BrianMartin
Does anyone use anything other than the hyper engineering model? I ask because being in Canada, these units are very expensive after shipping and exchange, let alone labour for installing it.. Expensive to the point that it really makes more sense to upsize the generator to handle an AC for example, instead of selling the customer a soft starter. Any other options out there?
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murphy
I use this one on my 3 ton air conditioner.  It was originally on a 7 kW generator but is now on a 20 kW generator.

http://www.gavazzionline.com/pdf/RSBS_HP.pdf

Make sure the capacitor(s) in the compressor cabinet haven't failed.  I check mine yearly.  I had a 45 mfd capacitor drop to 0.7 mfd.  That greatly increased the start current.
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Birken Vogt
So what exactly does the soft starter do?  I read that paper but it is not 100% clear. 

Just PWM to limit inrush current in a controlled manner?
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murphy
It only has to limit the current until the motor starts turning which creates the back EMF that takes over limiting the current down to the run value.  That only takes about 500 milliseconds.
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Geoff Z
LRA is typically 6 times RLA. LRA is experienced every time the motor starts from rest. The soft start brings the motor to a full run with more of a "ramp up" or gradual start. A benefit for the motor and generator. It takes about 8-10 starts for the soft start to learn the characteristics of the motor and see maximum result. Murphy is giving the best electrical explanation which I don't profess to understand myself. Mine is the average Joe I can remember this explanation. I just know we see impressive results with them. Allows many people to consider a smaller generator than they otherwise might need.
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Birken Vogt
But how exactly does it limit the current?  SCRs inside?
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murphy
This link will answer your question but it may also give you a headache.

https://electricalsolution.wordpress.com/2011/07/26/soft-starter-working-principle/
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Geoff Z

This principle is that by adjusting the voltage applied to the motor during starting, the current and torque characteristics can be limited and controlled.

Thanks Murphy. This statement makes a much better explanation than my attempt. I don’t have enough room in my brain for the rest. 

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ReedN
I bought one to put on my 4 ton heat pump before I installed my 22kW generator.  I love it.  Technically it wasn't necessary because the 22kW can handle the start current, but I feel better now there is less chance that the turn on spike does something crazy if I'm using the generator.  It has the added benefit that my lights don't dim when the heat pump starts (on city power) like it did before.

Most people could install themselves.  I was a little unsure at first, but I just drew out the starting configuration circuit and I drew out what they were having me do with each step of the changes.  Once I understood the changes they intended it was fairly easy to implement it following the step by step instructions.
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Brian Baughman
The HVAC soft starters are voltage ramped soft starters, meaning the the device slowly ramps up the voltage for motor starting.  This prevents a massive voltage dip when the motor starts and reduces the amount of current required to start the motor.  This also reduces the mechanical torque during motor starting.
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