Bad run capacitor or ?

Discussion in 'General Electronics Chat' started by chvyfan, Apr 18, 2008.

  1. chvyfan

    chvyfan Thread Starter New Member

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    I have an older Campbell Hausfeld Air compressor (2hp) that I bought probably 20 years ago, when they were pretty good quality.

    I used it pretty heavily early on restoring one of my first cars. For years I've had problems with it being able to start. As I flip the switch to turn it on, it tries to start, turning probably less than 2 revolutions, then stalling for a few seconds then pops the fuse. I always thought it was the motor getting weak. It acts as if the oil is REAL stiff and thick, and the motor doesn't have enough power to start it. My solution has been to drain the air compressor tank, and baby the starting. After about 10 - 20 times or so of trying to get it to start and having to switch it off before it blows the fuse, it will finally start and run. Once the motor is warmed up, it starts OK, as long as it isn't forever before it needs to start again.

    After doing some research online this weekend, I thought it was actually the start capacitor. (This is my first experience with capacitors.)

    I found the equivalent start capacitor at Grainger for $5 and replaced it, with high hopes it would sove my problem.

    No such luck!

    Now I'm wondering if it isn't the Run capacitor? I think I've found a replacement for this to, and am willing to invest the additional $10 to see if it works, if someone can give me a 50/50 chance.

    I found the following text on the capacitor:
    20 uf 370 vac 60 hz

    I also found this on Graingers site:
    Run Capacitor,20 MFD,370 VAC
    Motor Run Capacitor, MFD Rating 20, Voltage 370, 60/50 Hz, Round, Dia 2 In, Height 2 7/8 In, Width 2 In, 1/4 In Male Terminals, Temp Range -40 to 69 C
    http://www.grainger.com/Grainger/items/2GU23

    Is this the same spec? It looks the same other than the 20 UF vs 20 MFD.

    Does it sound like this could be my problem, and would you take the chance on getting another new part? I know it could also be a motor winding from what I've read, but since I can eventually get it to run, I'm thinking the winding must be good?

    Any help appreciated!!!
  2. thingmaker3

    thingmaker3 Moderator Staff Member

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    Can you tell if the centrifugal switch is working? Do you ever hear it click over when the motor gets up to speed?
  3. jpanhalt

    jpanhalt E-book Developer

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    The caps and motor are the first place I would look, just as you have. Another place is the pressure release valve. That valve is probably located where the tube from the cylinder head enters the tank. With the V-belt off the motor, does the motor start normally? If there is no V-belt, you might have to remove the pressure tube at one end for the same test. Based on what you describe, the pressure release would not be my first guess, but it is another factor to consider. In my experience, one gets less than a full revolution (i.e., it stops on compression) when the pressure release is bad. John
  4. chvyfan

    chvyfan Thread Starter New Member

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    Thingmaker3 - I wasn't familiar with a centrifugal switch is, but looking at a quick wikipedia definition, I do think it is working. It does seem that once it gets to a certain speed, it gets some extra ummpphhh.

    jpanhalt - I don't think it's the pressure relief value for 2 reasons: I hear a hiss once the motor shuts off and since I bleed the tank dry and it still struggles it wouldn't seem like the relief value. One test I should probalby do is to actually leave all the ports open when starting it too (not just zero pressure). I'll give that a shot this afternoon and post if it really fires up. I suspect it won't, just because even with zero pressure, but closed ports, it still struggles. It has a 20 gallon tank, so it would take several full revolutions before it really got any pressure at all.

    Thanks!!!
  5. jpanhalt

    jpanhalt E-book Developer

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    I agree. The relief valve is not my first guess. I mentioned it, because I had an old C-H compressor and that valve was a constant problem. As an aside, I did get the unit 1/2 price, because the dealer heard the hissing and thought the tank had a leak. :) So much for knowing what you are selling! John

    PS: If it is belt driven, I would try removing the belt. That will surely help pinpoint the problem.
  6. pfofit

    pfofit Member

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    After you remove the belt to see if the compressor is not seizing up. Turn the pulley by hand.

