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#1
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Need some electrical know-how
I have a very old table saw (runs off a pulley) that won't start
unless I give the pulley wheel a gentle spin just as I turn on the switch to the saw. I'd like not to have to start the saw this way (for obvious reasons), but don't know enough about electrical motors, capacitors, centrifugal switches, etc. to know how to fix this problem. Can anyone out there help me? Thanks. Lynn Willis |
#2
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Need some electrical know-how
On Mon, 11 Feb 2008 14:20:05 -0800 (PST), "
wrote: I have a very old table saw (runs off a pulley) that won't start unless I give the pulley wheel a gentle spin just as I turn on the switch to the saw. I'd like not to have to start the saw this way (for obvious reasons), but don't know enough about electrical motors, capacitors, centrifugal switches, etc. to know how to fix this problem. Can anyone out there help me? Thanks. Lynn Willis Sounds like the bushings of the armature of the motor may be worn out, and in need of replacement or some kind of lubrication. In the alternative, it might be that the armature brushes are worn, and their contact surface on the armature may be in need of cleaning. However, I am no motor expert, so you may want to run these possibilities by a professional. |
#3
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Need some electrical know-how
wrote in message ... I have a very old table saw (runs off a pulley) that won't start unless I give the pulley wheel a gentle spin just as I turn on the switch to the saw. I'd like not to have to start the saw this way (for obvious reasons), but don't know enough about electrical motors, capacitors, centrifugal switches, etc. to know how to fix this problem. Can anyone out there help me? If it is a capacitor-start motor, there is a good chance that the capacitor is bad. Also, table saws load up some motors with dust and cause the centrifugal starting switch to fail. |
#4
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Need some electrical know-how
If the motor case has a lump on the outside it is a capacitor
housing. Capacitors are fairly inexpensive and easy to change. You will need to open up the "lump", take the capacitor along with you. It will usually have 2 leads of the same color attached to the capacitor, it does not matter which one goes where - be very aware that capacitors can have a large dose of electricity stored up, don't be the path. If the motor has two lumps it has both a start capacitor and a run capacitor. If the motor doesn't have a lump, it is probably centrifugal switched to bypass the start windings. You would need to open the end bell with the weights. About all you could do would be to clean up any gummy residue that may be preventing the contacts coming back in to engage the start windings. It would probably help to tell the brand name. Virtually all tablesaws have pulleys with the exception of the newer, cheap direct drives. Your motor will have a plate telling the Volts, Amps, Horsepower, This information would also help. -- ______________________________ Keep the whole world singing . . . . DanG (remove the sevens) wrote in message ... I have a very old table saw (runs off a pulley) that won't start unless I give the pulley wheel a gentle spin just as I turn on the switch to the saw. I'd like not to have to start the saw this way (for obvious reasons), but don't know enough about electrical motors, capacitors, centrifugal switches, etc. to know how to fix this problem. Can anyone out there help me? Thanks. Lynn Willis |
#5
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Need some electrical know-how
" writes:
I have a very old table saw (runs off a pulley) that won't start unless I give the pulley wheel a gentle spin just as I turn on the switch to the saw. I'd like not to have to start the saw this way (for obvious reasons), but don't know enough about electrical motors, capacitors, centrifugal switches, etc. to know how to fix this problem. Can anyone out there help me? Other people have already given you a bunch of good advice about how to fix the motor. I thought I'd try to explain *why* it behaves this way: A single-phase induction motor with only one energized winding will not start rotating on its own. If you give it a push in *either* direction by hand, it will then accelerate to speed and continue running in the direction you started it. But it won't start. To avoid the inconvenience of manual starting, all single-phase motors have an additional winding of some sort. The second winding is mechanically rotated from the main winding, and it's fed with current that is somehow shifted in phase relative to the main winding. This creates an effectively rotating magnetic field, which makes the motor always start in one direction. Anything that prevents this second winding from getting power will also prevent the motor from starting on its own. The simplest design mechanically is the split-phase motor. A centrifugal switch is supposed to apply power to the second winding when the motor is stopped, but disconnect before it reaches full speed. Switch contacts can get burned, or the switch just wears out. A capacitor-start motor uses a capacitor in series with the second winding, again with a switch that opens when the motor reaches full speed. The switch can be bad, or the capacitor can be bad as well. A capacitor-run motor keeps the capacitor and the second winding connected all the time. Here, the second winding both provides reliable starting and more running torque. Again, a bad capacitor means it won't start. Dave |
#6
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Need some electrical know-how
Wow! Thanks to you all for the advice, and special thanks to Dave
Martindale for explaining the business with the two coils and the centrifugal switch. It was all very helpful. I'm hesitant to disassemble the motor to try to find the centrifugal switch -- I have a bad history with such things -- but I'm guessing that it's on one side or another of the motor, so I'll try blowing some high-pressure air in there to chase the sawdust away from the contacts. If that doesn't work, it's off to the motor shop we'll go. Thanks again for all the help. Lynn Willis Indianapolis/San Diego (winters) |
#7
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Need some electrical know-how
I also think it's the capacitor.
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#8
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Need some electrical know-how
Thanks for all the help. I took the thing to the shop, they replaced
the capacitor, blew out all the accumulated sawdust and cleaned the contacts of the stationary switch (whatever that is). The thing now runs like new. This motor has ventilation ports in the sides that suck in sawdust so I've put a deflector over the motor to keep that to a minimum. Maybe this thing's good now for another 50 years. Thanks again, folks. Lynn Willis |
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