Aluminium anodising power supply

[ceefna]

Hi, my first post and wish for some expert advice as my circuit knowledge is limited to say the least. I have been messing with hobby aluminium anodising for a while now and wish to progress from using a battery charger I have no control over to a power supply that I can pre set a current then I can work out how long to anodise the part for. Please have a look at the circuit I am going to use. I need an ouput of up to 15 amps so I want to know if it is possible to hook up 3 of these in parallel to get the req current, but the biggest problem is can I control all 3 with just one pot for current control and one pot for voltage control. I have already got the LM338's and LM117's so if anybody has a better circuit Idea using these regulators all info will be greatly appreciated. Just a quick note please try to be as basic as you can!!! as I said I can build from plan but thats about it. So to round up I need a 0-15A/ 0-30V DC.
Thanks for your time.

 

[shimniok]

I haven't played any with the 317 but the 78** regulators' data sheets usually offer a circuit diagram for increased current deliver involving a transistor.

 

[MikeMl]

You cannot independently set the current and voltage at the same time.

You can set the current, and the voltage across the cell will be determined by the electrochemistry going on inside the cell,
OR
you can set the voltage, and the resulting current through the cell will be determined by the electrochemistry going on inside the cell.

A standard lab supply with individually settable voltage and current limits will automatically switch modes and deliver either a constant voltage (while the current is less than the set current limit), or deliver a constant current (while the voltage is less than the set voltage limit).

Is that what you want to build?

 

[mvs sarma]

Hi, my first post and wish for some expert advice as my circuit knowledge is limited to say the least. I have been messing with hobby aluminium anodising for a while now and wish to progress from using a battery charger I have no control over to a power supply that I can pre set a current then I can work out how long to anodise the part for. Please have a look at the circuit I am going to use. I need an ouput of up to 15 amps so I want to know if it is possible to hook up 3 of these in parallel to get the req current, but the biggest problem is can I control all 3 with just one pot for current control and one pot for voltage control. I have already got the LM338's and LM117's so if anybody has a better circuit Idea using these regulators all info will be greatly appreciated. Just a quick note please try to be as basic as you can!!! as I said I can build from plan but thats about it. So to round up I need a 0-15A/ 0-30V DC.
Thanks for your time.

Perhaps Voltage is a not a criteria and a adjustable constant current source would do well. .
you may consider 24V battery chargers that output currents varying upto 30 amps.

 

[ceefna]

Hi guys, thanks for the replys. Yes i am wanting to build a supply that will deliver a constant current, voltage adjustment is not that important when anodising. I need to be able to set a low current when power first applied then adj to req ammount. Really need to build using the above ic's as i have already got these. Will the circuit I have posted work? and can you see any problems init.

 

[Mr RB]

You need constant current. As the anodised layer gets thicker the resistance rises and you need a constant current supply with lots of voltage headroom to try to keep the current up so the anodising continues. Most successful setups use a refrigerated tank, especially when doing "hard" anodising where the currents are higher and the anodised layer needs to be thicker.

I wouldn't worry about voltage regulation at all, just build a pure constant-current regulator. And the LM338's on some BIG heatsinks...

If possible could you post any pictures of your setup, pre-wash tanks, anodiser tank, dye boiler etc? Anodising is really cool.

 

[mvs sarma]

You need constant current. As the anodised layer gets thicker the resistance rises and you need a constant current supply with lots of voltage headroom to try to keep the current up so the anodising continues. Most successful setups use a refrigerated tank, especially when doing "hard" anodising where the currents are higher and the anodised layer needs to be thicker.

I wouldn't worry about voltage regulation at all, just build a pure constant-current regulator. And the LM338's on some BIG heatsinks...

If possible could you post any pictures of your setup, pre-wash tanks, anodiser tank, dye boiler etc? Anodising is really cool.

A rally nice treat . i enjoy this post Mr RB !

 

[ceefna]

Hi, you are right anodising is cool and the principles are so simple, amazing to think you can colour metal with organic dyes. Nearly any colour can be made from just mixing red,yellow and blue dyes. Have uploaded some pics of parts I did for my sons go-kart but unfortunatley cant post any pics of setup as all drained down ready for new power supply. I need to be able to get the same consistant results so you a totally right that constant current supply is the way to go. Could I use the current control circuit I have in my post? also do I need to put capacitors before and after the LM338's, last but not least is it possible to adj 3 of these circuits(connected in parallel to give me 15A) fron just one potentiometer or will each circuit need its own pot?
Regards

Ceefna

 

[Mr RB]

If you check the LM338 datasheet there should be an example of using a LM338 as a constant current source. Usually it just needs 1 resistor from the ADJ pin to the Vout pin to set the desired current.

With constant current sources you can just put 3 of them in parallel to give you more current. Then you could even use a couple of switches to switch each device in/out of circuit to give you some current control. I'm not an expert on anodising but I remember something from when I studied it before that you need to set current based on the surface area of the object being anodised.

Maybe you could use more switches to switch the values of resistor to set different currents? Or maybe someone here has a nice high-power adjustable constant current circuit.

(edit) Sorry forgot to say; nice colours! You seem to be getting good consistant colour coverage which some people have trouble with.

 

[ceefna]

Hi guys, please take a look at the circuit I have drawn. I'm going to build this if anybody can see problems with it please let me know.
Thanks again for your time

Ceefna