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Old 03-17-2019, 04:02 PM   #20
ben2go's Avatar
City: Upstate,SC
Country: USA
Vessel Name: Dutch Barge Caroliner
Vessel Model: Selway-Fisher 45' Teign Luxe Motor
Join Date: May 2012
Posts: 2,656
Originally Posted by C lectric View Post
At the risk of adding further to the "discussion" I will add this.

THere is the typical START capacitor which many single phase motors require to get going. Any smaller boat A/C unit will have this type of motor. They are fine if the supply has sufficient voltage capacity such as your house or the dock plug in if big enough or a decent size generator.

There is also a HARD START capacitor which is effectively just a larger capacitor then would normally be installed. They produce a stronger startup torque plus supply some of the initial start up current which means the motor gets through the high inrush current stage. They charge within a couple A/C cycles, far faster than the motor can get going thus partly the boost.

These Hard start caps. are fairly common in the RV world since many people have A/C s and want/ need to run them on a Honda/Yamaha 2000 W generator. That Hard start unit can make the difference between a startup or a tripped C.B. and a no start.

The SOFT START is an electronic control that actually that controls the voltage from a lower point to the motor ramping up the voltage to speed up the motor over a bit of time avoiding the high inrush current so avoiding the tripped C.B.. There are a couple different means of modifying the voltage the motor sees. Sounds like these may be gaining more favour in the RV world.

The Hard START caps are usually inexpensive for most small A/C, $75 or thereabouts and can often be user installed even if you don't know a lot. Often/usually can simply replace the existing capacitor in the original mounting spot. Be carefull about discharging the existing cap. as they can hold a dangerous voltage for a long period of time. Of course they won't always work.

The SOFT STARTS are much more money, or at least used to be when I played with similar, and are more involved to install. Larger also ,so may not fit in the A/C unit but need to be mounted elsewhere but they are effective.

There was a previous thread about this which I did not bookmark and the poster went with a SOFT START for good reasons. You might contact him with a PM through this site.

Found it:
Soft Starting for air conditioners with Micro-Air

Good post.

VFDs (variable-frequency drives) are being touted as the in thing for electric motors on a couple of other forums I follow. From my understanding these are mainly for AC voltage motors. They can be over the top expensive.
What a pain in the transom.

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