I'm totaly lost :(

[jtagger19]

I really hope some one can help me out
I'm totaly new at this
I'm working on an LCD system and came up to some Q maybe they are stupid Q but I'm really lost here .
I have a 20a-30v CC power supply
how do I stay in the 4.5amp/sq ft when doing less than 144 sq inches
( 1 sq FT)
ex I have 10 sq inches how do i figure out the amps I need to stay in the 4.5amp/sq ft range?
the lowest the amps that my rectifier goes is .1

and how do I know when to stop ??
the guide says once you reach PAR the amps drops , is this right
I tryed some 11sq in parts and they started to PITT awfully after 10 minutes at .5 amps

[mcaswell]

How many square inches in a square foot?

12 x 12 = 144 sq inches

4.5 amps per sq foot = 4500 milliamps (ma) per sq foot

to find out how many ma needed to do 1 sq inch 4500/144 = 31.25ma
(So call it 30ma per sq inch)

I take it you can calculate out how much is required to do 10 sq " now ?

[Fibergeek]

Pitting is the usual sign of anodizing with way too much current.

Your 20A 30V CC power supply should be 0-20A and 0-30V in range; there are two knobs on it, one for current, and one for voltage, right? It actually will go down to 0 Amps, but the digital (?) meter on it won't read below 0.1 A.

You calculate the required current based on the surface area of the part and the current density you want to anodize at:

Given; 10 sq.in. surface area, and 4.5 A per sq.ft. current density.

1. 10 sq.in. / 144 sq.in. = 0.069 sq.ft. The surface area in square feet.

2. 0.069 sq.ft. x 4.5 A/sq.ft. = 0.31 Amps. The current you need from the power supply.


The CC (Constant Current) power supply is set to provide 0.31 Amps as follows:

1. With the power supply turned off, connect the anodizing setup.
2. Turn the Current knob fully counterclockwise, and the Voltage knob fully clockwise.
3. Turn on the power.
4. Turn the Current knob clockwise until you read 0.31 Amps on the current meter.

The voltage will go to whatever value it needs to be to provide 0.31 Amps to the anodizing setup. The voltage will start very low, than rise for the next 5 minutes or so, and then settle down around 10-12 Volts for the rest of the anodization time. The 10-12 Volts assumes LCD electrolyte and 4.5 A/sq.ft. current density. If the voltage reads substantially more than that you have a connection problem and you are likely to have poor anodizing results.

In CC mode; the voltage will drop when you reach PAR, the current (amps) is held constant by the power supply. The resolution on your meters is not too good so you may have difficulty detecting PAR. Since the "720 Rule" applies to LCD as well as standard anodizing, you can use this or just anodize for 45-60 minutes.

The 720 Rule states that for an anodize thickness of 1 mil. (0,001") anodize for 720 Amps/sq.ft. x minutes, it also assumes an electrolyte temperature of 70 -72 deg. F.. In this example:

720 / 4.5A/sq.ft. = 160 minutes for a 1 mil thick layer.

In practice; for LCD a layer 1/3 to 1/2 of that will provide excellent dyeing, so you can reduce the anodizing time to 53-80 minutes or so. You can get into trouble with dissolution problems if you try for 1 mil thickness before you understand the whole process, and are getting good results consistently.