    I would pull the end cap off the motor to see if the centrifugal switch contacts are not dirty/cruded up..and to look for other loose over heated wire connections.

    Cap meters are nice if you have one, but if you get an ohm meter on your disconnected caps, short the terminals and check to see if they start out low ohms and rise to open/infinite over several seconds.

    It won't give you an accurate measurement of value but will tell you if it is open/shorted.

    Alternative crude test is with another known good cap of near equal capacitance can give you the number of seconds required to get to a certain resistance.

    For instance, if one 20 uF cap takes 10 seconds to reach 10M ohms and another takes 30 seconds then one of them has changed value. Maybe both are wrong, A man with two watches does not know what time it is, however, if you compare to known good cap then a ballpark of sorts can be achieved.

    Also these static tests do not account for stress of several hundred volts pounding the plates of the cap while in operation, which could break down the electrolytic .

    cheers
  7. SgtWookie

    SgtWookie Expert

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    What is the condition of the power cord? It may need replacement. Starting loads will be quite heavy, near the capacity of the cord when it was new. As the power cords get older, used & abused, the stranded wire inside can break due to all of the flexing and stress. The connections on the plug itself can get corroded. The outlet you're using may also be corroded/pitted.

    It's also possible that the contacts on the pressure switch have become fouled/pitted.

    Monitoring the voltage on the motor side of the pressure switch during starting would verify whether they are good or not.
  8. techroomt

    techroomt Senior Member

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    i would say a "belt off" test is not necessarily definitive. i just had a jointer motor with a bad start capacitor start fine under no load. if your motor is that old and under dusty conditions, i'd pull it, open it up, and blow it out. check out the centrifigul switch/plate and contacts as mentioned. replace both start and run caps, electrolytics go bad after those many years.
  9. chvyfan

    chvyfan Thread Starter New Member

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    OK so I tried it with open ports - still hesitated, though it did start (realize though that the compressor kicks back on at 80 or 90 psi, so zero psi isn't adequate).

    I have a direct drive compressor, so no luck starting it by hand, plus I think since I replaced that start capacitor, it wouldn't prove much (unless my new start capacitor was bad.

    I think what I need to know first is if the run capacitor was bad, would it still run once up to speed? Again, if I really baby it, I can get it to start. I am sure the centrifugal switch is good - I can see a spark as it switches over once up to speed, and I can hear it click back on shut down.

    Once it has run for 30 seconds, I can get it to start no problem (almost like I would say the motor, pump or oil has warmed a little). I'm almost certain the pump is good, as it has been doing this for years, and if it was bad it would have surely given out by now.

    One hard part in diagnosing it is once it "warms up" even a little, I have to wait hours for it to "cool" down before testing again.

    At this point, since it runs once up to speed, I'm almost assuming the run capacitor is good. I'll double check all the connections for a tight fit.

    One other thing to note - the cord at the outlet does get warm to the touch. The thing I would say to counter that is the compressor hasn't been moved much. It's lived in two homes, and pretty much been in the same spot in both the whole time - ie not much flexing of the cord.

    I also fully cleaned out the motor before my post - I had suspected worn bushings, but none in the motor. Cleaned it out really well at that time.
  10. SgtWookie

    SgtWookie Expert

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    If the cord is getting warm, that's not good. That means you're dissipating power in the cord or plug or wall socket instead of in the compressor motor.
  11. beenthere

    beenthere AAC Fanatic!

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    I've never seen this in a large motor, but I have seen motors get very gummy at the bearings. They would run ok if you helped them start, and did fine warmed up, but would not start cold. Does the motor turn easily by hand when it's cold? Or do you have to break it loose?
  12. SgtWookie

    SgtWookie Expert

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    He can't really tell, because the motor and compressor are one piece.

    Perhaps the bearings in the compressor itself are starting to come apart; or the cylinder ingested solvent which made the piston seal swell excessively. I have had the latter occur on pneumatic cylinders when I changed lubricants.

