CC/CV Power Supply

[royce]

Hi, all!
New to the firum and happy to have found it!

I am a hobby machinist and I am starting to add ALuminum Annodizing to my home hobby shop. The method I will be using requires a controlled current power supply for best results, but they are fairly expensive. ($3-400)
My requirements (ideally) are a 0-15V, 0-3A CC unit. Most units like this also seem to have Variable/controlled Voltage, but that is not a necesity for this dedicated power supply. I need to maintain a controled current density and let the power supply vary the voltage as the annodic material varies its resistance [as coating is deposited].
Whe the resitance peaks and the voltage starts downward....voila! She is done! For this part, a meter would be nice. I guess an built-in curent meter would be nice, too. ALthough both could be digital to keep costs down.

I can construct almost anything so if anyone has a schematic for such a power supply I woud greatly appreciate a look at it.

 

[Johnson777717]

hmm...controlled current. Well, here is a link to a site with a bunch of power supply circuits. I'm not sure if any are what you need, but the circuits may come in handy. Good luck!
https://www.commlinx.com.au/schematics.htm

 

[k7elp60]

Constant current power supply

I suggest using an LM338, as it is a 5 amp regulator. It can be configured as a constant current source that is adjustable in current. I don't think it
will go down to 0 current however. If you can give me a figure for minimum current I see I can provide you a schematic with parts list. I suggest that you consider a fixed supply about 20 volts and let the current regulator provide the adjustable current, thus the load voltage will be the 20 volts minus what is dropped across the regulator.

 

[Optikon]

Hi, all!
New to the firum and happy to have found it!

I am a hobby machinist and I am starting to add ALuminum Annodizing to my home hobby shop. The method I will be using requires a controlled current power supply for best results, but they are fairly expensive. ($3-400)
My requirements (ideally) are a 0-15V, 0-3A CC unit. Most units like this also seem to have Variable/controlled Voltage, but that is not a necesity for this dedicated power supply. I need to maintain a controled current density and let the power supply vary the voltage as the annodic material varies its resistance [as coating is deposited].
Whe the resitance peaks and the voltage starts downward....voila! She is done! For this part, a meter would be nice. I guess an built-in curent meter would be nice, too. ALthough both could be digital to keep costs down.

I can construct almost anything so if anyone has a schematic for such a power supply I woud greatly appreciate a look at it.

This design is possible for under $100 dollars I believe. Please dont assume making digital keeps costs low. In fact, you will have simpler circuits without digital capability (cheaper)

Try some searches for constant current source and add a voltage comparator with adjustable setpoint and you will have it. We can help you with the details but first try and find a reference design for the current source or use the others suggestions.

 

[royce]

Thanks for the lead. Johnson77777... Some great stuff there and I'm still looking at them.
K7, the reason for the [adjustable] constant current is due to the nature of the process of annodizing. Low, cntrolled current is safer and more predictable than uncontrolled current, as there is electrolyte involved which creates a mist. Also, the voltage will self-adjust upwards to maintain that constant current as the resistance by the work-piece raises due to the barrier layer being deposited. When it reaches its peak, the process will start to reverse itself & the voltage will start dropping. THis signals the end of the process and the operation is halted.

The minimum current I could operate with is probably about .25 amp.
So, an adjustable current of 1/4 amp to 5 amps would be perfect.
The voltage required would be between 1V & 15V. I believe these parameters would cover any home-level projects that I could handle in the tank I am setting up.
If more voltage were needed than the max of the supply at a given current, all that would happen is more time in the tank would be required to reach the peak.
These paramers have been estabished to get a good balance between Hardness, Time, and Porosity of the deposited annodic layer.
Typical time is somewhere between 20 minutes & 1.5 hours depending on the grade of Aluminum being annodized.

 

[Nigel Goodwin]

The minimum current I could operate with is probably about .25 amp.
So, an adjustable current of 1/4 amp to 5 amps would be perfect.
The voltage required would be between 1V & 15V.

You only need an adjustable constant current for this, ohms law applies to your anodising just as it does to a resistor. So by setting a constant current, the voltage across the tank will vary as the resistance of the tank varies.

