Re: [vox-tech] [no linux] High voltage circuits?

[Peter Jay Salzman <MAPSp@dirac.org>]

hmmm... i was hoping you wouldn't ask me this.  i'm a physicist -- i only
know the _principles_ of electronics.  can't actually design much myself!

but maybe a good place to start would be

     V_inductor = L dI/dt = I_through * R_of

looks useful, since the resistance of the inductor depends on the change of
current through the inductor.   perfect if you're getting a short surge of
current while the filament warms up (i assume this is a fast process).

it seems like you'd have to know the change in resistance between a cold
filament and a warm filament to start.

actually, aren't there current controlled transistors?  i forget most of
what i used to know about them, but i seem to recall that there are
transistors that control current through the collector/emitter depending on
what current is entering the base.  you could use this to "shunt" extra
current away.

i used to know a lot more as an undergrad, but i cleared out a lot of space
in my brain to store quantum gravity info.   :)   the best i can do would be
trial-and-error.   sorry!  (boy do i feel lame know!)

pete

On Tue 20 Mar 01,  9:50 AM, Mark K. Kim said: 
> Awesome -- that's really good to know.  Thank you!
> 
> Pete -- Adding an inductor sounds good.  What rating should I use?  (it's
> been a while since I've worked with inductors :)
> 
> -Mark
> 
> On Tue, 20 Mar 2001, Jeff DeFay wrote:
> 
> > Mark,
> > If you are using incandescent light bulbs, your current will be much higher
> > during the
> > brief time that the filaments are cold.  The 60 watt power consumption is
> > calculated
> > with the filaments at normal operating temperature;  introducing resistance
> > into the circuit
> > would also keep the effective resistance of the filament low by preventing it
> > from reaching
> > normal temperatures.
> > 
> > Regards,
> > Jeff DeFay
> > 
> > "Mark K. Kim" wrote:
> > 
> > > Anybody here ever work with high voltage circuits?  I'm creating a
> > > low-volage / high-voltage hybrid circuit for the first time; a digital
> > > circuit (low voltage, 5DCV) controls the logic portion, and uses two
> > > relays to control two light-bulbs (high voltage, 110ACV). And I'm
> > > wondering:
> > >
> > >    1. How much current usually goes through those 60W light bulbs?
> > >       How much current is required to make it look bright enough?
> > >
> > >       My guess would be:
> > >
> > >          110ACV * I = 60W
> > >          => I = 0.55A (max)
> > >
> > >       And I'm using a 1A relay rated at 120ACV, so my guess would be
> > >       that I can hook up this relay to the light bulbs directly.
> > >       But when I did that, once the light bulbs were turned on,
> > >       they stayed turned on (I couldn't turn off the relay connection
> > >       -- apparently the connections got fused together.)
> > >
> > >    2. So my idea was to force-limit the current.  I got new relays
> > >       (same kind) and bought 1W resistors (200 Ohms... actually, two 100
> > >       Ohm resistors soldered together.)  Once I got them in circuit,
> > >       it had two problems:
> > >
> > >       a. The light bulbs were too dark, and too slow to lighten up.
> > >          Apparently too much resistance?
> > >
> > >       b. I started seeing smokes come out around the resistors.
> > >          I don't know if this is because the resistors need to be
> > >          higher wattage, or if the current is melting the solder.
> > >          I'm pretty sure the electrical wires are good enough for
> > >          this project (it's rated at 700V), although if the solder
> > >          is melting (meaning it's at least 400 degrees Ferenheit)
> > >          then it could be also melting the electrical tape.
> > >          Ideas?
> > >
> > > I need to know if I need to switch to higher rated relays, and if so, to
> > > what.  Also I need to know if I need to use a different resistor and/or do
> > > not use solder.  I'd really appreciate any suggestions from anyone
> > > knowledgeable in this field.  Thanks!
> > >
> > > -Mark
> > >
> > > PS: I know this is off-topic but I figured someone here might know.
> > > Besides, we've been quiet on this list for a while.  Also, this circuit is
> > > for LUGOD anyway.
> > >
> > > ---
> > > Mark K. Kim
> > > http://www.cbreak.org/mark/
> > > PGP key available upon request.
> > 
> > --
> > Jeff DeFay
> > jfdefay@acm.org
> > (530)753-0774
> > 
> > 
> > 
> 
> ---
> Mark K. Kim
> http://www.cbreak.org/mark/
> PGP key available upon request.
> 

-- 
"Coffee... I've conquered the Borg on coffee!"               p@dirac.org
       -- Kathryn Janeway on the virtues of coffee           www.dirac.org/p