    Come to think of it - did you change the lubricant in the compressor around the time that you first started having problems? Or is it an oilless compressor?
  13. pfofit

    pfofit Member

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    From excessive current probably.
    As well a stalled motor will cause excessive current, heating the cord .

    or the run cap is shorted. New, not likely.:rolleyes:
    or start cap is not dropping out/shorted and causing excessive current draw. Although buddy thinks the cent. sw. is working.
    If the cord got hot then the motor windings are getting hot too. Most definately there is a temp/current overload wrapped into the windings. this may be why you have to wait after it runs a bit, or a bad cap see below.

    Not necessarily. After it heats up the electrolyte in the cap may be breaking down and nay be healing itself when it cools down.

    Start caps don't have to be exact in capacitance value, that's why they're sometimes are listed in a range of vales say 80 to 120 uF or MFD, however run caps need to be exact as a change of more than say 10 %(guessing) value will mess up motor efficiency and stuff and in the process cause overheating in the cap and motor windings.

    Have you looked around the terminal ends of the cap to look for oozing of gunk/tarry substance or bloating of the cap. Is it a metal can or a plastic case.
    some questions....
    When the motor won't run after running a bit are the caps hot?.
    What are the values of the cap"s", and how many do you have?
    Have you ohm'ed the caps?
    Also in the first post you mentioned a fuse blowing.
    What was the fuse value?
    What current rating is on the motor plate?
    120 VAC line or 220vac.? What country? 50-60Hz?

    If you disconnect the pipe to the unloader value and open the drain or outlet port to the tank, this would eliminate any load from the compressor.

    edit: If you have the end plate off is there a screwdriver slot in the end of the shaft for turning or can you turn the shaft by hand. do not nick the end of the shaft with vise grips etc were the bearing rides if it is a bushing type at the rear end..

    cheers
  14. flawdaboi407

    flawdaboi407 New Member

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    I also have an oldskool Campbell hausfeld U.S air series #hl700201 compressor that I got for free from work. Its a 2hp 20 gallon 115v 15amp 6.3scfm@90 and 7.9 scfm@40. Stamped on it says Made in U.S.A. and the head has hl-0008. Its a oil type NOT oiless. Its direct driveno belts.

    The problem:

    It works... but sounds noisey'er than normal/before and only stays on for 5-6 seconds, then the breaker in my houses fuse box jumps and I have to reset it. Keeps doing this.... Whats wrong? My boss said it lasted 15 years till now. I tryed it on a 15a GFCI circuit with only the compressor pluged in. I also tryed it on a 20a curcuit. But...the 15a breaker trips and the 20a doesnt but the compressor still shuts off.

    After some tests:

    The motor turns over by hand and seems to have compression. The electric motor turns smoothly. It has oil and the filter is clean. I tryed measuring the capacitors with a ohm meter but dont know what to look for. I have access to a Blue Point DMSC683A multi-meter and it does microfarad... just dont know how to use it.
  15. SgtWookie

    SgtWookie Expert

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    Even though your post is directly related to the original poster's topic, it is always better to start a new topic to avoid confusion.

    It sounds to me like your start capacitor may have gone bad.

    Try removing the belt from the compressor & motor pulleys. Then turn on the motor. Do you hear a slight "click" after the motor starts?

    If you hear a click, and then the motor stops running a few seconds later, then it's most likely the run capacitor.

    If you don't hear a click, then it's likely that either the start capacitor has gone bad, or the centrifugal switch is "stuck".

    It could also be that the motor's thermal protection contacts have gotten burned over time, and it's heating up more than usual.

    Take a look at the capacitor to see if you can read markings on it.
    You might find something like "120uF 250V".
    There may be multiple markings like that.
  16. flawdaboi407

    flawdaboi407 New Member

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    I brought both capacitors to Grainger to have them tested and there good. Tomarrow im going to bring the motor to get a free check/estimate. Thanks for the help.
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