Newbie question about CC power supplies>>

[Indy]

I just bought the LCD kit (hasn't arrived yet) and after reading certain threads it seems like investing in a CC power supply is a good idea. My question concerns which one should I purchase. I am only doing very small parts, about 1.2 square inches per part. Using the 720 annodizing calculator.xls it would seem that the 3 amp CC rectifier would be fine for me, and that I might even have to put in a few pieces at a time since the calculator says that it would require 0.03 amps per piece (less than the lower limit for the rectifier). Does this sound right?

Thanks in advance!

[Fibergeek]

You have it right.

A CC power supply will always provide better anodizing regardless of the scale. It also makes the job much easier.

The very small size of your work will require very accurate current measurements at low current levels, unusual for most anodizing applications. A real electronics laboratory CC/CV supply would be in order. You want accuracy down to 1 milliamp (0.001A). You might find one of these used on ebay, expect to spend several hundred dollars for a used one.
Alternately, you could use Caswell's 3A CC/CV rectifier with a minor addition. This will require a 1 Ohm 1% (at least) 3Watt (or larger) precision power resistor and a digital multimeter that is ACCURATE reading DC volts at 1 millivolt (0.001V). This won't work with a cheap $10 multimeter. Precision power resistors are available over the internet from Digikey or Mouser Electronics. You put the resistor in series with the positive output of the rectifier, and measure the current with the multimeter hooked across the resistor, it will read directly 1 millivolt = 1 milliamp. At your very low current levels, you will notice the inaccuracy of the meters on the rectifier, this is normal.

[neilfj]

Besides what Fibergeek said, you have a couple other options.

For a 1.2 sq/in piece anodized at 3 amps/sq ft = .025amps current setting.
If you anodize at a higher current density, say 6 amps/sq ft, your current setting would be .05 amp current setting. Doing 20 pieces at one time will bring your current setting up to 1.0 amps. If you don't have that many parts to do simultaneously, then put in a sacrificial piece of aluminum.

For instance, in addition to the part you want to anodize, connect up a 2nd piece of sheet aluminum, say 4" x 4" = 32 sq in surface area.

This sacrificial piece, plus the part, would total 33.2 sq in. At 6 amp current density, you would set the current at 1.4 amps. [(33.2 / 144 sq in) * 6 amp current density = 1.38 amps]. If you want or need to anodize at a 3 amp current density, just increase the size of the sacrificial aluminum to 5" x 5". [(51.2" / 144 sq in) * 3 amp current density = 2.13 amps]

Aluminum foil should work as the sacrificial aluminum and could be disposed of after each use. Or, you could use aluminum sheeting or a block/rod of aluminum, but you'd have to strip the anodizing that grows on it after every use.

[Indy]

that I can shoot for when I have a some experience under my belt. Very excited to get going