How to size motor start cap?

Relative to my previous post today I need new starting caps for a 3
HP single pahse 230 volt motor. Dayton (Grainger) no longer has any
info about this motor.
The caps that blew were connected in parallel. One was 560-552 MFD
and the other was 540-648 MFD. The caps were not original and they
were from China. From looking on the web it seems like this much
capacitance is a little high.
The motor is an old motor. Maybe 40 years old. Maybe older.
The cap housing is large enough for two caps and the wires
connecting the caps in parallel looks exactly like the wires going
into the motor from the caps. Same kind and color of insulation and
same look from aging. So the big cap housing appears to have been
meant to hold two round caps and not one big rectangular cap.
Maybe it was hard to get as much capacitance in the same space
years ago and that's why the two caps.
If the capacitance is too high can that stress the caps enough to
blow their guts out?
Thanks,
Eric

 

[John Robertson]

On 2018/07/18 1:18 PM, etpm@whidbey.com wrote:

Relative to my previous post today I need new starting caps for a 3
HP single pahse 230 volt motor. Dayton (Grainger) no longer has any
info about this motor.
The caps that blew were connected in parallel. One was 560-552 MFD
and the other was 540-648 MFD. The caps were not original and they
were from China. From looking on the web it seems like this much
capacitance is a little high.
The motor is an old motor. Maybe 40 years old. Maybe older.
The cap housing is large enough for two caps and the wires
connecting the caps in parallel looks exactly like the wires going
into the motor from the caps. Same kind and color of insulation and
same look from aging. So the big cap housing appears to have been
meant to hold two round caps and not one big rectangular cap.
Maybe it was hard to get as much capacitance in the same space
years ago and that's why the two caps.
If the capacitance is too high can that stress the caps enough to
blow their guts out?
Thanks,
Eric

I would contact a motor rebuild shop and see what they recommend. They
are the pros in this situation...

John

 

On Wed, 18 Jul 2018 13:18:42 -0700, etpm@whidbey.com wrote:

Relative to my previous post today I need new starting caps for a 3
HP single pahse 230 volt motor. Dayton (Grainger) no longer has any
info about this motor.
The caps that blew were connected in parallel. One was 560-552 MFD
and the other was 540-648 MFD. The caps were not original and they
were from China. From looking on the web it seems like this much
capacitance is a little high.
The motor is an old motor. Maybe 40 years old. Maybe older.
The cap housing is large enough for two caps and the wires
connecting the caps in parallel looks exactly like the wires going
into the motor from the caps. Same kind and color of insulation and
same look from aging. So the big cap housing appears to have been
meant to hold two round caps and not one big rectangular cap.
Maybe it was hard to get as much capacitance in the same space
years ago and that's why the two caps.
If the capacitance is too high can that stress the caps enough to
blow their guts out?
Thanks,
Eric

Well, I tried a smaller value, about 1/5 of what was connected before,
and the motor tries to start but just can't. So I know I need more
than 200 MFD.
Eric

 

[Dave M]

What's the model#/part# on the nameplate of the motor? Also, many
nameplates specify the required capacitors for the motor. Have you looked
there yet?

Dave M

<etpm@whidbey.com> wrote in message
news:997vkdln3vdqi8b9ksdg6md0jidp7l6ams@4ax.com...

Relative to my previous post today I need new starting caps for a 3
HP single pahse 230 volt motor. Dayton (Grainger) no longer has any
info about this motor.
The caps that blew were connected in parallel. One was 560-552 MFD
and the other was 540-648 MFD. The caps were not original and they
were from China. From looking on the web it seems like this much
capacitance is a little high.
The motor is an old motor. Maybe 40 years old. Maybe older.
The cap housing is large enough for two caps and the wires
connecting the caps in parallel looks exactly like the wires going
into the motor from the caps. Same kind and color of insulation and
same look from aging. So the big cap housing appears to have been
meant to hold two round caps and not one big rectangular cap.
Maybe it was hard to get as much capacitance in the same space
years ago and that's why the two caps.
If the capacitance is too high can that stress the caps enough to
blow their guts out?
Thanks,
Eric

 

On Wed, 18 Jul 2018 18:10:37 -0500, "Dave M" <dgminala@mediacombb.net>
wrote:

What's the model#/part# on the nameplate of the motor? Also, many
nameplates specify the required capacitors for the motor. Have you looked
there yet?

