A friend has just had his Ingersoll Rand compressor up and die on him.
Before it did so, it had the habit of dineing out on 140 uF motor start
capacitors. This is in 50 Hz 240V land. The old motor was 2Hp, Cap
start/ Cap run single phase, and the final death throes were when it
decided to eat the 32 uF run capacitor as well. The potential relay
appears to be OK (at least its not welded shut and has continuity on its
windings) and I am suspecting a shorted turn in the old motor's start
winding.

The compressor is rated at 150 Psi but the cutout is set to 100 psi.
It came with a three phase motor that we are hoping to put back on it.
Details as follows (the 'HH' is a symbol with both Hes sharing one
upright, 'O/' is the slashed greek O for phase angle):

HOLEC 'HH' heemaf
KMEP90L4/166/1
COS 'O/' 0.84
50 HZ 1400 rpm
1.5KW 240/415V 5.7/3.3A

I've allready rewired it for 240V delta and pullrope started it off load
, then tried 18 uF of run caps to make it self starting and it seems
pretty happy but still off load. I would appreciate advice on choosing
a suitable single run capacitor to also act as a start capacitor. as we
hope to be able to loose the potential relay and electrlytic as bioth
are too high maintenance. I belive 25 - 30 uF per horsepower is normal
and I presume 60 uF would be better than 50 uF for starting torque.
I also know that all caps over here need to be 20% bigger to get the
same reactance at 50 Hz as most of you get at 60Hz. Would there be any
advantage in going to say 80 uF (2x 40 uF caps work out much cheaper
than one 60uF!) I've only got 18uF of run caps around the workshop and
none of them are over 2 uF so we really need to get pretty close on the
first shot as I'll have to order them.

Its going to be occasional use as a backup compresser, tyres etc, small
air tools, maybe some spraying. Are we wasting our time expecting 2/3
the power, self starting off a static single capacitor phase converter?

I am going to measure the winding resistance and inductance today if I
can manage it so I have a little more data. I understand series
resonance is *A BAD THING* for a motor winding and I want to avoid it.
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.

I do *not* like leaving the larger start cap in the circuit. It usually will
buzz loudly. I had a buddy with a phase converter set up like that and it
was awful to work around. Finally I introduced him to Bob Powell who reworked
his converter to take the start cap out of the circuit (don't know how, but
knowing Bob, it was most likely a potential relay) and now it's nice and quiet.
In my experience potential relays are extremely robust and work just fine.

Your start capacitor needs to be big enough to reliably start the motor while
small enough so that too much current doesn't flow for your wiring. Bigger
means more current means faster starting for more initial cost. Smaller means
slower starting with less current for less money. Start caps can be electrolytic
and are thus cheap. Run caps should be oil-filled and cost much more, but for
a 1.5kw motor shouldn't cost that much. I can go look up recommended start
capacitance per horsepower but so can you. If you don't like the new Google
groups try groups.google.com.au - the Aussies still have a good google going
down there.

GWE

Ian Malcolm wrote:

The compressor snip came with a three phase motor that we are hoping to put back on it.
Details as follows (the 'HH' is a symbol with both Hes sharing one
upright, 'O/' is the slashed greek O for phase angle):

HOLEC 'HH' heemaf
KMEP90L4/166/1
COS 'O/' 0.84
50 HZ 1400 rpm
1.5KW 240/415V 5.7/3.3A

I've allready rewired it for 240V delta and pullrope started it off load
, then tried 18 uF of run caps to make it self starting and it seems
pretty happy but still off load. I would appreciate advice on choosing
a suitable single run capacitor to also act as a start capacitor. as we
hope to be able to loose the potential relay and electrlytic as bioth
are too high maintenance. I belive 25 - 30 uF per horsepower is normal
and I presume 60 uF would be better than 50 uF for starting torque.
I also know that all caps over here need to be 20% bigger to get the
same reactance at 50 Hz as most of you get at 60Hz. Would there be any
advantage in going to say 80 uF (2x 40 uF caps work out much cheaper
than one 60uF!) I've only got 18uF of run caps around the workshop and
none of them are over 2 uF so we really need to get pretty close on the
first shot as I'll have to order them.

"Ian Malcolm" wrote in message
...
A friend has just had his Ingersoll Rand compressor up and die on him.
Before it did so, it had the habit of dineing out on 140 uF motor start
capacitors. This is in 50 Hz 240V land. The old motor was 2Hp, Cap start/
Cap run single phase, and the final death throes were when it decided to
eat the 32 uF run capacitor as well. The potential relay appears to be OK
(at least its not welded shut and has continuity on its windings) and I am
suspecting a shorted turn in the old motor's start winding.

