I wonder if that's hot.

Even worse... I had carefully tuned the load line of an off-line switcher and then took the heat sinks off of some TO-220 devices.

THEN "I wonder if that's hot - I'll just touch it and see"

Thermally it wasn't hot at all, but the 400V P-P got my attention right away ;-)

...Jim Thompson

"Carl Smith"

You should have licked your finger first. Or the other method is to rapidly touch and remove your finger, allowing the slower nervous system to integrate the result over time. ;-) How many people have picked up a soldering iron by the business end? I'm willing to bet that the group of people having done it twice is the "null" set.

In a previous life working at one of the major computer manufacturers I was tinkering around inside a standard ATX computer power supply, with it powered up and running, of course.

I happened to touch the main heat sink and I got a zap like I never have before. At that instant my boss was walking by and saw me jump. So I said "That heat sink is hot."

When he said "Well, it is a heat sink" I realized he misunderstood what I meant, so I said "No, I mean electrically hot." :-)

I have ;-)

Did it once only... it's the kind of lesson that thoroughly sinks in ;-)

...Jim Thompson

I haven't done that with one sitting on the bench, but once I had one of those cheapo radio shack pencil irons plugged in with the cord going down the front side of my desk. I moved and bumped the cord and the iron fell off the edge of the desk. In milliseconds I went through the thought process that the hot iron was going to fall on the carpet and burn a spot in the carpet so I should catch it. So I caught the iron in mid fall. By the hot end.

A fraction of a second later my reflexes retracted my hand, and the iron continued its descent, and I ended up with a badly burned hand AND a burned spot on the carpet where it fell.

Seperately from 'picking up', some years ago, I was told that somebody had found there were two major groups of people who when they dropped things, reflexively pulled their hands 'away', rather than trying to grab the object. Electronic engineers, and surgeons.

Best Wishes

I like that approach.

Then again, if your FET starts smoking or a blob of molten metal comes out, that's also a hint that it's hot. Oh, and that unmistakable aroma of burnt semiconductor. Yummy.

(Did a stress test with a PWM I built about a year ago, controlling a large-ish (~50W) DC motor. My MOSFET melted. :)

"Carl Smith" schreef in bericht news: snipped-for-privacy@news.west.earthlink.net...

Not as bad as when you are on your knees under the desk, searching that lost screw, and the iron falls/slips into your collar, and you bang your head with great force against the desk, in all the panic. Then try to find the cord to pull the damn thing out. Ventilate room afterwards and have a well deserved break.

Add glass-blowers. It's a long time since I did any glass-blowing, but the memory lingers on.

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up

Funny how that works isn't it. I couldn't count the number of times I've been shocked, but I know that I picked a hot iron up once. That was about 25 or 30 years ago, I'm still pretty sure that number isn't going to increase. I was a young teenager then so I'm thinking that my sweaty palms saved the day, since I didn't get burned too bad at all (considering).

A friend was showing me how his AC-plasma display sustainer circuit board was safe to touch because the whole thing was floating, so you could not get a shock from touching any single component. Unfortunatley, he demonstrated by touching the case of one of the output transistors - instant second-degree-burn blister.

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aroma

A rule of thumb that I follow is that if you see ANY visible changes after applying power, you probably shouldn't touch it. ;-) The mixed blessing is that it will probably be cool again in just a moment.

BTW, I got to be a big fan of fuses when I saw the insulation "just fall off" all the wiring for my 8-track back in my younger days. When you really need to disconnect six feet of highly emissive copper, it's pretty hard to find a good spot to grab.

That's a "rip off your shirt and use it to yank the plug" moment.

Those copper wires were high voltage too, right?

I've heard some nice tales from rec.crafts.metalworking too, as you might imagine.

One was a guy who dropped a knife and promptly cought it with his foot, shall we say, lawn dart style.

Other tales of recognizing that the anvil / faceplate / general lump of cast iron should fall on the concrete and be damaged rather than crush your foot to a pancake.

I personally have never grabbed a soldering iron backwards, take that Jim! ;-)

Tim

-- Deep Fryer: a very philosophical monk. Website:

Bwahahaha! I only did it once... 38 years ago.

As for falling objects, I've demonstrated an amazing ability for dancing. Ask my sister. 50+ years ago she was mad at me about something and tossed a large schoolbook at me. I simply stepped to the side and let it go through the grillework of a very expensive cabinet in our parent's living room ;-)

...Jim Thompson

I once had the pattern of a TO-3P tab burned into my thumb, but I'm glad I didn't lick my thumb first - the reason for the burn was the 340VDC rectified mains connected to the tab, so the series resistance of my skin was somewhat useful to me in limiting the current.

I also dropped an old Weller soldering iron when sitting at a desk wearing shorts, and it dangled on my knee for a while before I figured out how to move it.

Chris

Hi

I used to work with this guy who without fail, on a daily basis, got a shock from something he was working on. Once he flew back from his desk after getting 110V accross his hands through his chest, I thought he was a gonner. Another time I saw him swipe the tip of a soldering iron with his finger in an attempt to get a chip resistor off instead of using the sponge ! Some people just don't get it !!

Alan

Is he still alive ?:-)

...Jim Thompson

Haha- good one: second degree burn + skull fracture:-)