Dave M

etpm@whidbey.com> wrote in message
news:997vkdln3vdqi8b9ksdg6md0jidp7l6ams@4ax.com...
Relative to my previous post today I need new starting caps for a 3
HP single pahse 230 volt motor. Dayton (Grainger) no longer has any
info about this motor.
The caps that blew were connected in parallel. One was 560-552 MFD
and the other was 540-648 MFD. The caps were not original and they
were from China. From looking on the web it seems like this much
capacitance is a little high.
The motor is an old motor. Maybe 40 years old. Maybe older.
The cap housing is large enough for two caps and the wires
connecting the caps in parallel looks exactly like the wires going
into the motor from the caps. Same kind and color of insulation and
same look from aging. So the big cap housing appears to have been
meant to hold two round caps and not one big rectangular cap.
Maybe it was hard to get as much capacitance in the same space
years ago and that's why the two caps.
If the capacitance is too high can that stress the caps enough to
blow their guts out?
Thanks,
Eric

I looked up the motor number and Grainger, which sells Dayton Motors,
no longer has data on the motor. Neither did an internet search yield
anything. And the motor nameplate doesn't specify the caps. I though
that maybe a newer Daytom motor would have the info but Grainger does
not list the caps required for the motors on their website or on the
motor nameplate. I can't understand why.
Eric

 

[Rheilly Phoull]

On 19/07/2018 4:18 AM, etpm@whidbey.com wrote:

Relative to my previous post today I need new starting caps for a 3
HP single pahse 230 volt motor. Dayton (Grainger) no longer has any
info about this motor.
The caps that blew were connected in parallel. One was 560-552 MFD
and the other was 540-648 MFD. The caps were not original and they
were from China. From looking on the web it seems like this much
capacitance is a little high.
The motor is an old motor. Maybe 40 years old. Maybe older.
The cap housing is large enough for two caps and the wires
connecting the caps in parallel looks exactly like the wires going
into the motor from the caps. Same kind and color of insulation and
same look from aging. So the big cap housing appears to have been
meant to hold two round caps and not one big rectangular cap.
Maybe it was hard to get as much capacitance in the same space
years ago and that's why the two caps.
If the capacitance is too high can that stress the caps enough to
blow their guts out?
Thanks,
Eric

Not sure which model you have but the caps are shown as in series on
this model ( Cap start - run )
https://www.grainger.com/product/DAYTON-3-HP-General-Purpose-Motor-6K145

 

[Jeff Liebermann]

On Wed, 18 Jul 2018 13:18:42 -0700, etpm@whidbey.com wrote:

Any reason for not disclosing the motor model number? Yes, I know
it's 40 years old and Granger can't find it.

There are two caps in most such motors. One is the "starting
capacitor". The other is the "run capacitor".
<https://www.youtube.com/watch?v=qsuzfz5qcIE>
<https://www.youtube.com/watch?v=OMd9QkinXz4>
I'm fairly sure they should NOT be wired in parallel.

For 220VAC, the starting cap should be about 30 to 50uF/kW.
3HP(mechanical) = 2.2kW so try about 90uF.

The run cap is usually about 5 - 20uF.

For the starting capacitor calculations, see:
<https://www.electricneutron.com/electric-motor/single-phase-capacitor-sizing/>
<https://www.quora.com/How-do-I-calculate-capacitor-value-for-single-phase-motor>
More:
<https://www.google.com/search?q=calculate+motor+starting+capacitor>

I couldn't find anything on calculating the run capacitor.


