Shopsmith Forums

SDSSmith wrote:Kris, to be clear, you got the Shopsmith for $100 and you paid Battels $37 to diagnose and replace the start capacitor? If so, looks like the you still owe the machine. Maybe you should buy it the 520 upgrade or something else nice. ]

It was not 'fried'! The capacitor was funky! Lack of use the cause of whatever the 'fault' was.

dusty wrote:You guys don't read the posts carefully enough. I have reported capacitor failures. They don't happen as frequently as some others but they do happen. I mean, after all, that is why there is a starter capacitor in these motors. They provide an additional current surge at startup when the motor demands a greater current than is required after the motor reaches run speed.

Like some people replace bearings whenever they go inside a motor, I also replace the start capacitor.

Actually they reduce the current surge, but that is not their purpose. They provide phase shift of the currents in one of the windings to provide a stronger rotating magnetic field at startup(when the armature is rotating much slower than the field rotation). Without it a larger surge exists that will trip a breaker if left on too long or burn out the motor due to the excessive current. Once the armature is rotating close to the magnetic field rotation, the current reduces and the extra phase shift is unnecessary.

Not totally exact, but close enough for a simple explanation.

Although they DO go bad, there are more likely culprits.

I would be curious just what was wrong with the one replaced in that ss that was probably not used for an extended period of time.

There is usually only three things that can go wrong with them - open, shorted, leakey(mini-short).

SDSSmith wrote:I am a mechanical guy. So I want to get this straight from an electrical guru. A nice clean machine that appears to have had little use and been stored in a dry (southern CA) climate is subject to capacitor failure due to lack of use. I would of thought it was just a bad capacitor. Hmmm.....

I would have thought it was the start switch contacts. Like you observed, the peek through the vent holes indicated almost new condition(as well as the rest of the inside of the headstock).

Capacitors are quite reliable devices and unless somehow contaminated at manufacture or somehow later, they do not go bad(excessive electrical stress not included, but that is a very unlikely event unless connected to an excessively high voltage source or a voltage surge).

They will break down if subjected to voltage excess. They may then become either shorted or acquire a resistive characteristic(leakey). They may also become open, but that is the result of a connection breakdown(the internal wires break etc.).

Since this ss was not used for an extended period of time, I would have looked at the start contacts first, then the capacitor terminals/connectors and start switch connections. Testing the capacitor itself would be last. This is I believe the order of the most likely cause of the starting problem.

I truly believe that inactivity would create the switch and connector problems and quite unlikely to cause a capacitor failure.

What we do not know here is any history of what if any any stresses the components were subjected to prior to that extended inactive period. For all we know, lightning struck near by and induced a voltage spike inside all that stuff!:eek:! Maybe even more than once.]unique[/B] to the start circuit.