Are the heatinks inside supplys supposed to be energized?

[signmeuptoo]

Hey guys, I have a question due to a "debate" in another forum:

I could swear I remember here some of you talking about not shorting the primary and secondary side heatsinks with each other or there would be a short of sorts. So that led me to believe that the heatinks are common to the power supply's circuit common runs, and are, as such, electrified.

Is this correct?

A fellow in another forum got a shock when he touched the heat sink of an energized power supply. Is that because of the above or is it because a chip was bad and shorted to ground and thus, shocked him? Are the heatsinks ground or are they common?

Thanks for helping clear this up in my mind.

[Oklahoma Wolf]

The primary heatsinks are usually live.

[rip97000]

sorry noob question here, but what purpose does that serve?

[cypherpunks]

Originally Posted by rip97000

sorry noob question here, but what purpose does that serve?

Better heat sinking. On power transistors, generally the back of the silicon wafer is one of the terminals, and is connected to the case. You can use an insulating washer, but if you can avoid the need for it, you'll have lower thermal resistance.

[signmeuptoo]

Are they generally live with Common or Hot?

[Oklahoma Wolf]

High frequency high voltage AC.

[madmat]

It tingles pretty good but it's not full high amperage AC. I've bridged the heatsinks on a running PSU with my hand one time, it took just once to stop me from doing that again. I've been hit with 220V single phase (one leg of a 440V setup) and it was a lot "harder" of a jolt than I got from the PSU.

[Silk_the_Absent1]

Yeah, I've taken a 220 hit myself. I was working on the furnace, and yes, I did turn off the breaker that was for it (just turned out there was another one that wasn't labeled). Went in through my finger, out my right leg to the linoleum tile floor. I had a friend that was an electrician here, said I was lucky it was a 220v hit, 110 would have been more likely to have done much more serious damage.

Still have the scar on my leg, where it was somewhat fused to the floor. This pic was taken a couple of years ago, but it still looks the same.

-Adam

[jonnyGURU]

Anyone here grab a hot spark plug or coil wire under the hood?

[Spectre]

Originally Posted by jonnyGURU

Anyone here grab a hot spark plug or coil wire under the hood?

Yes