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

 

On Wed, 18 Jul 2018 19:36:47 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Wed, 18 Jul 2018 13:18:42 -0700, etpm@whidbey.com wrote:

Any reason for not disclosing the motor model number? Yes, I know
it's 40 years old and Granger can't find it.

There are two caps in most such motors. One is the "starting
capacitor". The other is the "run capacitor".
https://www.youtube.com/watch?v=qsuzfz5qcIE
https://www.youtube.com/watch?v=OMd9QkinXz4
I'm fairly sure they should NOT be wired in parallel.

For 220VAC, the starting cap should be about 30 to 50uF/kW.
3HP(mechanical) = 2.2kW so try about 90uF.

The run cap is usually about 5 - 20uF.

For the starting capacitor calculations, see:
https://www.electricneutron.com/electric-motor/single-phase-capacitor-sizing/
https://www.quora.com/How-do-I-calculate-capacitor-value-for-single-phase-motor
More:
https://www.google.com/search?q=calculate+motor+starting+capacitor

I couldn't find anything on calculating the run capacitor.

The model number is 90653-N. The motor has only two wires coming out
to connect to the caps, so there is no starting cap. I tried a known
good cap that is about 200 MFD and it won't start the motor. The motor
tries to turn and I bet if I took the belts off it would start
spinning. The motor does spin easily enough but with the compressor
load it takes so long to spin up with the 200 MFD cap I'm afraid the
motor will overheat or the breaker will pop and so I turned it off
after a few seconds.
The compressor is a two stage air compressor that came with the
motor as a set. The compressor is unloading properly so the motor is
not trying to spin up a huge load and the motor has been spinning the
compressor just fine for the last 40 or 50 years.
I find it odd that there is no running cap but there just plain
aren't connections for one.
Eric

 

On Wed, 18 Jul 2018 19:36:47 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Wed, 18 Jul 2018 13:18:42 -0700, etpm@whidbey.com wrote:

Any reason for not disclosing the motor model number? Yes, I know
it's 40 years old and Granger can't find it.

There are two caps in most such motors. One is the "starting
capacitor". The other is the "run capacitor".
https://www.youtube.com/watch?v=qsuzfz5qcIE
https://www.youtube.com/watch?v=OMd9QkinXz4
I'm fairly sure they should NOT be wired in parallel.

For 220VAC, the starting cap should be about 30 to 50uF/kW.
3HP(mechanical) = 2.2kW so try about 90uF.

The run cap is usually about 5 - 20uF.

For the starting capacitor calculations, see:
https://www.electricneutron.com/electric-motor/single-phase-capacitor-sizing/
https://www.quora.com/How-do-I-calculate-capacitor-value-for-single-phase-motor
More:
https://www.google.com/search?q=calculate+motor+starting+capacitor

I couldn't find anything on calculating the run capacitor.

Looking again I see that there are TWO model numbers on the motor
nameplate. The top one is 5K483-D, which is a good number as I found
it on the Grianger website. The other model number is on the bottom of
the ID plate and it says Motor Model Number whereas the top model
number just says Model. I have never seen this before. Anyway, I
called Grainger because the cap(s) weren't listed. The guy at Grainger
had to pull a file but he did find the caps and there are two. Both
caps are 485-582 MFD and are wired in parallel. They are both start
caps and the motor has no run cap. I have two cap coming tomorrow but
they are 540-685 MFD. Will them maybe be a problem? In the meantime I
will try to get the proper caps.
Thanks,
Eric

 

[pfjw@aol.com]

OK - keep in mind that the tolerance in electrolytic caps is typically +100%/-20% unless noted otherwise.

Your larger caps will be just fine.


Peter Wieck
Melrose Park, PA

 

[Ralph Mowery]

In article <eb5f51d7-76a7-492f-9532-fbfc38381a48@googlegroups.com>,
peterwieck33@gmail.com says...

OK - keep in mind that the tolerance in electrolytic caps is typically +100%/-20% unless noted otherwise.

