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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DoN. Nichols writes:

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!

A rectified autotransformer is simply a DC power supply that is ground- or
neutral-referenced. Nothing wrong with that. Indeed, it protects against
certain faults. And it would be reckless to permit a floating supply to
operate in the presence of faults.

Being ground-referenced, such power supplies cannot be stacked, or used to
power grounded loads, which must be what leads to the fear of using them.
In some applications they cannot thus be used, but in many applications,
where the load is isolated, this is of *no* consequence, and rectified
autotransformers are economical and appropriate.

In article ,
Richard J Kinch wrote:
DoN. Nichols writes:

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!

A rectified autotransformer is simply a DC power supply that is ground- or
neutral-referenced. Nothing wrong with that. Indeed, it protects against
certain faults. And it would be reckless to permit a floating supply to
operate in the presence of faults.

Not if the hot and neutral are interchanged -- anywhere between
the breaker box and the Variac. Get a three-prong plug which someone
has cut the ground pin from, or an older one without a ground pin, and
the chances are that everything will be hot.

And with a bridge rectifier (which he is proposing), each side
of the load alternates being connected to the low or high side of the
feed with each half-cycle. Better to have an isolation transformer, and
to ground the proper side of the output power.

Being ground-referenced, such power supplies cannot be stacked, or used to
power grounded loads, which must be what leads to the fear of using them.
In some applications they cannot thus be used, but in many applications,
where the load is isolated, this is of *no* consequence, and rectified
autotransformers are economical and appropriate.

Consider my points above.

Enjoy,
DoN.
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--- Black Holes are where God is dividing by zero ---

Thank you all for your input so far.

I went to the library and got all the books I could find on power supplies,
and a couple of electronics textbooks. I've been slogging through the texts,
jeez I wish I had learned this stuff in school, when there was a teacher
around, to ask all my ?s!


I posted the basis of the power supply in the dropbox:
http://www.metalworking.com/dropbox/anodizer.jpg

Changes I intend to make are as follows.
Add an isolation transformer
Add a keyswitch for extra safety, as I have a 3 year old, and even though
it'll be on a high shelf, you never know...
use a momentary switch (trigger)
add a cap. for smoothing
add a DC voltmeter
and an ammeter

My transformer is rated 115v in, 0-135v out. 3A max.
the bridge I got is a kbpc3506w , which is rated for 420v, 35A, with a 400A
peak surge.
These are the only components I have got so far.

I have tried to crunch the numbers, and if I'm doing it right, I think the
resistors need to be bigger to give me an output of 2A, and that the
wattage ratings listed are too low. However, I don't know what the
resistance of the anodizing bath itself will be.

If anyone would help me figure the values I need for the power resistors,
cap, and cap drain resistor, I would greatly appreciate it.








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gene lewis wrote:
Thank you all for your input so far.

I went to the library and got all the books I could find on power supplies,
and a couple of electronics textbooks. I've been slogging through the texts,
jeez I wish I had learned this stuff in school, when there was a teacher
around, to ask all my ?s!


I posted the basis of the power supply in the dropbox:
http://www.metalworking.com/dropbox/anodizer.jpg

Gene, ya need to rotate your bridge -90 degrees.
Right now, it will blow the fuse on each half cycle.

--Winston

I came across this when looking for something else.
http://www.riversidemachine.net/item40480.ctlg

I was quite amused about the coca-cola.

gene lewis wrote:

Thank you all for your input so far.

I went to the library and got all the books I could find on power supplies,
and a couple of electronics textbooks. I've been slogging through the texts,
jeez I wish I had learned this stuff in school, when there was a teacher
around, to ask all my ?s!


I posted the basis of the power supply in the dropbox:
http://www.metalworking.com/dropbox/anodizer.jpg

Changes I intend to make are as follows.
Add an isolation transformer
Add a keyswitch for extra safety, as I have a 3 year old, and even though
it'll be on a high shelf, you never know...
use a momentary switch (trigger)
add a cap. for smoothing
add a DC voltmeter
and an ammeter

My transformer is rated 115v in, 0-135v out. 3A max.
the bridge I got is a kbpc3506w , which is rated for 420v, 35A, with a 400A
peak surge.
These are the only components I have got so far.

I have tried to crunch the numbers, and if I'm doing it right, I think the
resistors need to be bigger to give me an output of 2A, and that the
wattage ratings listed are too low. However, I don't know what the
resistance of the anodizing bath itself will be.

If anyone would help me figure the values I need for the power resistors,
cap, and cap drain resistor, I would greatly appreciate it.








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In article , Winston says...

http://www.metalworking.com/dropbox/anodizer.jpg

Gene, ya need to rotate your bridge -90 degrees.
Right now, it will blow the fuse on each half cycle.

Good call. I missed that one.

Jim


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please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
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DoN. Nichols writes:

A rectified autotransformer is simply a DC power supply that is
ground- or neutral-referenced. Nothing wrong with that. Indeed, it
protects against certain faults. And it would be reckless to permit a
floating supply to operate in the presence of faults.

Not if the hot and neutral are interchanged -- anywhere between
the breaker box and the Variac.

It is still ground referenced in that event.

Consider the full-wave rectified/capacitor-filtered output of an
autotransformer, with the wiper set to deliver a DC potential of V
across the + and - output terminals.

If the AC hot and neutral are wired properly, the + and - DC output
terminals are at +V/2 and -V/2 with respect to the neutral.

If the AC hot and neutral are reversed, the + and - terminals are each
at line voltage but offset by +V/2 and -V/2 respectively.

Neither case presents a problem to an isolated load.

I suppose if you thought of this as a way to get, say, a battery charger
for your car, where the load is not isolated but connected to the
vehicle chassis, then yes, it presents a big hazard. Or if you think
that a low (DC) voltage output is safe to handle bare-handed.

This is strictly for fully isolated loads.

"David Billington" wrote in message
...
I came across this when looking for something else.
http://www.riversidemachine.net/item40480.ctlg

I was quite amused about the coca-cola.

check it out: a comparison of the results of using T.S.P. vs Coke.
http://www-personal.umich.edu/~bobden/bob_titanium.html

a lot of cool stuf on this guy's main page too.




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gene lewis wrote:

Thank you all for your input so far.

I went to the library and got all the books I could find on power supplies,
and a couple of electronics textbooks. I've been slogging through the texts,
jeez I wish I had learned this stuff in school, when there was a teacher
around, to ask all my ?s!


I posted the basis of the power supply in the dropbox:
http://www.metalworking.com/dropbox/anodizer.jpg

Changes I intend to make are as follows.
Add an isolation transformer
Add a keyswitch for extra safety, as I have a 3 year old, and even though
it'll be on a high shelf, you never know...
use a momentary switch (trigger)
add a cap. for smoothing
add a DC voltmeter
and an ammeter

My transformer is rated 115v in, 0-135v out. 3A max.
the bridge I got is a kbpc3506w , which is rated for 420v, 35A, with a 400A
peak surge.
These are the only components I have got so far.

I have tried to crunch the numbers, and if I'm doing it right, I think the
resistors need to be bigger to give me an output of 2A, and that the
wattage ratings listed are too low. However, I don't know what the
resistance of the anodizing bath itself will be.

If anyone would help me figure the values I need for the power resistors,
cap, and cap drain resistor, I would greatly appreciate it.








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Remember when the wiper is 'full current' - the series resistors won't
keep the bridge or the expensive autotransformer from burning up. Place a
high wattage, low resistance such that a short at the load end does not
exceed the winding current allowed. (and the rectifiers as well).

Martin

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@ home at Lion's Lair with our computer
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder