can bad cap = hot motor?

[et...@whidbey.com]

I have an old Baldor grinder that's at least 80 years old. It is a
cap start and run motor. So the cap is always in the circuit of the
phase shifted winding. There is no centrifugal start switch.
It has always taken a long time to come up to speed but these
types of motors do that. However, it seems to take much longer to spin
up than my newer Baldor grinder motors that are wired the same.
The capacitor is a rectangular shape about 5/16ths of an inch thick
and maybe 1.5 x 2.0 inches. It has a brass case with cloth covered
wires coming out of the tar used to seal the case. I mention the cap
construction just to give an idea of how old it is.
I went through the motor a few years ago because the bearings were
bad. They had rawhide seals that had dried out, shrunk, and let grit
in. I replaced them with modern sealed bearings. The motor runs very
smooth. Just like a grinder motor should.
Today I used the grinder for about 1/2 an hour and it got pretty
hot. I was not loading the grinder very much because I was just
grinding points on tungsten TIG electrodes with a diamond wheel I have
mounted. Still, the motor got pretty damn hot. Could a bad cap do
this?
I suppose there could be some shorted windings. In any case, if a
bad cap could cause hot running I'll take the thing apart again and
replace the cap.
Thanks,
Eric

[peterw...@gmail.com]

If the cap is original to the motor, replace it. 80 years is a very long time for such a device, keeping in mind that AC-rated capacitors (80-year-old style) will deteriorate just by sitting on the shelf. A modern polyprop cap of the correct rating and voltage will outlive most of us here.
As to the motor itself, do you have an AC ammeter, with specific reference to the clamp-on type? If so, check each leg of the feed - they should be substantially the same when running, and substantially below nameplate when unloaded. If either of those statements is untrue of your motor, it is on its way out, however slowly.

But, to answer your question directly, yes, hot-running is a symptom of a failed cap - as is slow starting and poor load handling.

Peter Wieck
Melrose Park, PA

[et...@whidbey.com]

Yeah, I'm betting that the cap is as old as the motor. I'll take your
advice and replace it. I don't understand how the current can be
different if there are only two wires feeding the motor. What am I
missing?
Thanks,
Eric

[Michael Terrell]

On Friday, August 14, 2020 at 6:32:11 PM UTC-4, et...@whidbey.com wrote:
>
> Yeah, I'm betting that the cap is as old as the motor. I'll take your
> advice and replace it. I don't understand how the current can be
> different if there are only two wires feeding the motor. What am I
> missing?

If the capacitor's value is wrong, it doesn't provide the proper phase shift. That causes the motor to require more power to do the same work.

[Ralph Mowery]

In article <sm3ejf9e1rqjfl8pm...@4ax.com>,
et...@whidbey.com says...

> Yeah, I'm betting that the cap is as old as the motor. I'll take your
> advice and replace it. I don't understand how the current can be
> different if there are only two wires feeding the motor. What am I
> missing?
> Thanks,
> Eric
>
>

Not likely, but if one of the windings is shorted to ground or the
capacitor is leaking to ground the current could be different.

[Paul Drahn]

I suspect your motor has a single capacitor and is a split-phase motor.
Cap start, cap run requires two capacitors and the mechanism to switch
between the two.

A grinder has no reason the have a heavy load when it starts, which is
the reason for motors with two caps.

Paul

[Fox's Mercantile]

On 8/15/20 12:20 PM, Paul Drahn wrote:
> A grinder has no reason the have a heavy load when it starts, which is
> the reason for motors with two caps.

Well, actually it does.
It has the inertia of both grinding wheel to get up to speed.


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

[whit3rd]

On Saturday, August 15, 2020 at 11:33:43 AM UTC-7, Fox's Mercantile wrote:
> On 8/15/20 12:20 PM, Paul Drahn wrote:
> > A grinder has no reason the have a heavy load when it starts, which is
> > the reason for motors with two caps.
>
> Well, actually it does.
> It has the inertia of both grinding wheel to get up to speed.

The motor could certainly get it up to speed fast with a high torque,
but the user of a grinder can wait a few seconds before applying his
workpiece... so "low startup torque" :== "low startup load" is acceptable in this application.

