Our I.T. guy just came into work and overheard us discussing things, and he mentioned the $20 Supco SPP6E. He states that it's a capacitor that has to be installed on the actual A/C unit, but makes it easier to run while on the generator.
Hard-start kits, or Start Assist kits as some prefer, do nothing to reduce the load on the power source. They exist to increase the starting torque within the compressor, usually for old/worn compressors and/or due to excessive voltage sag during starting. Starting current would normally be something like 4-8 times the FLA of the motor, some of which is due to poor power factor, but mostly due to the motor starting off in a stalled condition as all induction motors do (it was off and therefore not turning, after all) with the current draw being very high for most of the ramp-up time, tapering off quickly as it approaches loaded speed.
(He also mentioned that the Yamaha 2400 has a 30 second surge when it needs it, whereas the Honda does not, but thats another discussion.)
Since my unit is already modified and out of warranty, I see no reason not to install the Supco SPP6E before completing the full install and save a little money in the long run.
It's just a capacitor with a potential relay to cut it out of the circuit once the rotor is up to speed. It will do nothing to cut energy consumption rate while running at speed. Nor will it do anything if the compressor starts normally, with no low-voltage problems other than potentially reduce current draw and time to speed a bit while starting. Which can help when running on a small generator.
Compressors use two-phase motors*, meaning there are two windings inside, one connected directly to the incoming power, the other connected with a capacitor in series with it. The capacitor 'delays' the current through the second winding, causing a time shift in the magnetic peaks. The higher the capacitance, the more the angular shift, and the greater the starting torque. Once it's up to speed, the start capacitor is cut out, and only the run capacitor remains on that second winding. Since it's spinning fast, only a small angular shift in magnetic peaks is required.
Hard-starting due to low voltage can be mitigated by increasing the angular shift in that second winding even further, which is what the start assist capacitors do. And that's all that they do.
So a start assist kit may be helpful when trying to start a compressor with a small generator that's limited in its ability to provide the high starting current needed, usually resulting in severe voltage sag during a start. An electronic generator may simply refuse to provide enough current, though, even with a start assist kit. But the kits are cheap enough, and there's no harm in adding one AFAIK.
*Two-phase meaning there are two windings that see current through each that is time-shifted slightly through combinations of resistance and capacitance and inductance - not to be confused with the two phase conductors of 240V which is still single-phase power at the source.
