Hi folks,
inspired by your tremendous help with my sister's clock (thanks
again!), I thought I might ask you on this issue as well. Recently I
inquired how the bargraph tubes work, and somehow we got to talk about
lightsabers ;-)
The thing is, I had to think about it all the time, and I finally
ordered some metal lightsaber hilt (much to my local folks'
amusement). Now for the challenge: I'd like to mount a neon tube in
this handle that glows red.
The neon tube is made of clear glass (so it is a true neon tube, not a
fluorescent light that are sometimes referred to as neon tubes as
well) with one electrode at the base, length about 1m, and 2.5cm
diameter. I have seen in the internet that these tubes can be driven
by a high-frequent AC voltage applied to this one electrode (Tesla
coil). So now I have several questions:
1. How do I build this power supply nice and compact so that it fits
in the hilt (length is 20cm, diameter 3cm)? My first thought was a
transformer being driven by some frequency on the secondary side,
inducing a rather high AC-like voltage on the primary side. But which
frequency is required, at which voltage and current?
Around 20-50kHz is common. Current is fairly low, a few mA to a dozen
or so, depending on the size of tube you're using and its capacitance to
nearby objects. Voltage can be a few hundred volts to a few thousand volts.
It sounds like you're thinking of using an ordinary power supply
stepdown transformer in reverse. This won't work very well, those
transformers are designed for 50-60Hz. You'll need a high frequency
transformer for this trick. Maybe one out of a CCFL inverter would do
the trick.
3. Will it be possible to create some "star wars" power-up /
power-down effect of the saber by either changing the frequency,
voltage or current of the power supply? I know it can be done (see the
link above) but what is varied? Looking at the schematic in the pdf
above I guess it is voltage and current.
I think the voltage is varied, possibly the frequency as well. The
current will tend to follow it.
You can buy a ready-made "scripting" transformer made for neon sign use
that does this, I suspect a small one would fit in the hilt. I used to
get 'em from Tech 2000 and Bertonee. Bertonee now does business as
Ventex, their model 12D10S runs on 12VDC, and offers 3000V@15mA out,
with scripting. It's pretty small too, and you could thermally couple
its heatsink with the metal housing to keep it cool.
http://www.ventextech.com/#gen4!12%20VDC
- John
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