Your larger caps will be just fine.


Peter Wieck
Melrose Park, PA

There are two things wrong here.

First this is an AC motor with AC capacitors. Electrolytics will not
work on AC as a general rule.

Newer capacitors, especially motor capacitors are much closer now in
tollorence.

I have one here that is rated +- 5% I keep as a spare for my heat pump.
Many are rated for a range of capacitance of about +- 10 % now.

 

On Thu, 19 Jul 2018 10:29:29 -0700 (PDT), "pfjw@aol.com"
<peterwieck33@gmail.com> wrote:

OK - keep in mind that the tolerance in electrolytic caps is typically +100%/-20% unless noted otherwise.

Your larger caps will be just fine.


Peter Wieck
Melrose Park, PA

Thanks Peter. Do you know why the MFD value of motor starting caps is
such a wide range? The specified caps are 485-582 MFD. Is that the min
and max of the cap? Do they spec them that way instead of using a
tolerance?
Eric

 

[pfjw@aol.com]

On Thursday, July 19, 2018 at 2:10:21 PM UTC-4, Ralph Mowery wrote:

There are two things wrong here.

First this is an AC motor with AC capacitors. Electrolytics will not
work on AC as a general rule. *Wrong.*

From Wiki:

Start capacitors above 20 ÂľF are always non-polarized aluminium electrolytic capacitors with non solid electrolyte and therefore they are only applicable for the short motor starting time. ... If a motor does not start, the capacitor is far more likely the problem than the switch.

A non-electrolytic cap, AC or DC of that rating would be as big as a football, or larger.

The motor is 40+ years old. That is not 'newer'.

That covers both *wrong* things.

Peter Wieck
Melrose Park, PA

 

[Ralph Mowery]

In article <f6bc1030-8362-47e2-8005-89352657ce64@googlegroups.com>,
peterwieck33@gmail.com says...

First this is an AC motor with AC capacitors. Electrolytics will not
work on AC as a general rule. *Wrong.*


From Wiki:

Start capacitors above 20 ľF are always non-polarized aluminium electrolytic capacitors with non solid electrolyte and therefore they are only applicable for the short motor starting time. ... If a motor does not start, the capacitor is far more likely the problem than the switch.

A non-electrolytic cap, AC or DC of that rating would be as big as a football, or larger.

The motor is 40+ years old. That is not 'newer'.

That covers both *wrong* things.

Peter Wieck
Melrose Park, PA

Winki lets anyone post anything.

My 50 uF capacitor is not electrolytic and rated for AC. It is no where
near footbal size. Not even beer can size. Even the 500 uF or so
capacitors for motor starters are no larger than a beer can if that
large.

People are quoting very old data. Maybe in 1950 the capacitors were
larger, but no today.

 

[pfjw@aol.com]

On Thursday, July 19, 2018 at 3:21:30 PM UTC-4, Ralph Mowery wrote:

In article <f6bc1030-8362-47e2-8005-89352657ce64@googlegroups.com>,
peterwieck33@gmail.com says...

First this is an AC motor with AC capacitors. Electrolytics will not
work on AC as a general rule. *Wrong.*


From Wiki:

Start capacitors above 20 ÂľF are always non-polarized aluminium electrolytic capacitors with non solid electrolyte and therefore they are only applicable for the short motor starting time. ... If a motor does not start, the capacitor is far more likely the problem than the switch.

A non-electrolytic cap, AC or DC of that rating would be as big as a football, or larger.

The motor is 40+ years old. That is not 'newer'.

That covers both *wrong* things.

Peter Wieck
Melrose Park, PA



Winki lets anyone post anything.

My 50 uF capacitor is not electrolytic and rated for AC. It is no where
near footbal size. Not even beer can size. Even the 500 uF or so
capacitors for motor starters are no larger than a beer can if that
large.

People are quoting very old data. Maybe in 1950 the capacitors were
larger, but no today.

