need to look at the watt or amp requirements on the specific device.

If it's a 1800 watt load, you could run it on a 2000 watt inverter. How long depends on the quality of the inverter (overheating, etc) and the size of your batteries. You wouldn't do it for long w/o running the batteries down.
Click to expand...

Batteries don't come into play with this, it a inverter style generator
 
Chip I have two 9500 btu ac's on my camper. I also have a digital load meter that is installed at the factory when the camper was built. Each ac unit pulls about 12 amps, except when the compressor kicks in, then each unit spikes the amps to 20-22 amps for a short time. Be careful not to supply a "brown" power supply! This will kill your generator and will also severely damage your ac unit. Also take into account your batteries in the camper, when they get drained from running water pump, lights or anything 12volt, the generator is also charging the batteries. A volt meter is the key not too over work the system. A coffee pot pulls more amps than a ac unit. We "dry camp" and we have come very aware of what it takes not to damage things in the grid. We have a diesel 7'500 watt gen and we have to be careful what we can run and when. If there is a doubt if the gen will pull a ac unit, it probably won't. Also if you are running a refrigerator on propane, the controls that tells the cooling unit to turn on or off the flame is controlled by 12 volts and that has to be recharged, and that is a fancy battery charger that will be supplied by..........your generator and that's will pull a surprising amount of watts for a long time! Camper manufacturing companies have been fighting this situation for a long time and it amazing that the owners of a camper has no clue as how to manage the power system. I've got friends that has argued that their refrigerator needs no power to run on propane! The same ones that also says that their freon must be low is the reason it doesn't work! They don't have freon in them!
 
Terry, if i am not mistaken you have an Onan marquis gold 7500, right?
If so then your 7500 is continuous forever with a surge of 15,200 watts.

Also dont confuse volts and amps, you want to make sure you aren't getting voltage dip, but voltage is not a measure of power consumption.

The problem is there is no universal standard for generator name plating. This extends from the small to that large industrial sets. A Honda or Onan inverter style will deliver listed name plate forever and have usually 2.25 surge capacity (the inrush when the compressor or fan motor kicks on) a Northern Tool genset or harbor freight piece will frequently peak at the nameplate.

BTW unless you have a 7500 meter in that camper you can not measure the inrush on your compressors kicking on, the duration is measured in cycles (1 cycle = 1/60th of a second) by the time any meter realizes there has been a voltage dip the voltage has recovered o the breaker has tripped. A coffee pot does not out draw an AC compressor.
 
Also Chip not every 13.5 BTU air conditioner is the same.
I will be glad to help you size it out before you spend a dime, call me.

What we need is either all the data off the AC name plate or at a very minimum a make model and vintage of it, as well as the same off the generator you are looking at.

Compounding the problem, as electric motors (such as AC compressors and blower fans) age by rule the starting current and in rush draw increase as the winding degrade.

Conversely as a generator ages, by rule its output decreases.

What works today when new may not work forever. And we are talking fairly short time frames(3-5 years depending on use) here.
 
Ron said:
A coffee pot does not out draw an AC compressor.
Click to expand...

That's not necessarily true.... what kind of coffee maker is Terry running? Big 10 gallon commercial job might out-draw that air conditioner... :lol:
 
I'm running a 12 cup perkulator, once it has perked it "idles" at 2 amps to keep the coffee hot, we have a AMP meter built into the coach. This is done because the breakers are rated this way and is easier to understand. On the 7,500 watt gen is a 35 amp circuit breaker. Yes the gen can run more but it is not intended to do so,hence the 35 amp breaker. The digital amp meter in the camper is very handy, also we have a analog voltmeter as well. Chip, I was trying to help, not make it over complicated. If the ac has a wall mounted control, it is usually is 12volt as well, not 110.
 
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