Motor start capacitors failing

[david brum]

Hi all

Maybe this is a curious coincidence, but I just had a 2nd start capacitor fail in a month. The first was on my 17" Shop Fox band saw. Today it was on my 8" Shop Fox parallelogram jointer. The band saw capacitor leaked goo all over. The jointer capacitor just got really hot and everything stopped. It tried to get the motor up to speed after cooling off, but no dice.

Does anybody have an insight about why these are failing? I'm not asking for a discussion about the evils of Asian machines, rather wondering if something in my electricity delivery might be to blame.

[Steve Juhasz]

Yes, it is because they are chinese made pieces of junk. I have a shop full of grizzly machines. Same factories as Shop Fox, just different color. Same chinese junk caps on my motors. My machines EAT capacitors. Some of them. At least 10 warranty calls for start caps.

However, there is a solution. The very first tech I spoke to on my first start cap failure, a 5HP table saw, said somewhat tongue-in-cheek to keep the saw running more. Turns out this is the correct answer. I have done research and found out the start capacitors that these motors use are only rated and designed to start about 15-20 times per hour. The larger motors are very heavy and the caps simply cannot turn them on over and over again. Keep in mind, these chinese caps are absolutely the cheapest money can buy. They are worth less than 1 dollar on the wholesale market. A high quality capacitor made in Japan with the same electronic specs is worth 20 times as much. And it can be started 50-60 times per hour. Since I started running the table saw and band saw more, keeping well under 10 starts per hour even on many 8 hour days, i have had ZERO start capacitor failures even with the same cheap caps.

[David Cefai]

A few years ago some engineers in Taiwan left their electrolyte company to form a new one. They stole the wrong electrolyte recipe and, since it did not have a couple of vital ingredients listed, were able to sell their product very cheaply.

There was an epidemic of failed motherboards and other computer cards about 18 months later. Your caps could date back to this.

[david brum]

Thanks, Steve. That's great info. I think I'll look into better capacitors next time they fail. It's not that they cost much, but it sure is annoying to have one fail in the middle of a project.

[david brum]

A few years ago some engineers in Taiwan left their electrolyte company to form a new one. They stole the wrong electrolyte recipe and, since it did not have a couple of vital ingredients listed, were able to sell their product very cheaply.

There was an epidemic of failed motherboards and other computer cards about 18 months later. Your caps could date back to this.

Both of these machines are around 4 years old, both with moderate use and fine until now. Both start capacitors look similar, perhaps from the same manufacturer. No country of origin is on the label. I imagine they're the same ones used on most Asian machines these days. Just odd that they failed at around the same time.

[david brum]

After reading David Cafel's idea about generally bad Taiwanese capacitors, I looked it up on wikipedia. Sure enough, there's something called "capacitor plague" which affected all kinds of electronic equipment. It sounds like this pertains mainly to circuit board size capacitors, but who knows?
http://en.wikipedia.org/wiki/Capacitor_plague (http://en.wikipedia.org/wiki/Capacitor_plague)

[Dan Hintz]

I would disregard that wiki page with its claims of the problem still occurring (the link to a 2010 article). Yes, it was a problem in the early 2000 range, but the problem was quickly recognized and remedied (to a degree... plenty of those caps floated around in stock for a while). The caps being made with the failed formula were relatively small in capacitance... power supplies and smaller, due to the level of capacitance possible with that particular formula. Even quality caps fail from time to time, but that "plague" is so engrained in people's memories every failure is now attributed to it. Lower quality caps will fail more often... I've probably lost 4-5 power supplies over the years due to failed caps, and they weren't part of the "plague". I try to do a post-mortem on every item that fails around here so I can determine if moving to another manufacturer / supplier is appropriate.

It's just sounds like you got some bad (cheap?) caps, David... I'd look for a high-quality replacement and be done with the problem. Look for a higher peak-voltage rating, if you can.

EDIT: Just so there's no confusion... I'm not saying some companies are not manufacturing failing caps, just that it's not due to the failed formula fiasco from the late-90's.

[Myk Rian]

If the caps had failed in the same motor, I would say there is a motor problem. But since that is not the case, put good caps in and continue with life.

[david brum]

Thanks guys!