Hi All,
First off, I'm a bumbler with little electronic theory and absolutely no electronic training whatsoever. Although I did almost get around to reading the owner's manual for my multimeter once. The only way I ever solve glitches in anything with wires, diodes, and what-not is by pathological single mindedness and a total aversion to spending the money for a new one. Mostly, it's the money thing. (Mostly.)
Anyway, to my ? I have 2 run capacitors, 1@50 µf and 1@60 µf wired in parallel (to produce 110 µf right?) from an AC hoist motor that hums but won't spin and isn't seized. My old standby test of charging then shorting the contacts with a screwdriver produces quite a pop from each one. But I have learned in my recent research that that just means they are holding some charge but not necessarily the right charge. Any other time I would run out and spend the $7 for a new start cap just to rule out the capacitor as the problem. But these are 2 high MFD and expensive run capacitors ~$40 each. No one local can test them and doing a resistance test doesn't tell me anymore than the screwdriver test. A guy in line behind me at the local electrical supply place told me a way that they can be tested with an amp meter.
He said that while connected to household current the amperage draw should be half the µf rating divided by 10. So, a 100 µf cap would be 100µf/2= 50 /10= 5 amps. Mine being 110 µf in parallel read 5.1-5.3 amps and individually draw 2.7 and 2.5. I tried and old 130 µf start cap and got a 6.6-6.7 reading. Seems like he was right BUT; I can find no other reference to this method anywhere. Is it just coincidence or does it work and no one else is sharing the secret? First of all, shouldn't voltage figure into the equation? Unless it does by the fact that all my caps were tested at ~123 volts with the 130 µf being rated at 240 and the 50 and 60 at 250, roughly 1/2 so the initial divide by 2?
Either way, assuming the caps are good, then checking the winding would be next. I've read and heard that if a high resistance is measured, the winding is bad. But, is resistance really a reliable way to check a motor winding? If the winding is shorted to itself, is the resistance really going to change much? If the problem is that the lacquer on the wire is broken down and turned the 1/2 mile of wire into a lump of copper, the current still has to pass through X no. of lbs. of copper so why would resistance across it increase significantly? I tried it anyway and got 1.4 Ω on the ccw (reverse) lead and 2X that, 2.8 Ω, on the cw (forward) lead. Doesn't sound like much resistance for so much wire but what do I know?
Any input would be appreciated.
First off, I'm a bumbler with little electronic theory and absolutely no electronic training whatsoever. Although I did almost get around to reading the owner's manual for my multimeter once. The only way I ever solve glitches in anything with wires, diodes, and what-not is by pathological single mindedness and a total aversion to spending the money for a new one. Mostly, it's the money thing. (Mostly.)
Anyway, to my ? I have 2 run capacitors, 1@50 µf and 1@60 µf wired in parallel (to produce 110 µf right?) from an AC hoist motor that hums but won't spin and isn't seized. My old standby test of charging then shorting the contacts with a screwdriver produces quite a pop from each one. But I have learned in my recent research that that just means they are holding some charge but not necessarily the right charge. Any other time I would run out and spend the $7 for a new start cap just to rule out the capacitor as the problem. But these are 2 high MFD and expensive run capacitors ~$40 each. No one local can test them and doing a resistance test doesn't tell me anymore than the screwdriver test. A guy in line behind me at the local electrical supply place told me a way that they can be tested with an amp meter.
He said that while connected to household current the amperage draw should be half the µf rating divided by 10. So, a 100 µf cap would be 100µf/2= 50 /10= 5 amps. Mine being 110 µf in parallel read 5.1-5.3 amps and individually draw 2.7 and 2.5. I tried and old 130 µf start cap and got a 6.6-6.7 reading. Seems like he was right BUT; I can find no other reference to this method anywhere. Is it just coincidence or does it work and no one else is sharing the secret? First of all, shouldn't voltage figure into the equation? Unless it does by the fact that all my caps were tested at ~123 volts with the 130 µf being rated at 240 and the 50 and 60 at 250, roughly 1/2 so the initial divide by 2?
Either way, assuming the caps are good, then checking the winding would be next. I've read and heard that if a high resistance is measured, the winding is bad. But, is resistance really a reliable way to check a motor winding? If the winding is shorted to itself, is the resistance really going to change much? If the problem is that the lacquer on the wire is broken down and turned the 1/2 mile of wire into a lump of copper, the current still has to pass through X no. of lbs. of copper so why would resistance across it increase significantly? I tried it anyway and got 1.4 Ω on the ccw (reverse) lead and 2X that, 2.8 Ω, on the cw (forward) lead. Doesn't sound like much resistance for so much wire but what do I know?
Any input would be appreciated.
