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General Forum => In the Work Shop => Topic started by: Bryanair on January 31, 2019, 10:51:20 AM



Title: Compressor not starting
Post by: Bryanair on January 31, 2019, 10:51:20 AM
My compressor lives in my unheated shed and when I brought it into the house the other day and switched it on nothing happened.  I have since read that the oil in it can thicken but it has been in the house a couple of days now and still no joy.  When I flick the switch nothing- no click etc.  I have checked the fuse in the plug and that is OK.  Searching the problem on Youtube only brings up videos of guys with big industrial compressors.  Has anyone any suggestions before I start pulling it apart?


Title: Re: Compressor not starting
Post by: strat-o on January 31, 2019, 10:57:30 AM
Seems like the main killer of compressors (I'm talking A/C here) is the capacitor.  Not sure if these small compressors use one but that would be my first check when tearing into it.


Title: Re: Compressor not starting
Post by: SP250 on January 31, 2019, 03:09:39 PM
Now thats interesting.
I have exactly the same problem with my Vacuum pump.
Brought it in from years of storage in the garage and checked fuses etc., put a meter across all the conections I can get to and the start switch - nothing.
Its an AC motor so what does the capacitor do? 
Is it the same thing as the two can shaped things on the one side of some of the bigger ESC's for outrunner motors we use in models?
I emailed the service dept of the manufacturer a week a go in the USA but got no reply.
Where do you find how to strip, clean, check & fix these things?

Cheers John M


Title: Re: Compressor not starting
Post by: Ex Member on January 31, 2019, 04:44:20 PM
The capacitor(s) create the required phase difference in the windings to create a rotating field.  This is only needed for a single phase motors.  Three phase motors don’t need them due to the fact that each of the three phases (each connected to a different field winding) are already out of phase...

Check for continuity in the windings, be careful round the caps, they can store quite a charge, and are happy to deliver it all in one go if shorted.

It’s perhaps a mechanical thing, is there any way to turn the shaft of the compressor?

Andrew



Title: Re: Compressor not starting
Post by: Robmoff on January 31, 2019, 05:29:45 PM
I bought a brand new, expensive Vac pump of similar configuration to that about 15 years ago. It would not start, did all the checks then went for the 50 mile trip to the supplier. The lad there said 'yes, they do that sometimes if they haven't run for a while', grabbed the protruding 1/2 inch of the motor shaft and gave it a flick round. It burst into life! Never had any more trouble with it, though I might do next time, it's been in the shed for at least five years.    :D


Title: Re: Compressor not starting
Post by: Konrad on January 31, 2019, 05:49:29 PM
I bought a brand new, expensive Vac pump of similar configuration to that about 15 years ago. It would not start, did all the checks then went for the 50 mile trip to the supplier. The lad there said 'yes, they do that sometimes if they haven't run for a while', grabbed the protruding 1/2 inch of the motor shaft and gave it a flick round. It burst into life! Never had any more trouble with it, though I might do next time, it's been in the shed for at least five years.    :D
Plus One for that.
Sticky brushed and dirty commutators are often the problem. A light tap on the housing often works.


Title: Re: Compressor not starting
Post by: fred on January 31, 2019, 11:17:06 PM
You 'Could remove the front cover exposing the con rod and try manually cycling the thing 'might be gummed stuck.. or not.
 The one in the photo (and most others beyond Car tire inflators) have INDUCTION motors  no commutators/brushes.
See the little black round thing on the back of the compressors Cyl head ??
That's the pressure switch.. it's kinda Critical for compressor function :-).
These can get stuck  from long non use, and even occasionally fail.
  Remove the rear chrome cover on the compressor and using a Meter check for continuity... everywhere...
 from power line in.. to switch terminals.. to Press sensor/switch .. to motor terminals.

Fair guess it's down  to a bit (?) of terminal Corrosion resulting from the typically warm and sunny climes of the Sceptered Isles.
 Where Rust was first invented.


Title: Re: Compressor not starting
Post by: SP250 on February 01, 2019, 04:11:09 AM
Thanks for all the suggestions.