Go to any site, any manufacturer - and you will find motor-start caps to be electrolytics. Really. Better yet, just open one up. And, exactly, how do you think they are made?


Peter Wieck
Melrose Park, PA

 

[Ralph Mowery]

In article <b78946c6-8a01-46e0-93a3-b27b98dd9172@googlegroups.com>,
peterwieck33@gmail.com says...

Go to any site, any manufacturer - and you will find motor-start caps to be electrolytics. Really. Better yet, just open one up. And, exactly, how do you think they are made?


Peter Wieck
Melrose Park, PA

This will be my last post on this thread. There is no use in me trying
to educate a person that will not be educated . Unless you can point me
to a page that specifies an electrolytic capacitor for a run and/or
start capacitor for an AC motor. And I do not mean the capacitors used
in a varitabble speed drive, just an ordinary AC motor.

If you go to the last sentence or two it will tell you that they are not
suited for use on AC lines.


Here is a quote from your belovied Wiki

https://en.wikipedia.org/wiki/Electrolytic_capacitor


Reverse voltage

An exploded aluminum electrolytic capacitor on a PCB
Standard electrolytic capacitors, and aluminum as well as tantalum and
niobium electrolytic capacitors are polarized and generally require the
anode electrode voltage to be positive relative to the cathode voltage.

Nevertheless, electrolytic capacitors can withstand for short instants a
reverse voltage for a limited number of cycles. In detail, aluminum
electrolytic capacitors with non-solid electrolyte can withstand a
reverse voltage of about 1 V to 1.5 V. This reverse voltage should never
be used to determine the maximum reverse voltage under which a capacitor
can be used permanently.[51][52][53]

Solid tantalum capacitors can also withstand reverse voltages for short
periods. The most common guidelines for tantalum reverse voltage are:

10 % of rated voltage to a maximum of 1 V at 25 °C,
3 % of rated voltage to a maximum of 0.5 V at 85 °C,
1 % of rated voltage to a maximum of 0.1 V at 125 °C.
These guidelines apply for short excursion and should never be used to
determine the maximum reverse voltage under which a capacitor can be
used permanently.[54][55]

But in no case, for aluminum as well as for tantalum and niobium
electrolytic capacitors, may a reverse voltage be used for a permanent
AC application.

To minimize the likelihood of a polarized electrolytic being incorrectly
inserted into a circuit, polarity has to be very clearly indicated on
the case, see the section on "Polarity marking" below.

Special bipolar aluminum electrolytic capacitors designed for bipolar
operation are available, and usually referred to as "non-polarized" or
"bipolar" types. In these, the capacitors have two anode foils with
full-thickness oxide layers connected in reverse polarity. On the
alternate halves of the AC cycles, one of the oxides on the foil acts as
a blocking dielectric, preventing reverse current from damaging the
electrolyte of the other one. But these bipolar electrolytic capacitors
are not adaptable for main AC applications instead of power capacitors
with metallized polymer film or paper dielectric.

 

[Jeff Liebermann]

On Thu, 19 Jul 2018 09:14:06 -0700, etpm@whidbey.com wrote:

On Wed, 18 Jul 2018 19:36:47 -0700, Jeff Liebermann <jeffl@cruzio.com
wrote:

On Wed, 18 Jul 2018 13:18:42 -0700, etpm@whidbey.com wrote:

Any reason for not disclosing the motor model number? Yes, I know
it's 40 years old and Granger can't find it.

There are two caps in most such motors. One is the "starting
capacitor". The other is the "run capacitor".
https://www.youtube.com/watch?v=qsuzfz5qcIE
https://www.youtube.com/watch?v=OMd9QkinXz4
I'm fairly sure they should NOT be wired in parallel.

For 220VAC, the starting cap should be about 30 to 50uF/kW.
3HP(mechanical) = 2.2kW so try about 90uF.

The run cap is usually about 5 - 20uF.

