Re: bleeder resistor power supply

Hi,

A 3K resistor across a 20,000 uF capacitor has a 60 second time
constant (20,000 E -06 times 3,000). Things are considered pretty
much discharged after 3 time constants (180 seconds here, or 3
minutes.

Regarding 60VDC being lethal; get a grip. When I was 18 and in school
a long time ago, I worked summers at a company now long defunct that
built servodrives for the military.

I was an electronic technician. During the lunch hour I and a couple
of other technicians would entertain ourselves with a Tektronics
transistor curve tracer.

What made this instrument unique was the ability to output 0 to
300VDC to a pair of test leads. The victim would hold the leads, one
in each hand, while the other would crank up the voltage until the
victim would cry uncle.

My experience from that was with sweaty hands (good electrical
contact), you would just begin to feel a tingle at 80VDC, get a
little uncomfortable at 120VDC and cry uncle at 160VDC because you
could no longer let go of the leads.

Mind you, the current would go up one arm, go thru the chest and
heart, and out the other arm. The current would reach about 100 mA
before it became unbearable. I'm still alive today.

Unless you are standing in a bucket of salt water, use a pacemaker
and three weeks away from a myocardial infraction, 60VDC will not
hurt you.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "HighTech" <hightechsystems@h...> wrote:
>
>
> -----Original Message-----
> From: Hugh Prescott [mailto:hugh@a...]
> Sent: Wednesday, October 17, 2001 8:28 AM
> To: CAD_CAM_EDM_DRO@y...
> Subject: Re: [CAD_CAM_EDM_DRO] bleeder resistor power supply
>
>
> Greetings
>
> However the cap discharge circuit you propose will not discharge
the caps to
> zero voltage.
>
> It will discharge to some low voltage depending on the resistor and
LED
> cutoff current.
>
> Red, yellows, greens. leds are around the 2v range unless you have
low
> voltage variety then they can be 1.2v.
> Blue leds are aroun the 5v range and white around there also.
> The capacitor is going to leak down to 0v anyway over a period of
time.
> But this is not in the lethal range you can touch a 24v supply and
not feel
> anything.
> Right around 60v dc is the lethal range but all the conditions have
to be
> right and it has to go across you heart to stop it. Just be careful
with
> high voltages.
>
>
>
> I would try it and check the remaining voltage across the caps, it
may be
> enough to damage semiconductors and or surprise you when you
accidentally
> short circuit the caps.
>
> Was in St. Louis yesterday and visited the surplus electronics on
Natural
> Bridge road just west of I-170. They had a few power supply's in
the range
> of 5 to 48 volt and 10 to 40 amps. One other I saw was a 5 to 50
variable
> that appeared to be in the 100 amp range no nameplate to give the
> information but wire size, rectifier and cap size plus monster heat
sinks
> and fans indicated it could deliver some serious amps.
>
> Hugh