Hmmm.. Ok, so I re-created the circuit the same way with the ST limiter, R1=47 Ohms, and R2 a 1668 max Ohm pot (again in series, simulating load).
If you have 17V usable with those CCOV3 regulators that means that there's 20-17-1.25V (1.75V across the regulator, right?
Raised R2 from low until the very first signs of IOut beginning to drop (less than 0.1mA drop). Measured VR2... 16.75V. Honestly not sure where to get a proper reading across the regulator. Measured voltage across VOut and Adjust... 1.21V (I know this is the one supposed to be 1.25v right). Measured voltage across VIn and Vout... 1.65V. Measured voltage across VIn and Adjust... 2.88V but a bit unsteady (was this config interfering with the limiter's logic?)
Anyway it would've been my guess that the proper way to read voltage across the regulator would be from VIn to VOut, right? With a 16.75 VR2 figure, I was expecting a 2V regulator figure... I guess 1.65V is close? 0.35V missing somewhere? I measured voltage across the milliammeter (I am using my earlier, part-busted multimeter to measure voltage/resistances now, while leaving the ammeter in series)... 0.04V.
Well anyway we're mostly on target here.
1.75V * 0.0155 = 27.125mw heat dissipation in the regulator (thats 0.027125 watts). It shouldn't even get warm.
Something is obviously wrong with those CCOV3 regulators. What you got with the other one makes perfect sense.
Remember I said in electronics "exact" is a word we never use. You're in the right range though with those true ST regulators.
Perhaps you're right and the others are some cheap chicom knock-off that have serious limitations or perhaps even 2nds someone got their hands on from a third party manufacturer for next to nothing and branded them to look like an ST. Fraud IS a big issue in the semi industry and much less so with the big, complex parts like processors and more so with the "jelly bean" parts. Thats why, as a company making electronics devices, you always buy from reputable distributors where there's traceability directly to the manufacturer who made the part. Costs a little more but in the long run saves you money for fewer returns, dealing with issues that might even have you recalling something, ...
mm, makes sense. Well, I know how to identify the ST models now and what store I got them from. Will no longer use the others.
Try to lower the current at the top end (voltage across load at 17V) and see how low you can go before things start getting squirrely. I bet you'd hit 5ma.
Ok, if I'm understanding this correctly, you're saying increase R2 until VR2 = 17V (or whatever causes IOut to begin dropping), then incrementally increase R1 in order to decrease stable IOut, each time re-increasing R2 in order to reattain VR2 = 17V at that IOut level, then watch IOut for a minute each time, looking for a point where the regulator is no longer maintaining a stable IOut reading.
Alright, following this procedure, I got IOut (stable) down to 2.51mA, which took 7110 Ohms of R2 to start making IOut and VR2 start jumping around. I then pulled R2 back to 7030 Ohms, which brought IOut back to a stable 2.51mA, and VR2 to 17.15V (I noticed that as I kept installing more resistors and pots to achieve higher R2's at lower IOut's, the VR2 that would cause IOut to destabilize kept creeping up by small amounts). At this point I have installed just about every pot and resistor I have to achieve these levels and cannot test any further down (need to pick up some 5k resistors) - but indications are that (if I am doing this right) it could keep performing lower.
Attaching a shot of my setup for this test for posterity.
I really am getting a stable 2.5mA IOut when R2 (load-simulator) is anywhere between 1k-7k Ohms. If I am testing this correctly, this is the test to determine what minimum levels my LM317T can regulate current down to in this current-limiting config, right? Is 2.5mA stable an unreasonable level to believe this LM317T is performing at? Maybe this particular ST component is exceeding its minimum expected performance by quite a bit? What
would be an unreasonable level to expect an LM317T to possibly perform to?
Regardless of all of this, if I understand Kephra's directions correctly, I'm basically never going to want to run at 2.5mA anyway. Just trying to understand this circuit at this point. Now that I have this knowledge I may like to build more of them possibly at various specifications in the future.
