More questions about checking starting caps

Short answer on measuring caps with a DVM is:

If the reading is *NO MORE THAN* 20% higher than the label capacitance it is probably OK.

Lower by more than 10%, it is probably bad.

Problem is that with a VOM with, at best, a 9V battery in it cannot really test a line-voltage cap properly. And leaky caps may give a falsely high reading. So, a 60% over-label reading suggests (not guarantees) it is probably bad.

An ESR meter is better.

And testing a cap at full voltage is best of all.

Bridging in more capacitance is a mixed bag. Does no good if the cap is leaky. Does good if the cap is open.

Peter Wieck Melrose Park, PA

AIUI you could have cap(s) leaking or a faulty switch contacts. Soldering a wire to short the starting switch could tell you which. Obviously don't power the motor for >5 seconds like that.

NT

Soldering a wire across switch contacts won't work easily because the switch is a contactor. What I'm gonna do is get someone to look at the contactor when I turn on the breaker to see if it pulling in. If it is pulling in then I'll remove it and check the contacts. Then replace them if need be. If the contactor doesn't pull in then I'll need to find out if the coil is bad or if it isn't getting power. I will still need to check the caps if the contactor is working properly. Eric

that makes no sense

That might get you there.

NT

I will still

If the cap tests shorted with DVM it is obviously bad.

If the caps test good with DVM it may be good or it may be bad under load.

Best test is to buy a cap that is close to the required value to use as a test.

If it works, buy the right cap and be happy you had an inexpensive repair of an expensive machine.

As it turns out it was a loose connection buried deep in the electrics box. One of the spade connectors on the coil in the contactor was loose. NOT easy to find. Even though the wiring in the phase converter is neat there are a lot of wires and many of these wires hide the contactor coil connections. Fortunately not the ten caps connected in parallel that are used for starting the thing were at fault. Eric

On 8/25/2017 6:15 PM, snipped-for-privacy@whidbey.com wrote: ... What I'm gonna do is get someone to look at the

Too late for this problem, but next time you need a second set of eyes, set up your video recorder as the witness.

If you don't have someone handy simply set your phone in video mode and have it record what happens with the contacts when you hit the power. Then you can review moment to moment changes.

John ;-#)#