In article , gene lewis wrote:
"axolotl" wrote in message
...
[ ... ]
Powerstats or Variacs are autotransformers- the terminal connectors have
a wire path to the incoming AC line. Do not use this as a power supply
without a transformer for isolation.
Amen!
For titanium, (IIRC) the anodizing
voltage tops out at about 75 volts, so you would need to scrounge a
transformer with a 120V input and a 50 or 60 Volt output to feed a full
wave bridge. Drive the input of the transformer with the
autotransformer. Fuse the secondary of the transformer. Show your results
[ ... ]
Thanks.
Actually, when anodizing titanium there is a second (3rd 4th.....) order of
colors created at higher voltages. The most useable colors are created in
the first 2 orders, which run from 20 to around 130V. That is why I wanted
output to be up to 150V (or whatever I can get out of this transformer.)
Well ... depending on the autotransformer, you can either get up
to full line voltage (whatever it happens to be at the moment), or
significantly higher. Some Variacs (and other autotransformers) are
tapped, to produce voltages above the input voltage, and will give 140
VAC out for 117 VAC input. This would allow you to get 198 VDC out with
the bridge rectifier and a filter capacitor.
So
from what you said above, I assume that if I got a 1:1 isolation transformer
would give me the full 120V range? I was told that after rectifying the ac
to dc I would gain voltage, like a 20% increase, but that seems
counter-intuitive to me.
More than 20%. More like 40%.
AC is not a constant voltage, but rather a constantly varying
voltage in sine wave shape. It goes from zero up to a peak, back down to
zero, then to a negative peak, and back up and keeps repeating.
Now for slow-responding things like heaters and light bulbs
(which also depend on the heat generated), the power is neither the
peak, the zero-crossing, nor the average. Instead it is something
called the RMS (Root-Mean-Square), which is can be determined by
dividing the peak voltage by the square root of 2 (1.414). That is the
voltage used when naming the power line voltage. So -- to determine the
peak voltage, you multiply by the square root of two, thus adding 41.4%
to the RMS voltage.
When you rectify the voltage, and feed that into a capacitor,
you get the peak voltage, unless it is heavily loaded relative to the
capacitance, in which case you get a ripple, with the voltage following
the sine wave up to the peak, and then discharging at a slope determined
by the capacitance and the load current. In most cases, this will still
be above the RMS voltage, so there will be some boost.
Now -- I don't know whether the titanium's color will be
affected by the peak voltage or the average, so I would suggest that you
have plenty of capacitance to keep things near the peak voltage, so you
know where you are.
Anyhow, I had planned to use the isolation transformer, along with a
built-in GFCI outlet for safety, and using a momentary-on switch so as to
prevent accidents.
O.K. Better. The transformer should eliminate the most likely
path for shocks, unless you accidentally ground one of the output sides.
The design is essentially like this:
http://www.warnerknives.com/anodizer.htm , but with more safety, and a
capacitor for smoothing. I may also use a UPS to keep line voltage stable
for more repeatable results.
Also check out this: http://mrtitanium.com/anodizer.html The dimmer switch
deal seems a bit hokey for me, but I like the added safety features.
Do you notice any glaring faults in these designs?
There are not enough safety features in either. There is no
isolation between the power line and the load.
The dimmer alone would not work, but with the light bulb as a
load, it might work -- depending, again, on whether it is sensitive to
average or peak voltages. The peak output on a dimmer set low is rather
unprecitable.
Good Luck,
DoN.
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