# BTU's to WATTS or Amps



## Redfishr (Jul 26, 2004)

I have a new camper.
It has a 13,500 btu A/C and I need to know how big of a generator I need.
I was gonna go with the 2.5 kv and it only has 20 amp plugs on it.
Thats fine as long as my AC doesnt draw more than about 15 amps or so. I can put a 30 to 20 amp adapter on it.
I know if the amperage gets too high I could melt the plug. 
I aint gonna let that happen.
I just dont know how to convert BTU's to Watts or amps.
I know I could just run it and take a load check with an amp meter, and I may have to do that....
But theres bound to be a formula...


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## mikes451 (May 21, 2004)

Not sure this will help but I just got a 6000 BTU window unit and it says 5 Amps on the box. I mainly got it in case a hurricane knocks power out for a couple of days. Somebody told me thought that when it is first turned on it can draw up to 3 times the running Amps for a second or so.


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## Psycho Trout (May 26, 2004)

I know you are not going to run that 13.5K BTU unit ona 2.5k watt generator. Forget it. you will need at least a 5k or bigger to run it and something with a even beter surge. Don't have the formula handy, sorry.


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## greg77 (May 22, 2006)

*conversion*

1 BTU = .000293 kilowatt-hour


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## Psycho Trout (May 26, 2004)

Here it is. 

Btu/hour x 0.293 = watts

13500x0.293 - 3995.5


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## Freshwaterman (May 21, 2004)

found one formula BTU per hour x 0.293 = watts
watts / volts = amps
hope this helps


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## grayfish (Jul 31, 2005)

Btu's do not convert to watts. Btu/hour will however convert to watt-hours. (Btu's x 0.293)

Not exactly what you are going to need to size a generator. Check out the manufactures web site and using the model number of your unit you should be able to get the specs on your unit. Remember that electric motor startup can draw better than 2 times the run current. Sometimes a lot more, depending on the condition of the unit and genset. I have seen 5kw units trip running similar sized A/C units in hot weather.


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## mudhog (May 9, 2005)

If you use the formulas in books it will give you 32 amps FLA (full load amp) but most campers are rated to work on 30 amps this is what you need to look at for generator sizing. I looked hard to find a generator that will put out 30 amps most will run all kinds of multible circuits but only 20 amps. The one I got is a 6000 kw w/ 2- 30 amp plugs and I had 2 campers run on it with no problem but its big and cost about 2 grand you can find cheaper and smaller ones that will run 1 30 amp circuit that will run your camper fine.


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## Redfishr (Jul 26, 2004)

Thanks guys......for an exact load check, I'm gonna get an amp meter (I have one) and hook it up to the circuit..
I can see startup load and run load that way..
Thanks again......R.R.


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## 85LoneStar (Feb 26, 2006)

The unit should have a label near the power supply that displays the power requirements.
That requirement is at startup, when the highest load is required.


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## Redfishr (Jul 26, 2004)

Psycho Trout said:


> I know you are not going to run that 13.5K BTU unit ona 2.5k watt generator. Forget it. you will need at least a 5k or bigger to run it and something with a even beter surge. Don't have the formula handy, sorry.


I've done some more research and found out that YES a 2500 gen will start and run a 13.5K unit .
I found a guy on a camper forum that shows how he tested the EF2400iS Yamaha and the 13.5 on his camper only drew 11.5 amps when running up to 15 for a couple of seconds during start up of the compressor.
The Yamaha has a 500 momentary start up buster for 20 seconds.
But he had all the photos of his amp meter during all of his test and photos of camper, generator, etc....
I'm gonna get the Yamaha EF2800iS, it only weighs 64 lbs and has a 30 amp plug built in as well as 20 amp ones. Tank,(3gallons) lasts about 10 hrs.
I'm good with all of this......


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## Chunkn' Charlie (Dec 30, 2004)

Your RV has 30 amp hook up. So you need a 3600 watt gen. (For all practical purposes) all you are going to get out of a 30amp hook up at an RV park is 3600 watts.

I recomend a generator with at least 5500 surgewatts.

I have a "Genaerac" 4600watt but it has surge watts up to 5800. It does everything I need it to do :Micro wave, 1500btu A/C, TV satalite.


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## TomCat (Jan 6, 2006)

I'll need a BTU

To cool a BUT 
As big as a TUB


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