Well, if you want 25ma max, that'd be R=1.25/0.025 = 50 Ohms assuming your pot can achieve 0 Ohms. If not, figure out what it can do at best and then subtract that from 50Ohms and go with that. On the low current end, 5ma would be a total resistance of 1.25/0.005 = 250Ohms but if you can go lower in current, take that current and divide it into 1.25 and go with a pot around that. I realize the general availability is 250, 500, 1000,... At 500Ohms you'd be able to hit 1.25/(500+50) or 2.27ma (probably won't get there with that regulator but who knows?). At 250, 1.25/(250+50) so 4.167ma. The math is simple.
Remember, the regulator maintains 1.25V across the resistor+pot so the equation is simply
R = 1.25/<current in amps>
<current(amps)> = 1.25/R
Right. Duh. I've been so deep in the weeds just trying to get this circuit to work the last couple weeks that I guess I forgot that I don't really have to take my load resistance into account when designing this circuit... because that's already been calculated with Kephra's formula (a solution of 99.9% distilled water and 0.1% of 1 Molar Sodium Carbonate solution) ... right? I guess that produces an always-the-same Load resistance at the start of a run, that will only go down by a (small-ish?) amount by the end of the run with the solution now containing some silver nanoparticles.
Anyway, so OK, all I really need to keep in mind is the measurements across VOut-Adj. The voltage between the 2 always being 1.25, the resistance between the 2 always being the adjustment pot + safety resistor, and the current between the 2 being the resulting desired IOut into the cell.
Don't really have to do the calculations for the whole circuit, other than making sure I have plenty of voltage across the cell (sounds like with 15V you're in pretty good shape with a sodium carbonate electrolyte). Doesn't stop me from being curious what the typical resistance in this cell is. I did try setting up the cell and measuring it - got an extremely unstable reading somewhere in the hundreds of thousands of Ohms. That can't be right, I must not be measuring that correctly.
Got it. Just have to decide what parameters I will choose. I have considered I may hammer out my bullion bar into a higher-surface-area anode, with which apparently I can use up to 40mA or so - I may try building a circuit that can handle that.
I managed to find a couple of the tiny 10 turn blue square trimmer pots that you have mentioned. They're 500 Ohms. I like them, I'm intending on using one of them. I'm reading 2 Ohms at their minimum before the reading gets
squirrely. So if I go for the 40mA max, I suppose I will try to make the safety resistor about 23 Ohms.
Do you have an understanding on what happens inside these 10 turn trimmer pots when you turn them all the way to one end of their range, but keep turning? Normal 1 turn pots have a maximum turn range and then just won't turn farther. I want to make sure once I solder this circuit together, that I don't do permanent damage to the pot each time I try and max out the amperage.
17V with 20V input I'd consider rather good. That means the real headroom of the regulator in this particular topology is only 1.75V which seems really good. For sure as the current increases the regulator is going to require more headroom but at these lower currents perhaps not. All good.
Nice. I'm feeling good about it.
To be fair, I only measured one of my 3 ST-built LM317's for what maximum voltage it could push across the simulated cell with my 20V input. Perhaps testing this on my other 2 tomorrow will be my final test before going forward.
Thanks for all your assistance here, Gene. It has been both a good exercise for the old noggin, as well as a great crash course on electricity and electronics that's gotten me a working product.
The main item for tomorrow I think will be to set everything up to make my first batch of basic colloidal silver - straight through the breadboard. Had all the reagents and sundries for a 20ppm uncapped for a little while now.
If all goes well, (color looks good and all), I will look to figure out adding a couple capacitors to the circuit (still want to figure that out) and solder it together.
Also looking at making the double transistor circuit for extra credit since I mostly get everything now and have pretty much everything I need I think. Have a few 2N3904 TO-92's that the clerk assured me would work the same as 2N2222's. idk if that's true or not.
Finally if successful it is my intention to make a step by step thread named "The Absolute-Complete-Idiot's guide to building your own current limiter". Maybe we can help more people learn to make true colloidal silver for the cheap cost it aught to be - I get the impression most people here are shelling out for the lab bench power supplies.