Members W. M. Hellinger Posted December 7, 2008 Members Share Posted December 7, 2008 How about rigging up a starter motor for your compessor motor? I've thought about doing that on my compressor.When I was a kid, my folks had a Lawnboy lawnmower... equipped with a 2-cycle motor that was really tired. I was charged with keeping the lawn mowed. Our family also had an old un-powered reel push mower. I was faced with either making the Lawnboy start or use the reel mower. The Lawnboy's motor was so wore-out it couldn't be started with the rope pull unless it was good and warmed up... and even then it was iffy. So I rigged up a V-belt pully on top of the Lawnboy's motor and used a electric motor to start the 2 cycle gas motor. Link to comment Share on other sites More sharing options...
Members xmlguy Posted December 7, 2008 Members Share Posted December 7, 2008 The line voltage at the motor stays steady @ 125v during start-up? Electric compressors have such a high startup current, which is why they have the capacitor in the first place as a reserve supply, that tracing the voltage drops throughout the circuit during startup seems imperative to find the fault. There should be a voltage drop somewhere with the motor at its full stall current, the question should be where is the drop occuring and how much is it? At least that's my line of thought. Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted December 7, 2008 Members Share Posted December 7, 2008 Electric compressors have such a high startup current, which is why they have the capacitor in the first place as a reserve supply, that tracing the voltage drops throughout the circuit during startup seems imperative to find the fault. There should be a voltage drop somewhere with the motor at its full stall current, the question should be where is the drop occuring and how much is it? At least that's my line of thought. That's pretty much the question I was begging. An 18ga. line has MOL the same unloaded voltage as a 4ga. line. A really tired breaker has the same voltage output when it's on as a new breaker. Link to comment Share on other sites More sharing options...
Members srp72ee Posted December 8, 2008 Members Share Posted December 8, 2008 If your compressor is doing this "whether the tank is full or empty", sound like a starting capicitor, The price of starting caps range from $4.50 to $20 for the "typical" single phase motors from Grainger. Many local Heating/Cooling/Plumbing places have capacitors on the shelf as well. A motor this size is not worth taking to a repair shop... If the caps are 20ish years old... they're tired... Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 8, 2008 Members Share Posted December 8, 2008 The starting cap induces a phase shifted current in the starting winding which is how the motor starts. It can only last for a short duration or the winding will fail. That's what the internal centrifugal switch is for. Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted December 8, 2008 Members Share Posted December 8, 2008 The starting cap induces a phase shifted current in the starting winding which is how the motor starts. It can only last for a short duration or the winding will fail. That's what the internal centrifugal switch is for. yes... and in your experience, have you found, as I have, that a single phase motor (like that on an air compressor) has almost no hope of starting under any kind of load without a functional starting winding system? IME: without a functional starting winding system, they usually just sit there and humm... loudly for a few seconds till the breaker trips. Link to comment Share on other sites More sharing options...
Members Gary in NJ Posted December 8, 2008 Author Members Share Posted December 8, 2008 IME: without a functional starting winding system, they usually just sit there and humm... loudly for a few seconds till the breaker trips. Bingo! That's what happens. So here's my to-do list: 1) Replace starting cap 2) Replace compressor oil 3) Replace compressor air filter I'll let you all know how this works out. Thanks for the great advice. At one point I had the compressor wired for 220VAC. I may put a 220 outlet in my garage just for this compressor. Link to comment Share on other sites More sharing options...
Members mtmra70 Posted December 8, 2008 Members Share Posted December 8, 2008 Just when I thought certain aspects of pro-audio were confusing, they create this thread to throw a curve ball at me.......my head hurts..... Link to comment Share on other sites More sharing options...
Members Ear Abuser Posted December 9, 2008 Members Share Posted December 9, 2008 yes... and in your experience, have you found, as I have, that a single phase motor (like that on an air compressor) has almost no hope of starting under any kind of load without a functional starting winding system? IME: without a functional starting winding system, they usually just sit there and humm... loudly for a few seconds till the breaker trips. +1- A three phase motor doesn't need a starting capacitor becuase the three phase voltage creates a rotating magnetic field which drags the rotor around with it. A single phase motor uses the capacitor to create a bit of phase shift in the voltage fed to the starting coil. This creates enough of a rotating magnetic field get the motor going, then the starting winding is switched out. I was at a friends house once and he said "my furnace won't run, it just hums then the breaker trips". I opened the blower compartment, gave the blower wheel a push and off it went. He was amazed. Just needed a new cap. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 9, 2008 Members Share Posted December 9, 2008 Just when I thought certain aspects of pro-audio were confusing, they create this thread to throw a curve ball at me.......my head hurts..... A speaker is just like a motor. Same principle. Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted December 10, 2008 Members Share Posted December 10, 2008 A speaker is just like a motor. Same principle. One big difference is that underpowering an AC electric motor can damage the motor, but underpowering a speaker doesn't in it'self damage the speaker. Link to comment Share on other sites More sharing options...
Members mtmra70 Posted December 10, 2008 Members Share Posted December 10, 2008 A speaker is just like a motor. Same principle. And like a speaker, it is simple. Its all the other stuff that gets more complicated...lol Link to comment Share on other sites More sharing options...
Members pro1-54 Posted December 10, 2008 Members Share Posted December 10, 2008 A speaker is just like a motor. Same principle.Tell that to NASA Link to comment Share on other sites More sharing options...
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