Replacement Motor For 14x40 Lathe

Mike,

Thanks for the short video on shorting out capacitors. I learned at a early age what capacitors can do to you if you are not paying attention, give you one heck of a jolt of electricity! Luckily, it was a very small capacitor. I've built several static type of phase converters over the years, grouping various size capacitors together for use in them. When you have several electrolytic capacitors grouped together in parallel, things get very excited shorten them out to work on a converter. I get gun shy every time I have to shorten a group of them out. Some of the ones I've built have the resistor across the tabs, but even then, I've shorted one or two that still had juice in them.

People, be careful handling them and follow Mike's advice on discharging them.
 
I'm an anti-screwdriver discharge guy. I don't like to see the current spike when you just arc one out. I prefer a resistor and a couple of clips. Really doesn't take long, and is safe for you and the cap.
 
If you have a single phase motor now is it driven by a VFD ?
You probably already do so but from what I've read the lathe should come to a complete stop before reversing.
Also the motor sheave can make noise if it gets loose. Gotta loosen the belts to check it and while the belts are loose try running the motor with no belts and check the load end for play.
 
The current spike when discharging an electrolytic capacitor won't hurt it. The only things that damage them are over-voltage and heat. They are somewhat nonlinear and have a relatively large esr so running too much AC through them for too long will cook them but a single isolated pulse does no harm.

Something to watch out for: electrolytics have a sort of "memory effect". Charge one to its full rated voltage, hold it there for a bit, discharge it to zero, wait a bit, and you may find that it now has a significant voltage on it.
 
I must respectfully disagree with John on this one. Every capacitor has a charge/discharge design factor. They are limited to prevent damage to not only the foil anode material, which can suffer from heat, but also the electrolyte composition can be changed. Net effect generally is a shortened life. This is even reflected in the design frequency at which they can operate. Too high a frequency can kill them. In effect, when you short across them (which I have done - guilty) the operating frequency is infinitely high, even for one cycle. There are formulas to determine how fast a cap can safely (and I mean without harm to the capacitor) be brought to theoretical zero, which is an interesting topic of it's own. It's only milliseconds, but nonetheless, it is a factor that is specified by the mfg. and declared safe.

Now if you don't care if you shorten the life a little, and don't mind a notch in your screwdriver......go for it. I'll use a resistor.

Per Nippon-Chemi-com....mfg of electrolytic caps.

John, no argument intended, just presenting the facts as I understand the mfg design and intent. I respect what you say and your expertise.
 
What ever method suits you,
PLEASE, just short a cap before attempting any service!
 
Concur with Tony Wells, I build tube gear with high voltage power supplies, always use a bleeder resistor to bring down the charge in a capacitor. After discharge, I might short the capacitor just before removal to dissipate any memory/residual charge. The capacitors can hold a charge for a long time, so do not assume that since you haven't used a machine for awhile that the capacitors are discharged. When dealing with banks of capacitors, there is a tremendous amount of charge held in the capacitors unless there is some form of bleeder resistors across the terminals, and even then they can take some time to fully discharge. When I purchase old high voltage military oil can type capacitors, they always come with a wire across the terminals when packaged new.

From another source: Electrolytic capacitors may become permanently damaged by excessive peak currents with rapid discharge/charge, which will definitely occur during short-circuit events. The reason is that (a) the internal resistance will cause a momentary, but large power dissipation (heat!) and (b) the distribution of the current spike inside the capacitor will not be formed evenly across the large area of the aluminum foil and hot spots may occur. The electrolyte may vaporize along these small zones and damage to the insulating aluminum oxide layer may occur as well. If you're lucky, the capacitance will decrease just a bit or the top of the can may change its shape into something like a dome. If you're very unlucky, the cap may fail and heat up quite a bit (and eventually blow). This applies to different types of capacitors, not just electrolytic types.
 
sounds to me like it's in the centrifugal switch assembly, others may have different opinions.
 
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