Weird shock - Getting accident prone, or something...

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Weird shock - Getting accident prone, or something...

Postby chrismb » Sun Jul 22, 2012 3:16 pm

OK, so I've just finished building some electronics kit today that works off of +/-10V to ground.

A TO-3 transistor is the main switch driving an electromechanical valve.

I was just putting it through its paces and left it for a while. So this should have had no more than 10V on its collector can. I press my thumb on the can to judge the temperature - and I got a right good shock!

I measured the max volts that had been on the can and my meter said it was only going up to 5.9V, to ground, during the switching.

What the heck?!

No word of a lie - I've got a big report to get out for next week and on Friday, just gone, I was busy away in front of the computer and I thought 'I hope my computer doesn't break down'. Two minutes later, pfff! The graphics card went, all I got was a fuzz on the screen. So I phone up the IT services help and while I'm on that call, the phone network in the building goes down!

Yesterday, my wife wanted me to go into the attic. All my torches are broken. In one the AA batteries always die, in another there is some intermittent connection and you have to keep tapping it to make it work. The other two rechargeable lantern types I bought to replace these, one the bulb has gone recently, and the other no longer holds a charge for more than a minute. So my wife sets up an extention lead and a desktop light. I say to her 'there will be a power cut while I'm up here', she laughed ... and would you Adam 'n' Eve it, there WAS a power cut - one that apparently cut out a half of the whole of the West Midlands for a few hours, in fact.

I'm sure there are all good reasons for this, but it seems to defeat the laws of statistics - in the latter case I hear it was down to people stealing copper cable from the trunk lines!!

But now an electric shock off of 6V ?!?! My arm still hurst from it! Somehow the 1.5J of energy that should've been in the caps managed to dissipate into my arm.

Have I got to be careful of 6V now, too!!.... I've heard the electric shock death from the lowest voltage was a Navy guy who died off of a 9V battery when he touched its terminals with a cut on his hand. Don't know if that's true, but I'm more inclined to believe it now!
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Re: Weird shock - Getting accident prone, or something...

Postby Jerry » Sun Jul 22, 2012 3:49 pm

You may have had a small wound or something on your finger. Once you have a path to your salty insides even 6v can give you a good jolt.

Other than that, we may need to rename you "The walking EMP"
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Re: Weird shock - Getting accident prone, or something...

Postby Doug Coulter » Mon Jul 23, 2012 7:01 am

Inductive kickback from a solenoid can easily hit over 10x the original voltage. You didn't mention a diode snubber on the valve. Had that one myself a time or two before I learned how inductors work.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
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