[sage]

I haven't analyzed the peak voltage process mentioned here to any great extent but I too think there is something incorrect with the practicle aspects of it.
I have experimented with waiting for the voltage to peak and then start declining and ended with crazy times and bad results. I even logged the voltage with a Fluke logging voltmeter and there was no appreciable drop in voltage over any reasonable time with 6061 alloy that I could see.
I just stick with my tried and true method of calculating amp-minutes per square inch - which is my way of calculating the same thing as the 720 rule.
If any body cares it goes like this.

Take square inches and multiply by 5 amp-minutes.
This gives the amp-minutes required for the part.
Divide by a current your supply and connections can handle - say 2 amps.
This gives the time required in minutes to complete the anodizing.

If the time is too long (only becasue your impatient) adjust the current until your happy with the time. I usually try to get things done in less than 120 minutes if possible.

eg.
20 square inches x 5amp-minutes per sq.in = 100 amp-minutes.
100 amp-minutes divided by 2amps gives 50 minutes.

So the bath is set for a regulated 2amps for 50 minutes exactly.

You might find (like I have) that the LCD acid being very weak means that the voltage to get the 2amps flowing is quite high, maybe higher than your supply can deliver. This problem gets worse for small parts. It's a simple matter of adjusting the current to get a usable voltage and re-doing the calculation to find the time. Use the constant CURRENT setting of the supply.

If you juggle these figures in the 720 calculator you get the same results. I just find it easier (always have) to think about the amp-minutes required to get the job done. No calculators required. Forget the peak voltage thing.

PS> I've had good results from 5 amp-minutes per square inch quoted here to over 10 amp-minutes per square inch. I did a bath of red last week. Dye was very obviously getting into the part in about 30 seconds, was a dark shade after 20 min, gave off almost nothing in the boiling stage and the finished coating was hard and durable as a rock.


Dave Sage