For the starting capacitor calculations, see:
https://www.electricneutron.com/electric-motor/single-phase-capacitor-sizing/
https://www.quora.com/How-do-I-calculate-capacitor-value-for-single-phase-motor
More:
https://www.google.com/search?q=calculate+motor+starting+capacitor

I couldn't find anything on calculating the run capacitor.

Looking again I see that there are TWO model numbers on the motor
nameplate. The top one is 5K483-D, which is a good number as I found
it on the Grianger website.

Bingo.
<https://www.grainger.com/product/DAYTON-3-HP-General-Purpose-Motor-5K483>
More:
<https://www.google.com/search?q=dayton+5K483+motor>
There are TWO wiring diagrms for suffix BB and BA with different
capacitor wiring schemes. I guess you have the BB suffix since it has
2 caps in parallel.
<https://www.grainger.com/ec/pdf/5K483_4.pdf> BB suffix
<https://www.grainger.com/ec/pdf/5K483_6.pdf> BA suffix

I couldn't find a reference with the exact capacitor value(s). The
parts list should have the Dayton capacitor part numbers on it
somewhere. Possible source to double check the values:
<http://www.emotorpro.com/capacitors.aspx>

The guy at Grainger
had to pull a file but he did find the caps and there are two. Both
caps are 485-582 MFD and are wired in parallel. They are both start
caps and the motor has no run cap. I have two cap coming tomorrow but
they are 540-685 MFD. Will them maybe be a problem? In the meantime I
will try to get the proper caps.

I've never seen anything like that but I guess it's possible,
especially since Grainger was able to find documentation on the motor.
The capacitance range of the new caps overlaps about 1/3 of the range
of the originals. Not great, but it will probably at least start.
Start caps are only used for increasing starting torque until the
motor is up to speed. The motor might complain a little starting with
too much capacitance, but once it starts, it should be ok. I've also
never seen a 3HP motor without a run capacitor. Weird.

To cover some of the other comments:

Start caps are always non-polarized electrolytics. For the
non-believers see this video where the mad bomber puts 220VAC across a
start capacitor to easily disassemble it.
<https://youtu.be/OMd9QkinXz4?t=360>
Notice the electrolyte oozing out of the capacitor before it blows
out. Looks like the guy has done this more than a few times in the
past. Run capacitors are also non-polarized, but beside electroltyic,
can also be oil filled. Not the best document on the topic but at
least covers some of the details:
"DIFFERENCE BETWEEN RUN AND START CAPACITORS"
<http://www.capacitorindustries.com/wp-content/uploads/Run-and-Start-Capacitors.pdf>

According to various web piles, the listed tolerance on most motor
starting caps is usually +/-6%. When a range of capacitance is
specified, that includes this tolerance. However that doesn't seem to
be the case here as the 540-685 cap is a much wide tolerance range. If
the capacitor is a nominal 612uF, then that range would be the same as
612uF +/-12%.


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

 

[Jeff Liebermann]

On Thu, 19 Jul 2018 18:09:05 -0400, Ralph Mowery
<rmowery28146@earthlink.net> wrote:

>This will be my last post on this thread.

Oh, be nice, or would trial by combat be a better way
to settle the matter?

Unless you can point me
to a page that specifies an electrolytic capacitor for a run and/or
start capacitor for an AC motor.

Are these sufficient?

<http://www.keltroncomp.org/index.php/prdcts/ac-motor-start-capacitor>
Note the lack of polarity markings.
Keltron Aluminium Electrolytic Motor Start capacitors
are manufactured...

From the Gainger catalog under Dayton:
<https://www.grainger.com/category/capacitors/capacitors-and-accessories/motor-supplies/motors/ecatalog/N-19eb>
These electrolytic, nonplarized capacitors are designed for
normal intermittent service on single-phase AC motor starting
circuits.

