Im not surprised that you are experiencing problems. Almost everything that you are doing is wrong. To divide up the work; I'll take the electrical issues, there are other members here who can address the prep issues, anodization details, dyeing & sealing. That way no one gets stuck with all of the typing. Don't worry, we'll get you on track, we've done it for newbies many times.
First off; you should reconsider doing the 3 or 4 pieces (which is it?) together; it will be a lot cheaper and easier, I'll show you why.
Using 4.56 sq.ft. as the example, we can calculate the required power supply current (Amps) and the power supply peak voltage required. I am also assuming the LCD anodizing process, which is ideal for learning anodizing, not to mention the the lowest cost and safest process.
LCD operates over a current density range of 3ASF (Amps per Square Foot) to 6ASF, with 4.5ASF as the median value.
The numbers are in this order, ASF, anodization time, power supply current(A), peak power supply voltage(V), and peak power dissipation in the tank in Watts(W).
For a surface area of 4.56 sq.ft.:
3ASF, 120 minutes, 13.7A, 8.8V, 121W
4.5ASF, 90 minutes, 20.8A, 11.4V, 269W
6ASF, 60 minutes, 27.4A, 13.2V, 362W
We can draw some observations from these numbers, and apply them to your example.
1st. you can forget your "20A" battery charger. If you actually measure what the charger is putting out (using the multimeter in your tool box) you will find out that it isn't 12V at 20A, its more like 10.7V at 10A. All battery chargers are rated for driving a partially discharged battery, which is about 6V. An anodizing or plating circuit is a grounded load. Notice that I said circuit, is is a circuit, and all of the electrical math and physics applies exactly.
2nd. Look at the power dissipation; these values in Watts show how much heat will be dumped in the tank, like there was an electric heater of that Wattage in it. You'll have some nasty problems with dissolution if you allow the electrolyte temperature to get warmer than 75 deg. F.. You will need some kind of cooling system.
If I assume that your 3 or 4 pieces are all the same size, you can reduce the required current and the power dissipation by 3 or 4 if you anodize them individually. If they aren't the same size, the reduction for each piece will be proportional to its surface are. This may allow your battery charger. However, you must have a way to measure the current and control it by varying the voltage. The lamp dimmer controlling the battery charger will work, but its a PITA.
If you don't control the current, it will be way too high when you start anodizing, this usually immediately damages the connections and you fail.
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