The compressor is rated at 150 Psi but the cutout is set to 100 psi.
It came with a three phase motor that we are hoping to put back on it.
Details as follows (the 'HH' is a symbol with both Hes sharing one
upright, 'O/' is the slashed greek O for phase angle):

HOLEC 'HH' heemaf
KMEP90L4/166/1
COS 'O/' 0.84
50 HZ 1400 rpm
1.5KW 240/415V 5.7/3.3A

I've allready rewired it for 240V delta and pullrope started it off load ,
then tried 18 uF of run caps to make it self starting and it seems pretty
happy but still off load. I would appreciate advice on choosing a
suitable single run capacitor to also act as a start capacitor. as we hope
to be able to loose the potential relay and electrlytic as bioth are too
high maintenance. I belive 25 - 30 uF per horsepower is normal and I
presume 60 uF would be better than 50 uF for starting torque.
I also know that all caps over here need to be 20% bigger to get the same
reactance at 50 Hz as most of you get at 60Hz. Would there be any
advantage in going to say 80 uF (2x 40 uF caps work out much cheaper than
one 60uF!) I've only got 18uF of run caps around the workshop and none of
them are over 2 uF so we really need to get pretty close on the first shot
as I'll have to order them.

Its going to be occasional use as a backup compresser, tyres etc, small
air tools, maybe some spraying. Are we wasting our time expecting 2/3 the
power, self starting off a static single capacitor phase converter?

I am going to measure the winding resistance and inductance today if I can
manage it so I have a little more data. I understand series resonance is
*A BAD THING* for a motor winding and I want to avoid it.
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.


Ian

You have several interesting things going on in this post. I understand
that you have a single phase motor that you suspect to be "dead". And you
want to replace it with a 3 phase motor that has no idler so it must start
and run from single phase. In addition, you want information on "balancing
capacitors" for the 3 phase motor, after is gets up to speed.

It would be difficult for me to agree that the single phase motor is
"dead". I would inclined to try evaluating the single phase motor. It
isnt normally difficult to disassemble an induction motor with no
centrifugal switch.
Also, it is possible that the capacitor that is being eaten is objecting
to the voltage across it. That could be the result of alot of things.

You are *not* wasting your time by designing a start up system so that 3
phase motor can get loaded to even 3/4 its name plate rated HP. You are
aware of the need for cooling the motor. It probably wont run at full
(3/4) HP for long anyway. You can build something to automatically spin up
the 3 phase motor from single phase.

If you are right when you estimate that the compressor will not need full
motor HP when pumping to only 100 PSI, your main problem will be to include
an excellant unloader. Also, it would be prudent to also include an
overcurrent cut out for that condition where the motor gets stalled.

Another thing I'd consider is the pulley size. A smaller motor pulley
would lessen the load on the motor.

It reads (to me) like you expect to improve the power delivering ability
of the 3 phase motor that drives the compressor pump, by including balance
capacitors. That could easily be a big project. I'd consider the small
amount of power increase associated with balancing would make that time
poorly spent.

Jerry

Jerry Martes wrote:

Ian

You have several interesting things going on in this post. I understand
that you have a single phase motor that you suspect to be "dead". And you
want to replace it with a 3 phase motor that has no idler so it must start
and run from single phase. In addition, you want information on "balancing
capacitors" for the 3 phase motor, after is gets up to speed.

It would be difficult for me to agree that the single phase motor is
"dead". I would inclined to try evaluating the single phase motor. It
isnt normally difficult to disassemble an induction motor with no
centrifugal switch.
I have'nt personally inspected it internally. My friend has and
couldn't see anything obvious. The bearings are good, the centrifugal
fan and shroud are present and reasonably clean and it hasn't let the
'holy smoke' out. I have seen it eat a start capacitor, the run
capacitor survived that time. The compressor pump is in good condition
and has a working unloader.
Also, it is possible that the capacitor that is being eaten is objecting
to the voltage across it. That could be the result of alot of things.
Well these are 400VAC rated start caps on a 240VAC system. The motor
starts and runs, but blows the vent on the Start capacitor on the first
start. I belive the potential relay fails to cut out. I can put that
on a variac and see what it takes to keep it in, and how much current on
its current winding but I dont want to blow another start cap. There are
too many of them lined up on the window sill allready. Would it be
worth rope starting it and checking the voltage on the start winding
with that winding isolated? I hope that might give me some indication of
a shorted turn.

