Why you should use a CONSTANT CURRENT power supply

[mcaswell]

I am in the throes of rewriting/updating the manual, and I came across this old article by the late Fibergeek, developer of the LCD Anodizing System.

I felt it was worth posting here, as it could solve many peoples problems. It also pretty much shouts out not to use batter chargers and ordinary 'rectifiers'.

A CC power supply also greatly benefits anodizing. Since the anodize film is an insulator, the changes in electrical characteristics during the process are much larger than in plating. CC operation provides a uniform anodize pore structure all the way down to the base metal. This promotes even and deep dye penetration, and the consistent pore structure provides a better looking and stronger anodize coating than if the pores are distorted by changes in the current. For this reason Caswell Inc. recommends the use of CC for any and all anodizing applications.

[cprocess]

Re: Why you should use a CONSTANT CURRENT power supply

This is good information. Another benefit of using constant current is that it enables you to use the "Rule of 720" to calculate anodizing time to get a specific thickness. This rule states that it takes 720 amp minutes per square foot to produce one mil of oxide coating. In application, divide 720 by your current density (in amps per square foot). This will be the time required to produce 1 mil of oxide coating. For example, if I have 2 square feet of surface area to anodize, rectifier is set on 40 amps (= 20 amps per square foot), I divide 720 by 20 = 36 minutes to apply 1 mil of oxide coating.

[sswee]

Re: Why you should use a CONSTANT CURRENT power supply

If you are anodizing at 20 ASF, you are not anodizing with LCD. It opens up a large can of worms for newbies to try anodizing outside of LCD parameters.
SS

[SylantBill]

Re: Why you should use a CONSTANT CURRENT power supply

I have been using a 12 voly 50 amp car charger and having different results each time. I can't figure the 720 rule because a lot of my parts are screws and nuts and pieces under 1 sq inch. How does someone figure the 720 rule with these small parts.

[acidrain]

Re: Why you should use a CONSTANT CURRENT power supply

I have been using a 12 voly 50 amp car charger and having different results each time. I can't figure the 720 rule because a lot of my parts are screws and nuts and pieces under 1 sq inch. How does someone figure the 720 rule with these small parts.

A current controlled (CC) power source is essential to good repeatable results.
Also, if you check the 720 rule calculator, you'll see that (depending on the current density you are using) 12 volts probably isn't enough.
At any rate, you'll need to accurately measure and hold the current (amps) that are going to the part (just let the volts do whatever they need to in order to maintain the amps).

Carefully measure the surface area of 1 part, and multiply by the number of parts in the batch. For smaller runs, it may be beneficial to add a sacrificial part. This will help even out any small measurement errors that are multiplied out by the number of small parts.

For example, you have 20 bolts that are .6 sq. in. each.
.6 x 20 = 12 sq. in.
Convert sq. in. to sq. ft... 12 sq. in. divided by 144 sq. in. (144 sq. in. in a sq. ft.) = .08 sq. ft. (rounded off).
Run these alone at 6 amps per sq. ft. current density = .48 amps for 120 minutes for 1mil.
This is a very small amount of current, and depending on your PS, may be impossible to control. Adding a sacrificial piece will increase the surface area, which will be easier to control:
Add a 6in x 6in x 1/8in piece of aluminum... 6 x 6 = 36. 36 x 2 (both sides) = 72. add the 1/8in edges... 24 x 1/8 = 3.
12 sq. in (20 bolts) + 72 + 3 = 87 sq. in.
87 divided by 144 = .6 sq. ft. (rounded off).
.6 x 6 amps per sq. ft. = 3.6 amps for 120 minutes for 1 mil.
3.6 amps is much easier to control than .48 amps.

[Haiden Morgan]

Re: Why you should use a CONSTANT CURRENT power supply

If you are anodizing at 20 ASF, you are not anodizing with LCD. It opens up a large can of worms for newbies to try anodizing outside of LCD parameters.
SS

Like what? Would you ahve to refrigerate the tanks to run higher A/SF to get shorter production times? What is this can of worms? We anodize often but would love to run higher amps to improve yield time. Currently we use around 5-6 A/SF as suggested by many out there. I am all about tackling cans of worms though, so please elaborate.

[Janke]

Re: Why you should use a CONSTANT CURRENT power supply

Like what? Would you ahve to refrigerate the tanks to run higher A/SF to get shorter production times? What is this can of worms? We anodize often but would love to run higher amps to improve yield time. Currently we use around 5-6 A/SF as suggested by many out there. I am all about tackling cans of worms though, so please elaborate.

Really its just heat. If you have a chiller and good agitation go for it man! I know spanky runs 10asf all day long.

[spankey666]

Re: Why you should use a CONSTANT CURRENT power supply

Like what? Would you ahve to refrigerate the tanks to run higher A/SF to get shorter production times? What is this can of worms? We anodize often but would love to run higher amps to improve yield time. Currently we use around 5-6 A/SF as suggested by many out there. I am all about tackling cans of worms though, so please elaborate.

LCD is just that !! Low Current Density, Janke is correct in saying i run at 10asf quite happily, and have gone upto 14 in the past but results can be varied. the whole objective of the anodising anodising process is to create a stable repeatable balance between layer growth and dissolution to create a decent pore matrix to enable dye ingress. too high temp or acid concentration and the dissolution over powers the poor growth and the pores become too large and the dye falls out, too low and the pores are too small and the dye wont go in. with lcd, running any higher than 10-12 asf and you are going to run into problems as the acid is too weak to create the correct size pores and pore density for good colour saturation. agitation will need to be very vigorous to stop localised over heating and associated dissolution. LCD was devised as a method for people to use at home, with relatively safe chemical concentrations and which can create excellent repeatable results with a minimum of fuss. it was not created for high speed commercial purposes. there are several good plating books that explain commercial processes and electrolyte concentrations, and there are also lots of other chemicals you can add to your (stronger mix )electrolyte to stop burning / dissolution, none of this is covered on this forum. so as for opening a can of worms, cant comment but there are so many different ways to anodise and lots of different electrolytes that can be used as well as concentrations .you will need to pick your process, research it well and experiment until you perfect it with out messing up your work, or you can stick with a process that has proven results and reliability with the trade off of being time consuming. BTW, whats your website about ? all pages are dead links ??

[Riadh]

hello
i find a used current adjustable power supply 2000 watts starting from 12 volts to 26 volts and from 0 amperes to 80 amperes , i want to ask you if this power supply can do the job..anodizing small and larger pieces of aluminium. this power supply start from 12 volts , when starting with 12 volts do this can mess up small parts or i have to start with less volts ?? thanks riadh akousticar@yahoo.fr