06-04-2012, 09:02 AM
Hi,
The following links might help a bit Rob;
http://community.ashworthcollege.edu/gro...g-problems
http://www.allaboutcircuits.com/vol_2/chpt_13/9.html
I'm having similar problems with the motor on my belt grinder; it won't self start but a tug on the drive belt gets it running.
I've already stripped it and cleaned the centrifugal switch but the problem remains. I think your motor will also have a centrifugal switch and this switch remains closed when the motor is at rest but once power is applied current flows through it to activate the "Start winding". The "Run" winding is permanently connected so at power up both windings are energized but once the motor comes up to speed the centrifugal switch clicks open dropping the start winding off line but the run winding remains energized hence the motor runs as normal.
I think it possible both our motors are suffering from open circuit start windings and a resistance check should confirm this. The start and run windings will have just two connections each; one to each end of the coil. It is easy to check continuity as each winding is identified a reading will be obtained; it's just a matter of taking a reading across the wires but all the wires will need disconnecting first to be sure. If the windings are good there should be a continuity reading across two pairs; if only one reading can be obtained across one pair then it's highly likely the start winding is open circuit and if the problem isn't something simple like a loose connection throw the motor away. Take a note of connections before disconnecting.
Before retirement I worked at Brook Motors here in Huddersfield for 24 years and must be one of the few guys in the country to physically handle well in excess of a million motors. These motors ranged from fractional horse power that could be lifted with one hand to motors weighing more than three tons. I was in logistics and at the height of production we were a central hub for our six factories. I lived and breathed electric motors and I couldn't switch off ; being in logistics we had to get all the motors out to our customers; the job was highly stressful and when I finally came down with shingles I saw the writing on the wall; get out before it kills me.
During all this time it was only natural that I picked up information and by being inquisitive I can now take a three phase motor; disconnect all six leads and re-connect in either Star or Delta by taking simple continuity checks. My big Startrite combination woodworking machine has three 3 phase 3HP motors fitted but with a bit of re-wiring and a pair of capacitors this machine has been running from single phase 240V for over ten years. One pair of capacitors runs all three motors as the motors are in-dependably switched allowing only one motor at a time to run.
I find such projects to be highly interesting but of course doing such work can be lethal to a novice so I'm never happy to divulge the techniques involved.
Kind regards, Col.
The following links might help a bit Rob;
http://community.ashworthcollege.edu/gro...g-problems
http://www.allaboutcircuits.com/vol_2/chpt_13/9.html
I'm having similar problems with the motor on my belt grinder; it won't self start but a tug on the drive belt gets it running.
I've already stripped it and cleaned the centrifugal switch but the problem remains. I think your motor will also have a centrifugal switch and this switch remains closed when the motor is at rest but once power is applied current flows through it to activate the "Start winding". The "Run" winding is permanently connected so at power up both windings are energized but once the motor comes up to speed the centrifugal switch clicks open dropping the start winding off line but the run winding remains energized hence the motor runs as normal.
I think it possible both our motors are suffering from open circuit start windings and a resistance check should confirm this. The start and run windings will have just two connections each; one to each end of the coil. It is easy to check continuity as each winding is identified a reading will be obtained; it's just a matter of taking a reading across the wires but all the wires will need disconnecting first to be sure. If the windings are good there should be a continuity reading across two pairs; if only one reading can be obtained across one pair then it's highly likely the start winding is open circuit and if the problem isn't something simple like a loose connection throw the motor away. Take a note of connections before disconnecting.
Before retirement I worked at Brook Motors here in Huddersfield for 24 years and must be one of the few guys in the country to physically handle well in excess of a million motors. These motors ranged from fractional horse power that could be lifted with one hand to motors weighing more than three tons. I was in logistics and at the height of production we were a central hub for our six factories. I lived and breathed electric motors and I couldn't switch off ; being in logistics we had to get all the motors out to our customers; the job was highly stressful and when I finally came down with shingles I saw the writing on the wall; get out before it kills me.
During all this time it was only natural that I picked up information and by being inquisitive I can now take a three phase motor; disconnect all six leads and re-connect in either Star or Delta by taking simple continuity checks. My big Startrite combination woodworking machine has three 3 phase 3HP motors fitted but with a bit of re-wiring and a pair of capacitors this machine has been running from single phase 240V for over ten years. One pair of capacitors runs all three motors as the motors are in-dependably switched allowing only one motor at a time to run.
I find such projects to be highly interesting but of course doing such work can be lethal to a novice so I'm never happy to divulge the techniques involved.
Kind regards, Col.
Happiness is a wreck of a cabinet to restore.
