Help with Compressor Motor Capacitor/s
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  1. #1
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    Default Help with Compressor Motor Capacitor/s

    I was given a 5hp air compressor I'd like to get going again.

    It's a small (60gal) Ingersol Rand with a 5hp 220v single phase motor and a 2 cyl compressor pump.

    The pump doesn't gulp/expel air when rotated by hand.

    The motor appears OK (no physical damage, no burned smell) rotates freely, but the capacitor cover is missing and so is what was inside. It appears to be a single-wide "can" to hold a single capacitor, and there are 2 leads that go into where the can sat, but the capacitor is missing.

    I did some searches here and it seems 5hp motors should have a START and a RUN capacitor, and indeed another 5hp motor I have has a double-wide can on the top of the motor casing and likely holds TWO capacitors.

    Is it likely my compressor with NO capacitor needs only ONE capacitor, and if so, would it be a Start or Run capacitor, and what value capacitor/ voltage rating should I install to make sure the motor actually works (before I purchase a new compressor pump)?

    I rebuilt my last compressor, (an 80 gal IR T-30) with a new 5hp Century motor and a Harbor Freight "V" 2 cylinder single stage pump*, and I am very pleased with the units performance, but am open to other suggestions for lower cost pumps as well.

    Thanks,
    Bob

    *The compressor was an IR T-30 had a burned out 7.5hp industrial motor that must have weighed 75 pounds, and the pump was a 2 stage pump that weighed 130 pounds according to the specs, and which appeared to be good, but I figured it was "overkill" for my uses and went with 5hp and a pump that didn't weight 170 pounds by itself.

  2. #2
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    Do you have a model number for the motor? That'll go a long ways.

    Sent from my SM-G973W using Tapatalk

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    Thanks-

    Here is a link that SHOULD show the ID tag on the motor if it will work.

    Picture Link: https://www.screencast.com/t/jZEeN6XPe

    If the link doesn't work for you, I can try to copy all of the numbers to a text. At one point I called Ingersoll Rand about the motor and they said it was "too old" and that they could not help me.

    They DID say the 60gal compressor I had was equipped with what turned out to be a poorly made compressor pumps that generally self-destructed relatively early in their lives, and as a result, they do not provide any customer support for that model any longer. It appears to be almost all aluminum except the crankshaft and is so light it cab be lifted by one's pinky finger by the aluminum pulley. The CSR said the tank and motor were OK (in general) and they recommend rebuilding the compressor with a new design pump even before failure as catastrophic failure was not "if," but "when."

    The motor has only a 1/2" shaft, but otherwise seems to weight what a 5hp should weigh (some electric motors seem way too small and light for their rated HP, which is probably a "peak" HP for only transient measurement).

    Bob

    motor.jpg

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    https://www.practicalmachinist.com/v...uestion-332391

    They built those compressors in favor of filling up fast with high rpm motors. Self destruction is accelerated and they assume you will buy another compressor from them. If you like the pump more than the motor then get a 1725-1750 rpm motor.

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    Quote Originally Posted by rons View Post
    https://www.practicalmachinist.com/v...uestion-332391

    They built those compressors in favor of filling up fast with high rpm motors. Self destruction is accelerated and they assume you will buy another compressor from them. If you like the pump more than the motor then get a 1725-1750 rpm motor.
    Sorry, but you are talking about the compressor pump. I have no question or interest in the pump whatsoever, and asked about the MOTOR.

    The pumps all failed to my understanding as they rand them at almost 2000rpm.

    As I explained in my text I am installing a DIFFERENT pump that will run at 1000rpm, but need to know what capacitor to use on my motor.

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    My last 5hp single phase motor had a run capacitor explode. There were two 30uF capacitors for running and two motor start capacitors 161-193uF in parallel.
    The motor was on a compressor that had a short fill pipe. Now I have a VFD using soft start and a 50 foot fill pipe (to the tank). Much easier on the
    motor. Only thing is that the unload time after the motor stops is 30 seconds. Would not use a single phase motor again unless I had a long fill pipe
    and/or a soft start control on the motor.

    Not responsible if you blow something up. All motors are not the same and the start value may be different.

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    Interesting story, but unless I want to spend about $1100 to get 3 phase service run from the pole into my shop through an expensive new service panel, I think I'm stuck taking my chances with a single phase compressor motor.

    My unloader works within about 3 seconds of motor cut-out.

    A longer fill pipe WOULD be nice, though.

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    How many leads into the capacitor can? 2-wires suggest a single capacitor, 3-wires a run-start capacitor and 4 wires suggests the possibility of 2 separate capacitors.

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    Quote Originally Posted by bobinyelm View Post
    Interesting story, but unless I want to spend about $1100 to get 3 phase service run from the pole into my shop through an expensive new service panel, I think I'm stuck taking my chances with a single phase compressor motor.

    My unloader works within about 3 seconds of motor cut-out.

    A longer fill pipe WOULD be nice, though.
    I'm using a VFD and three phase motor after the single phase motor was removed.
    The long fill pipe is part of a water extraction system I made. The cost was mostly the price of 50' of 7/8" OD copper.
    Since the picture I machined aluminium support rails with PVC tape in between the copper and aluminium. The original pipe was 1/2" and 3' long.

    dsc_0999.jpg

    I don't consider you to be stuck with anything. It makes sense to use what you already have

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    Lots of variables here. First, that motor is alot like the pump in that its built cheaply and not meant to last. Its high rpm helps it to develop the torque and horsepower. 15 amps at 230 volts is a little over 4 hp. As far as caps goes, it probably only had one, the value is anybodys guess. Does it have a start switch? Is the cap in series with the start switch? Most compressors have 2 caps, one run and one start. If the motor has a start switch, it probably was a start cap. Such motors are cap start, induction run. If not, then just a run cap. These are called permanent split capacitor (PSC) motors. Can you find another one to look at?


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