Hi Peter, Thanks for the plug. We dozens of anodizer down under.
Easy to do.
You’re welcome. Nice to see that I not only onee who needs to
prrroofread betterrr befur hitting sent… (grin)
The big power supply you describe would be great accept for the
size. There are smaller Variac type transformers about. A 10amp
would power a bath big enough to anodize a bike frame!
Yes, I know. I mentioned those big ones simply because, at least ten
years ago, they seemed to be a lot more common in cheap surplus
electronics shops, for dirt cheap prices (I found a couple once in a
Salvation Army store for five bucks each…) The smaller 3 am Stako
variacs are more suited but I’ve not usually seen them at much of a
discount. Perhaps you have…
A lot of power and dangerously high amperage. Not to be played with
Again, correct. The higher amperage though, can be nice if you want
to use this for, say, electroplating or electroforming. Usually, one
then gets the higher amperage from a larger step down transformer, so
the output is 0-12 volts or something like that, but with these large
variacs, there’s no reason the variac can’t be fed by a smaller step
down. Again, saves money. No other reason. Oh, and a too-large variac
does have one advantage. The variacs have one main weak point, and
that seems to be the connection to the movable tap. Too high a
current through one, and those seem to be where they burn out. And
the old used surplus units sometimes blow out before they should. So
an oversized variac means you’ll blow the fuse first, instead of the
variac itself. As for dangerous amperage, at the voltages used for
anodizing titanium, a whole lot less amperage is also dangerous.
Doesn’t take much to kill at 140 volts. The smaller unit one might
make from a smaller variac needs just as much concern for safe
We made a very nice little one for years based on a 3 amp Staco
variable transformer and a #4314 full wave bridge. It should be
noted that reading the DC voltage output on these gets a bit dicey.
The out put is dirty DC and for a volt meter to actually predict
the finale voltage that the bath will see some smoothing is
required. The need is to smooth the voltage as it goes to the
meter. The bath will take care of itself.
That’s why the capacitor (minimum) or a resistor/capacitor filter.
For a bath, of course you don’t need a filter, since as you say, the
ripple takes care of itself just with the nature of a bath. But with
good output filtering, less heating and potential burning would take
place in the case of a small bath or, in the use of brush anodizing
(questionable safety there, without an isolation transformer…)
You can help the whole issue of a meter by not using a digital
voltmeter. use the old analog dial meters, and the meter will show a
decently repeatable reading for any given setting. It’s the
mean/average, of course, not the peak voltage, but it’s reasonably
repeatable, so usable. With filtering, of course, it’s much better.
The main other issue to mention with a capacitor filter is that one
should use a fairly high value resister in parallel with the
capacitor to bleed off it’s charge when the circuit is turned off.
Again, a safety thing… As to accuracy of the meter for getting a
desired color, it’s simple enough to start with a slightly lower
voltage setting and increase it till you get the desired color. That
way, differences in current load won’t throw you off too much.
Now, with all that nonsense said, I’ll also say that while I used
one of my home built anodizers for many years, when I finally bought
a decent digitally controlled one (from Bill, of course), it was a
distinct improvement in safety, repeatability, and ease of use. I’ve
not used the old patched together one since, (actually I sold it last
year to a young hopefully up and coming artist who couldn’t yet
afford a commercial one). (another plug for Bill Seeley and Reactive
Metals. great folks to do business with, or to share dinner with at
a SNAG conference… )