I need to make sure understand, since I am about to wire things together.
I have a 7.5hp idler motor for my soon-to-be-built RPC. My questions concern the run cappacitors
Question 1: When sizing the run caps to help balance the 3rd leg, my calcualtions show I need between 90 and 120 mF. Does that mean I need that value per leg or total. For instance, I have 2, 50mF run caps and plan to put one between L1-L3 and the other between L2-L3. Is this correct that it will give me the 100mF I need, Or do I need 100mF on each leg?
Question 2: My run caps are duel run 50/5mF. Where to plug wires? From L1 to Com on cap, out HERM on Cap. to L3?
Hi Investigator,
(all dependent on load and service voltage!!!)
Answer:1- you will have 2 different capacitor values when balancing a RPC.
phases A and B will be supplied voltage (for this purpose) their running voltage is 240vac between poles
phases A and C will have one supplied leg and one generated leg, their running voltage may be as low as 200vac between poles
phases B and C will have a generated leg and a supplied leg, their running voltage may be around 226vac between poles
if you were to treat phases A-C, exactly like Phases B-C, you would throw the motor back out of balance by application of too much capacitance on the B-C phase that may only require 30 or 40 mF of balancing capacitance.
phases A-C in this scenario would require the most capacitance maybe as much as 80 or 100 mF (all dependent on load and service voltage and rotation!!!)
Answer 2: when using air conditioning dual capacitors,
Com will get the supplied leg, the Herm terminal will connect to the generated leg.
the other terminal on the dual cap is 5mF, that's normally for the Air conditioner's fan- watch out it can still bite you even though it may not be connected.
please be careful when handling capacitors, discharge them before handling them- it could save your life.