You are *not* wasting your time by designing a start up system so that 3
phase motor can get loaded to even 3/4 its name plate rated HP. You are
aware of the need for cooling the motor. It probably wont run at full
(3/4) HP for long anyway. You can build something to automatically spin up
the 3 phase motor from single phase.

We are confident we can get it to spin up OK, it shouldnt see much load
for the first few turns unless someone has turned it off at the wall and
forgotton to trip the unloader. I have allready suggested additional
cooling.


If you are right when you estimate that the compressor will not need full
motor HP when pumping to only 100 PSI, your main problem will be to include
an excellant unloader. Also, it would be prudent to also include an
overcurrent cut out for that condition where the motor gets stalled.
Yes, I plan to rework the old control box which includes a circuit breaker.

Another thing I'd consider is the pulley size. A smaller motor pulley
would lessen the load on the motor.
The other motor is 2900 RPM and each has its own pulley. I'd look at
going a third smaller but delivery is more important than pressure.
We'd settle for backing off the pressure switch to 90PSI.

It reads (to me) like you expect to improve the power delivering ability
of the 3 phase motor that drives the compressor pump, by including balance
capacitors. That could easily be a big project. I'd consider the small
amount of power increase associated with balancing would make that time
poorly spent.

Well I am just trying to get a feel for what I can get out of it without
breaking the bank. If we can get 75% rated power, we'll be rather
happy. What approximate power increase can we expect from decent
balancing?

Thanks for your assistance. We are going to have a shot at it. Plan B
is buy in new control gear and plan C is replace the motor. I dont like
plan C :-(
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.

Grant Erwin wrote:

I do *not* like leaving the larger start cap in the circuit. It usually
will
buzz loudly. I had a buddy with a phase converter set up like that and it
was awful to work around. Finally I introduced him to Bob Powell who
reworked
his converter to take the start cap out of the circuit (don't know how, but
knowing Bob, it was most likely a potential relay) and now it's nice and
quiet.
In my experience potential relays are extremely robust and work just fine.
Well thats an option. I was hopeing to 'simplify and add more lightness'
but we are willing to go for seperate start and run caps if we have to.


Your start capacitor needs to be big enough to reliably start the motor
while
small enough so that too much current doesn't flow for your wiring. Bigger
means more current means faster starting for more initial cost. Smaller
means
slower starting with less current for less money. Start caps can be
electrolytic
and are thus cheap.

But not if they behave as disposable or even one-shot items :-) I think
the problem is duty cycle related, if it cycles to often, pop goes tha
cap. I was planning on caps rated for continuous duty and compromise a
bit on starting torque.

Run caps should be oil-filled and cost much more,
but for
a 1.5kw motor shouldn't cost that much. I can go look up recommended start
capacitance per horsepower but so can you. If you don't like the new Google
groups try groups.google.com.au - the Aussies still have a good google
going
down there.

Gooogle groups here is still good.

Thanks for yoyr assistance.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.

"Ian Malcolm" wrote in message
...
Jerry Martes wrote:
Ian

You have several interesting things going on in this post. I
understand that you have a single phase motor that you suspect to be
"dead". And you want to replace it with a 3 phase motor that has no
idler so it must start and run from single phase. In addition, you want
information on "balancing capacitors" for the 3 phase motor, after is
gets up to speed.

It would be difficult for me to agree that the single phase motor is
"dead". I would inclined to try evaluating the single phase motor. It
isnt normally difficult to disassemble an induction motor with no
centrifugal switch.
I have'nt personally inspected it internally. My friend has and couldn't
see anything obvious. The bearings are good, the centrifugal fan and
shroud are present and reasonably clean and it hasn't let the 'holy smoke'
out. I have seen it eat a start capacitor, the run capacitor survived
that time. The compressor pump is in good condition and has a working
unloader.
Also, it is possible that the capacitor that is being eaten is
objecting to the voltage across it. That could be the result of alot of
things.
Well these are 400VAC rated start caps on a 240VAC system. The motor
starts and runs, but blows the vent on the Start capacitor on the first
start. I belive the potential relay fails to cut out. I can put that on
a variac and see what it takes to keep it in, and how much current on its
current winding but I dont want to blow another start cap. There are too
many of them lined up on the window sill allready. Would it be worth rope
starting it and checking the voltage on the start winding with that
winding isolated? I hope that might give me some indication of a shorted
turn.

You are *not* wasting your time by designing a start up system so
that 3 phase motor can get loaded to even 3/4 its name plate rated HP.
You are aware of the need for cooling the motor. It probably wont run
at full (3/4) HP for long anyway. You can build something to
automatically spin up the 3 phase motor from single phase.

