Electrical Question about bulge in Capacitor

[John Galt III]

I am hoping I have a bad capacitor, since that may solve my air handler fan problem. I removed the 10 microfarad, 370 VAC oval capacitor, a GE model from 1986, and see that it has a 1/8 inch bulge between the terminals, on the body of the capacitor (end). The bulge is almost perfectly round, not quite, and has a dimple in the middle of it. Sorry, no pic! Googling results in some pics of capacitors with the same type of bulge, but the they don't say if it is a good or bad capacitor. Thanks in advance!

 

[Sunset]

Probably, pretty hard to tell without a photo.
However, the repair is easy and cheap if you do it yourself. (just short with insulated screwdiver the terminals after turning off the breaker).

I did my A/C for ~$15 , bought it at Grainger as I could pick it up after order online.

<edit> I see you already removed it, but will leave my comment for newbies.

 

[Sunset]

You motivated me to look , as mine was obvious so I didn't bother.
It seems with a multimeter you can test the capacitor:

https://www.electronicshub.org/how-to-test-a-capacitor/

 

[John Galt III]

Sunset, thanks. Yes, I shorted the two terminals with a screwdriver, but only after I removed the cap. My internet research found a variety of suggestions about when to short it, before or after removal, and some people even said that shorting it would damage it (if it were good) and that you should use a 'capacitor discharge tool'. I have spent an enormous amount of time getting to this point, in the interest of 'not causing more damage'. I could just buy a new cap, install it, and see what happens, but I think I'm going to buy a multimeter with capacitance function, at Harbor Freight for $23, and test it first.

 

[Car-Guy]

Bulges in AC Caps usually mean they have gone bad, but still handle them with care.

 

[street]

Bulges in AC Caps usually mean they have gone bad, but still handle them with care.

Yep! With voltage caps and cap banks if one is bulged it has gone bad. Capacitors are a dangerous piece of equipment. When not in use and stored they need to be shunted out. Be very careful when taking damaged cap out.

 

[njhowie]

Capacitors are cheap - just buy new one and replace. Probably less expensive than the multimeter. Bulge indicates it should be replaced regardless.

 

[JoeWras]

Capacitors are cheap - just buy new one and replace. Probably less expensive than the multimeter. Bulge indicates it should be replaced regardless.

Came here to say it.

OP removed it and inspected it. With that knowledge, OP is capable of replacing it with a new.

 

[Surewhitey]

We just had one go bad in the 1995 garage door opener. Just oozing black junk near the terminals...$20 & back in biz.

 

[ShokWaveRider]

I have changed a few on my AC units over the years. Just buy the correct one and replace it. It will not do any harm and give you peace of mind. I even keep a spare for both my ACA units.

 

[ERD50]

We just had one go bad in the 1995 garage door opener. Just oozing black junk near the terminals...$20 & back in biz.

That reminds me, many years ago, I was doing some adjustment on our garage door, and was running it up and down to get the adjustments right. It didn't strike me as excessive, there would be a little time between cycles as I adjusted the limits, or checked for smooth operation.

But after a while, I start seeing smoke come out of the unit! So I stop, check, and IIRC, it was coming from that big electrolytic ('tin can') cap. It seemed OK after it cooled down, I don't think I ever replaced it (though I may have at some point, memory fails), and I don't recall having any problems.

But if it bulged, and you've already taken it out - yes, replace it!

-ERD50

 

[John Galt III]

Capacitors are cheap - just buy new one and replace. Probably less expensive than the multimeter. Bulge indicates it should be replaced regardless.

That's my next decision. It would be good to know exactly what the capacitance is in the old capacitor, and test the new capacitor before installing. The multimeter at Harbor Freight is only $23 and it would be good to have it around for possible future use. Or I could never use it again, lol. But its only $23. And gets good reviews online. Cen-tech 11 function multimeter. The cap is online for $6 to $20 from various places. I will probably go to Grainger which is nearby and get it. Probably $20 at Grainger, based on previous quotes from them for similar capacitors, and I will feel good about the quality of the part. I took a (fuzzy) pic of my capacitor bulge. See attached. Thanks for the replies !

