Why are is my voltage screwy?

[jbrink]

I am using Caswell's recommended 1:3 ratio 3 gallons battery acid to 9 gallons of water. I am using a 2/10/50 manual battery charger connected via the dimmer method.

I have a digital multimeter attached to the aluminium wire going to the part (anode) and also attached to my cathode. I am anodizing a part exactly 1 sq ft, so I am feeding it 4.5A, well actually just under 4.5.

The voltage starts off at around 12.5V, but seems to go down over time instead of up like everyone elses seems to. Is there a reason for this?

Thanks.

[jbrink]

Here's an example.

Process started at 12:58pm

12:58 - 12.53v
1:18 - 12.22v
1:30 - 11.85v
1:49 - 11.84v
2:01 - 11.93v
2:09 - 12.10v
2:22 - 12.05v

Process ended at 2:22

Did not take color well at all.

Any clue to my problem would be much appreciated. Thanks.

[Fibergeek]

It sounds like you haven't grown a reasonable anodize layer at all.

When you start; dimmer set to its lowest setting, and power applied, there should be a few volts at most across the work. It will then rise over a period of several minutes to 9V or more, as you adjust the voltage to keep the current constant. I hope you aren't using the ammeter on the charger to measure current, they are very inaccurate (like 50% off) in most cases.

1 sq.ft. work size is very large for a charger as you describe. I measured the voltage and current from a new Sears 12V 10A manual charger some time ago. With a 3 Ohm power resistor across it, it put out 11 Volts at 3.66 Amps, when loaded with 2 Ohms it's output was 10.7 Volts at 5.35 Amps. All battery chargers are rated for driving a partially discharged battery, not a grounded load like a power resistor or an anodizing setup. This is why you won't get 12V at 10A out of it when anodizing. On your charger; the 2A setting is for a slow trickle charge, the 10A setting is for normal charging. The 50A setting will put out "50A" only for a few seconds, purportedly to assist starting a motor that has a weak battery.

You will see better results if you improve your electrical connections, if you started at 12+ V they are very bad. Also reduce the size of the work to 1/4 - 1/2 sq.ft. if you are going to use that charger.

[jbrink]

I was using this charger in a 1:1 ratio bath before I switched over to 1:3. It was working fine then, of course I was using the shunned let it rip method. Deep colors, tough anodize layer, scratch resistant wise.

I decided to switch over to LCD since everyone seems to be praising it, and caswell supports it. Unfortunatly I'm having problems now. Red and Yellow dyes were what was giving me bad colors and not absorbing. I just bleached out the red and dropped the part in blue.

It seems to be holding the blue just fine, we will see how it looks after sealing. If the blue holds, but my reds and yellows don't I am going to assume it may be a PH problem. I have heard the red is very sensitive to PH, more so than the other colors. I'm not too sure about yellow.

Anyway, thanks for the reply Fibergeek, you are very helpful. This forum would be lost without you and Neomoses.