I'm trying to size the A/C loads in my house for a generator, but I can't get a strait answer on how to calculate the start load. I put my meter on each of the 2 phases and it never reported any surge it just built up to the A/C's running watts. Yet I've read from 2 times to 5 times the running watts from different sources. Hopefully I can get a strait answer from you guys. Thanks in advance!
A/C Start load
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Re: A/C Start load
Bigjohn
I think you are referring the the method of determining the Over Current device for the A/C. The code allows up to 175% of the A/C FLA.
The post is trying to determine the size of a generator to run his A/C unit.
Blink
What kind of meter are you using? If its a digital you may have a max and min button. Press it and the meter will record the max inrush.
The inrush is too fast to pick up with out this feature.
Bigjohn
I think you are referring the the method of determining the Over Current device for the A/C. The code allows up to 175% of the A/C FLA.
The post is trying to determine the size of a generator to run his A/C unit.
Blink
What kind of meter are you using? If its a digital you may have a max and min button. Press it and the meter will record the max inrush.
The inrush is too fast to pick up with out this feature.
Re: A/C Start load
The problem with trying to figure start current for an A/C unit is the fact that the compressor is only trying to turn the motor mass itself. The compressor section should be unloaded with zero pressure differential between the pressure side and the suction side.
Most motors need that very high start current to work against a load. Just remember that a motor that is sitting still looks very much like a short circuit until it starts turning. That very short spike in current should not drag down a generator unless it is already close to generating its maximum output.
That 175% of full load amperes is a very good starting point.
The problem with trying to figure start current for an A/C unit is the fact that the compressor is only trying to turn the motor mass itself. The compressor section should be unloaded with zero pressure differential between the pressure side and the suction side.
Most motors need that very high start current to work against a load. Just remember that a motor that is sitting still looks very much like a short circuit until it starts turning. That very short spike in current should not drag down a generator unless it is already close to generating its maximum output.
That 175% of full load amperes is a very good starting point.
Re: A/C Start load
Bob, I have an Ideal Snap around digital volt-ohm-ammeter, all it has is a data hold
Grlsound, Bigjohn states 175% of the RLA for motors, but you said total load so I'm assuming that you mean for the circuit, which seems resonable since 175% of my A/C load for this wing is 28amps, and the A/C is serviced with a 30 amp breaker.
So, I should assume close to the breaker size for starting of an A/C load then? Thanks everyone.
Bob, I have an Ideal Snap around digital volt-ohm-ammeter, all it has is a data hold
Grlsound, Bigjohn states 175% of the RLA for motors, but you said total load so I'm assuming that you mean for the circuit, which seems resonable since 175% of my A/C load for this wing is 28amps, and the A/C is serviced with a 30 amp breaker.
So, I should assume close to the breaker size for starting of an A/C load then? Thanks everyone.
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