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Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Hi im planning on working around 2.5kv and 100uf storage , it might not be much but it will kick like a mule. Im after a foolproof way to wake my arragent ass if I get to cocky, anyway I would like something like the below pic ,that when it senses a hand will flick a switch and discharge the cap throught a thin wire making a bang as a warning. I would like the thing to be made out of passive compents and just push logic gates at worse. Any help apprecated
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
No, forget it. You cannot rely on any sort of active protection to keep you safe.
At 2.5kV, the voltage is just about low enough that good insulation can be made to keep you safe, but you will have to pay attention to all the details. Much higher voltage and the only thing that will do is a minimum distance of fresh air.
The question you are really asking is 'how can I be inattentive when around operating HV stuff?' The answer to that is, you can't. There are old HV experimenters, and lazy HV experimenters, but no old, lazy HV experimenters.
It's impossible for one to be on ones guard 100% of the time, attention fatigue will set in and you will make mistakes. So I like to make a clear distinction between 'safe' and 'unsafe' working around my dangerous gear. I only ever power it from one specific incompatible socket, no exceptions. I have a plug for that socket with a green light on it, attached to my chicken stick and earthing clips. I only ever 'work as if safe' when the green light is on. No green light, assume everything is hot, be mindfull. When I've finished dangerous working, I unplug the kit. I can't physically plug in the green light without picking it up, and now have the earthing stuff in my hand, which reminds me to earth all my capacitors before plugging it in. It's failsafe in that if the light fails, I assume hot, rather than having a red light on the kit which could fail dangerous. Once I see green, I can relax.
It may sound a complicated scheme, but it works for me and I'm still around to write about it. You need to come up with your own way of working that can tolerate anything failing, ideally several things failing at once, and you will still be protected. Your low voltage jumps less easily than higher voltages, at 2.5kV you would get away with many errors that 10kV would punish you for. So if you devise a method that works for you, review it radically if you go up in voltage.
I guess the summary of my scheme is 'if you don't *know* it's positively safe, so unplugged, caps shorted, then stay the f*k away'.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Ask yourself this: If my employee was working on this live apparatus and got injured, how would I prevent being accused of not providing safe environment.
Ever seen what happens when a bird or rat blows up something electrical ?
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Was also think about a cicuit that would short the mains wire to the device to trip a Rcd or fuse, but not quiet sure how to remove power from the caps, will have a bleed resistor but that will be effective after 1 min, and then you still have to check with a multimeter the voltage level.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
The only safe way to do it is to turn off the power, wait for the bleed resistors to work, then short the caps with a chicken stick, just to be sure.
That's the minimum. There is plenty of other stuff you could do as well, but you still need to isolate everything and positively verify that everything is safe.
I made a mistake once, and had 240 volts across my chest. I've told the story here a couple of times. I'm lucky I was eventually thrown clear, otherwise I wouldn't be here today.
EDIT: I now insulate the live side of the switch inside the enclosure, just in case. In fact I try to insulate everything I can these days.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I'm stating the obvious here, but unplug everything, keep one hand in your pocket, use a chicken stick to discharge everything and stop if you are tired.
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safty with charged caps, foolproof method
(the original old pilots, bold pilots rhymes better)