Yes I have taken a cover or two off and rotated the shaft (by the cooling fan attached) but it is fairly stiff (twin boxer piston pump).
Looks like a mechanical strip and lube on the cards and then see what I can find out on the electrical side.

I truly believe that aeromodelling teaches you how to be a master of all trades not just a jack! - best education I ever had.

John M


Title: Re: Compressor not starting
Post by: Bryanair on February 01, 2019, 04:59:00 AM
I took the front cover off and turned the crank and con rod.  All seems OK.  Next step will be to check the electrics.


Title: Re: Compressor not starting
Post by: Bryanair on February 01, 2019, 08:04:53 AM
Faulty on/off switch!  Thanks for the advice chaps.  Bryan


Title: Re: Compressor not starting
Post by: Bryanair on February 01, 2019, 03:00:30 PM
I have now found a Youtube video of my airbrush with some interesting tips on cleaning the cylinder head and reed valve.

https://www.youtube.com/watch?v=qxR-1zGH0MQ


Title: Re: Compressor not starting
Post by: Squirrelnet on February 01, 2019, 03:58:16 PM
Bryan

Very pleased to hear that you have sorted your compressor out and are up and running again. The youtube video is a great reference thanks for posting it.

I've been following this thread with interest as I have just bought the same compressor, its performed very well so far but good to know the weak points. I didn't even realise it was an induction motor.

John

 Good luck with the vacumn pump, hope you get it sorted

Chris


Title: Re: Compressor not starting
Post by: SP250 on February 02, 2019, 05:36:05 AM
Thanks Chris

Got this weekend free of work and BMFA stuff, so modelling and vac pump strip it is - might even get the T100C crankcases into the oven as well to fit the new main bearings and start that rebuild too.

John M


Title: Re: Compressor not starting
Post by: Squirrelnet on February 02, 2019, 06:14:33 AM
T100C sounds fun, did you buy it as a project or is this refurb ? Not that hot on Triumphs but presumably a Tiger scrambler ?



Title: Re: Compressor not starting
Post by: SP250 on February 02, 2019, 10:23:53 AM
Chris

Yes a 1972 500 twin with the high level pipes on the LHS - last of the drum braked 500's.
Imported from the US in about 2005 as a reasonable bike/project with many new spares.

John M


Title: Re: Compressor not starting
Post by: Squirrelnet on February 02, 2019, 01:01:25 PM
Sounds like a nice project


Title: Re: Compressor not starting
Post by: Bryanair on March 11, 2019, 05:42:25 PM
By replacing the switch I got the compressor to start and run.  The problem now was that it would reach operating pressure but after spraying for a bit it would rock about and not start up cleanly.  I followed the guys on the video and found bits inside the cylinder just as they described.  I cleaned it all up and my compressor now runs like it should.

Bryan


Title: Re: Compressor not starting
Post by: SP250 on March 11, 2019, 06:09:33 PM
Well, I stripped and cleaned and lubed (dry graphite lube) the pistons and cylinders of the vac pump. 
Oiled the big end sealed bearings on the crank and mechanically its now fine. 
But the electric motor still won't start even with a flick round.
What do I try next?

John M


Title: Re: Compressor not starting
Post by: ffkiwi on March 11, 2019, 06:26:51 PM
Have you checked the capacitor?-as mentioned in earlier posts-if it is a duff capacitor your motor won't start..period. And my experience is that these are the weak link in some of these 'industrial' type electric motors. I've had two go on two separate Emco Compact 5 lathes over the years....and their motors (500W) are about the size you find on a home type compressor.....

 ChrisM
 'ffkiwi'


Title: Re: Compressor not starting
Post by: fred on March 11, 2019, 09:52:07 PM
Don't believe these types actually Have a start /run  capacitor  ;)
 Check  ALL connections and meter the motor (ohms..short circuit continuity etc)
although smell of burnt windings insulation would be pretty obvious .
Likely a bad wire .. connection.. Or switch. Also the pressure switch can fail .. Meter it.
Whatever the issue, it will probably end up being a Dohhh ! moment.


