# Electro Etching PSU suggestions please!

Discussion in 'The Projects Forum' started by Mark1964, May 22, 2016.

1. ### Mark1964 Thread Starter New Member

May 22, 2016
11
0
Hi folks,

excuse me if this is a simple request.....

I need to build a power supply for electro etching, unlike electro forming or plating supplies which use 12 volts it needs to work in the 0 to 3 volt range and provide at least 6 amps

I would like the design to include the following.

· Voltage selector, adjustable in 0.5 volt steps up to 3 volt.

· Constant current control up to 6 amps.

· Short circuit protection.

· Volt meter.

· Current meter.

I could build a high current regulated supply but I am unsure about how to implement current control in an effective way. The more 'bullet proof' the design the better. I have looked at buck converters etc but prefer the DIY route.

Any pointers would be gratefully appreciated.

Regards

Mark

2. ### #12 Expert

Nov 30, 2010
18,078
9,617
This has been done several times on this website, but here's the problem: You can't do both at the same time.
The definition of a voltage supply is that the voltage stays constant as the load changes.
The definition of a current supply is that the voltage changes as the load changes.
The next problem is that a person who asks for both at the same time doesn't know it can't be done and therefore probably doesn't know what he really needs.
Trying to design for a person that doesn't know what he really needs is impossible.
Think about what you really need.

3. ### Mark1964 Thread Starter New Member

May 22, 2016
11
0
Hi,

I need to maintain a constant 1 volt across the anode and cathode plates. The 1 Volt stops off gassing and produces a very even
and clean etch.
I appreciate the impedance fluctuates depending on factors such as solution conductivity, anode
and cathode distances and size.
Thanks I'm learning fast!

4. ### Dodgydave AAC Fanatic!

Jun 22, 2012
7,527
1,242
Sounds like you need a variable voltage dc from 0.5v to 3v that can withstand 6amps or more, you can do it with a Linear psu or smpsu, a Linear psu will create more heat.

5. ### #12 Expert

Nov 30, 2010
18,078
9,617
This design really sucks in analog. Either you start with a capacitor the size of a coffee can or you waste 5 times as much power as the load requires.
Here's an idea that is very dependent on part numbers, very simple, and rather cheap. Start with a transformer, 2.5V center tapped and add 2 diodes. The result is a pulsed output at 120 pulses per second and a voltage limit about right for the 1 volt requirement at 6 amps.

Rectifier = MBRF10H150CTG

The transformer produces 1.77 volts peak and the diode eats up about 0.94 volts when it's cold and decreases to 0.65 volts when it is hot enough to boil water.
That gives you 0.82 volts peak when it's cold to 1.2 volts peak when it's hot.

Can you etch with a pulsed supply? Sure.
Can you keep the diode below the boiling point of water? Sure. Just bolt it to a heat sink.
Can you live with a one output, purpose built etcher? That's up to you.

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6. ### Mark1964 Thread Starter New Member

May 22, 2016
11
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Thanks AAC,
I like the simplicity of your suggestion and according to some info i have, pulsing may actually
be beneficial, so this circuit could be perfect.
I have been etching for some time now on the same size plates, both anode and cathode 200 x 100 x 2mm and 1 volt seems to give the best results. I'm unsure if different plate sizes will require different voltages.
I will certainly try this out...
Many Thanks

7. ### #12 Expert

Nov 30, 2010
18,078
9,617
My moniker is pronounced, "Number Twelve".

The voltage shouldn't change, the current does. This design is good up to 12.7 amps.

• ###### Transformer-rectifier-output-current-ratios.pdf
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Last edited: May 22, 2016
8. ### Mark1964 Thread Starter New Member

May 22, 2016
11
0
Thank's "Number Twelve"