The only thing you need to know, is what is the highest voltage you will ever need - plus a little extra in reserve. You don't want to have masses too much voltage, it will just get your regulator hotter - but you must have enough for it to be able to supply enough voltage in order to reach the current it's set to.

 

[royce]

You only need an adjustable constant current for this, ohms law applies to your anodising just as it does to a resistor. So by setting a constant current, the voltage across the tank will vary as the resistance of the tank varies.

That is exactly right and to the point.
As per those who have come before me at this annodizing hobby, the most voltage I will need is 15V, so we can say 18V is safe (a 3V reserve).

As for digital vs. analog, I can go either way. The tolerances are pretty wide with annodizing, and the constant-current method eliminates the concern over critical time, temperature and voltage.

 

[crust]

The national semiconductor data sheet for the LM317 has a circuit for a 5A CC/CV power supply. It needs only the LM317T, opamp and a handful of discrete components.

As an aside, I am currently designing a lab quality (but not lab price) CC/CV power supply for hobbyist use.

 

[k7elp60]

CC regulator

The attached circuit is for an adjustable constant current source. The drop across the regulator can be about 3 volts and the voltage drop across the adjustable resistor will be 1.25 volts thus the 20 volt input.
The size of the reostat may seem large 25W, but that is the dissipation for the whole reostat. When it is near 0 ohms it will still be dissipating some
heat. A good sized heat sink is necessary for the LM338 as it has internal current and power dissipation shut down if the current and power are exceeded. Hope this helps.

 

[royce]

Wow, that's pretty straight forward! Thanks!

So, just to make sure I understand this all correctly:
The above circuit, when supplied with a 20VDC input, will provide me with an adjustable (via R3) constant current that will automatically adjust the voltage up & down as the resistance at the output changes.
Correct?

What do you recommend I feed this with at the input to get what I need? Regulated 20VDC? At 5 Amps?

 

[k7elp60]

CC reegulator

Yes you are correct. You can put an ammeter in series with the output to monitor the current. There are a number of digital multimeters that are in the $20.00 range that measure up to 20 amps. The input does not need to be regulated, but if it is it will probably work better.
Good luck

 

[royce]

Excellent, and thank you again!

I will go with a regulated 20VDC power supply just to keep things under better control. Is a 5 Amp transforer enough or should I go higher than the 338 is designed to handle, say 7 or 8 AC 5 Amp rating
Full wave Bridge Rectifier
I'll need a votage regulator to produce 20 VDC
I shouldn't need current limiting as the Constant Current control will govern the current draw...Correct?

 

[k7elp60]

CV/CC power supply

Royce,
I didn't address the 20 volt power supply, as there are a lot of variables that I do not know. One is the duty cycle. In other words if for example you are supplying lets say 3 amps to the tank, how long will the 3 amps
need to be supplied, and what percentage of ripple will the tank stand?
For linear power supplies like you described, a transformer, a bridge rectifier, a filter and a regulator you may want to read a previous post that I made on 12/28/03 in the general electronics chat. Here is the url"
https://www.electro-tech-online.com/threads/how-do-i-connect-this-uln2308.5476/#post-25903.
It would be possible to use a LM338 as a voltage regulator also.
Course what you read on that post is my opinion and the results of a some
tests I did. I will be glad to help you in any way I can.

 

[royce]

Duty Cycle: @3Amps, which will probably be the highest current that will be used in this set-up (current is calculated by the surface area of the work piece) the system might run for as long as 90 minutes.

As for PSU specs...let's just say that I would like it as good as is practical for a beginner like me to build (with high hopes & ambitions!). I don't have the knowledge to discuss ripple & long term stability. I do know that I have seen specs based on a 15V 0-1 Amp system from others doing this setup and they mentioned things like:
Current Regulation: +/- .01% from 0-1 Amp
Absolute Accuracy: +/- .5%from 0-1 Amp
Long Term Stability: Better than .1% over a 3 hr. period
This current control system was powered by an HP Printer 15V/800mA power cube. Only small test pieces were done with this system.

I hop this helps.

 

[royce]

I just read through the post you sent me to...very interesting. Funny how the values seem to closely match those of my experiment.

From what I gathered, I would want to use larger caps to have a lower ripple, or possibly more than one cap. Again, I suppose since I am building it, I might as well build the best that I can [within reason of cost & design].