Science Buddies: "Ask an Expert"

I'm helping my nephew make a colloidal silver generator; but, the only wall-wart I had to give him that was close to the right voltage (30VDC) has too high an amperage - 400mA, when 1mA is optimal. I don't have a clue what to tell him about bringing down the amperage. The project is to demonstrate the resulting colloidal silver killing mold in a dish of jello; so, I want him to have the best "product" possible. We've both been doing a lot of reading on-line (I've found it REALLY interesting; and, plan on trying to make some myself, when I can find the time.) Everything seems to indicate that very low amps result in very small ions (which are supposed to be the best) being produced; but, I don't know much about electronics. What size of what will he need? Am I correct in assuming that he can just hook it in line with alligator clips?

Kathy74868 - I don't know anything about colloidal silver generators, but what I've briefly looked at suggests that for optimal operation you need a DC current of between 0.5 and 1.0 milliamperes. Further, the ionic properties of your solution changes dramatically. The 20-30 VDC is needed at the beginning of the generation process, but as the solution becomes more ionized, current flow increases dramatically. What is required is a constant current power source that limits your current to a fixed level, no matter what the ionized levels of your solution are (changes in load). There are two inexpensive ways to do that. There are commercially available current limiting diodes (CLD's) that can be purchased in the range of 1.0 mA. This will be dependent on your proximity to good local electronic component distributors. Mail order from places like DigiKey may not fit your schedule. The second solution is pretty simple, just make your own current limiting circuit using a junction field effect transistor (JFET). The device (probably less than a dollar) and a variable resistor can be assembled to do the job using your 30 volt wall unit. Basically, the gate of the JFET is tied to the source terminal. Adding a resistance between the source and gate allows you to vary the current specification. Use an inexpensive multimeter to test the setup. Attached is a link to an application note from Vishay describing the circuit. Good luck.

Rick Marz

Thank you for steering me to Digikey. They were extremely helpful. I ordered a 10W, 30K ohm resistor for him. If we start tinkering with colloidal silver on a long term basis, we can get more elaborate; but, for his project, this seemed like a quick, simple, and inexpensive solution.

After looking around, I've also suggested to him that he add a milk (lifespan) demonstration, with the jello mold kill-off being a demonstration of the reason for the improved lifespan of the milk. He's going to check with his biology teacher today, to see if it would be okay to change it.

For anyone wanting to use this project idea, the best person I found to order the .9999 silver wires from was the fellow who runs http://www.colloidalsilverguy.com He was very helpful; and, the least expensive. He even sent a copy of the assay report with the wire. He's out on the west coast; but, he shipped really fast.

I'm confused by your 10W 30Kohm resister purchase if it is a fixed resistor. If you put a 30 Kohm resistor directly across the 30VDC power source, Ohm's Law tells me that 1mA of current will flow (30v / 30Kohm = 1mA) and that 30mW of power will be turned into heat in this resistor (1mA * 30v = 30mW). The 10W rating is considerable overkill.

If it is actually a variable resistor, then it makes perfect sense as the resistor won't burn up as long as you don't go below 300 ohms. If you put a mA DC current meter in the loop, you can adjust the resistor to keep the current in the 0.5 to 1.0 mA range as the ionization of the solution increases and reduces the solution's resistance.

Thank you for the head's up Craig. That was just what the tech I talked to at Digi-key said would work. As I mentioned in my original post, I know NOTHING about electronics. I can set up my own (110/220v) breaker box; but, get me into anything below basic 12v stuff; and, I'm lost. I just have a tendency to tackle stuff and try to learn as I go. (LOL, My head's still spinning from my recently concluded, self-inflicted, self-taught, 3-month "crash course" in wireless networking. To describe that as "getting dumped into the deep end of the pool without water wings" would be a bit of an understatement... ) On that fiasco, I was able to find enough on the net; and, pick the brains of the folks at netgear, to eventually get a 600' range wireless network set up out here on my 7 acres; but, when trying to find out electronics info. of any sort, I've always run into problems. Part of me was a bit dubious about getting involved in this project, beyond tossing him an old ac to dc adaptor I had laying around collecting dust; and, ordering his wire for him with my card. As I've looked into all this colloidal silver stuff with him, I've gotten really interested in seeing how things turn out. (That's, obviously, on top of wanting to see him get a good grade...)

bleep I thought of today, that MIGHT work: What do you think about putting a plain old dimmer switch (or a volume switch from an old radio) between the adapter and the alligator clip? I have several of them laying around in my shop trailer. Am I correct in assuming that this (or, anything else, for that matter) would go on the + side? I'm still trying to find the replacement leads for my meter. There were some in a box that I got at an auction several months back; but, they never made it into the bag with my meter. The old leads got puppy-chewed on the end that plugs into the meter, a couple of years ago.

BtW, His teacher gave the okay on him including the milk curdling test. LOL, I think he's starting to get her curious about this colloidal silver stuff, too. If even half of what I'm reading is true, it's not surprising that the pharmacutical companies do everything they can to try to discredit this stuff! Even if just the part about it keeping milk from going bad is true, I'll be making one myself. He's trying a preliminary test with some "CS" that he made by just hooking the clips directly to the wires; and, when I talked to him tonight, he saif that the glass of milk without the silver is already starting to smell kind of bad; but, the one with the silver still doesn't have any smell. He said that batch of "CS" had turned out sort of amber colored; and, that it was supposed to be clear. When he comes out this weekend, he's going to bring me a jar of it to use as a sinus wash, to see if it helps my chronic post-nasal drip problems. If it does, I'll "be sold on it;" since, I've had that problem since I was 5 and got my 1st dog. Nothing the doctors have given me have ever really worked; and, not being around dogs isn't an option which I'm willing to follow... I'll report back how the preliminary experiments turn out; since, he doesn't have internet access over at my sister's place. (She wasn't very well prepared to take on a 16 year old boy when her daughter lost custody of him in late Feb. Fortunately, he's a smart kid; and, surprisingly together for the environment he came out of. In addition to my own interest in this stuff, that's another reason why I'm going a little further than what might normally be appropriate to help with a project that he's going to get a grade on. Besides, it's a biology class; not an electronics related class. Maybe I'm just feeling a little defensive tonight. I was talking to a friend of mine today; and, she implied to me that my helping him research how to build and optimize the generator might be considered "cheating." If any of us could afford to buy him a commercially sold generator, it would've been acceptable; and, I doubt that building his own will really get him any extra points; so, I really don't see how my helping is cheating... If there are any teachers reading this who could clarify that point for me, I'd appreciate it. All of my "kids" have 4-legs and tails; and, I graduated HS in 1972. We didn't even have self-designed experiments as a part of our grade back then.)