Re: ATM Re: [VacuumX] 24" vacuum chamber is getting closer :)

["pbunn" <pbunn@patbunn.com>]

You have a 120 volt dimmer rated at 16 amps at 120 VAC and a step down
transformer with a 24:1 ratio.

Therefore:

The stepped down voltage with the dimmer at full voltage is 120 /24 or 5
volts

The tranformer rated VA is 900 or better , probably a bit better, so the
maximum current available si

900 VA / 5 volts or 180 amps

The resistance of the tungsten filament is approximately .025 ohms cold ,
but rises substantially and quickly with temperature
much like an incandescent light bulb..

At full voltage with the dimmer on at 120 volts, the secondary voltage is 5
volts and the secondary current at the filament is:

5 volts / .025 initially or 200 amps, but immediately dropping to
substantially less at the filament heats

You also have substantial connection resistance between the tungsten
filament and the wiring, so the system probably never sees more than 16 amps
and probably quite a bit less. The triac can withstand substantial overload,
500 % or so at short time spans , so the filament heat up would be no strain
at all.

Pat Bunn



----- Original Message -----
From: "James Lerch" <jlerch1@tampabay.rr.com>
To: "VacuumX mailing list" <VacuumX@yahoogroups.com>
Cc: <atm_free@yahoogroups.com>; "ATM List" <ATM@shore.net>
Sent: Monday, January 05, 2004 12:51 PM
Subject: Re: ATM Re: [VacuumX] 24" vacuum chamber is getting closer :)


>
> ----- Original Message -----
> From: "Dominic-Luc Webb" <dlwebb@canit.se>
>
> > For your system, the wire appears to be 0.0813 cm diameter (area is then
> > 0.0052 cm^2). The resistivity of Tungsten is 5.51e-6 Ohm*cm. This should
> > works out to about 1.06e-3 Ohm*cm. For your entire series circuit:
> >
> > 1.06e-3 * 6 * 4.0 = 0.025 Ohm  (intuitively, this sounds about right)
>
> I agree, sounds about right :)
>
> >
> > I am not sure what to say about your dimmer vs my dimmer and dimmers in
> > general. You discuss a few volts and hundreds of amps, which makes me
> > believe you have done something very different from me (voltage-current
> > conversion).
>
> My setup is pretty simple
>
> 120vac 600 watt residential dimmer switch from hardware store
> 24:1 transformer (salvaged from dead 900va UPS)
>
> 120vac -> Dimmer -> Transformer -> Filaments
>
> > Here is what I have done and how dimmers work as I understand
> > them.
> >
> <snip>
> >The BT139 triac I have chosen is
> > rated at 230 VAC @ 16 Amp.
>
> I'm not an electronics expert by any means, but what happens if your triac
> exceeds 16 amps?  I was under the impression that you can't exceed the
amperage
> rating of the device no matter what the voltage may be at that moment...
(But I
> could be wrong!)
>
> >We both seem to be using the "bombs-away
> > Pentagon approach" at present.
>
> Actually, I can reliable control the temperature from very dull red to
white hot
> and any where in between.
>
> The method I currently use to evaporate goes like this:
>
> #1 Increase dimmer position until transformer starts to hum
>
> #2 Decrease dimmer position to lowest transformer "hum" (if too low repeat
step
> #1)
>
> #3 Hold this setting until filaments reach a dull red and Aluminum melts
and
> wicks (but won't evaporate)
>
> #4 Once Aluminum has wicked, increase power to medium yellow and hold
until
> Aluminum has evaporated
>
> #5 After aluminum has evaporated, I've played with trying to "anneal" the
> tungsten by various methods, but all have resulted in the still very
brittle
> tungsten that breaks with the slightest touch.. :0
>
> >
> > This brings us back to your fragile filaments. Perhaps much of that
> > breaking is due to extreme temperatures you are using. As per our
earlier
> > discussions about sublimation, a lower temperature might be desirable.
> > Another issue is that you must recall that dimmers (the type I refer
> > to) are causing oscillatory phenomena which can be transduced into
> > filament vibration. This could be minimized by changing components,
> > changing the "dimming level" or changing the filament structure or the
> > nature of the support for the filament so as to dampen vibrations. I
believe
> > you have an oscilloscope and you may be able to detect some of this
> > at the 2nd or 3rd harmonic for your line frequency (60 Hz*2 and 60Hz*3).
> > Not sure, just a thought.
>
> Fortunately, the tungsten doesn't fail until after its completed its job
:)  I
> think the problem is once the tungsten gets "hot" as it cools it
crystallizes
> and fractures more easily..
>
> >
> > I will do more work on my dimmer and electrodes before posting a web
page
> > with specific circuit board and part numbers. I will now also consider a
> > 120 VAC version. More ideas are welcome.
>
> I just got your other email, have you done any experiments yet?
>
> James
>
>