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

 

On Thu, 19 Jul 2018 15:32:39 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Thu, 19 Jul 2018 09:14:06 -0700, etpm@whidbey.com wrote:

On Wed, 18 Jul 2018 19:36:47 -0700, Jeff Liebermann <jeffl@cruzio.com
wrote:

On Wed, 18 Jul 2018 13:18:42 -0700, etpm@whidbey.com wrote:

Any reason for not disclosing the motor model number? Yes, I know
it's 40 years old and Granger can't find it.

There are two caps in most such motors. One is the "starting
capacitor". The other is the "run capacitor".
https://www.youtube.com/watch?v=qsuzfz5qcIE
https://www.youtube.com/watch?v=OMd9QkinXz4
I'm fairly sure they should NOT be wired in parallel.

For 220VAC, the starting cap should be about 30 to 50uF/kW.
3HP(mechanical) = 2.2kW so try about 90uF.

The run cap is usually about 5 - 20uF.

For the starting capacitor calculations, see:
https://www.electricneutron.com/electric-motor/single-phase-capacitor-sizing/
https://www.quora.com/How-do-I-calculate-capacitor-value-for-single-phase-motor
More:
https://www.google.com/search?q=calculate+motor+starting+capacitor

I couldn't find anything on calculating the run capacitor.

Looking again I see that there are TWO model numbers on the motor
nameplate. The top one is 5K483-D, which is a good number as I found
it on the Grianger website.

Bingo.
https://www.grainger.com/product/DAYTON-3-HP-General-Purpose-Motor-5K483
More:
https://www.google.com/search?q=dayton+5K483+motor
There are TWO wiring diagrms for suffix BB and BA with different
capacitor wiring schemes. I guess you have the BB suffix since it has
2 caps in parallel.
https://www.grainger.com/ec/pdf/5K483_4.pdf> BB suffix
https://www.grainger.com/ec/pdf/5K483_6.pdf> BA suffix

I couldn't find a reference with the exact capacitor value(s). The
parts list should have the Dayton capacitor part numbers on it
somewhere. Possible source to double check the values:
http://www.emotorpro.com/capacitors.aspx

The guy at Grainger
had to pull a file but he did find the caps and there are two. Both
caps are 485-582 MFD and are wired in parallel. They are both start
caps and the motor has no run cap. I have two cap coming tomorrow but
they are 540-685 MFD. Will them maybe be a problem? In the meantime I
will try to get the proper caps.

I've never seen anything like that but I guess it's possible,
especially since Grainger was able to find documentation on the motor.
The capacitance range of the new caps overlaps about 1/3 of the range
of the originals. Not great, but it will probably at least start.
Start caps are only used for increasing starting torque until the
motor is up to speed. The motor might complain a little starting with
too much capacitance, but once it starts, it should be ok. I've also
never seen a 3HP motor without a run capacitor. Weird.

To cover some of the other comments:

Start caps are always non-polarized electrolytics. For the
non-believers see this video where the mad bomber puts 220VAC across a
start capacitor to easily disassemble it.
https://youtu.be/OMd9QkinXz4?t=360
Notice the electrolyte oozing out of the capacitor before it blows
out. Looks like the guy has done this more than a few times in the
past. Run capacitors are also non-polarized, but beside electroltyic,
can also be oil filled. Not the best document on the topic but at
least covers some of the details:
"DIFFERENCE BETWEEN RUN AND START CAPACITORS"
http://www.capacitorindustries.com/wp-content/uploads/Run-and-Start-Capacitors.pdf

According to various web piles, the listed tolerance on most motor
starting caps is usually +/-6%. When a range of capacitance is
specified, that includes this tolerance. However that doesn't seem to
be the case here as the 540-685 cap is a much wide tolerance range. If
the capacitor is a nominal 612uF, then that range would be the same as
612uF +/-12%.

