Picked up an older Craftsman drill press that runs on 110VAC. Stand and everything looks great. Problem is the motor doesn't run, just hear a click when you turn it on. I got it for $20. Friday, I took the belt off the motor and it spins freely and it will run with help, I spin it then turn it on. Today, Sunday, I went out and pulled the motor off, and split the case. There is a capacitor for starting the motor. No obvious signs of cap being bad, not bulging or smelly, no deformation. Now, how do I check this cap with a volt/ohm meter? I know I could just get another motor with the same rating as the one on there, but I like to tinker and if the cap is bad, why not just replace that? Thanks.
electrical motor wizards
- Thread starter Louie70Dart
- Start date
-
67Dart273
Well-Known Member
Could be either the cap or the start switch. Some multimeters have a cap checking feature and some do not.
You cannot really check a cap with a "straight" multimeter without a specialized cap checking feature, but you CAN get 'an idea.' This was easier, "back in the day" with analog meters, which used higher voltage batteries for the higher resistance ranges.
Start by trying you your meter on X100. If the cap has a bleeder resistor across the terminals, you'll have to disconnect it.
Hook up the leads, the meter (if it has an analog bar scale) should start out low and go up high in resistance. The higher the capacity of the cap, the longer this takes. If it shoots up instantly, it might be an "open" cap. This is hard to describe without having some caps to try, of similar value
If it "hangs" at a fairly low reading, it is leaky or shorted.
You might be able to manually manipulate the centrifugal start switch and check the contacts with your meter.
You cannot really check a cap with a "straight" multimeter without a specialized cap checking feature, but you CAN get 'an idea.' This was easier, "back in the day" with analog meters, which used higher voltage batteries for the higher resistance ranges.
Start by trying you your meter on X100. If the cap has a bleeder resistor across the terminals, you'll have to disconnect it.
Hook up the leads, the meter (if it has an analog bar scale) should start out low and go up high in resistance. The higher the capacity of the cap, the longer this takes. If it shoots up instantly, it might be an "open" cap. This is hard to describe without having some caps to try, of similar value
If it "hangs" at a fairly low reading, it is leaky or shorted.
You might be able to manually manipulate the centrifugal start switch and check the contacts with your meter.
The cheapo meter I have will read microfarads, 2 ranges, 200 and 2k. nothing happens on the meter, stays at zero. When I check resistance, that is where I get the increasing resistance. Cap is rated at 378-454 MFD
Came from either radio shack or hft. not sure. Not the greatest cause I won't need a real good one for what I do.
67Dart273
Well-Known Member
Poo, LOL. Turns out there is different versions of those. Did I misunderstand? Is there actually a cap check scale(s)? A better photo would help
Found these, neither has a cap scale Best you can do is use the 20K or 200K resistance scale
Found these, neither has a cap scale Best you can do is use the 20K or 200K resistance scale
DesertRat
Leading edge boomer
JMHO but change the capacitor and be done with it. Could have a centrifugal crossover from start to run but if it wont start it is most likely the start capacitor. Good luck!
:coffee2:
:coffee2:
67Dart273
Well-Known Member
In some areas caps ain't all that easy to get, "quick." It could just as easily be the switch.
Centrifugal crossover. I think it has that. Here is the picture of the meter. HFT, basic freebie. I don't plan on getting to the moon with this. LOL Only difference is mine is yellow and nothing but digital multimeter on it.
I checked the switch, 0.00 continuity, so that checks. Not the contacts, maybe they are bad? Looked online, Sears replacement motor is over $300.....LOL. I can get a cap through grainger. MFD is 378-454, grainger has one 378-455. Around $12.00 and looks to be in stock. But if that isn't the problem, then I spent money I didn't need to. The search continues.....LOL
Here it is. Pic of model and s/n.
Upon further research LouieDart,
Found the series,
same motor used in drill press/band saw/table saw/ planer...
What I could not find was an application specific wiring diagram...
Could be...
Cap start,
Repulsion start,
Resistance start,
Split cap start....
All the above 'classes' have been incorporated into 'Sears builds'...
I'm with DesetRat on this one...
" JMHO but change the capacitor and be done with it."
My reasoning is simple, this is a low end machine, = low end cap start controls
Post the repair validation !!! inquiring minds want to know !
Found the series,
same motor used in drill press/band saw/table saw/ planer...
What I could not find was an application specific wiring diagram...
Could be...
Cap start,
Repulsion start,
Resistance start,
Split cap start....
All the above 'classes' have been incorporated into 'Sears builds'...
I'm with DesetRat on this one...
" JMHO but change the capacitor and be done with it."
My reasoning is simple, this is a low end machine, = low end cap start controls
Post the repair validation !!! inquiring minds want to know !
Looking at replacement parts, things are limited at best. Not many available.
If you're not in a hurry there is a good chance that I can come up with that cap, will drop it in the mail for free, let me know. Nothing wrong with shotgunning here, can't make it worse. BTW 67Dart273 it's so cool hearing someone who knows about old school troubleshooting!!!
Old trick charge the cap with a 9v battery for a few seconds then see if it sparks when grounded out or check it with a volt meter and see a dc spike.
67Dart273
Well-Known Member
Louie, start caps are generic, pretty much. Just get at least the voltage rating, and "in the range" of capacitance.
Here is an excerpt from Mouser Electronics. I've ordered from them, last time about a year ago. They are VERY easy to deal with, and don't have a minimum order
www.mouser.com/ds/2/88/PSU-24058.pdf
You can also check out I would guess Ebay Graingers, and if you are in any kind of decent town, a refrigeration / HVAC supply if they will sell you retail. Johnstone Supply, but last I knew, "wholesale only."
You can check the resistance on x100 and let the meter slowly raise on the scale and then reverse the leads and see if it pegs in the other direction quickly. This is not a true test but will give you an idea if it doesn't respond. The meter actiually puts a charge into the capacitor and then when you reverse the meter leads it dsicharges. If bthe motor will run after you turn the shaft quickly to get it started -it's either the capacitor or the start winding in the motor..
Yeah, graingers is where I find the close replacement. And the resistance slowly climbed the one way when I checked resistance, like less that 30 seconds? Shoot, I have an old dish washer I'm not using, it runs. Maybe look to see if that motor is close to what is in the drill press? But not until I get my deck back together. Thanks everyone!
Here's a 'how to' on debugging startup caps with either an analog or digital multimeter:
http://www.wikihow.com/Check-a-Start-Capacitor
http://www.wikihow.com/Check-a-Start-Capacitor
-
