Discharging a capacitor

[Greg Crawford]

Wow, I never thought this question would generate answers like this.

First, I have to say I assumed it to be a capacitor. It doesn't feel like any static shock I've ever gotten (I've gotten some real doozies off sandblasters), rather just like touching a hot 110 volt wire, complete with the tingling in the muscles. There's also no spark or "click" like static generates.

Does every light do the same thing? I can't say all of them for sure, but it is more than just one. I don't feel like being a human volt meter, so I'm not going to go grab all the plugs to find out.

Are they made in China? Of course, isn't everything? I have about half a dozen of these, all the cheapest you can get at the BORGs. I've tried the higher-dollar lights, and one of them gave off such a fireworks show I didn't think I'd get it unplugged before it started a fire! The other one worked for about a year and now it just goes off after about 15 minutes. It has to be unplugged for 10 minutes or so to re-light, then just does the same thing. The cheap ones at least work. I've also tried the hard-wired type, but replacing ballasts is more maintainence than replacing these, plus more expensive.

So far though, it sounds like I'm the only one experiencing this. I'll try to tag any that do give me a jolt and see if there's some common thread. If so, I'll try to determine which kind they are and avoid them in the future.

One other question, if they are holding voltage, wouldn't that light an incandescent bulb on the same outlet for a short time after the switch was off? For that matter, would it make a difference if I simply unplug the light verses turning off the circuit before unplugging it? I'll have to try to keep that in mind.

Thanks for all the brain power. Some of you really, REALLY know your stuff about electrical matters.

Greg

[Eric Gustafson]

First, I have to say I assumed it to be a capacitor.

Right! Excepting the electronic ballasts, these fixtures use an inductive ballast to generate the higher voltage needed to light up. I have never seen the circuits, but I bet there should be a discharge resistor across the inductor to bleed off voltage when you turn off the light. Perhaps the ones you have are either missing the bleed resistor or are designed improperly. I wonder if the lights you have are UL listed?

[Chris Padilla]

If you know how much voltage is across the cap, you can apply Ohms law to get the instantaneous DC current.

V = I * R

Ah, good old Circuit Theory 101.

[Chip Lindley]

Umm, why are we touching the plug ends anyway??? DUHH! If getting *bit* is abnormal, take the fixture back. If its broke, DO Fix it!!

[Paul Atkins]

[COLOR="rgb(72, 209, 204)"]-one of them gave off such a fireworks show I didn't think I'd get it unplugged before it started a fire[/COLOR]
What actually are you touching when you get this jolt? Is this conduit wiring? Sounds like maybe a ground/neutral problem with your wiring. Are they plugged into 220? Use a meter and check the grounds and hot leads. Or let Mikey do it. We don't want to se you get fried.

[Rob Young]

Ah, good old Circuit Theory 101.

Sometimes known as Circuss Theory when things aren't working right.

Likewise, Electro-Magnetic becomes Electro-Magic...

[Chris Padilla]

Sometimes known as Circuss Theory when things aren't working right.

Likewise, Electro-Magnetic becomes Electro-Magic...

After finishing grad school in EE, my job was as an EMC (electromagnetic compliance) engineer and everyone called it Black Magic. Now I'm on the PCB getting chips talking to each other at multi-gigabit speeds (SI).

[Ken Garlock]

If you want some fun, take a piece of steel wool, and while holding it with insulated pliers, jam the steel wool across the offending two terminals.

In a college physics class I took a 5 mfd 5,000 volt oil filled capacitor to class. I had charged it to about 500 volts in the morning before leaving for school. The physics class was the last class of the day, when I placed the steel wool across the terminals of the cap, it sounded like a firecracker going off. Of course, some of the steel wool went up in smoke.

Ah, the good old days before boring TV lectures.

[R Mousel]

I seem to remember a recall on some 4' lights for this very reason. Don't remember where I saw it though. I think they were from HD but can't be sure.