Power to start/run a 5-ton heat-pump

bczoom · Mar 6, 2008

OK, I have a generator and a heat-pump.

The brochure for the generator says it'll start/run a 4-ton heat pump.

Well, mine is a 5-ton.

The gen is a 15Kw continuous, 22.5Kw surge. Can/will it start/run a 5-ton heat-pump? I must be missing something as I don't see anything big in the heat pump for starting/running. The strip heaters are another matter, but I have them off.

Thoughts/advise?

Melensdad · Mar 6, 2008

You need to know and post the start up draw on the heat pump. Without that I don't know if we can help you with an answer. But if you can find that, it will provide you the answer.

thcri · Mar 6, 2008

BC find the LRA Amps on the unit or compressor. Also does your unit start the compressor first and then the blower a bit later. That will help you. But to answer your question I would guess not. If the book says 4 they really mean 3??

murph

bczoom · Mar 7, 2008

My model is the one on the far right (RHE60A2A)

LRA for the compressor is 169.

How does it pull that many amps when it's only using a 60 amp breaker?

Anyway, I guess my generator won't be starting that compressor...

DaveNay · Mar 7, 2008

bczoom said:
My model is the one on the far right (RHE60A2A)

LRA for the compressor is 169.

How does it pull that many amps when it's only using a 60 amp breaker?

Anyway, I guess my generator won't be starting that compressor...

This might have some useful information in it......or not.

bczoom · Mar 7, 2008

Thanks Dave,

I was looking at that exact document before I did the model lookup for my heat pump.

That document says (in Table 1) that I need about 12.5Kw for starting. So, according to that, it will start it (as I have 22.5Kw for surge).

What I'm not understanding is LRA.
When Amps = 169 and Volts is 240, I theoretically need close to 40Kw to start it. Is that right?

Here is the detailed specs on my generator and highlights below.
# Rated Watts 15,000
# Surge Watts 22,500
# Voltage (Vac) 120/240
# Output 125/62.5
# Generac V-Twin
# OHVI 992cc
# 30 HP

thcri · Mar 7, 2008

BC,

That 169 LR Amps is only for a few seconds, as the compressor gets going the amps will drop way back down to the RLA (Running Load Amps) You circuit breaker can handle a surge like that for a while. Kind of like pushing a stalled car, hard to move but once moving not so bad to push.

I am not real familiar with Generators but I am assuming the surge rating is what will handle starting a motor?

murph

bczoom · Mar 7, 2008

thcri said:
I am not real familiar with Generators but I am assuming the surge rating is what will handle starting a motor?

Correct.

XeVfTEUtaAqJHTqq · Mar 7, 2008

What could you damage from testing it? Wouldn't the heat pump just not start if it couldn't get the power? Maybe the motor bogs down and dies?

Just curious.

bczoom · Mar 7, 2008

PBinWA said:
What could you damage from testing it? Wouldn't the heat pump just not start if it couldn't get the power? Maybe the motor bogs down and dies?

Just curious.

AFAIK, if there's insufficient volts (possibly amps as well), you create what's similar to a brown-out. Unlike a black-out where the power quits completely, a brown-out is a low-voltage situation. Unless a circuit is protected, it'll normally fry any electronic parts of whatever you're trying to start.

I've lost TV's, microwaves... to brown-outs. I don't want to take a chance with something as expensive as the heat pump unless there's a very good chance it will run.

XeVfTEUtaAqJHTqq · Mar 7, 2008

bczoom said:
AFAIK, if there's insufficient volts (possibly amps as well), you create what's similar to a brown-out. Unlike a black-out where the power quits completely, a brown-out is a low-voltage situation. Unless a circuit is protected, it'll normally fry any electronic parts of whatever you're trying to start.

I've lost TV's, microwaves... to brown-outs. I don't want to take a chance with something as expensive as the heat pump unless there's a very good chance it will run.

Thanks, I probably would have cooked my heat pump! :bonk:

I'm one of those "stand back - let's give it a try" type of people. :pat:

Bulldog1401 · Mar 7, 2008

FLA on startup occurs for fraction s of a second. That is why a smaller than rated circuit breaker will tolerate it.

If you attempt to start an electric motor with insufficient power, it will turn slower that it should. When it turns slower that it should, it will pull more current that its windings can handle, and will burn out.

If it does not start right up, abort you attempt immediately, and get a bigger generator.

Start up current for a motor is usualy at a minimum of 3x the running current. If it starts under load, it can be 5x. Your generator may have to have approx 5x the start currrent in surge capacity to start it.

ghautz · Mar 8, 2008

Another factor to consider is other loads on the generator when the AC starts. If the generator is the sole source of power to the house, other heavy loads (water heater, range, dryer, etc.) might be on when the AC cycles. That could easily overload the generator.

bczoom · Mar 9, 2008

ghautz said:
Another factor to consider is other loads on the generator when the AC starts. If the generator is the sole source of power to the house, other heavy loads (water heater, range, dryer, etc.) might be on when the AC cycles. That could easily overload the generator.

I've written up directions to connect and run the generator.
As part of it, I put red tape in the breaker box at each breaker that's to be turned off prior to starting the generator. Basically, everything that's 220 will be turned off.

Power to start/run a 5-ton heat-pump

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