Start capacitor on electric motor (compressor)...

[mvbighead]

Having a starting issue with a compressor motor. FIL bought it for me at an auction, and it ran once, but now when I turn it on it just buzzes.

I've done a fair share of googling, and from that information I have checked that the motor and pump both spin freely when not under power.

I can see that the sucker is drawing a lot of power when turned on, but it just hums.

From this information, it was suggested to me that it may be the start/run capacitor. Some models have both, but this thing only has one.

Here is my pic of the start capacitor:

I can't seem to find an exact match on the interwebs, but I've seen people suggest to look for something close. This lead me to this:

http://www.ebay.com/itm/Motor-Start...170?pt=LH_DefaultDomain_0&hash=item564644bffa

60hz/50hz/110-125VAC to my existing 60hz/110vac.

Question is, should this work? Or should I look for something different?

 

[PottedMeat]

http://www.ebay.com/itm/Motor-Start...170?pt=LH_DefaultDomain_0&hash=item564644bffa

60hz/50hz/110-125VAC to my existing 60hz/110vac.

Question is, should this work? Or should I look for something different?

that will be fine, you match the capacitance value and for voltage you have to at least equal the original rating.

if that doesn't work, check the start winding centrifugal switch at the base of the motor. see if it needs cleaning.

 

[mvbighead]

Ugh, I just measured (as they provided measurements on their item), and it is a bit too long and wide. Gonna see if I can find another one.

 

[mvbighead]

http://www.ebay.com/itm/270-324MFD-...084?pt=LH_DefaultDomain_0&hash=item19d769f20c

This looks closer to the fit. Gotta double check, but I may be ordering this soon. Compressor looks a little rough, so replacing this regardless shouldn't hurt.

 

[phucheneh]

Wait...is that 'megafarads'?

What the shit are you working on again? Thermonuclear reactor?

 

[mvbighead]

Eh, it's an old 3/4 HP General Electric Compressor Motor. Figured this was as good a place as any to get advice on how to fix her up.

 

[Howard]

Wait...is that 'megafarads'?

What the shit are you working on again? Thermonuclear reactor?

microfarads. Supposed to be μF but people use MFD instead. Americans, go figure.

 

[Mandres]

if that doesn't work, check the start winding centrifugal switch at the base of the motor. see if it needs cleaning.

ding, ding, ding!

Decent pics here:

http://www.woodworkingtalk.com/f12/repair-your-bandsaw-other-motor-crash-course-46405/

 

[mvbighead]

Mandres, thanks 1,000,000 times for that link. Thanks!

 

[jagec]

Wait...is that 'megafarads'?

What the shit are you working on again? Thermonuclear reactor?

It would have to be a LOT bigger than that if it was in megafarads.

But yeah, it bugs me too that they misuse the "M" prefix on motor capacitors.

 

[mvbighead]

Well, got the new capacitor. Same deal. Looks like I'll have to take the motor apart. In thinking about all of this, I dunno that the size of this will be as big as I want, and with my birthday being today, I've got the wife talked into letting me buy this:

http://www.harborfreight.com/Air-Co...iMTU5Ljk5IiwicHJvZHVjdF9p ZCI6Ijc3NzQifQ==

Normally $220, now $160 with coupon.

I think I am pretty set on buying that and selling the broken one to my brother for the $40 I gave for it on the condition that he can get it working again. IE - If he can't fix it, he won't owe me $40 for it.

Just figure the 4.7 SCFM at 90PSI is pretty darned close to the 5.0 that most things need. The price is right, and the other compressor I have from HF works, just not powerful enough. 0.6 CFM at 90PSI is pretty darned pathetic.

Any thoughts gents? At this point, I figure I just want something that will actually build pressure a lot better than what I have. I use it from time to time on impact wrenches, but I also have a cordless Craftsman C3 that I like. I am thinking this one should do darn near everything I need it to for a good ten years or more (provided it lasts that long).

 

[LTC8K6]

Keep in mind that it will basically need it's own 115V circuit.

 

[mvbighead]

Good point, I don't think that'll be a problem.

 

[mvbighead]

Well, got the new compressor yesterday. Got it setup, but kept flipping it's own breaker (maybe not the right term). Finally got started after flipping the reset several times. After plenty of research, I realized that the compressor oil was probably keeping the motor from starting correctly due to the compressor pump being cold and not spinning completely freely. I've gone through the break-in suggested by the manual, and just recently added some IngerSol AllWeather Synthetic Compressor oil. We'll see if that fixes it tomorrow on the next cold start.

The general consensus seems to suggest that standard oil (and the cheap HF oil) gums up pretty bad and keeps the pump from spinning well in cold weather. Synthetic should allow it to spin more freely and fire up correctly, as suggested by most. Guess I'll just wait and see.

 

[nedfunnell]

mvbighead,
I borrowed a DeWalt compressor to use yesterday when it was 40 degrees out. It didn't want to start either, and was tripping the motor breaker also. The problem was the 50' 14 gauge extension cord I had it on. Even though it's enough cord for most things, the voltage drop under the compressor's starting load (with cold oil too) was enough to increase the current draw and trip the breaker. I plugged it directly into an outlet and it started fine. It also started again without too much drama on the extension cord after it had that 'warm up run'.

 

[slag]

mvbighead,
I borrowed a DeWalt compressor to use yesterday when it was 40 degrees out. It didn't want to start either, and was tripping the motor breaker also. The problem was the 50' 14 gauge extension cord I had it on. Even though it's enough cord for most things, the voltage drop under the compressor's starting load (with cold oil too) was enough to increase the current draw and trip the breaker. I plugged it directly into an outlet and it started fine. It also started again without too much drama on the extension cord after it had that 'warm up run'.

Excellent information. I've experienced the same thing with a craftsman compressor. Took one back even, got another, and it did the same thing. Finally dawned on me that it was the extension cable. /facepalm.

 

[mvbighead]

Ugh, well I am still having problems, and I have it plugged straight into the wall.

Anymore, it is starting eventually, but she needs to warm up. Maybe I should try a different outlet. I do notice that some lights tend to flicker when the thing kicks on. Back to LTC8K6 advice of finding an outlet that is on its own breaker.

For what is is worth, it has yet to trip the house's breaker, just it's own.

 

[mvbighead]

Well, I checked my garage breakers, and I have 2. A 15 amp with EVERYTHING on it, and a 20 amp with my garage fridge on it. Sucks, but there is only one outlet on that 20 amp breaker (at least in the garage which it's labeled for). Dragged the compressor over to that outlet, and it fires up first time every time. I rolled it back, tried again on the old outlet, won't start.

Problem now is that outlet is right next to my door/fridge/trashcan/bench. I don't really have room for the compressor there. I think I am going to have to find a 16ft heavy gauge extension to get it on the other side of my bench where I have space for it.

Anyhoo, thanks for the tip LTC8K6. It started sticking in the back of mind, I tried it, and sure enough, it needs a breaker with a little more oomph and a little less on it.

 

[LTC8K6]

I'm glad it's something you can deal with, and not a bad compressor.

 

[mvbighead]

Found a 12 gauge 15amp 25ft extension for 19.99, and it works perfectly on that as well. Got it in a more convenient spot, and now all is well.

Thanks again.

 

[namita]

thanks