--- Donald Chester <[EMAIL PROTECTED]> wrote:
> > > > > >From: "Jim candela" <[EMAIL PROTECTED]> > > >Humans are expendable, but don't destroy them hard > to find capacitors! :-) > > It's no less safe to discharge them gently, first > using a resistor then > discharging directly, than discharging them with a > "bang." > > Besides, if you discharge them with a "bang" a tiny > piece of molten metal > could hit you in the eye. > > I don't normally wear safety goggles while working > inside a transmitter. > That itself could be a hazardous distraction. > > Don k4kyv > > > Don, All good points. I was trying to put this into perspective where safety concerns must prevail over equipment concerns every time. That said, we can design gear and write safety policies to achieve both. I like to put a large wire wound resistor in series with a capacitor bank before the DC goes to a RF PA or modulator. It could be a 50 watt 50 ohm resistor. This will have little impact to normal operation, but in case of a fault by either a chicken stick, or a internal tube arc, the peak current is defined as I = E/R instead of near infinity and beyond. This approach will protect your precious capacitors too. A bleeder should be used before the series resistor with something like a 5 minute discharge time. So combine this with a sign saying to wait 5 minutes or longer after removing AC power, and to short out the B+ with a chicken stick. When done, safety requirements are met. Of course any Yahoo can still get around, and either kill themselves, and or destroy the rig. It's hard to make something idiot proof. At the company I work for, some Yahoo used a chicken stick to defeat a gravity assisted grounding bar. Then a 90kv 100ma supply turned on, and arced to his foot, and out his right butt cheek into the floor. His life was saved when a metal door slowly closed, and interrupted the arc, which allowed him to limp away. The need to defeat interlocks did not exist, and the whole issue was he was not aware of the danger, and work arounds so that he didn't need to risk his life. At an old job I once had, an engineer (a ham to boot) would routinely isolate his chair, and workstation, and go up to 40,000 volts to work on something HOT. When he was done, he'd use a fiberglass rod to hit the HV off button, and then take a 200 meg-ohm resistor in his hand and touch the far end to earth ground. Then he'd step down, and go do something else. He did that all the time. You didn't dare get too close to him, or try to shake his hand! I saw him get nailed one day where he was at 40kv, and reaching up to something at 150kv, and he got too close. I saw no less than 6 long snaps into his hand as he waited for the Hippotronics 1D21 thyratron to kick in, and disable the supply. He then stepped down and walked away...white as a ghost. Jim JKO ____________________________________________________________ > AMRadio mailing list > Home: > http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul > Courson/wa3vjb >
