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Compressor start current
ChrisJ
Member Posts: 16,260
I'm looking for typical start currents for a 3 ton scroll just out of curiosity.
My 2 stage Copeland Ultratech claims 83A LRA.
My 2 stage Copeland Ultratech claims 83A LRA.
Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
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RLA at least on mine, is 15.3Amattmia2 said:For induction motors the typical LRA is 5x-10x the RLA.
But what is the expected real life current during starting?Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment0 -
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It's a LOT. I agree with all of the above.
This is why a standby generator has a hard time starting inductive (motor) loads. The transformer on the pole by your house may only be 10kva (10,000 volt amps) but can pass many times that rating for short times starting motors. The generator on the other hand will only produce its rating and that's it.
Why do you ask @ChrisJServing Northern Maine HVAC & Controls. I burn wood, it smells good!1 -
After working on it on and off for two years I finally got my generator together and home for testing.Solid_Fuel_Man said:It's a LOT. I agree with all of the above.
This is why a standby generator has a hard time starting inductive (motor) loads. The transformer on the pole by your house may only be 10kva (10,000 volt amps) but can pass many times that rating for short times starting motors. The generator on the other hand will only produce its rating and that's it.
Why do you ask @ChrisJ
It's pieced together from a home standby generator that was rated 10KW on LPG and 10-20% less on natural gas. I'm running it on natural gas. The actual alternator says it's rated for 12KW with a 10% overload for 2 hours out of 24 but the 570CC vtwin can't run it at full power.
To my surprise, it managed to start my 3 ton air conditioner although it did sound like a person getting punched in the gut. It definitely went WOT for a second or two.
But it did it, and didn't seem to cause any issues. I was also surprised my ECM blower ran fine on it as well as my ICM fan controller on the condenser fan.Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment0 -
I thought you might be dealing with generator stuff, which is why I went down the RABBIT trail.
ECM motors (that is saying motors twice ya know) are generally not too picky about power that is a bit dirty.
You must be super luxurious having A/C on generator power! 😁
In my area a 10kw generator will run pretty much everything in a home, but we dont have much residential aircon. A generator will run a mini-split quite easily though (ECM) again.Serving Northern Maine HVAC & Controls. I burn wood, it smells good!2 -
For comparison, I periodically work on a heavy direct drive fan on a 3HP 230V motor. The starting current exceeds 2000A (my meter maxes out at 2000).
If your compressor has any differential pressure across it, you may be in a similar circumstance.
I’ve had previous success converting std compressor starting system to “Capacitor Start, Capacitor Run” in situations where the high starting current lasts too long.
Good Luck
Pat1 -
Pat_Collins94 said:For comparison, I periodically work on a heavy direct drive fan on a 3HP 230V motor. The starting current exceeds 2000A (my meter maxes out at 2000). If your compressor has any differential pressure across it, you may be in a similar circumstance. I’ve had previous success converting std compressor starting system to “Capacitor Start, Capacitor Run” in situations where the high starting current lasts too long. Good Luck Pat
I'm confused, how can a motor exceed it's LRA spec? I mean, that's what it draws literally stopped.Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment0 -
Time, it all happens within the fraction of a second.
Other factors come into play within that fraction if the motor is turning, perhaps the back EMF contributes to the very high momentary current draw.
If locked, compressor seized up, it might be a different animal.0 -
Capacitor start-capacitor run AKA a hard start kit. One would probably make it start easier0
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I had one on it right after I installed the unit and it seemed to like to "bang" on startup. Never figured out why, if it was due to it being a 2 stage compressor etc but I pulled it out and now my ICM fan controller occupies the space.EBEBRATT-Ed said:Capacitor start-capacitor run AKA a hard start kit. One would probably make it start easier
Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment0
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