 

[ERD50]

That's my next decision. It would be good to know exactly what the capacitance is in the old capacitor, and test the new capacitor before installing. The multimeter at Harbor Freight is only $23 and it would be good to have it around for possible future use. Or I could never use it again, lol. But its only $23. And gets good reviews online. Cen-tech 11 function multimeter. The cap is online for $6 to $20 from various places. I will probably go to Grainger which is nearby and get it. Probably $20 at Grainger, based on previous quotes from them for similar capacitors, and I will feel good about the quality of the part. I took a (fuzzy) pic of my capacitor bulge. See attached. Thanks for the replies !

A little multimeter isn't much of a test of a cap like that. If it tests bad, it is likely bad, but if it tests 'good', it could still be bad in many ways. Leakage, dielectric breakdown, etc. That meter tests charge time with a low voltage signal, but that cap is operating on 240 line voltage with higher peaks and phase shift.

I've used a test where you put a light bulb in series, and measure voltage and current and work out the impedance at line frequency. A much better test. This can also be done in-circuit with a clamp on AC current meter. Should be pretty easy to get links for that.

-ERD50

 

[ncbill]

I am hoping I have a bad capacitor, since that may solve my air handler fan problem. I removed the 10 microfarad, 370 VAC oval capacitor, a GE model from 1986, and see that it has a 1/8 inch bulge between the terminals, on the body of the capacitor (end). The bulge is almost perfectly round, not quite, and has a dimple in the middle of it. Sorry, no pic! Googling results in some pics of capacitors with the same type of bulge, but the they don't say if it is a good or bad capacitor. Thanks in advance!

Just buy a new one.

Amrad (made in USA) HVAC capacitors are available on Amazon.

Looks like this would work for you:

10 uf/Mfd 370/440 VAC AmRad Oval Universal Capacitor

 

[John Galt III]

Update: I bought a multimeter that said it tested capacitance up to 20 microfarads. Got it out of the shell pack, and lo and behold, it has 2 slots to insert a different type of capacitor, but not mine. Undaunted, I McGuyvered 2 wires to connect the old capacitor to the slots. Got a reading bouncing around 5.0 microfarads, so it is bad. Oh, I bought a new capacitor from Grainger, for just $5, and it tested at 10.1 microfarads, Great ! Close enough. Got a question though. I also used the Ohms method of testing both capacitors (set Ohms on multimeter at a high number, like, 10K, then hook up probes, and expect to see number slowly rise to infinity) and they both tested as dead. Just got a '1' showing on the readout. For both good and bad capacitor. Why would that be?

 

[Car-Guy]

The multimeter at Harbor Freight is only $23 and it would be good to have it around for possible future use. Or I could never use it again, lol. But its only $23. And gets good reviews online. Cen-tech 11 function multimeter.

IMO, a good multimeter is one of the best tools you can buy. In importance, it ranks up there with a hammer, screwdriver and pliers as "must haves". If you don't know how to use one.... "Learn".... It's easy, useful and will be helpful for a lifetime.

 

[OldShooter]

...I took a (fuzzy) pic of my capacitor bulge. See attached. Thanks for the replies !

That bump looks to me like an artifact of the manufacturing process, not a swollen cap.

 

[ERD50]

... Got a question though. I also used the Ohms method of testing both capacitors (set Ohms on multimeter at a high number, like, 10K, then hook up probes, and expect to see number slowly rise to infinity) and they both tested as dead. Just got a '1' showing on the readout. For both good and bad capacitor. Why would that be?

A reading of "1" seems strange. Are you sure that's not some sort of "overload" or "open" reading?

Short the cap, connect to Ohmmeter while shorted. you should see something near zero Ohms.

Remove the short (while the cap is still connected to the meter). Do you see the slow rise, or does it just go to "1" immediately? Try this on the 1M and 1K scales as well.

Once it is at "1", disconnect the cap, what do you see? On both good and bad? As you say, the cap should eventually fully charge, the current from the meter goes to near zero (there will be some small leakage current), and an ohmmeter would then be reading infinite, or "overload" or equivalent. And that should be the same once the fully charged cap is removed.

-ERD50

 

[Telly]

That bump looks to me like an artifact of the manufacturing process, not a swollen cap.

Absolutely! After your comment, I looked at the pic. Then checked my pullouts collection of Aerovox oval caps from the 1980s. They all have the same somewhat irregular bump, and all were fine when I pulled them. Looking at mine, it may be a solder bump from an internal connection. Certainly not connected electrically to either side of the cap element . Maybe a backup case ground, to make sure the top metal insert of case is grounded, and not depending only on the top crimp? Dunno.

