Is it my motor or Run / Start capacitor ?

[Mario G.]

I have a 5 hp 230 V AC motor on a 20 gal tank /air compressor.

When given to me by the past owner, he said it needs a new electric motor.
Since I do not have a 240 line outlet in my home, as yet anyway. I plugged
this 230 v AC motor into a 120 V ac outlet, just to see what it will do.
Well what I got was the motor did indeed spin very fast, with out it being
belted to drive the air compressor pump and all looked just fine, with out
tripping the circuit breaker, then I belted it back to the compressor pump
and started it up again, all seemd fine for about 2 / 3 min. then noticed
the compressor slowing down a little at a time with every revolution it
made, then it tripped the breaker. So even though the correct voltage was
not supplied. Can my problem be a Run capacitor or the start capacitor , how
do I test these two capacitors .Since the motor did indeed spin with out a
load I hope it is just one of the two capacitors that is prcblem only. If it
truly is the motor , does it pay to have it fixed (re-wound) or get a new
one. this one has a pivot base. Any help appreciated.

 

[jriegle]

I have a 5 hp 230 V AC motor on a 20 gal tank /air compressor.

When given to me by the past owner, he said it needs a new electric motor.
Since I do not have a 240 line outlet in my home, as yet anyway. I plugged
this 230 v AC motor into a 120 V ac outlet, just to see what it will do.
Well what I got was the motor did indeed spin very fast, with out it being
belted to drive the air compressor pump and all looked just fine, with out
tripping the circuit breaker, then I belted it back to the compressor pump
and started it up again, all seemd fine for about 2 / 3 min. then noticed
the compressor slowing down a little at a time with every revolution it
made, then it tripped the breaker. So even though the correct voltage was
not supplied. Can my problem be a Run capacitor or the start capacitor , how
do I test these two capacitors .Since the motor did indeed spin with out a
load I hope it is just one of the two capacitors that is prcblem only. If it
truly is the motor , does it pay to have it fixed (re-wound) or get a new
one. this one has a pivot base. Any help appreciated.

The 240 volt motor is not going to be able to supply much torque on 120
volts. As the pump builds up pressure, the more load on the motor and it
stalls. have the caps checked and feed it the correct voltage!
John

 

[Paul]

Less voltage = more current = more heat = goodbye motor.

Wrong! Here's another guy who thinks everything follows Ohm's law.

Most likely, when his motor, due to it being overwhelmed by the load and not
being provided with the proper supply, stalled. This caused the impedance
of the windings to go down very low. The motor windings then will draw lots
of current and trip the breaker since it's basically a short-circuit at that
point. Unless he left the motor in that condition for a long time or
repeated the act, I doubt very much it would burn out the windings.

You should be able to visually see any such severe winding damage through
the vent holes - and smell it for that matter. Check the caps and the CS
switch before condemning the windings.

 

[Ross Mac]

I have a 5 hp 230 V AC motor on a 20 gal tank /air compressor.

When given to me by the past owner, he said it needs a new electric motor.
Since I do not have a 240 line outlet in my home, as yet anyway. I plugged
this 230 v AC motor into a 120 V ac outlet, just to see what it will do.
Well what I got was the motor did indeed spin very fast, with out it being
belted to drive the air compressor pump and all looked just fine, with out
tripping the circuit breaker, then I belted it back to the compressor pump
and started it up again, all seemd fine for about 2 / 3 min. then noticed
the compressor slowing down a little at a time with every revolution it
made, then it tripped the breaker. So even though the correct voltage was
not supplied. Can my problem be a Run capacitor or the start capacitor , how
do I test these two capacitors .Since the motor did indeed spin with out a
load I hope it is just one of the two capacitors that is prcblem only. If it
truly is the motor , does it pay to have it fixed (re-wound) or get a new
one. this one has a pivot base. Any help appreciated.

Perhaps you can pickup the 240 volts from the main panel and rerun your test
with the correct supply. If you don't know how to do that call an
electrician.
Odds are the windings are good if they don't smell bad from their trip to
"overcurrent land"...You should be able to ring them out and get a reading
of a couple of ohms or so,
though, I don't know what the motor rating is and what "exactly" to expect.
It would apparent, at least, that the windings were toast if they were open
or high resistance and
a reading of a fraction of an ohm might imply a short....There is no
exactness here....just a quick test method.
As far as testing the capacitors....I don't know how well you are equipped
so your best bet would be to swap them out with a couple from surplus or
just buy new ones.
Sometimes surplus caps can be bad too....Try http://www.mcmaster.com/ and
type motor capacitor at the prompt and match the voltage and capacitance
ratings. I bet
you can find a couple for 5 or 6 bucks each. Good luck with your new
toy....Ross

 

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Less voltage = more current = more heat = goodbye motor.



Wrong! Here's another guy who thinks everything follows Ohm's law.

How does his statement "Less voltage = more current = more heat =
goodbye motor."
indicate he thinks everything follows Ohm's law?