Will My Generator Run My 4 Ton Air Conditioner?

[apittmanii]

Hello -

I flx and flip generators, and have come across a low hour Honda EB11000. I am trying to determine whether to keep this one for our home use. I can not figure out if after installing a transfer switch, this EB11000 will power our air conditioner.

Besides the air conditioner I will need NO MORE than 1500 running watts with very little to no starting / surge watts.

Photo 1: the electrical tag from the air conditioner.
Photo 2: the specifications of the generator
Photo 3: photo of the generator

My confusion is because the A/C tag says 96.0 LRA (Locked Rotor Amps): "The current you can expect under STARTING conditions when you apply full voltage. It occurs instantly during start up."

But the A/C tag details that the minimum circuit amps is 27, and the max circuit breaker is 40 amps (both of which are much lower than the 96 starting amps of the A/C.

Thank you for your help.

 

[Stuart in MN]

Minimum circuit amps on the a/c is 27.8, the max output of the generator is 39.6. It will probably work. It sounds like you're pretty handy, the easiest thing may be to temporarily wire the a/c directly to the generator and see if it will start and run.

 

[txvwnut]

It might but I’ll say probably not. My 7500 won’t pull my 2ton unit at start up but it would pull my neighbors 1ton easily.

 

[wyliesdiesels]

The thing youre confused about is explained with a term called in-rush current.

Motors inherently have in-rush currents that can be anywhere from 4x-8x FLA.

This is for fractions of second.

Hard to say whether the 11KW genny could handle it. Only way to know is to temporarily wire it up and find out.

 

[Ole Slewfoot]

I think you might need one of these or similar...
https://hvacdirect.com/4-5-ton-scro...MI4PyL98jR1wIVmMhkCh2PGw37EAQYBCABEgKyvvD_BwE

 

[James-W]

You mentioned this generator was for home use. I don't understand how all you need is to run an air-conditioner and not the rest of the house. I mean, you have lights in the house, refrigerator, all sorts of appliances, not to mention electronic equipment. Are you planning on not using any of these things while using the generator?

 

[apittmanii]

Some great feedback here- I agree the next step is to wire up the compressor and see how it performs. I’ll do that and post the results here.

 

[apittmanii]

Motors inherently have in-rush currents that can be anywhere from 4x-8x FLA.

This is for fractions of second.

Thanks for the clarification - that’s exactly what tripped me up. I’ll give it a try without a transfer switch and see how it runs.

 

[mm08822]

I think you need 15-17KW gen to start that a/c unit properly.
Too small a unit will harm both the generator and or a/c unit. The output voltage will severely dip and the gen will struggle to recover. The gen breaker may trip before it recovers.

A/c units cycle too frequently to not have sufficient power delivery to them. Otherwise the a/c unit's life will be short.

 

[apittmanii]

You mentioned this generator was for home use. I don't understand how all you need is to run an air-conditioner and not the rest of the house. I mean, you have lights in the house, refrigerator, all sorts of appliances, not to mention electronic equipment. Are you planning on not using any of these things while using the generator?

The A/C is important for our particular situation. We will just need the 1500 watts in addition to this as noted in the original post.

 

[theoldwizard1]

A "hard start kit" might be worth a shot. Basically it is an extra starting capacitor.

A "locked rotor amps" on an A/C compressor, is higher than normal starting current. A locked rotor typically only occurs when the compressor is shut off before it reaches full operating RPM and then it is immediately turned back on. Something has to give with that much current. I think most A/C compressors have an automatic reset breaker that will trip IF there is adequate current available.

 

[mm08822]

A "locked rotor amps" on an A/C compressor, is higher than normal starting current. A locked rotor typically only occurs when the compressor is shut off before it reaches full operating RPM and then it is immediately turned back on. Something has to give with that much current. I think most A/C compressors have an automatic reset breaker that will trip IF there is adequate current available.

When a motor is first started the rotor is stopped. It draws the locked rotor amps initially. As long as the motor can start turning, the rotor current decreases b/c the cemf is building up. The initial current decreases from this max value until the rotor gets up to slip speed where the current then approaches the motor FLA’s which is the minimum value.

If the motor cannot rotate at startup, the cemf will remain zero and the LRA’s will sustain until the o/l’s trip or the cb.

You're confusing duration of LRA with that of inrush current magnitude.

 

[48RON54]

I have never had an issue sizing a generator to a motor load by making sure rated amperage of generator is 1.5->2 times the running amps of the motor to cover inrush.

I would test it though......Yes, its low hours but really the only way to know for sure is to hook up the AC to it.

 

[prostreetamx]

The reason your house breaker can handle the rather large LRA of your A/C is that panel breakers are rated for that ,very temporary, inrush of current without tripping. You also have a larger potential amp supply in your house panel than a typical portable genny. Your generator is limited by its electronics and motor speed to provide an amp load that might not be available instantly for LRA loads and the breakers in the generator might not be able to handle the load and cause a big voltage drop. I have 2 separate portable generators that I will try on my loads. I have a sub panel already set up for one and will attempt to supply one of my 3 ton A/C compressors separately with another one.

 

[American Locomotive]

Only way to find out is to give it a try.

The reason why it says 96 LRA on a 40A breaker, is because breakers have a trip curve. It takes a substantial amount of current to get a breaker to trip instantly. Most breakers will deliver several times their rated current without tripping (for a brief amount of time). I've pulled nearly 200 amps starting a big motor on a 30A 240v breaker once. It didn't trip because the draw was only for a second or so.

 

[mm08822]

Only way to find out is to give it a try.

The reason why it says 96 LRA on a 40A breaker, is because breakers have a trip curve. It takes a substantial amount of current to get a breaker to trip instantly. Most breakers will deliver several times their rated current without tripping (for a brief amount of time). I've pulled nearly 200 amps starting a big motor on a 30A 240v breaker once. It didn't trip because the draw was only for a second or so.

Breaker trip curves are one thing. Generator surge capacity is another. In your example above, what was the energy source - grid or gen?

 

[walta]

My guess is it will start and run because this AC unit has a scroll compressor, which have much smaller starting loads than the piston type compressors.

Walta

 

[EOC_Jason]

Generators are kind of finicky, if I had to guess my money would be that the breaker trips on the generator. Likely the only way to tell though would be to hook it up and see what happens, I would also monitor the voltage & amperage while doing so...

A hard start kit may or may not help in this scenario. It basically gives an extra 'kick' to get the compressor moving.

Personally I wouldn't do it because you will likely burn up your compressor if it cycles a bunch on that size of generator from the voltage dip (assuming the breaker didn't trip).

 

[yeldogt]

I was told need 13k for starting a 3 ton -- 17K for a 4T and 20k for 5T. And that's depending on the unit.

Funny -- I was told the old piston compressors actual need less starting amps w/R12 vs the new various types of compressors using R410 ... of whatever it is.

My old 4t York monster was on a 30amp line and my new Carrier 3T needed a 40 -- real pain as it had to be rewired.

 

[Done That]

All I will add to the discussion is that Bryant unit uses a 2-stage scroll compressor and has an Evolution control board in it as well, so be carefull with any testing as that is a pricey board if you let the smoke out.

 

[EOC_Jason]

Funny -- I was told the old piston compressors actual need less starting amps w/R12 vs the new various types of compressors using R410 ... of whatever it is.

R22 runs at a lower pressure than R410a so there would be less resistance on startup.

 

[nehog]

96 LRA for the AC. Generator maxes at 39 amps. Doesn't sound good to me.