Compressor Rated Amps

[newoldtech]

I was checking a compressor that I could tell was not the factory installed one. It was a single phase, 44,000 Bristol. The label on the compressor only gave the lock rotor amps of 102. Is there some formula or trick to know what the running(RLA) amps are rated?

[Hrdworkingacguy]

http://www.bristolcompressors.com/ab...-applications/

Try that...

[Yuma]

Many text books say take the LRA and divide by 5 for RLA (and then use 80%).
I tell my students to divide by 6. You get the same results more or less.

Yuma,

[newoldtech]

Many text books say take the LRA and divide by 5 for RLA (and then use 80%).
I tell my students to divide by 6. You get the same results more or less.

Yuma,

The LRA on my compressor was 102, and I read 15.5

102 divided by 6 is 17. So its pretty close. I will remember it. Thanks.

[penderway]

An important note about FLA, RLA and LRA as they pertain to PSC (Permanent Start Capacitor) Compressors and PSC Fan motors.

Compressor RLA (Rated Load Amperage) and Fan Motor FLA (Full Load Amperage) are located on the condenser or heatpump nameplate.

Compressor RLA is the current drawn at the highest load conditions for which the compressor is rated to operate. Typically 115°F outside 80°/67° inside.

The compressors internal overload will typically open at 1.5 times the Compressors RLA during continuous operation (or if the maximum temperature at the overload is reached).

Fan Motor FLA is the amperage drawn at the motors full-load torque and horsepower. For Fan motors this is minimally affected by temperature and humidity so it doesn't change. Motors have this on their nameplate as well as the unit nameplate, compressors do not.

FLA is also sometimes referred to as the Running Load Amperes and should not be confused with the Rated Load Amperes.

For compressor FLA (a.k.a. Running Load Amperes) It can be obtained from the manufactures electrical performance data that displays the kW at various conditions of temperatures and pressures.

With the compressors actual voltage, amperage and power factor, the kW can be calculated and then compared to the performance data at actual conditions to determine if the compressor amperage is what the manufacturer intended it to be.

The FLA is determined by the motor manufacturer and is used to select the correct wire gauge, motor starter, and overload protection devices necessary to serve and protect the motor/compressor.

For compressors, neither FLA or RLA is on the nameplate of the compressor. This is because the compressor manufacturer does not determine the actual application or conditions at which the compressor will be operated.

LRA (Locked Rotor Amperage) is located on the compressor nameplate. LRA is the maximum current spike during a motor start. If the compressor motor was electrically fine, but mechanically locked, it would draw at or near the nameplate LRA.

For troubleshooting PSC fan motors, the actual amperage (with access doors in place) should not be less than 25% or over 10% of the motors FLA on the motors nameplate.

For troubleshooting PSC compressor motors:

While operating, the actual amperage should not be greater than the RLA on the unit nameplate. The formula given by Yuma, LRA divided by 5 for RLA, then RLA times 0.8 for FLA, is an adequate guess for when the manufactures data is not readily available. A low compressor amperage by itself, does not indicate a compressor failure.

If powered but not rotating (humming), the actual amperage should not be more or less than 10% of the LRA on the compressor nameplate. If <>10%, the compressor windings, line voltage or external components are at fault.

Rotating or not, if the actual amperage is somewhere in between the RLA and LRA, then the compressor windings, line voltage or external components are at fault.

References-
http://www.achrnews.com/articles/115...-amperage-data

https://books.google.com/books?id=eS...%20RLA&f=false

http://iaeimagazine.org/magazine/199...ump-equipment/

[rcstl]

An important note about FLA, RLA and LRA as they pertain to PSC (Permanent Start Capacitor) Compressors and PSC Fan motors.

Compressor RLA (Rated Load Amperage) and Fan Motor FLA (Full Load Amperage) are located on the condenser or heatpump nameplate.

Compressor RLA is the current drawn at the highest load conditions for which the compressor is rated to operate. Typically 115°F outside 80°/67° inside.

The compressors internal overload will typically open at 1.5 times the Compressors RLA during continuous operation (or if the maximum temperature at the overload is reached).

Fan Motor FLA is the amperage drawn at the motors full-load torque and horsepower. For Fan motors this is minimally affected by temperature and humidity so it doesn't change. Motors have this on their nameplate as well as the unit nameplate, compressors do not.

FLA is also sometimes referred to as the Running Load Amperes and should not be confused with the Rated Load Amperes.

For compressor FLA (a.k.a. Running Load Amperes) It can be obtained from the manufactures electrical performance data that displays the kW at various conditions of temperatures and pressures.

With the compressors actual voltage, amperage and power factor, the kW can be calculated and then compared to the performance data at actual conditions to determine if the compressor amperage is what the manufacturer intended it to be.

The FLA is determined by the motor manufacturer and is used to select the correct wire gauge, motor starter, and overload protection devices necessary to serve and protect the motor/compressor.

For compressors, neither FLA or RLA is on the nameplate of the compressor. This is because the compressor manufacturer does not determine the actual application or conditions at which the compressor will be operated.