[et...@whidbey.com]

I guess the cap could indeed be leaking to ground. It has a brass case
after all and the case may be touching metal. I will be replacing the
cap and that will hopefully solve the heating issue. I'm certain it
will speed up the startup.
Eric

[Ralph Mowery]

In article <cc120e40-5b93-49c8...@googlegroups.com>,
whi...@gmail.com says...

>
> > Well, actually it does.
> > It has the inertia of both grinding wheel to get up to speed.
>
> The motor could certainly get it up to speed fast with a high torque,
> but the user of a grinder can wait a few seconds before applying his
> workpiece... so "low startup torque" :== "low startup load" is acceptable in this application.
>
>

I doubt the grinder really has that much inertia to prevent starting.
It may tke some time to get up to full speed. Most hard starting is
like air compompressors and refrigeration compressors unless they have
some sort of unloader.

[tabb...@gmail.com]

Maybe you can restuff it rather than dispose.


NT

[et...@whidbey.com]

While I can see the draw of keeping all the old stuff intact or
appearing so this cap is weird. It's a rectangle about 5/16 inch
thick. Modern motor caps are a lot different in shape.
Eric

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

[Fox's Mercantile]

On 8/18/20 10:54 AM, et...@whidbey.com wrote:
> While I can see the draw of keeping all the old stuff intact or
> appearing so this cap is weird. It's a rectangle about 5/16 inch
> thick. Modern motor caps are a lot different in shape.
> Eric

Ignore Tabby, they tend to not read an entire thread before making
some, typically, useless suggestion.

[Jeff Liebermann]

On Sat, 15 Aug 2020 10:20:08 -0700, Paul Drahn <pdr...@jodeco.com>
wrote:

>I suspect your motor has a single capacitor and is a split-phase motor.
>Cap start, cap run requires two capacitors and the mechanism to switch
>between the two.
>
>A grinder has no reason the have a heavy load when it starts, which is
>the reason for motors with two caps.
>
>Paul

Agreed. However, the official name is a "Permanent-Split Capacitor
Motor" which has one permanently connected run capacitor. The "Split
Phase" motor has no capacitors. See:

Two-winding Machines
<https://people.ucalgary.ca/~aknigh/electrical_machines/other/split_phase.html>

Permanent-Split Capacitor Motor
If run efficiency and vibration are important, but start
torque can be compromised, the capacitor can be left in
the auxiliary circuit at all speeds. Sizing the capacitor
to provide balance at a particular load point, the
backwards field can be eliminated, improving efficiency
and eliminating torque pulsations. Eliminating the
centrifugal switch can reduce the manufacturing cost
significantly. The trade-off is lower starting torque,
since the capacitor is not sized to provide balance at
starting, but for run conditions

The design has the disadvantage of having low starting torque, which
is the cause of the slow start. At 80+ years old, I would guess(tm)
that the capacitor is as dead as the bearings that were replaced. As
it gets old, the ESR starts to climb which I presume was the cause of
the observed heating.

Drivel: My experience with motors was mostly with industrial sewing
machines at my father's lingerie factory. At the time some of the
older motors would exhibit the symptoms of a shorted winding. What
was happening was that some motors were not designed to handle
sustained high temperatures. The copper motor wire would expand
slightly, cracking the old enamel insulation. New enamel was quite
flexible, but old enamel became brittle. My guess(tm) is it took
about 40 years to cause problems. Insulation failures were mostly
around sharp wire bends. I think varnish insulation did the same
thing, but at the time, I couldn't tell the difference between varnish
or enamel insulated motor wire. Therefore, when working with really
old motors, I always look for loose insulation flakes, which might be
an indication of impending shorts.

--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[tabb...@gmail.com]

On Tuesday, 18 August 2020 16:54:25 UTC+1, et...@whidbey.com wrote:

You gave its dimensions earlier. It is presumably a flat paper cap. I meant restuff with higher v non-motor caps.


NT

[et...@whidbey.com]

Modern motor run caps are all large. They use a lot of material. It
can't be they do this just because of tradition.

[Michael_A_Terrell]

et...@whidbey.com wrote:
>
> Modern motor run caps are all large. They use a lot of material. It
> can't be they do this just because of tradition.

Start caps are AC electrolytics. Run capacitors are AC rated film,
or in case of that 80 year old cap, paper insulation. They are large, to
dissipate the heat from continuous operation.

