Lathe Capacitor Burnout

wdteipen · Post by **wdteipen** » Sun Mar 29, 2009 6:13 am

Today my Delta Midi Lathe motor run capacitor burned out. I went online to shop for a new one and low and behold the exact part is "obsolete" and no longer available. A replacement can apparently be purchased from Delta for $40 plus S&H which is ridiculous. The specs for the capacitor is 30mf, 300 VAC, 50/60 Hz, max. temp 70 deg. I've searched online for a replacement and can only find capacitors with a 330 or 370 VAC rating. Can either of those be used without ill effects? Any advice on this repair would be greatly appreciated. A better online source would be great too. I looked for a source for oil filled capacitors and couldn't find a good one.

Post by **KurtHuhn** » Sun Mar 29, 2009 9:46 am

Either of the two capacitors you found should work. The important number is actually the charge capacity, or the uF rating. The voltage spec is only the maximum voltage that the capacitor can handle being charged with, not the amount that it delivers to the circuit. Since you're connecting it to a 120V source, it will only deliver 120V to the motor circuit.

You don't need an oil filled capacitor for this application. A simple aluminum electrolytic or film cap will work just fine, and will be much less expensive. Mouser electronics (www.mouser.com) has these in stock at anywhere from $9 to $30+. Use the search term "AC motor run capacitor 30uf" and you'll get a decent number of hits. Just be sure that you get the right package size - some of these can be downright huge, and won't fit in the capacitor cover on the motor.

Frank · Post by **Frank** » Sun Mar 29, 2009 2:16 pm

The replacement cap doesn't have to be exactly 300 VAC nor exactly 30uF. "In the ballpark" will still work fine. Follow Kurt's advice.

staffwalker · Post by **staffwalker** » Sun Mar 29, 2009 3:44 pm

Check <www.surpluscenter.com> run a search for capacitors. They have dozens of 30 mfd cap. Just look for 30 mfd, don't worry about the voltage as long as it is 300v or higher. You can buy new ones here at 4 to 6 bucks, used ones at 2 to 4 bucks. I've ordered from them before with fast no problem service.
bob gilbert

wdteipen · Post by **wdteipen** » Sun Mar 29, 2009 6:42 pm

Perfect! Thanks for the info fellas.

Post by **KurtHuhn** » Sun Mar 29, 2009 7:59 pm

staffwalker wrote:Check <www.surpluscenter.com> run a search for capacitors.

I love that place! I get all kinds of bits and pieces from them.

Frank · Post by **Frank** » Sun Mar 29, 2009 9:46 pm

KurtHuhn wrote:
staffwalker wrote:Check <www.surpluscenter.com> run a search for capacitors.
I love that place! I get all kinds of bits and pieces from them.

Gads, I think I bought a used oscilloscope from them almost a couple of decades ago!

staffwalker · Post by **staffwalker** » Mon Mar 30, 2009 3:38 am

I bought two new 12 to 130VDC motors with inverters so I can run them on AC from SW, with shipping the total bill came to less than 30 bucks. Now I need a cheap controller so I can play with them. They used to have one for 20-30 bucks but seem to be out at the moment. bob

Anvil · Post by **Anvil** » Mon Mar 30, 2009 8:14 am

You know what's kind of funny? I hear you guys talking about this place all the time on this forum and so I looked them up. Lo and behold! They are right here in town! Now the only thing that does for me is save on shipping but I still thought it was funny.

wdteipen · Post by **wdteipen** » Sun Apr 05, 2009 1:02 am

Okay, so I replaced the run capacitor and flipped the switch and all I got was a hum. I gave the headstock a spin and......nothing. Is the motor fried?

Post by **KurtHuhn** » Sun Apr 05, 2009 10:10 am

That's really tough to tell without sticking a DMM on the motor and giving it a once-over. Did you get a cap as close to the old specs as you could find? AND, I don't know if this affects your or not, but "mf" does not equal "µf" - even though some places will notate it as such. BEWARE!

mf = milifarad
µf = microfarad

A mf is significantly more than a µf, but some supply houses have a hard time finding the "µ" symbol on their keyboard (Mac users, hit option option-m).

Again, I don't know if this is part of your problem or not, but I thought it was worth mentioning.

Now, it is possible that the motor IS burned out. This is unusual, but it happens, especially if the motor ever got really hot due to load or excessive voltage. When a motor is "burned out" that means that the thin layer of lacquer on the copper windings has deteriorated, and you're getting electron migration across the windings rather than through them - a short circuit, basically. There's no way to fix this yourself, you need to replace the motor or have it rewound.

wdteipen · Post by **wdteipen** » Sun Apr 05, 2009 7:38 pm

The motor did overheat when the capacitor started smoking and did sound a bit rough. I bought a run capacitor that is 30 millifarads and I noticed the original capacitor is 30 microfarads. Could be that you are right. How would I know the equivalent? Also, is a run capacitor the same as a motor start/ motor run capacitor? I purchased a run capacitor and I read somewhere that the Delta midi requires a start/run capacitor. I figured that if that was the case it would have at least started up when I gave it a spin. I researched replacing the motor and found that the Delta midi is discontinued and the motor cannot be ordered.

The good news is that I went out and bought a Rikon Mini and it's much nicer than the Delta. I'd still like to fix the Delta though. I suppose I could find a motor with the same or smaller dimensions or get the one I have fixed.