Originally Posted by laura970
Thompson installed a Coleman Soft Start on our ORV. It's labeled as AC Start Capacitor on our invoice. It was only $35. They were uncomfortable with the MicroAir.
Just be aware that a soft-starter and a hard-start capacitor are two different things to solve two different problems.
The hard-start capacitor simply increases starting torque to compensate for the loss of torque during low-voltage conditions, or on aging units that are having a hard time starting even on closer-to-rated voltage. The original start capacitor is sized to provide an adequate starting torque with normal starting voltage range, which will be less than the rated voltage due to the high current draw. Starting torque drops like a stone with voltage reduction (as the square of the actual to rated voltage ratio) and a compressor may not be able to start at all when the voltage gets pulled down too far, even though it has almost unlimited current available from the utility. And speaking of current, a hard-start capacitor is likely to increase current draw while starting.
Soft-starters, on the other hand, limit the starting current to way below the LRA value of the compressor, with the fan already running (they start the fan first). It's far more complex than just another big capacitor and relay. This allows starting on a very limited current source, like a generator. Soft-starters have been around for a couple or few decades by now, and are used on 3-phase motors mainly. We use them on large motors run off generators (like 250 hp or more) since you'd need a giant generator just to get it started, which is expensive and wasteful in the long run. Single-phase soft starters are relatively new, but do work as advertised, but they're not cheap.
Neither system changes the running current once it's started, though.