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Author Topic: 240 volt roof air  (Read 1578 times)
Scott Bennett
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« on: July 03, 2013, 09:11:45 PM »

Would a 240 volt roof air 13,500 btu be able to run on a 1500 watt 240 volt generator?


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Scott & Heather
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« Reply #1 on: July 03, 2013, 09:55:56 PM »

Doesn't matter what voltage the unit is, it's the starting wattage and running wattage that makes the work. Typically, if an air conditioner needs 1500 watts to run, it would need double that wattage to start it-especially when it's hot. Good Luck, TomC
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« Reply #2 on: July 04, 2013, 04:37:37 AM »

1500 watts at any voltage will not work for the a/c roof unit, it would take an older Onan 2500 watt to have a chance, Generac and other econ wannabee gensets would require about 5000 watts.
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« Reply #3 on: July 04, 2013, 06:12:50 AM »

I'm curious where you found a 240 volt roof top A/C unit?  Is it European?
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Scott Bennett
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« Reply #4 on: July 04, 2013, 06:51:41 AM »

Yes, I don't own one, but yes, european model. Basically wanted to know if the higher voltage would allow for less watts needed...i'm an electricity dummy.
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Scott & Heather
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« Reply #5 on: July 04, 2013, 08:14:17 AM »

Amp X Volts = Watts. You are 1/2 right, The higher voltage will draw less Amps, Not Watts.
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« Reply #6 on: July 04, 2013, 08:18:38 AM »

 Grin
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« Reply #7 on: July 04, 2013, 09:27:26 AM »

Doesn't matter what voltage the unit is, it's the starting wattage and running wattage that makes the work. Typically, if an air conditioner needs 1500 watts to run, it would need double that wattage to start it-especially when it's hot.

This is absolutely true - the starting surge usually requires an over-size generator to get the roof unit running. Double the wattage is probably a safe rule of thumb.

You can mitigate this somewhat with a "soft start" kit for the the roof AC that uses a larger capacitor to bring down the starting surge current requirements.

Or an even better way is to use an inverter that can supplement your generator power with battery power for the duration of the starting surge. This way you can size your generator for the average running load, not the peak surge load.

Cheers,

  - Chris
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« Reply #8 on: July 04, 2013, 10:04:54 AM »

Some of the new portable inverter generators could start a roof air. I would still go with no smaller then 2000 watts with closer to 3000 watts better. 

It doesn't matter whether it's 120vac @ 12.5 amps or 1500vac @ 1 amp, it's still 1500 watts and you need a 1500 watt generator to create it. Good Luck, TomC
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« Reply #9 on: July 04, 2013, 10:28:46 AM »

You must also be aware of the frequency.  Many European models will be 50Hz.
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« Reply #10 on: July 04, 2013, 06:22:03 PM »

That 50 hz air conditioner might take 1800 watts if it was run on a 60 hz generator because the compressor would likely run 20% faster than normal.

It's something to consider.

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« Reply #11 on: July 04, 2013, 07:43:21 PM »

A/C starting with other running loads running may prevent it from even starting--even if the gen set is way larger than you think you need.  Relays needed?  Also the environment comes into play.  If you are very hot outside and at very high altitude, good luck with that marginal gen set...it just might not work at all.  Like already answered better; sometimes a 50 Htz A/C unit and a 60 Htz genset may not mix.  Faster; (with all potential concerns) and hotter?  HB of CJ (old coot)
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« Reply #12 on: July 04, 2013, 08:04:09 PM »

A 1,500 watt 240 volt generator would be pretty small for 240 volt.  Most with 240 volt are 3000 watts and up.
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« Reply #13 on: July 05, 2013, 05:19:27 AM »

Ok, so my 3000 watt generator isn't producing more watts in 240 volt mode?


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Scott & Heather
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« Reply #14 on: July 05, 2013, 05:34:48 AM »

Watts are watts no matter what voltage.  Amps will change as voltage changes.  Your generator produces the same amount of power no matter if 240 volt or 120 volt.

You don't use any less power by going with a 240 volt rooftop.  You're better off with 120 volt for ease of replacement and repair.  You also won't have to deal with 50 hz versus 60 hz.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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« Reply #15 on: July 05, 2013, 06:40:21 AM »

Volts and amps are the two sides of a teeter totter.  Watts are the pivot point in the middle.

Brian
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« Reply #16 on: July 05, 2013, 07:05:58 AM »

Brian

I've been a wire-wiggler for a long time and have often struggled to give an analogy of Volts X Amps = Watts to my wrenching friends.  (let's not go into power factor!). Your explanation is great!  May I use it?

I've finally figured out that torque X rpm = horsepower. Sort of. So then a gear reducer is a transformer.

Ted
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« Reply #17 on: July 05, 2013, 07:29:11 AM »

By all means use it.  I am surely not the first to think of it, but it just came to me when reading this thread. 

Brian
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« Reply #18 on: July 05, 2013, 08:56:17 AM »

In any case,  now that the electrical miracle is ruled out,  there is no benefit to using a 240 rooftop.  It will only complicate life.  We used to run an AC on a 3500 w. A good 3000 may do it too,  but it is good to have a bit of reserve.
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Seangie
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« Reply #19 on: July 05, 2013, 04:20:34 PM »

Scott -  don't do it.  I've got 240v AC and already we are feeling the complications/limitations of using 240v.  Add to the fact that its 50hz and your just complicating things.

It would be one thing if it was a super pizazzical AC unit that cooled the entire coach with exuberant features but if its just saving a few bucks to use something that's available it might be more trouble than its worth.

-Sean


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« Reply #20 on: July 06, 2013, 09:02:45 AM »

Just a note here, if you are looking to use a small generator, the Honda 2000's can be put in tandem, so you can use one or both depending on your needs.  There would certainly be enough power for one AC with both, while using only one for smaller things like charging batteries.
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Scott Bennett
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« Reply #21 on: July 06, 2013, 08:17:15 PM »

Thank you so much for the explanations. Love reading every one of your responses. Love the teeter totter example. Ok, so now that I've figure that out, I won't consider a 240 volt model. Sean confirmed by personal experience that it can be a pain.


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Scott & Heather
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