I wonder if that's hot.

Howdy!

First rule of soldering - Never Ever Solder In The Nude.

Especially if you're male.

Solder splatter WILL find *ahem* certain delicate organs ...

RwP

In article , Anthony Fremont wrote: [...]

I dropped one on my foot. The cord works to turn it pointy end down. The fine tip punches right through the top of a running shoe. I don't bring an iron out past the edge of the bench any more.

These days, I use a Metcal and it has a short cord. I also solder less. The prototype has 0402 components in it so I try to get others to do the soldering.

On 23 Feb 2006 13:59:35 -0800, snipped-for-privacy@yahoo.com wrote in Msg.

It's actually burnt epoxy resin.

The stench potential is amazing. Once I was called to look at a $100k piece of laboratory electronics that had literally gone up in smoke. A guy had tinkered with it at a spot that he (somewhat rightfully) thought was safe, when suddenly thething stopped working and stenched up an entire laboratory tract. He was of course terrified that he had just terminally ruined a tenth of a million worth of equipment -- and to add insult to injury, colleages, attracted by the odor of catastrophe, came nosing in.

Turned out that he had accidentally shorted out the (short-circuit proof) +/- 18V supply rails from which the inidividual boards of the unit were powered. Each board was subdivided into several subcircuits, and each of those was powered by their own indvidual 78L15/79L15 pair, but the designer had omitted the output-input protection diodes.

Took me about an hour to replace about one or two dozen of the damn things and add the diodes. I didn't give too many details as to what the trouble had been, I just fixed it and saved the life of the lab unit and that of the guy using it. He worships me to this day.

About a year later the same thing happened to myself with another unit of the same model. Man was I glad that I knew right away what was wrong otherwise I would just have dropped dead.

robert

On Thu, 23 Feb 2006 21:38:13 GMT, Anthony Fremont wrote in Msg.

Soldering iron -- pah. Of course I picked up one at the wrong end, exactly once, about 25 years ago.

But what's much worse is working with hot glue. It's almost as hot as solder, sticks like crazy and seems to have infinite heat capacity.

robert

There are a number of ways to turn off a SCR; one way is to pull current out of the gate, but make sure to limit the reverse voltage (below 5V) so you do not zener the gate...

Hmm I always assumed SCRs had to be reverse-biased, what are the typical turn-off characteristics then?

Tim

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

Robert is speaking of the GATE voltage relative to CATHODE.

Current below the holding current spec, or ANODE negative relative to CATHODE will turn it off.

...Jim Thompson

Yeah, note correction in my quoted text.

So is his statement BS, and SCRs cannot be turned off by the gate?

Tim

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

It's possible, under some conditions (especially at low anode current) but the characteristics are not specified.

Devices which are specified for this kind of operations are called GTO thyristors. I believe they are pretty much extinct, for a variety of reasons.

Best regards, Spehro Pefhany

Funnily, they are still common, but only in relatively large devices. They are used in things like welding supplies, and traction drives for locomotives, electric shovels etc., often with ratings in excess of 3000A.

Best Wishes

Ralph, you forgot to say "don't ask me how I know this!"

Mark

Yes - check it with the back of your finger - that way, when you get burned, you can still use the finger. ;-)

Cheers! Rich

My Mom was fond of telling about the time when I learned to keep my hand off the top of a hot stove. I wasn't big enough to actually _see_ the top of the stove, but she said it left a mark. It was only a couple of years later when I learned to keep my thumb out from between the prongs of a wall plug, so I guess I had an advantage by the time I got to the really dangerous stuff, like soldering. ;-)

Cheers! Rich

Hold the back of your hand close to the potentially hot element. For some reason there are a pile of "hot" sensors on the back of the hand. ...no need to get blistered at all.

I dropped mine, and caught it in midair. once. For a few seconds I was rather pleased with myself. For a few days, I was somewhat cross :) now I leap backwards, and ensure I only pick it up by the handle.

Cheers Terry

google McMurray-Bedford commutator.

A place I worked at used to make these. a few years back a customer returned an 80A 400Vac drive for service, after 28 years of continuous operation. One SCR had failed, but alas no low-Tq SCRs could be had that would fit in the available hole. The McMurray-Bedford commutator coils were air-cored, wound on 8" dia. formica formers. The entire unit was in a box big enough to fit 3 very tall engineers. We offered to replace it with a UD3-70, about 18" x 24" x 6". The customer said "no thanks, we want it back, its so reliable". In the end we bought it off them for our museum. At the time, our 660A drive was about 1/2 the volume of the old

A GTO is basically an SCR with a monstrous gate-cathode FET....

Cheers Terry

I just accidentally killed my latest smps. I was playing with the line voltage, when I accidentally reached for the wrong knob, and wound my

to add insult to injury, my next step was to fit the aux supply diode, and run the unit thru soak testing....

Cheers Terry

maybe. I burnt a soic-8 into my finger that way - mountains of cross-conduction in a sync. rect.

Cheers Terry

Hmm, I don't get anything beyond parts of curriculum.

Am I to guess that these are gate-turn-off drives, or coils that couple the turn-on dV/dt, dI/dt to the opposing SCRs, pushing their terminal voltage down? (Think inductive supplied (shorting commutation) H-bridge.)

Ah...

Tim

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