Jet capacitor burned up starting or running one?

[Rob Stegmann]

So I was doing a project turning down some 3” pvc pipe and smelled something strange, thought it was the pipe. Came back about 30 minutes later to do a little more and the smell got real bad and I noticed the motor was smoking, unplugged it and lucky I didn’t burn up the house.

My 1ho motor has two on it, the bottom black one is fried. Is it a starting or running motor capacitor and any idea best place to buy the replacement one? I just found thus site and appreciate any help. Thanks!

Motor is not a variable speed one.

[John K Jordan]

You didn't say what model lathe. You could take the capacitor to a motor shop or a place that specializes in industrial electrical components and they might be able to match it up.

You don't have to use an exact replacement as long as the rating meets the original. The problem might be finding one that fits in the same space as the original since capacitors are often housed in a steel welt on the side of the motor. Some info on start vs run: https://en.wikipedia.org/wiki/Motor_capacitor

The capacitor on one of my Jet mini lathes failed when on loan to a kids turning class. The lathe would run (in either direction!) when I turned it on then started it spinning by hand. (That lathe only had one capacitor). The problem I had was I could not find a capacitor locally that had the right rating and was small enough to fit in the housing. Some people have made a way to mount a physically larger capacitor.

You might call Jet. They should carry an exact replacement that will fit in the space. I bought a capacitor for the Jet mini from them. It came quickly.

The problem might be the cost. For the mini lathe Jet charged at least 5 times what an an equivalent capacitor should cost. I grumbled and bought it anyway. As a comparison, a capacitor also failed on my 18" Rikon bandsaw and Rikon charged a reasonable price. Shame on Jet.

JKJ

[Pat Scott]

Your capacitor is burned pretty bad! Can you still read the label on it? Hopefully the label is on the bottom, you might have to remove the cap to see. There are numbers on the label that you can Google to find a replacement. If not I would call Jet as John suggested and either buy one from them or see if the can give you the specs and ratings so you can buy one elsewhere. A local motor repair shop might have caps (if you know the specs).

[Paul F Franklin]

You can just make out the values in your second pic. If I read it correctly, it's 25 uf (microfarads) at 250 VAC. All you need to do is find a 25 uf cap rated at 250 VAC or higher that will fit in the space. You can go higher in voltage rating but stick to the capacitance value (25 uf).

[eta:] it is most likely the run cap, so pick a cap rated for motor run use. Mcmaster is one source, digikey another. Often motor caps have a range of capacitance values; pick one where 25 is in about the middle of the range.

[John K Jordan]

You can just make out the values in your second pic. If I read it correctly, it's 25 uf (microfarads) at 250 VAC. All you need to do is find a 25 uf cap rated at 250 VAC or higher that will fit in the space. You can go higher in voltage rating but stick to the capacitance value (25 uf).

If not familiar with electronic components, just be sure it is a non-polarized capacitor intended for motors, not polarized like an electrolytic capacitor commonly used in electronics. A polarized capacitor, with an anode and cathode, will indicate which conductor is positive and which is negative. In my experience the voltage is usually not marked DC. An electrolytic capacitor may explode if used in an AC circuit.

[Rob Stegmann]

Thanks for info. The other cap is a 125v/type 200mfd so I guess that is the start cap. I’m searching for the run one to replace. Any reason why this one burned up so bad? Lathe ran with it burning so I guess motor is not bad, I hope! Need to work on my project so hope to get a new part locally tomorrow.

[Paul F Franklin]

The materials inside dry out due to age and heat and eventually they fail. Especially run caps since current is flowing through them whenever the motor is running. Start caps only see current flow during motor startup. Except when the start switch fails to open; then the start cap will fail quickly.

A short in the motor windings can cause a cap to fail quickly as well, but that is not common.

[Alex Zeller]

It very well could be your starting cap and the switch stuck on. When starting a motor there's a switch inside the motor that will turn off once the motor is spinning. If it doesn't turn on the motor will not start spinning. If it doesn't turn off the starter cap will eventually burn up as it's only designed to be used for a short period of time. If the switch is bad you will most likely burn up your replacement cap.

[Paul F Franklin]

If one cap is 25 uf and the other is 200 uf, the 25 uf is the run cap.

[Robert D Evans]

I've found a good selection of capacitors on Amazon and Ebay. I've bought them for my drill press and AC units. They seem to all be made in either Mexico and China. You have your choice.

[Pat Scott]

Any reason why this one burned up so bad? Lathe ran with it burning so I guess motor is not bad, I hope!

There are others here that know way more about this stuff than I do. I had to replace both caps on my bandsaw a month ago. I was using the saw when I heard a pop. The saw kept running so I figured something vibrated off my outfeed table and fell on the floor. Later when I went to use the saw again it would turn on for 1 second, pop the breaker, and shut off. That's when I looked at the caps and saw the case(s) was cracked. I know enough to know that's not a good thing! A little Googling showed that the symptom I had is typical of a bad start cap. But since the run cap case was cracked also I replaced them both.

In talking with Jesse at Eagle Tools (where I bought my Agazanni), I was running my 220v saw on a 20A circuit when I should have been running on a 30A minimum with 40A better. He was surprised my saw ran as long as it did on such an underpowered circuit. My previous 220v bandsaw with 1.5hp motor worked fine on a 20A circuit, when I got my new saw with 4.8hp motor I didn't even think about upgrading circuits. The funny part was I had a 30A plug on the power cord but had it plugged into a 20A circuit. I immediately upgraded the circuit breaker and wire to 30A to get me up and running again and plan to upgrade to 40A soon.

You didn't say if your saw is 115v or 220v, but make sure your circuit is big enough to support it. The owners manual should say what size circuit is recommended.