Constant Current Regulator Project

[Kephra]

A friend asked me to make him a constant current regulator. 
Here is how I made him one for under $10 in under an hour.

I started with a premade circuit board from Radio Shack.  ($2.49)


The board can be cut so that 4 regulators could be made from the one board.  I just snapped it apart with pliers.


I inserted the 7805 regulator chip into the board


Bending the leads holds it in place before soldering.


Here the leads are soldered and cut.


A 680 ohm resistor is inserted.  This protects the 7805 for 36 volt operation.


And a 2.2K ohm resistor to set the current.


Resistors are soldered and leads cut.


A red and green lead wire are inserted though a drug vial cap (non child proof)
Yeah, its really green, but sure looks black.


Then the lead wires are connected to the board and soldered.


The finished board is inserted into the drug vial (Cheap!)


Testing the regulator using 4 nine-volt batteries.  It is regulating at 5.66 ma with 4 batteries with the electrodes shorted.


Lets try just 3 batteries..  we get 5.84 ma with the electrodes shorted.


Lets try it out!


14 Minutes later, we have 20ppm CS!  I started with 250ml water, 3 mg salt, and 1/8th teaspoon of Benefibre (dextrin).


I was trying for about 6 ma current, and got 5.66 to 5.8.
Its not pretty, but it is quite functional

The red wire goes to the positive battery terminal, and the green goes to the anode.  The negative battery terminal goes directly to the cathode.

While brewing the test batch, the voltage across the electrodes was about 11 volts, so it would have easily worked as well with 3 batteries instead of 4.

When using a constant current regulator, the way to tell that it is actually regulating is to check the voltage across the electrodes.  With a 7805 type regulator, the electrode voltage should be less than the battery voltage minus 8 volts.  If its higher than that, the regulator is not regulating because the conductivity of the water is too low.

[Liam]

Just got mine finished.  I was able to do it just using your pictures.  I tried it out with a batch using corn syrup and salt, and it was the easiest silver I have ever made. 

Thanx

[Dutch_Jon]

Hi

This looks easy as pie and pretty understandable for me, I'd like a stab at it.
 
I have a couple questions so I'm risking of sounding noobie and I'm am not fluent
in electronics quite yet, so  please correct me where I'm wrong.

So isn't the 7805 a 5 volt  regulator? so how are you guys getting 11 volts
across the electrodes. is it there some sort of voltage loss in the circuitry

And can't you use just two batterys?  I have no problem using 3 or 4
I'm just curious how all this works   

[Kephra]

Yes, the 7805 is a voltage regulator chip.  However, wired as shown, it is a current regulator.

Normally, the 7805 would have the common terminal wired to ground, but in this case, the common terminal is being used as the output.

The chip will maintain a constant 5 volts across the sense resistor  (out to common terminal).  It does this by varying its internal resistance between the in and out pins.

[Dutch_Jon]

OK thanks Kephra

I'm understanding what you are saying pretty
much I think I'm seeing how your running
the green (lead?) off the center ground...hmm

you must excuse my ignorance, so since this is
a current regulator, is that the same as they call
a current limiter?   

also if the input voltage is lower say 12v dc 300mA
via wall transformer do you know how that might
effect the voltage etc. for our purposes? 

[Kephra]

OK thanks Kephra

I'm understanding what you are saying pretty
much I think I'm seeing how your running
the green (lead?) off the center ground...hmm

Yes, the 7805 acts like a smart resistor, and I am taking the output from the common.  The sense resistor is connected between the output pin and the common, and the current flows through the sense resistor.  Internally, the circuitry keeps the voltage across the sense resistor at exactly 5 volts by changing the resistance between the input and the output pins.  Since the voltage across the sense resistor is 5 volts, that sets the current through the sense resistor by ohm's law.

you must excuse my ignorance, so since this is
a current regulator, is that the same as they call
a current limiter?   

A current limiter and current regulator are not the same.  A limiter allows the current to fluctuate up to a certain level, and then stops it from going any higher.  A regulator keeps the current constant without fluctuations.

also if the input voltage is lower say 12v dc 300mA
via wall transformer do you know how that might
effect the voltage etc. for our purposes?

The 7805 regulator needs higher voltage than that.  To make colloidal silver, you should have at least 8 volts across the electrodes, so the output of the regulator has to be capable of 8 volts, and higher is better.  Since the regulator itself loses 8 volts, the minimum input should be 16 volts.  It would be better to use two or three 9 volt batteries to power it.

[Dutch_Jon]

Thank very much Kephra, I'll build it.