Hard Start Kit

[readydave8]

I periodically have customer complaint of lights flickering when Heat Pump starts.

Rarely been able to solve.

If long power line to house, I assume voltage drop and recommend that their HVAC co. install hard start kit.

The feedback from most recent such customer was that HVAC tech said that installing hard start kit would shorten life of compressor.

Is that true? Is soft start kit a better option?

 

[StarCat]

A correctly installed Hard Start Kit will trim the instantaneous inrush current. It is significant and can be caught on a recording style meter such as Fluke 87.
This notion that it will shorten compressor life is something I have never heard in 31 years of HVACR service. How could that be so if you are reducing the starting current? I am sure the motor experts can chime in. I have seen start gear on units 20-30 years old and still running.
Of course now everything is built right on the edge.
There are some other threads where this is discussed. I do advise it.
You will never get perfect light behavior on that kind of load in residential.

 

[Eddie702]

Agree with @StarCat

A hard start kit will do the opposite and make the compressor last longer, start easier

 

[Jraef]

A Hard Start kit is just an additional starting capacitor and a way to disconnect it once the compressor motor has started (usually a Potential Relay). This is because the compressor motors are PSC (Permanent Split Capacitor) type which is a low starting torque motor. Generally if there is no voltage drop issue that's fine, but if there is, a Hard Start kit can help to overcome that VD. In doing so, the motor will put out more torque during startup. IF THE MOTOR IS ALREADY FAILING, the added torque might accelerate the demise of bearings and mounts, but generally on a healthy motor, it will have no adverse effect.

But f you are ALREADY having a voltage drop problem, THAT is harming the motor windings by adding unnecessary heat, so by having it pass through the acceleration current surge faster you are actually LOWERING the stress on the motor.

 

[falconewk]

I thought this podcast from Bryan Orr @ HVACRschool was pretty interesting (specifically with regards to hard start kits: I’ve been thinking about putting one on the heat pump at my house).

Hard Start Kits, Stay Brite #8, AHR, and More - HVAC School

In this podcast, we talk about hard start kits and Stay Brite #8. We also discuss products from AHR: CoreMax cores, notched belts, and more.

www.hvacrschool.com

 

[kwired]

A Hard Start kit is just an additional starting capacitor and a way to disconnect it once the compressor motor has started (usually a Potential Relay). This is because the compressor motors are PSC (Permanent Split Capacitor) type which is a low starting torque motor. Generally if there is no voltage drop issue that's fine, but if there is, a Hard Start kit can help to overcome that VD. In doing so, the motor will put out more torque during startup. IF THE MOTOR IS ALREADY FAILING, the added torque might accelerate the demise of bearings and mounts, but generally on a healthy motor, it will have no adverse effect.

But f you are ALREADY having a voltage drop problem, THAT is harming the motor windings by adding unnecessary heat, so by having it pass through the acceleration current surge faster you are actually LOWERING the stress on the motor.

If motor is hard to start because of drop in line voltage, hard start may make that drop even worse. It will cause more phase shift between main and Aux winding to produce more starting torque. Depending on how severe the VD is may or may not help it get to speed faster, but will likely draw the voltage down even more because more torque will demand more current and which will cause even more VD.

If voltage is simply on the low end of what is acceptable but doesn't dip significantly when starting, it maybe is a good thing to use the hard start kit just to reduce the starting time and the additional heating of windings during that process.

There is no one size fits all answer to this question.