Greetings Jeff,
Thanks for the help.
As it turns out the motor I have is suffix D. The guy at Grainger
found that exact motor and he too was surprised that it did not not
have a run cap. The power factor of the motor, according to the label,
is 1.15. Wouldn't a run cap improve that a bit?
Maybe because the motor was paired with a compressor with a large
flywheel the pulsing torque from a single phase motor without a run
cap was not considered a problem because the flywheel would smooth
things out.
My best bench and pedestal grinders are Baldor motors with run caps
and they run very smooth. Virtually no vibration. This makes a
difference when sharpening drills and grinding tools.
In any case the motor never runs hot and the compressor seems fine.
Since there are two caps connected in parallel I can connect caps of
different values as long as they add up to the correct value needed,
right? I ask because I was told that if a smaller and larger value cap
are connected in parallel the lower value cap will work harder and so
fail sooner.
Changing the subject, this is the second time I have called
Grainger where they have had to look in a filing cabinet for
documentation not in the computer. The previous time was for a
compressor and I was given the number for some guy in a warehouse in
the Midwest. I told him what I needed and he riffled through some
files, found what I needed, and then scanned and emailed me the
documentation on the compressor. I think that's pretty good service.
Especially since Grainger wasn't gonna be able to sell me new parts to
fix the compressor.
A part was missing from the unloader assembly and the
documentation enabled me to make a new part and wind a new spring and
now the compressor works properly.
Eric

 

[Jeff Liebermann]

On Thu, 19 Jul 2018 16:12:13 -0700, etpm@whidbey.com wrote:

As it turns out the motor I have is suffix D. The guy at Grainger
found that exact motor and he too was surprised that it did not not
have a run cap. The power factor of the motor, according to the label,
is 1.15. Wouldn't a run cap improve that a bit?

Yep. That's the purpose of the run capacitor.
Start on Page 19:
<https://www.scribd.com/document/6883830/Tutorial-Motor-Basics-Lecture>
The way it works is when stopped both the start and run caps are in
parallel. When the motor gets up to speed, a centrifugal switch opens
and disconnects the start cap leaving the run cap in the circuit. That
means if you try to add a run cap, you'll need to decrease the value
of the start cap by the same amount. Since you're already have too
high a capacitance on the two parallel start caps, this will mean that
you'll be replacing at least one of the two new capacitors.

Maybe because the motor was paired with a compressor with a large
flywheel the pulsing torque from a single phase motor without a run
cap was not considered a problem because the flywheel would smooth
things out.

My guess(tm) is the start winding was intentionally undersized (which
is why the start cap is so large). Exactly why, I don't know.

My best bench and pedestal grinders are Baldor motors with run caps
and they run very smooth. Virtually no vibration. This makes a
difference when sharpening drills and grinding tools.

In any case the motor never runs hot and the compressor seems fine.
Since there are two caps connected in parallel I can connect caps of
different values as long as they add up to the correct value needed,
right? I ask because I was told that if a smaller and larger value cap
are connected in parallel the lower value cap will work harder and so
fail sooner.

Nope. Two caps in parallel will distribute the current going through
them by the ratio of the capacitive reactance (Xl - 1/(2Pi*f*c). The
larger capacitor will have the smaller series reactance and therefore
draw the most current. However, in the motor, we have a resonant
situation, where the run capacitor has a capacitive reactance equal to
the inductive reactance of the motor run winding, and therefore cancel
each other leaving just the winding resistance to dissipate any power.
That's also the ideal power factor point. So, if you parallel a mess
of capacitors to make a run capacitor with the correct value for PF=1,
then the capacitors will dissipate zero power.

Changing the subject, this is the second time I have called
Grainger where they have had to look in a filing cabinet for
documentation not in the computer. The previous time was for a
compressor and I was given the number for some guy in a warehouse in
the Midwest. I told him what I needed and he riffled through some
files, found what I needed, and then scanned and emailed me the
documentation on the compressor. I think that's pretty good service.
Especially since Grainger wasn't gonna be able to sell me new parts to
fix the compressor.

Impressive but what will they do when the warehouse guy retires?

A part was missing from the unloader assembly and the
documentation enabled me to make a new part and wind a new spring and
now the compressor works properly.
Eric

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