New Start Capacitor exploded like a bomb!

[KB1LTG]

Well I tried wiring the Start cap to the black "Side", black terminal to Yel terminal marked V1 and the run cap to black terminal and to V2. I started the compressor and all seemed fine until about 4-5 seconds. The new start capacitor exploded violently, sending plastic, hot electrolyte and metal fragments all over the shop, one of pieces of plastic cut my face badly, just glad it was not my eye! Never in all my life have I seen or heard a capacitor explode like this one did, it literally sounded like a gunshot went off!

Back to the Wile E. Coyote school of Engineering for me, I suspect the NC switch on the start circuit of the motor may be stuck in the NC position and is failing to open up when the motor comes up to speed, leaving the start cap in the circuit causing the problem or I have it wired up incorrectly?

Thoughts anyone?

I searched online for "Exploding Capacitors" and the general school of thought is that they do not "Explode" when they fail, let me be the first to cry BS after my little incident yesterday I will post some pics of the shell and guts of the cap, it was a 250V, 300UF black electrolytic start cap I bought at the hardware store yesterday morning.

Here is a link to the OP where I was asking for wiring help on my Speedway Compressor, http://www.garagejournal.com/forum/showthread.php?t=330070&referrerid=158116

 

[toplessHO]

I had a cap explode in an old Stereo amp when I shut it off.
put a dent in the cooling screen and sounded like a shotgun
BTW it was a metal case.
A rule of thumb on old ones that could be dried out and internally shorted(most likely what happened here) was to bring voltage up slowly.

 

[pepi]

There is a slight differance in failed and wired incorrectly................

 

[PSYKO_Inc]

I blew up a capacitor back in my younger days. My 16 year old self had just gotten my first ride and installed a killer sound system (at least it seemed killer to me at the time.) I was getting some distortion in my speakers, and decided to add bass blocking capacitors. I didn't realize they were supposed to be in series, and not parallel. Cue some Metallica, and BANG! Sounded like a .22 went off in the truck, and little bits of white fiber went everywhere. Smelled terrible. These are the lessons you remember

 

[dutchgray]

I hope it was a proper start capacitor and not a DC only one. Also 250v rating is not enough for use on 220v

 

[uart]

Yes, electrolytic capacitors definitely do explode if run at too higher current or too higher voltage or if run on AC when designed for DC (some electrolytics are designed for AC, but they're actually two DC capacitors wired back to back in series).

Most motor start capacitors are polypropylene film rather than electrolytic.

 

[Sine Swept]

Wire a polarized capacitor backwards and it will blow

 

[2oolhound]

I've had photographic lighting units capacitors blow several times. My big unit was a 3000 watt/second power pack. Good thing they are in steel enclosures otherwise there'd have been a lot of shrapnel judging from the audio volume of the blasts.

 

[jayoldschool]

In high school electronics class, the day we learned what happens when caps are wired backwards was epic. There are probably still holes in the drop ceiling tiles...

 

[exmaxima1]

Yes, electrolytic capacitors definitely do explode if run at too higher current or too higher voltage or if run on AC when designed for DC (some electrolytics are designed for AC, but they're actually two DC capacitors wired back to back in series).

Most motor start capacitors are polypropylene film rather than electrolytic.

I think you meant motor run caps. Run caps need a low esr, continuous duty, and modest mfd capacity which lends itself to poly film caps. It would be difficult to produce high mfd/high vac poly start caps..

 

[frank_c]

In high school electronics class, the day we learned what happens when caps are wired backwards was epic. There are probably still holes in the drop ceiling tiles...

First guy who left the lab usually had a capacitor turned around. We learned real quick, either don't leave the room, or double check everything once you get back.

 

[Mr_fixit]

I used to blow them up on purpose when I was in college, many years ago. . Hook up a extension cord to a capacitor rated for maybe 15 volts dc, plug it in and pop, goes off like a fire cracker. do this at your own risk.

 

[gungatim]

the smell of a blown cap is something you never forget. Blew my first one up at 12 yo. wired an intercom incorrectly to 120v...mom was not happy...

be careful with the really old ones, they can have PCB's in them...

 

[uart]

I think you meant motor run caps. Run caps need a low esr, continuous duty, and modest mfd capacity which lends itself to poly film caps. It would be difficult to produce high mfd/high vac poly start caps..

Yeah, thanks for the correction. The capacitors I've recently replaced were on small grinders (without centripetal switches), so yes they were run capacitors not start.

Just checked now and most start capacitors (particularly on larger machines) are non polarized electrolytics as you say.