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previous: Steve Daniels (Small Bear Electronics) Thanks for the notes. I did do some... -- 6/18/2000 10:21 PM

Re: don't use a car battery to anodize

6/19/2000 5:33 AM
Joe	Re: don't use a car battery to anodize I guess when I think of a battery charger I think of high-current, unfiltered, unisolated DC. It may be possible to overstate the safety issues but a lot of things are easy to overlook. There are a lot of articles on anodizing but many that I've read (especially on the internet) are completely off the wall. "Current density" is only part of the equation. Anodizing works by equilibrium and the voltage determines the maximum thickness of the oxide. 12 volts will work okay, but 18 volts will produce a thicker coating, and will dye to a richer color. Even if the current is lower than the "recommended" density, the oxide will eventually grow to reach the thickness equilibrium determined by the voltage applied. It will just take longer. In this sense, voltage is more important than current density for anodizing, although a resonably high current density is of course desireable. 500 cold-cranking amps from a car battery is probably overkill, though. I've beautifully anodized parts with a 4 amp 18 volt power supply in about 20 minutes if that explains anything. Perhaps one of these days I'll rewrite my anodizing article to explain everything more completely. A word on dyes, I would highly recommend Jacquard's silk dyes from an art store. The pores in silk are tiny like aluminum, which means the dyes are more or less interchangable.

6/19/2000 5:33 AM

Joe

Re: don't use a car battery to anodize

I guess when I think of a battery charger I think of high-current, unfiltered, unisolated DC. It may be possible to overstate the safety issues but a lot of things are easy to overlook. There are a lot of articles on anodizing but many that I've read (especially on the internet) are completely off the wall.

"Current density" is only part of the equation. Anodizing works by equilibrium and the voltage determines the maximum thickness of the oxide. 12 volts will work okay, but 18 volts will produce a thicker coating, and will dye to a richer color. Even if the current is lower than the "recommended" density, the oxide will eventually grow to reach the thickness equilibrium determined by the voltage applied. It will just take longer.

In this sense, voltage is more important than current density for anodizing, although a resonably high current density is of course desireable. 500 cold-cranking amps from a car battery is probably overkill, though.

I've beautifully anodized parts with a 4 amp 18 volt power supply in about 20 minutes if that explains anything. Perhaps one of these days I'll rewrite my anodizing article to explain everything more completely.

A word on dyes, I would highly recommend Jacquard's silk dyes from an art store. The pores in silk are tiny like aluminum, which means the dyes are more or less interchangable.

Replies:

Steve Daniels (Small Bear Electronics) Thanks for the details. I will not ... -- 6/19/2000 1:34 PM