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Barry Harvey

Everything’s Better After the First Explosion

Barry Harvey
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Brad Albing
Brad Albing
5/21/2013 12:18:58 PM
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Re: Have a first hand experience
I know Barry - he is an engineer with expertise in multiple areas - electrical, electronic, and IC design. Of course, Barry is not recommending that you blow things up. If he did, you're right - his manager would probably have a talk with him regarding the need to not do that in the lab.

Instead, ths is more of a learning situation - learning how to deal with inevitible situations such as these.

And it's difficult to deal with situations such as these in PSpice. It won't tell you that the capacitor blew up or that PC board traces vaporized.

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WKetel
WKetel
5/19/2013 6:03:01 PM
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Re: A fundamental goof, allright, a big one, too.
The strongest shock that I got was while pressing the reset buoon on a STD buss controller card rack. That happened because the disconnrct switch was directly above it on the panel, (thanks, John C.), and the hookup was tempoary, so it was not dressed correctly. It was a hot and sweaty August day, so just the very slightest touch made good contact. I jumped straight back about 8 feet, and then jumped around because of being so very startled. That scared everybody else a lot more than me.I explained to them that the time to be afraid would be when I hit the floor and didn't get up. No real damage was done except for a few jokes about "electric Bills".

I was more careful avter that event.

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Brad Albing
Brad Albing
5/19/2013 5:40:41 PM
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Re: A fundamental goof, allright, a big one, too.
On a sort of related note, I once brushed my hand up against a 480VAC, 3-phase rectified DC bus (part of a welder) - so that was around 700VDC. Just a glancing touch, luckily. You haven't lived 'til you've bumped up against a 700VDC bus. And sometimes not afterward too.

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DaeJ
DaeJ
5/18/2013 5:20:57 PM
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Master
Re: Have a first hand experience
I am not sure high voltage circuit with transformer was tested it the company lab, if this has been happed in the company lab, engineer might report to manger for safety concern, unless this explosion is for any purpose. Secondly, there are lot of nice simulation tool such as Pspice. Without actual board implementation, any circuit behavior can be roughly predicted.  I burned Cap a few time, not exploded something. It sound like you are electrical engineer handling high voltage  not electronic engineer, who test less than 12 voltage in the most case.

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antedeluvian2
antedeluvian2
5/18/2013 4:11:27 PM
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Newbie
Re: A fundamental goof, allright, a big one, too.
WKetel

although the flash-burn from plugging in a 3-phase plug that had an errant strand of copper was much more painful. That "bang" cleard all thre phases 30 amp fuses, and the noise was quite loud. Did you know that copper vapor is a much better conductor than solid copper? The reason is that it is an ionized plasma,

I once walked through the basement labs at Cutler-Hammer where they had been (and probably still do) testing circuit breakers. The conductors that were bolted to the wall were these huge copper bars. I think "bar" is a misnomer, "beam" would probably be better. I don't remember exact sizes but they would have had crossectional areas of more than a few square inches.

And there was this copper residue splattered all over the walls. There must have been some pretty big bangs.

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WKetel
WKetel
5/17/2013 7:50:34 PM
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Re: A fundamental goof, allright, a big one, too.
I have yet to get a serious DC shock, although I have had a few hot wire burns from yanking out wires with the insulation melting, when I knew that there was no fuse to stop the curent and letting the thing continue would have been VERY EXPANSIVE. AN adequately motivated individual can break a #12 stranded wire very quickly with the right motivation.

But AC shocks are a different story, although the flash-burn from plugging in a 3-phase plug that had an errant strand of copper was much more painful. That "bang" cleard all thre phases 30 amp fuses, and the noise was quite loud. Did you know that copper vapor is a much better conductor than solid copper? The reason is that it is an ionized plasma, which is also the reason that arc-flash is so very deadly. 

As far as  learning from disasters goes, I much prefer to learn from the incidents that other people have. It is usually safer, and does not damage one's reputation the way causing explosions does.

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Barry Harvey
Barry Harvey
5/17/2013 1:53:12 PM
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Re: A fundamental goof, allright, a big one, too.
I think everyone who works with high voltage eventually gets shocked.  It helps to be stupid I guess, but not necessary.

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Barry Harvey
Barry Harvey
5/17/2013 1:50:44 PM
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Re: It can be expensive
Actually they are like beer cans in this case.  They're about half the size of electrolytics I last used in similar service, but still deadly.

So, electrolytics mainly explode when reverse-biased, or when they are abruptly charged after decades of discharge.  Shorting them doesn't seem to hurt them, but it will hurt whatever discharges it.

I'm more concerned about grabbing onto a high-voltage DC line since there probably is some such big capacitor ready to fully discharge into you before you can let go.  Grabbing the AC is more benign (assuming you're not well grounded) since you should be using only one hand to probe things (other hand in pocket joke) so you don't complete a circuit with current coursing through your chest.

Do these things and laugh at your timid peers.  Of course after your first shock you get really careful and thoughtful.

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Barry Harvey
Barry Harvey
5/17/2013 1:39:44 PM
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Re: Have a first hand experience
Yes, safety is good.  I use a variac followed by an isolation transformer to apply first power.  The isolation transformer allows safely grounding the secondary side so you can use an oscilloscope to troubleshoot.  The variac (which does not isolate) allows you to slowly raise the input voltage while measuring so that if there is a fault, the fault current is low and you can perhaps find bugs without destroying devices.

The explosion came from external wires connected wrong.

And, oh yes, I turn power on to an unfinished project while my head and hands are offside or behind something in case something does fly out. 

You know, power projects just blow up occasionally.  We shouldn't be afraid, but we should be intimidated and think two steps ahead of what you're doing.

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WKetel
WKetel
5/16/2013 8:45:52 PM
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Artist
Re: Letting out the genie
But none of those was as exciting as the time our lab manager went to check the 480 volt terminals of a large motor, and he had the meter leads plugged in across the 10AMP current measuring terminals, becuse the tech whose bench he grabbed the meter off of had used it to check current for me on some other project. When he made the connection the 250 volt fuse failed but kept on conducting, the meter probe leads sort of evaporated, and the meter suffered a great deal of internal damage, not covered by warranty. The lab manager survived with only some minor burns on his hands and arms, and returned to work the next day. Since then I always check meter connections before using the meter. I was able to learn from his experience.

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Page 1 / 4   >   >>
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