--
Never piss off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)

[tabb...@gmail.com]

On Wednesday, 19 August 2020 17:15:06 UTC+1, et...@whidbey.com wrote:

You could always look up what properties motor run caps have.
But did you also notice that even a 1930s paper cap lasted 80+ years? Modern film caps are massively better & smaller.


NT

[et...@whidbey.com]

I know modern caps are much better than old caps. However, why do you
suppose it is that motor run caps are so big for their voltage and
capacitance ratings compared to other non-polarized caps? I'm serious.

[peterw...@gmail.com]

> I know modern caps are much better than old caps. However, why do you
> suppose it is that motor run caps are so big for their voltage and
> capacitance ratings compared to other non-polarized caps? I'm serious.

That is not a bad question at all:
a) Because they are AC-rated caps.
b) Because the nature of a motor starting puts a tremendous load on the cap for a very short time, so they must be robust enough to absorb that shock, repeatedly and reliably, in addition to the actual voltage involved. So, whereas the actual operating voltage may be say.... 240 VAC, the start-cap must be rated (at a minimum) of 150% of the operating voltage.
c) Typical NP caps are used a great deal in audio applications, where the voltages are small, and the frequencies high.
d) Motor Run caps start around 370V, or so, are typically of much lower capacitance than a start-cap (and whereas replacement voltage may be higher, replacement capacitance should remain very close or identical to OEM).

Hope that helps.

[tabb...@gmail.com]

Of course motor rated caps have advantages. So do higher rated non-motor caps.
But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough.


NT

[peterw...@gmail.com]

> But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough.

We do not know that at all. What we do know is that *FINALLY* Eric has gotten around to dealing with it.

[Fox's Mercantile]

What we do know, is that Tabby is consistent about posting irrelevant
comments.

[et...@whidbey.com]

So you suggested that I stuff the old cap with a new cap(s). I knew
new motor run caps were too big to fit in the old cap case. You
suggested I use modern caps with the same ratings. I wondered why
motor run caps are still so much physically larger than caps with the
same specs but which are not motor run caps. Then you post the answer
above. I am not sure why you even bothered.

[et...@whidbey.com]

I was going to go back in time to replace that cap but my time machine
was serviced byb me after a few gins so instead I waited until I
bought the grinder in real time, used it for a couple years, posted a
question about it here and now I have a new cap coming.

[bruce bowser]

On Sunday, August 23, 2020 at 8:11:26 PM UTC-4, et...@whidbey.com wrote:
> On Sun, 23 Aug 2020 07:20:43 -0700 (PDT), "pf...@aol.com"
> <peterw...@gmail.com> wrote:
>
> >
> >> But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough.
> >
> >We do not know that at all. What we do know is that *FINALLY* Eric has gotten around to dealing with it.
> >
> >Peter Wieck
> >Melrose Park, PA
>
> I was going to go back in time to replace that cap but my time machine
> was serviced byb me after a few gins so instead I waited until I
> bought the grinder in real time, used it for a couple years, posted a
> question about it here and now I have a new cap coming.

Good stuff with orange juice and 2 or 3 banana liquors. I wonder what an 80 year-old gin bottle would fetch today.

[ohg...@gmail.com]

On Sunday, August 23, 2020 at 8:11:26 PM UTC-4, et...@whidbey.com wrote:

> On Sun, 23 Aug 2020 07:20:43 -0700 (PDT), "pf...@aol.com"
> <peterw...@gmail.com> wrote:
>
> >
> >> But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough.
> >
> >We do not know that at all. What we do know is that *FINALLY* Eric has gotten around to dealing with it.
> >
> >Peter Wieck
> >Melrose Park, PA
> I was going to go back in time to replace that cap but my time machine
> was serviced byb me after a few gins so instead I waited until I
> bought the grinder in real time, used it for a couple years, posted a
> question about it here and now I have a new cap coming.
> Eric
>

If you get that time machine working, go back to 1964 and tell Ford to use galvanized sheetmetal on the Mustang. Thanks.

[Sjouke Burry]

How do you teach a gin bottle to fetch?????

[RosemontCrest]

You can't teach an old gin bottle new tricks.