Title: Re: Compressor not starting
Post by: SP250 on March 12, 2019, 06:03:17 AM
Ok Chaps - out with the multi meter again.
Obviously continuity through a switch or windings I can check, but what am I looking for with a capacitor?
TIA
John M


Title: Re: Compressor not starting
Post by: Robmoff on March 12, 2019, 09:45:29 AM
Depends on what sort of meter you have.
A quick and dirty check is to use a good digital meter set to ohms. That will give you a reading which will change as you keep the meter connected, basically you are measuring the flow of current into the capacitor through the resistance of the measuring circuit, that should start large and decrease as the capacitor charges, you may then be able to measure a declining voltage on the capacitor.
A more reliable method is to charge the capacitor through a resistor and measure the voltage continuously, then stop the charge  while still monitoring the voltage to see if it self discharges too rapidly, and finally discharge through a load. It's a lot of faf, you need to work out the voltage and current limits and ideally compare the results to a known good example.
You won't be pleased to hear that I recently scrapped a filling cabinet draw full of start capacitors after hoarding them for about 30 years.  ::)


Title: Re: Compressor not starting
Post by: strat-o on March 12, 2019, 10:50:37 AM
What Robmoff said is correct.  You can think of a capacitor as being like a fast-acting rechargable battery--quick to charge, quick to discharge.  So testing one would be similar to testing a rechargable battery only quicker.  They should be relatively inexpensive, however.  Cheap enough, perhaps, to forgo testing and simply replace it.  Of course this would be a no-brainer if the capacitor is a connector type.  If it's a soldered-in-place type, the replacement is riskier.


Title: Re: Compressor not starting
Post by: SP250 on March 12, 2019, 05:04:30 PM
Thanks for the replys Rob & Strato. 
If you translated that into English Rob I might stand a chance of understanding it.

It's a soldered on capacitor which has MOT 212-6128 then PRS 145 MFD 125 VAC printed on it.
All of which mean nothing to me.
About 2" diameter and 4" long with 2 red wires soldered to its connections.

John M


Title: Re: Compressor not starting
Post by: Robmoff on March 12, 2019, 07:11:15 PM
It WAS in English, would you prefer Welsh?  ;)

Ok I'll bring a meter with me next time I'm in Shawbury, could you have one lead of the capacitor unsoldered ready?

I'll also try to get a new spare one for you, should only be a tenner or so; but I find your numbers a little odd. 145 microfarads I understand, but that is higher than I would expect, though the motor may have an unusual wind. 125 Volts AC I also understand but that definitely seems too small, I would expect 350 to 450 volts. What voltage does the pump run on, mains or through a low voltage transformer?


Title: Re: Compressor not starting
Post by: SP250 on March 12, 2019, 07:47:58 PM
Rob
Its a Yank 110v motor/vac pump and I have a 240v down to 110v transformer for it which checks out ok and runs a small 110v compressor fine.

I have unsoldered - alright cut one end off the wire to the capacitor.
On a "decent" multi meter with the ohms set to lowest setting and tone, it gives a rising reading to about 1800 in about a second.
On 200mv setting (lowest) it discharges so fast I can't read the numbers going down to 0L.
What does that tell us?

John M


Title: Re: Compressor not starting
Post by: Robmoff on March 13, 2019, 07:32:32 AM
110v explains the 120VAC, though the safety margin is a bit smaller than you would expect on a UK system, that's yanks for you! BUT since it is a 60Hz motor the capacitor will not be giving you the same phase shift, which is what it's there for. I would not have thought it was that critical, but I guess if it's already on the 'slow' limit the change in frequency might push it over the edge. Has this pump ever run on 50Hz?
Without a known good one to compare, you test does seem OK, though you could rerun the tests and measure the voltage on the 10v range.
Just had another thought, the start capacitor opeerates through its own coil through a centrifugal switch. You could check the contiuity of that lot by measuring what the capacitor was connected to, and leave it disconnected as it would confuse things no end.


PS See my sig line!