LRA (Locked Rotor Amperage) is located on the compressor nameplate. LRA is the maximum current spike during a motor start. If the compressor motor was electrically fine, but mechanically locked, it would draw at or near the nameplate LRA.

For troubleshooting PSC fan motors, the actual amperage (with access doors in place) should not be less than 25% or over 10% of the motors FLA on the motors nameplate.

For troubleshooting PSC compressor motors:

While operating, the actual amperage should not be greater than the RLA on the unit nameplate. The formula given by Yuma, LRA divided by 5 for RLA, then RLA times 0.8 for FLA, is an adequate guess for when the manufactures data is not readily available. A low compressor amperage by itself, does not indicate a compressor failure.

If powered but not rotating (humming), the actual amperage should not be more or less than 10% of the LRA on the compressor nameplate. If <>10%, the compressor windings, line voltage or external components are at fault.

Rotating or not, if the actual amperage is somewhere in between the RLA and LRA, then the compressor windings, line voltage or external components are at fault.

References-
http://www.achrnews.com/articles/115...-amperage-data

https://books.google.com/books?id=eS...%20RLA&f=false

http://iaeimagazine.org/magazine/199...ump-equipment/

Nice post!

[shellkamp]

An important note about FLA, RLA and LRA as they pertain to PSC (Permanent Start Capacitor) Compressors and PSC Fan motors.

Compressor RLA (Rated Load Amperage) and Fan Motor FLA (Full Load Amperage) are located on the condenser or heatpump nameplate.

Compressor RLA is the current drawn at the highest load conditions for which the compressor is rated to operate. Typically 115°F outside 80°/67° inside.

The compressors internal overload will typically open at 1.5 times the Compressors RLA during continuous operation (or if the maximum temperature at the overload is reached).

Fan Motor FLA is the amperage drawn at the motors full-load torque and horsepower. For Fan motors this is minimally affected by temperature and humidity so it doesn't change. Motors have this on their nameplate as well as the unit nameplate, compressors do not.

FLA is also sometimes referred to as the Running Load Amperes and should not be confused with the Rated Load Amperes.

For compressor FLA (a.k.a. Running Load Amperes) It can be obtained from the manufactures electrical performance data that displays the kW at various conditions of temperatures and pressures.

With the compressors actual voltage, amperage and power factor, the kW can be calculated and then compared to the performance data at actual conditions to determine if the compressor amperage is what the manufacturer intended it to be.

The FLA is determined by the motor manufacturer and is used to select the correct wire gauge, motor starter, and overload protection devices necessary to serve and protect the motor/compressor.

For compressors, neither FLA or RLA is on the nameplate of the compressor. This is because the compressor manufacturer does not determine the actual application or conditions at which the compressor will be operated.

LRA (Locked Rotor Amperage) is located on the compressor nameplate. LRA is the maximum current spike during a motor start. If the compressor motor was electrically fine, but mechanically locked, it would draw at or near the nameplate LRA.

For troubleshooting PSC fan motors, the actual amperage (with access doors in place) should not be less than 25% or over 10% of the motors FLA on the motors nameplate.

For troubleshooting PSC compressor motors:

While operating, the actual amperage should not be greater than the RLA on the unit nameplate. The formula given by Yuma, LRA divided by 5 for RLA, then RLA times 0.8 for FLA, is an adequate guess for when the manufactures data is not readily available. A low compressor amperage by itself, does not indicate a compressor failure.

If powered but not rotating (humming), the actual amperage should not be more or less than 10% of the LRA on the compressor nameplate. If <>10%, the compressor windings, line voltage or external components are at fault.

Rotating or not, if the actual amperage is somewhere in between the RLA and LRA, then the compressor windings, line voltage or external components are at fault.

References-
http://www.achrnews.com/articles/115...-amperage-data

https://books.google.com/books?id=eS...%20RLA&f=false

http://iaeimagazine.org/magazine/199...ump-equipment/

Don't mean to nitpick; but PSC stands for "permanent split capacitor"

Everything else was spot on, though!

[penderway]

Nice post!

Thanks, had some time to kill

Don't mean to nitpick; but PSC stands for "permanent split capacitor"

Everything else was spot on, though!

Dang! and I can no longer edit it

[Core_d]

Dang! and I can no longer edit it

We'll let it slide this time

[Hunter844]

Good post, can I stamp that on my techs forehead?

[Younes Thabet]

FLA is also sometimes referred to as the Running Load Amperes and should not be confused with the Rated Load Amperes.
For compressor FLA (a.k.a. Running Load Amperes) It can be obtained from the manufactures electrical performance data that displays the kW at various conditions of temperatures and pressures.

Isn't FLA= Rated Load Amps and not Running Load Amps!!!

[HVACmedic911]

The LRA on my compressor was 102, and I read 15.5

102 divided by 6 is 17. So its pretty close. I will remember it. Thanks.

IN HEAT MODE OR COOL MODE? USSUALLY WITH CORRECT CHARGE AND NORMAL CONDITONS IN AC MODE YOU WILL HAVE HALF THE FLA AS YOUR RLA.. LRA/5=FLA FLA/2=RLA