tank size vs acid concentration

[whistule]

If you weaken the concentration of the electrolyte does that have a similar effect to making the tank bigger to increase the cathode > aluminium part distance. Could this be an easier way to solve the problem of over heating during the process?

Any help much apprec.

[Fibergeek]

Weakening the electrolyte will reduce it's conductivity, thus it adds another small resistance to the total anodizing circuit. This is a very poor way to get the required current limiting.

In the "stone age" of anodizing, when the power sources really were "rectifiers", the only method available to limit the current in large setups was reducing the cathode area. DeForest's vacuum tube triode wasn't invented until about 30 years later, so electronics didn't yet exist. Rheostats did exist but they would need to be enormous and hugely expensive if used for this, so they were not. When the cathode area is smaller than the anode (the work) area, the area mismatch will provide current limiting. This is very difficult to correctly do in practice, and there is no longer any excuse to use this, even for amateurs. Increasing the cathode distance will reduce the current slightly, but not nearly enough for current limiting.

Overheating is caused entirely by too much power dissipation in the electrolyte. The best solution is to not dissipate excessive power in the first place. This is one of the greatest drawbacks of voltage mode anodizing; if you aren't adjusting the voltage constantly, you will wind up with too much voltage, which means too much current also, and the excess power is dissipated as heat. Current mode anodizing does not have this problem. This is better known in Physics as Newton's Law of Conservation of Energy. You may have never heard of it, but it's just as real and absolute as the Law of Gravity.

[whistule]

Ah ha. So ideally you would want to limit the current idependantly from the voltage by adjusting at the power supply but home anodisers will probably find it easier to adjust the voltage with the effect of changing the current - which should happen proportionaly but for the heating of the electrolyte which also increases current. I can now see why everyone is trying to keep the temperature of their home anodising down.

Thanks.

[Fibergeek]

You almost have it.

If you were using a lab power supply, and you put it in constant current mode (current source) the necessary voltage adjustment is done by the power supply automatically. You don't have to do anything.

If you don't have a lab power supply, you can mimic one well enough for anodizing by using a variable voltage source. You do this by constantly watching the current, and you adjust the voltage so that the current stays the same. The variable voltage source can be as simple as an ordinary lamp dimmer with a battery charger plugged into it. You start with the voltage source set to the lowest voltage you can set. As the anodization increases, you will be adjusting the voltage upwards.

Download and read the new LCD directions, all of this is explained there, lamp dimmer and all.

[NeoMoses]

Where are the new LCD instructions? I looked around on the main site, but didn't find them. Could someone point me to them, please?

***Edit, I found them. They're in the Technical Support Section. ***
[feels dumb now...]

[whistule]

Hey Fiberbod. Its all light from your direction. Ta.

[Fibergeek]

Whistule,
Judging by your moniker and your diction, I'd guess you are in the UK, am I correct? Unlike Mike I don't speak the Queen's English, so it follows I have problems understanding the "Queen's Slang". Your response means that you're starting to get the idea, right?

My moniker is Fibergeek, one day I will explain it's meaning, I don't understand "Fiberbod".

[whistule]

Sorry Fibregeek. Yes I am in the UK - using such diction is considered endearing in Scotland - but it's only now you mention it that I realise how twisted it is. I was basically using loads of words where one would have done - thanks.

I'm wiring a lamp dimmer so I'll give it a try and see how I get on.

[Fibergeek]

Whistule,
Don't take it the wrong way, I've nothing against slang, it's considered endearing here too. But our slang is quite different than yours, understanding it is sometimes a problem. We colonials are always ignorantly assuming ours is the only. I for one, will accept "anodise" and "Fibregeek" as entirely correct spelling as well.

Back to anodising:

When putting your dimmer assembly together, keep in mind that the only thermal path for heat sinking a dimmer is through it's front panel. Use a metal cover plate on the electrical box you mount it and the receptacle in. not a plastic plate. Also for electrical safety, ground the metal cover to the green (ground wire) in the power cord. I believe you use a different color for the earth connection, but I don't know what it is.

[whistule]

No probs. Thanks for that cooling info. Earth wires are green with abit of yellow over this way. I've got the dimmer wired in and it seams fine but I have anodised for 90 mins at 4.5A/sqft and the colour is taking well but is not deep enough even after being in the colour bath for 45 mins.

My previous experiences make me think that this is a result of the anoditic layer being too thin - anodising at higher current densities gave much deeper colours so my natural reaction would be to increase the current density but this would seam to contradict your advice as it would create smaller pores. What would you recommend?

The only other thing I can think is I am using the same concentration of acid as for the previous anodising system and maybe its be erroding the layer - The acid currently has an S.G. of 1.100 (I know you don't really think S.G. is important but I have changed the acid concentration so many times fine tuning it for the previous system that it is the only rough measurement I have of the acid concentration).

Other parameters are: acid temp 57deg. F. Voltage 8.6v