 

[street]

A reading of "1" seems strange. Are you sure that's not some sort of "overload" or "open" reading?

Short the cap, connect to Ohmmeter while shorted. you should see something near zero Ohms.

Remove the short (while the cap is still connected to the meter). Do you see the slow rise, or does it just go to "1" immediately? Try this on the 1M and 1K scales as well.

Once it is at "1", disconnect the cap, what do you see? On both good and bad? As you say, the cap should eventually fully charge, the current from the meter goes to near zero (there will be some small leakage current), and an ohmmeter would then be reading infinite, or "overload" or equivalent. And that should be the same once the fully charged cap is removed.

-ERD50

This ^. Shunt it out then do your measurements.

 

[ERD50]

Absolutely! After your comment, I looked at the pic. Then checked my pullouts collection of Aerovox oval caps from the 1980s. They all have the same somewhat irregular bump, and all were fine when I pulled them. Looking at mine, it may be a solder bump from an internal connection. Certainly not connected electrically to either side of the cap element . Maybe a backup case ground, to make sure the top metal insert of case is grounded, and not depending only on the top crimp? Dunno.

Yes, but replacing an electrolytic cap from 1986 is probably prudent regardless!

And he already has it out. 3/4 of the battle is over. Just replace it. The rest is just academic.

-ERD50

 

[John Galt III]

A reading of "1" seems strange. Are you sure that's not some sort of "overload" or "open" reading?

Short the cap, connect to Ohmmeter while shorted. you should see something near zero Ohms.

Remove the short (while the cap is still connected to the meter). Do you see the slow rise, or does it just go to "1" immediately? Try this on the 1M and 1K scales as well.

Once it is at "1", disconnect the cap, what do you see? On both good and bad? As you say, the cap should eventually fully charge, the current from the meter goes to near zero (there will be some small leakage current), and an ohmmeter would then be reading infinite, or "overload" or equivalent. And that should be the same once the fully charged cap is removed.

-ERD50

I got the meter to show some numbers, by moving the ohms up to 200K ohms. It does the same thing shorted or not shorted. Numbers jump around for 1 second, then goes back to '1'. The instructions mention the '1' but don't say what it means. They say if it shows '1', move the Ohms setting one notch higher and try again. So I moved it up a few notches, and got the numbers jumping around for a second, then back to '1'. numbers like 934, 153, 478, just all over the place, then back to '1'. And this is the bad capacitor I'm talking about. I already put the new cap on my air handler.

 

[John Galt III]

Yes, but replacing an electrolytic cap from 1986 is probably prudent regardless!

And he already has it out. 3/4 of the battle is over. Just replace it. The rest is just academic.

-ERD50

I installed the new cap. The cap may be working as it should, but the fan motor still does not come on. It is a two terminal cap, and I hooked up the wires exactly as they were before. There isn't any positive and negative terminal situation to worry about, right? No markings on the old or new cap for that.

 

[OldShooter]

Absolutely! After your comment, I looked at the pic. Then checked my pullouts collection of Aerovox oval caps from the 1980s. They all have the same somewhat irregular bump, and all were fine when I pulled them. Looking at mine, it may be a solder bump from an internal connection. Certainly not connected electrically to either side of the cap element . Maybe a backup case ground, to make sure the top metal insert of case is grounded, and not depending only on the top crimp? Dunno.

Yeah. Without having the component in hand it's hard to tell, but my guess would be a solder case seal. Maybe after evacuation or a nitrogen fill?

 

[Out-to-Lunch]

I got the meter to show some numbers, by moving the ohms up to 200K ohms. It does the same thing shorted or not shorted. Numbers jump around for 1 second, then goes back to '1'. The instructions mention the '1' but don't say what it means. They say if it shows '1', move the Ohms setting one notch higher and try again. So I moved it up a few notches, and got the numbers jumping around for a second, then back to '1'. numbers like 934, 153, 478, just all over the place, then back to '1'. And this is the bad capacitor I'm talking about. I already put the new cap on my air handler.

The "1" is the DVM saying that the resistance is greater than the range you selected. This will, of course, also be the case if you have a completely open circuit. Note that the "1" is in the leftmost location, not where a valid reading of 1 Ohm would reside. Look at about 0:28 of this video:

https://youtu.be/zXBiWREKY3E