"Bob Swinney" wrote in message
news:bISOb.99680$8H.144430@attbi_s03...

Agreed! What is the function of the 400 ufd Cp? Is that the start
capacitor for the 25 HP (idler) motor? What about the "20 ufd Cs"? Are
they run capacitors? If so, they aren't nearly large enough for a 25 HP
idler and 10 HP load motor. Theory has it that run caps should be at
least
25 X 30 ufd or 750 ufd. Insufficient amount of run cap will give the
symptoms you mentioned, esp. when trying to run a loaded air compressor.


Woops, I made a typo on previous post. I should have said a 200uF Cs
capacitor.
(Cp is between L1 & L3, Cs is between L2 & L3, Cpf is between L1 & L2.)
I have 1800uF worth of start caps between L1 & L3 which I momentarily switch
on to start.

The voltages I measured with different caps are as follows:
Cp Cs V1-2 V1-3 V2-3
0 0 238 211 204
100 0 238 222 210
200 0 239 237 217
300 0 239 246 220
400 0 239 256 230
400 100 240 256 244
400 200 240 257 255
400 300 240 258 265
400 400 241 258 276
500 200 239 267 261
500 300 240 268 271
600 100 241 276 259
600 200 240 276 268
700 100 241 287 267

I didn't go with all 800uF on Cp as the V1-3 was getting pretty high.

With Cp of 700 and Cs of 100, the compressor currents at 150psi are I1=21A,
I2=29A, I3=30A. This is with the compressor starting with no pressure in the
tank. It still won't start at 135psi.

I can email anyone an excel file of this if the columns don't come out
right.

Thanks,
Jeff Borning