8mm Forum: Definition of technical term

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Posted by Brad Kimball (Member # 5) on July 13, 2019, 09:33 AM:

What is a motor run capacitor and can it be repaired or replaced? My Chinon 7000 runs for a minute or two and then it acts like a mower running out of gas. It lags with a hiccup intermittently. Belt is good and it’s well lubricated. A picture would be very helpful. Thanks.

Posted by Mike Spice (Member # 5957) on July 13, 2019, 09:40 AM:

everything you need to know about start/run motor capacitors

Posted by Steve Klare (Member # 12) on July 13, 2019, 12:46 PM:

They can't be repaired, but they can be replaced.

You worry about three things in order of importance.

1) Capacitance:
These are there to introduce a phase shift into a current. It's what makes the motor spin. The capacitance shout be dead on.

2) Voltage:
This is a rating so the cap doesn't blow up. Going higher is fine. Going lower? No!

3) Size
Ideally you should find a new one that mounts in the exact same way and place as the old one. Frankly if you can meet capacitance and voltage requirements, making a fairly neat kludge mounting it up seems fine.

You need to find the cap and get the capacitance, voltage and size from it. I'm thinking a pretty large cylinder with two fat wires soldered to it: pretty close to the motor.

If you can find the exact part, that's awesome, but a lot of these old parts are obsolete now. We're lucky these days, with all these ceiling fans we have there are a ton of motor run caps available, it's just a challenge finding a good replacement.

Then again, it doesn't have to be the cap. I'm finding on my ST-1200HD it's more and more likely the motor switches. If I work them before I apply power, it runs like a champ. In the long term this means I'll probably have to replace the switches, which I am not looking forward to!

Posted by Mike Spice (Member # 5957) on July 14, 2019, 05:07 AM:

I would also add, if you are not familiar with the dangers of capacitors, they can hold a powerful charge for quite sometime.

Motor capacitors in any shape or form will certainly hold a charge big enough to frighten the heck out of you should you accidentally catch the terminals.

Before you investigate removing an old capacitor.....

There are guides on you tube how to discharge capacitors safely, but don't be tempted just to short to earth.

I built a lead with a large resistor in it for this purpose.
Croc clip one end, test point the other, and i can discharge a capacitor in seconds, safely.

If you have a test meter, put it across the capacitor to witness the charge they can hold onto, in some cases, for many weeks after a power off.

Posted by Maurice Leakey (Member # 916) on July 14, 2019, 05:56 AM:

It's really a starting capacitor which throws a charge to kick over the motor for it to start. Once started it does not do any other work.
I suggest the motor problem lies elsewhere.

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