When sizing a buck boost transformer for a motor.
Do you size it per the Full Load Amps of the motor, or, to the size of the OCPD protecting the feeder to the Controller ?
size it to the amount of current you are boosting. In other words lets say you are boosting a 208 volt system to 230. That results in a ratio that results in a roughly a 10% boost in voltage. apply that same 10% to the 230 volt motor current and you then have the amount of current that is actually being boosted. Using a 5 hp single phase motor for instance. draws 28 at 230. 10% is 2.8 ampsx230 volts for a result of 644 va. I would use a 1 kva transformer for this.Anyhow this is the way I have always done it and it has worked very well for me. Done lots of small propane pump motors where 208 was all that was available and by the time you got to the end of the line 110 or more feet fron the source you would have 195 volts or so. I would then use this formulae to size my boost buck and worked just fine.
