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On 9/1/15 3:25 PM, wt5y wrote:
I'm at the point I need to add some motor run caps, I'm thinking the same that go on your ac units in the 40-50uf 330-440v variety unless someone has a better sugestion. Looks like I will need around 150uf per transformer I have 3 12/60 NST. Biggest question is do I run all 9 parallel or run about 3 strings of 3 to each? Would before or after the EMI filters make a difference.
Blowing 20 amp fuses on variac, don't have a clamp meter and my dmm is only good to 10 amps inline. I was going to add some and then start measuring the current?
John Cooper
I'm not sure that PFC will help. All PFC does is change the phase of
the current relative to the voltage. It won't reduce the current.
If you're popping the fuse on initial power up, what you're seeing is
the magnetization current for the transformers (inrush current), if you
happen to turn it on at the wrong point in the sine wave. (e.g. it's
that "thump" when you apply power).
The inrush can be as big as 10 times the normal current.
How about changing to a slow blow fuse or a circuit breaker with the
appropriate timeconstant.
You could also rig up some sort of resistor in series that gets shorted
soft start.
Each of your 12/60s is 6 amps full load current, so you're running
pretty close to 20 amps normally. Something like 5-10 ohms in series
would limit the current.