Soft Start for A/C

[CharlieJ]

Anyone have experience with a soft-start unit with their residential A/C unit? Looking for feedback.
Like the one pictured below:

All I've seen are positive reviews. I would enjoy the quieter starts and ability to run the A/C with my backup generator.

 

[AZjeff]

No experience with residential but installed one in the travel trailer and it works as advertised. I can start and run the AC with a 2500W generator. Came with good installation hardware and USA made. Not cheap but worth it.

Demo:

 

[UncleDave]

Yes, I have experience with several designs, from a simple hard start capacitor upgrade, to the more sophisticated black box style units.

They are a great idea even if you have enough genset, they greatly speed up the hot restart.

 

[sloinker]

I use a boost start capacitor on the compressor. I am more interested on maximizing the life of that motor. In industry we used a lot of 3 phase soft starts and VFD's with longer start ramp times. We mostly just had line contactors that allowed full inrush current. In my 45 years in the industrial electrician trade I came to realize that the full current line contactor motors outlived their brethren soft start and VFD peers. I know why the VFD motors don't last as long. Non true sinusoidal waveforms cause excess heat and eddy currents. The soft starts? Have no idea. I know one of the selling points of soft starts is longer motor life, I would like to see actual evidence to back up this claim. I do get the starting of large loads on a generator that can't achieve peak power within the load in a timely manner. Good application in that case.

 

[We're Metals]

I use a boost start capacitor on the compressor. I am more interested on maximizing the life of that motor. In industry we used a lot of 3 phase soft starts and VFD's with longer start ramp times. We mostly just had line contactors that allowed full inrush current. In my 45 years in the industrial electrician trade I came to realize that the full current line contactor motors outlived their brethren soft start and VFD peers. I know why the VFD motors don't last as long. Non true sinusoidal waveforms cause excess heat and eddy currents. The soft starts? Have no idea. I know one of the selling points of soft starts is longer motor life, I would like to see actual evidence to back up this claim. I do get the starting of large loads on a generator that can't achieve peak power within the load in a timely manner. Good application in that case.

Boy you dont know how badly I want to understand the majority of this.

Following thread, I have wondered about purchasing one of these for long term A/C Longevity.

 

[oldcodger]

I installed one on my home 4 ton unit 3 years ago. It lowered the inrush current by about 60%. Don't know about extending the life of an AC but it makes the start up much smoother. It lowered the inrush current by about 60% on my home 4 ton AC unit.
Easy to install if you can follow the directions. Depending on your AC brand you might have to consult MicroAir for some specific instructions.

 

[Chevyc10]

I install hard start on every unit I work on. And I can run central A/C with generator. They prevent lights dimming/flickering on start up.
Never seen one like your photo. I use Kickstart or Supco.

 

[sloinker]

I forgot about all of the WYE-Delta starters/Motors for long inertia starts like in large compressors and fans.
I'm no HVAC guy but I think a Hard Start is the same as a boost capacitor that cuts in and out utilizing an internal or external relay. The soft starts reduce inrush current by delaying full voltage and possibly controlling frequency. Not very familiar with them.

 

[jtwrace]

I just installed mine yesterday!

 

[KJSmith]

Boy you dont know how badly I want to understand the majority of this.

There is a reason HVAC guys carry hard start kits on the truck.
My basic understanding.

A hard start kit is an extra capacitor and relay.
When the compressor comes on, it gives a quick jolt of voltage that INCREASES starting torque.
Gets the motor running faster.
Can help overcoming pressure differentials or other issues that can make compressors a little harder to start.
You can, see in other threads, they are used by HVAC guys industry wide.
They work.
A lot of units come from the factory with them already installed.

Soft start kits do the opposite.
They try to ramp up the voltage slower.
They also DECREASE torque.
A compressor having starting issues will not be helped.
A gen set trying to start that unit may be helped.

Ask yourself.
Will a compressor having a hard time starting be helped by more or less torque?

If your goal is to help your HVAC, a hard start kit will do the job.

If your goal is to help an undersized gen set run your HVAC, soft start may help.
If your unit has starting issues on normal power, soft start can hurt.

I often wonder how many guys that advocate soft start kits for HVAC units have ever worked in the industry.

As far as I know? HVAC supply houses don't carry soft start devices.

 

[Chevyc10]

There is a reason HVAC guys carry hard start kits on the truck.
My basic understanding.

A hard start kit is an extra capacitor and relay.
When the compressor comes on, it gives a quick jolt of voltage that INCREASES starting torque.
Gets the motor running faster.
Can help overcoming pressure differentials or other issues that can make compressors a little harder to start.
You can, see in other threads, they are used by HVAC guys industry wide.
They work.
A lot of units come from the factory with them already installed.

Soft start kits do the opposite.
They try to ramp up the voltage slower.
They also DECREASE torque.
A compressor having starting issues will not be helped.
A gen set trying to start that unit may be helped.

Ask yourself.
Will a compressor having a hard time starting be helped by more or less torque?

If your goal is to help your HVAC, a hard start kit will do the job.

If your goal is to help an undersized gen set run your HVAC, soft start may help.
If your unit has starting issues on normal power, soft start can hurt.

I often wonder how many guys that advocate soft start kits for HVAC units have ever worked in the industry.

As far as I know? HVAC supply houses don't carry soft start devices.

You are correct!!!
I own HVAC supply stores. And sell thousands of hard starts for HVAC and refrigeration. Never heard of a soft start till this site.

 

[KJSmith]

You are correct!!!

I don't pretend to know everything, but I did spend 45yrs in the industry.

The only soft start devices I ever saw were on Liebert wall packs.
You could identify them by the black carbon/ scorched marks around them.
I never replaced one.
Just left them, unless they blew the wires off the terminals.

I wonder how many soft start devices have been installed on units that already have hard start kits installed.