We are confident we can get it to spin up OK, it shouldnt see much load
for the first few turns unless someone has turned it off at the wall and
forgotton to trip the unloader. I have allready suggested additional
cooling.


If you are right when you estimate that the compressor will not need
full motor HP when pumping to only 100 PSI, your main problem will be to
include an excellant unloader. Also, it would be prudent to also
include an overcurrent cut out for that condition where the motor gets
stalled.
Yes, I plan to rework the old control box which includes a circuit
breaker.

Another thing I'd consider is the pulley size. A smaller motor pulley
would lessen the load on the motor.
The other motor is 2900 RPM and each has its own pulley. I'd look at
going a third smaller but delivery is more important than pressure. We'd
settle for backing off the pressure switch to 90PSI.

It reads (to me) like you expect to improve the power delivering
ability of the 3 phase motor that drives the compressor pump, by
including balance capacitors. That could easily be a big project. I'd
consider the small amount of power increase associated with balancing
would make that time poorly spent.

Well I am just trying to get a feel for what I can get out of it without
breaking the bank. If we can get 75% rated power, we'll be rather happy.
What approximate power increase can we expect from decent balancing?

Thanks for your assistance. We are going to have a shot at it. Plan B is
buy in new control gear and plan C is replace the motor. I dont like plan
C :-(
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.


Ian

I'm thinking that your main problem will be to get the 3 phase motor to
start spinning when fed single phase.
I'm thinking that the start winding is commonly cut off when the motor
reaches about 80 % of its normal, unloaded, RPM.

Although I wouldnt have courage enough to advise you to dig into that 3
phase motor to make it a better single phase motor, that can be done. I
have gone inside the 3 phase motor and disconnected the unused, third stator
winding and use it as a start winding across the single phase line with a
start capacitor in series. The start torque is quite high when that is
done. But, if you can get the compressor to start with the "phase-O-matic"
approach, thats likely to be much more satisfactory.

I wonder if you have considered increasing the volume of the air supply
tubing between the pump and the check valve in the tank. That allows the
pump to be rotated more revs before the load kicks in. But, maybe you have
an unloader that isnt dependent on air pressure.

Jerry

A three phase motor will deliver about 2/3 power on single phase with
no caps at all.
I would try to find someone that has some run caps that will let you
borrow them to find out what you need. If you were closer, I would
lend you some. This week I wandered through the local scrap yard and
picked up a 24 ufd 440VAC cap and a few other items. At $.40 / lb the
cap was not very expensive. Try your HVAC repair places.
Dan

Lots of good advice on this thread - a few extra
comments may help.

I second the suggestion that your "single phase"
motor may not be faulty. The usual failure pattern of a
start winding is severe overheating leading to smell of
burning, eventually followed by smoke and complete failure.

A surviving isolated shorted turn is a pretty rare
event. When it occurs, because the turn is closely coupled
to the rest of the winding, very large currents flow and
this rapidly heats the turn to insulation failure point.
This inevitably leads to failure of the whole winding.

The repeated failure of the start capacitor is more
likely to be due to excessive multiple or prolonged start
cycles either, because the motor is not man enough for the
starting load, or because the potential relay is not
disconnecting the start capacitor early enough.

This leads to internal overheating of electrolytic
start capacitors with eventual failure.

If this is the case, a change to an oilfilled paper
or polymer start capacitor or easing the starting load by
reducing the size of the drive pulley is the way forward.

I put he inverted commas round "single phase"
motors because some manufacturers do not supply true single
phase motors but simply use an appropriately rated standard
3phase machines fitted with start and run capacitors.
Because the 3phase machine has no provision for a
centrifugal switch a potential relay has to be used to
switch in the starting capacitor. I think it possible that
your "single phase" motor is of this second type.

It may be no coincidence that the capacitor
values used on your machine are pretty close to the
appropriate sizes for start and run capacitors for a 2HP
240v 50Hz 3phase machine. This means there is a chance that
you have two 3phase machines and one could be used as an
idler to ease the starting load.

If you decide to bite the bullet and change the
motor, separate start and run capacitors will be essential.
Don't skimp on the size of the starting capacitor -
compressor duty is is pretty demanding. 130 uF is pretty
minimum - 150uF or a bit more is better. The run capacitor
is much less important, 30 uF is OK but if you're not using
the full 150 psi rating you could use a smaller capacitor or
possibly no run capacitor at all.

Jim