start capacitor

[miggymarky]

I am looking to replace my start cap on my old Ingersoll rand 3hp comp (single phase),trouble is there is no numbers anywhere on it or writing.also its a complete sealed unit all round,so how do l know which one to buy.

 

[piman]

Hello Marky,

if there is no markings left on the capacitor, take it to a motor rewind workshop, and tell them the size of the motor, they should be able to sell you a capacitor that will be pretty near to what is needed.

Alec

 

[miggymarky]

No probs thanks mate

 

[miggymarky]

Just to recap on this.my compressor was left covered in the garden last year for around 8 weeks,and now when switching it on the motor just hums and if left switched on for a minute it will smoke,so I am assuming its the cap on top.is there a way of testing this.I have taken the motor apart and sprayed wd40 in it to no avail.comp is an old 3hp Ingersoll rand from around the 1950 s.

 

[p0689109]

Have you checked that the pump is not seized?
Just a thought.
Regards, Michael T

 

[normspanners]

If motor has drawn in damp you can 'dry' them in an oven with a VERY ! low heat, for a long period. The smoke could be the wd40?
but I think Michael T has a good point.

 

[miggymarky]

It does turn easy by hand with the belt attached so I would say pump is ok.

 

[eil]

Take the belts off and run it on its own that will eventually dry it out, It will have difficulty starting in this weather so your capacitors need to be in good condition. What state is the oil in the compressor. Put a pic up of the motor that you have on it see if someone has the same one.

Are you trying to start it with an extension lead by any chance.

 

[superls]

power it up and spin the pully on the end see if it spins, if it does chances are it is the start cap

 

[miggymarky]

No I plugged it straight in the socket,but saying that I have never had it running at our new house and its a different fuse board here,its more updated .yes I did spin it with the belt off but no good.

 

[normspanners]

has this motor got two caps, in other words a start cap and a run cap?
some motors can have a combined start run caps, also there can be a centrifugal switch on some hi torque ie compressor motors, that is used for start up this may not be connecting properly due to corrosion, with it standing outside, so that the start winding is not actually being allowed to work, this normally can be heard as the motor slows down after being switched off as an audible 'click', when it gets to approx 600/800 rpm the switch is usually at the fan end. I have started a motor by winding a strong starting string around the pulley with no belts on it, do NOT tie the string just wrap it, so when pulled it rotates the motor in the same direction as normal as soon as the string comes off the pulley hit the power switch to on whilst the rotor is still spinning as fast as possible if the motor runs then leave it running to dry it and the centrifical switch may work the next time having been exercised

 

[eil]

Doesn't look good if it doesn't run when spun by hand and then power switched on, how long was this minute you left it smoking for, also when you had it running the opposite direction to what it was originally did you swap some wires around, have you re-checked your wiring. Does this motor run off a 13amp plug.

 

[brewdexta]

I bought one of these for my 2HP motor on my Clarke compressor when the old one died they have one approx a third bigger so this will probably do it if it is the cap.

 

[miggymarky]

Yes it runs off a 13 amp plug,and there is only one cap directly on top of the motor.I am led to believe its an old brewery compressor and don't really give much cfm if its any help.

 

[eil]

If that is a 3hp motor which i seriously doubt, it would likely have two 100uf capacitors in that tube on the top, its more than likely a 1.5 or 2hp at the most, I say this because an old 3hp cap start induction run would not run off a 13amp plug. I think you might as well take it to someone to check it out properly for you, seeing that you have let out some of the magic smoke from it.

 

[miggymarky]

Probably right,apparently when I had it the motor had not long been rewound.As for HP of the motor,I only have the previous owners word as there are no markings on the comp anywhere.

 

[CompoSimmonite]

I had an old Burgess motor on a Myford lathe that refused to turn over when plugged in. I was told change capacitor but that didn't make any difference and turned out to be the centrifugal switch that kicked in when motor turned had stuck. Simple clean got it working OK.

Paul h

 

[CompoSimmonite]

If that is a 3hp motor which i seriously doubt, it would likely have two 100uf capacitors in that tube on the top, its more than likely a 1.5 or 2hp at the most, I say this because an old 3hp cap start induction run would not run off a 13amp plug. I think you might as well take it to someone to check it out properly for you, seeing that you have let out some of the magic smoke from it.

The new Clarke 3hp motor (110V) I've bought to convert my compressor from 3 phase has two start capacitors but no run capacitor. You cna tell the difference between start and run capacitors but the casing. Start are plastic and would fail is used as a run whereas run are metal casing and will work as a start (but are dearer to buy hence manufactures used plastic).

Paul H

 

[miggymarky]

Where is the centrifugal switch,don't know to much about compressors

 

[eil]

The new Clarke 3hp motor (110V) I've bought to convert my compressor from 3 phase has two start capacitors but no run capacitor. You cna tell the difference between start and run capacitors but the casing. Start are plastic and would fail is used as a run whereas run are metal casing and will work as a start (but are dearer to buy hence manufactures used plastic).

Paul H

That bit about start caps having plastic casings and run caps having metal casings is not quite right I'm afraid, an older start cap would have been more likely to have been metal and a greater amount of run caps are plastic cased nowadays. you are quite right in saying that a start cap wouldn't last long if fitted instead of a run cap though. a motor with only a start cap or even two connected up in parallel is called a cap start induction run motor.
Why have you opted to replace your three phase motor with a 110v single as opposed to a 220v one.