Explain how AC soft-start accessory works

Motorapido

Please help me understand how air conditioner soft-start accessory kits work. As I preparing to perform a few repairs on a Coleman RV air conditioner, I was reading DIY tutorials for RV air conditioners, and I ran across many recommendations that I upgrade my RV air conditioner with a soft-start kit. The explanation is that it allows you to run your RV air conditioner when only plugged into 15 amp power, without tripping breakers in the RV or the house. I don't know much electrical theory, but I am guessing that the soft-start kit simply adds an extra starting capacitor for the compressor. However, these kits cost (I know we aren't supposed to discuss price but I think this is a gray area) about 25 times the cost of a typical AC compressor start capacitor. So there must be much more to them. And as a follow up question, on modern RVs (mine is ancient), do they simply build the RV air conditioner with soft-starting circuitry from the get-go? Seems like that would make sense.

ChrisJ

Motorapido said:

Please help me understand how air conditioner soft-start accessory kits work. As I preparing to perform a few repairs on a Coleman RV air conditioner, I was reading DIY tutorials for RV air conditioners, and I ran across many recommendations that I upgrade my RV air conditioner with a soft-start kit. The explanation is that it allows you to run your RV air conditioner when only plugged into 15 amp power, without tripping breakers in the RV or the house. I don't know much electrical theory, but I am guessing that the soft-start kit simply adds an extra starting capacitor for the compressor. However, these kits cost (I know we aren't supposed to discuss price but I think this is a gray area) about 25 times the cost of a typical AC compressor start capacitor. So there must be much more to them. And as a follow up question, on modern RVs (mine is ancient), do they simply build the RV air conditioner with soft-starting circuitry from the get-go? Seems like that would make sense.

An extra capacitor allows more current to the start winding.  That's how a hard start works 

As far as I know a real soft start works by ramping up the voltage using an algorithm.  I believe they work very well.

flat_twin

I'm using a Micro Air soft start unit on our 13.5k Coleman Mach roof air. The most convincing video demo of the Micro Air was one that showed amps required with and without. It seems to work exactly as advertised. We've used our air conditioner on a 20 amp circuit with heavy cord. Also limited use with our Honda inverter generator but it starts and runs on it OK.

JUGHNE

Not a soft start issue but an observation concerning hard starting motors.

RV AC was tripping 20 Amp CB when set up at new location.
There was a 50' 16 gauge ext cord neatly coiled up on the ground in about a 18" circle.
Only a 10' cord would have been needed.

The 50' was replaced with a 25' 12 gauge not coiled up but just snaked around on the ground.

The coil was creating a "choke" effect on the current flow and not allowing motor start.

Changing the cord "fixed" the problem.

Another case was a table saw with the same coiled cord set up.
The saw would be very slow coming up to speed.

The coils were scattered around the corrected the problem.
The saw started right up normally.

The carpenter did not believe that caused it and proceeded to neatly recoil his cord again and let the motor suffer, after I walked away.

He could not "see" what difference the "choke" coil would make for the start up, even though the saw was started correctly numerous times.
He thought I was just being a wisea$$ electrician.

He was one of those guys who had hit himself in the head with his hammer a few too many times.

JakeCK

JUGHNE said:

Not a soft start issue but an observation concerning hard starting motors. RV AC was tripping 20 Amp CB when set up at new location. There was a 50' 16 gauge ext cord neatly coiled up on the ground in about a 18" circle. Only a 10' cord would have been needed. The 50' was replaced with a 25' 12 gauge not coiled up but just snaked around on the ground. The coil was creating a "choke" effect on the current flow and not allowing motor start. Changing the cord "fixed" the problem. Another case was a table saw with the same coiled cord set up. The saw would be very slow coming up to speed. The coils were scattered around the corrected the problem. The saw started right up normally. The carpenter did not believe that caused it and proceeded to neatly recoil his cord again and let the motor suffer, after I walked away. He could not "see" what difference the "choke" coil would make for the start up, even though the saw was started correctly numerous times. He thought I was just being a wisea$$ electrician. He was one of those guys who had hit himself in the head with his hammer a few too many times.

I've never heard of that before. Now I feel like going out to the garage and playing around with my 1960's Sears table saw.

JUGHNE

It might happen and maybe not.

But it worked for the 2 cases mentioned above.

A saw motor with a start cap might make a difference.

RV AC would have had only a run cap.

Let us know.....

hot_rod

this