More questions about checking starting caps

[et...@whidbey.com]

Well, this morning the phase converter won't start at all. There is
a button that can be pressed that energizes the contactor that
connects the 10 starting caps to the motor. This button bypasses the
time delay relay that energizes the contactor. Pressing the button has
no effect at all, the motor just hums.
I don't know yet if the contactor is pulling in or not because I
cannot see into the electrics enclosure while throwing the breaker
that turns on the phase converter. Even though I can press the bypass
button while throwing the breaker I cannot see the contactor. I'll
have to get another set of eyes to look inside while I turn the
converter on.
Getting on subject, I have a DVM that has a capacitance measuring
function. Measuring half a dozen known good oil filled caps the
readings on the meter match very closely, within one MFD, the value
printed on the caps. If I measure the caps in the phase converter and
they measure close to the value printed on the case does this mean the
caps are probably good? Is there another test I can perform with the
meter? And since there are 10 starting caps connected in parallel
could just one or two bad caps cause the starting problem?
Thanks,
Eric

[pf...@aol.com]

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

[tabb...@gmail.com]

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

[et...@whidbey.com]

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

[tabb...@gmail.com]

On Friday, 25 August 2017 23:15:08 UTC+1, et...@whidbey.com wrote:

> On Fri, 25 Aug 2017 14:56:50 -0700 (PDT), tabbypurr wrote:
> >On Friday, 25 August 2017 19:33:59 UTC+1, et...@whidbey.com wrote:

> >> Well, this morning the phase converter won't start at all. There is
> >> a button that can be pressed that energizes the contactor that
> >> connects the 10 starting caps to the motor. This button bypasses the
> >> time delay relay that energizes the contactor. Pressing the button has
> >> no effect at all, the motor just hums.
> >> I don't know yet if the contactor is pulling in or not because I
> >> cannot see into the electrics enclosure while throwing the breaker
> >> that turns on the phase converter. Even though I can press the bypass
> >> button while throwing the breaker I cannot see the contactor. I'll
> >> have to get another set of eyes to look inside while I turn the
> >> converter on.
> >> Getting on subject, I have a DVM that has a capacitance measuring
> >> function. Measuring half a dozen known good oil filled caps the
> >> readings on the meter match very closely, within one MFD, the value
> >> printed on the caps. If I measure the caps in the phase converter and
> >> they measure close to the value printed on the case does this mean the
> >> caps are probably good? Is there another test I can perform with the
> >> meter? And since there are 10 starting caps connected in parallel
> >> could just one or two bad caps cause the starting problem?
> >> Thanks,
> >> Eric
> >
> >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.
> >
> >

> Soldering a wire across switch contacts won't work easily because the
> switch is a contactor.

that makes no sense

> 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 might get you there.


NT

[mako...@yahoo.com]

I will still
> > need to check the caps if the contactor is working properly.
> > Eric

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.

m

[et...@whidbey.com]

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

[Bob Engelhardt]

On 8/25/2017 6:15 PM, et...@whidbey.com wrote:
... 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. ...

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

[John Robertson]

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.

> 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
>

John ;-#)#

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