Current Limiting Diodes - Page 1
Forum section: electronics / projects

author: Trailboss
author_rank: Contributor
timestamp: February 20, 2017, 02:24:13 am
content: I am helping my niece working on an electrolysis project to produce silver nano particles (colloidal silver).A simple process applying a potential to the anode and cathode in a electrolyte solution.The electrodes are pure silver rods (anode and cathode are silver), the solution is dilute sodium carbonate in distilled water.The applied voltage should be 24 volts DCCurrent should be limited to around 1 to less than 5 ma.I was going to lend her my current regulated power supply, when I thought a simpler solution might be to just use a low power 24 volt DC walwart and put a 1 or 2ma current limiting diode in series with the electrodes.RL would vary over time as the electrolyte becomes more conductive due to the silver ions being produced, but looking at the data sheets I think this simple solution would be viable?any thoughts appreciated

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 20, 2017, 04:17:14 am
content: If you need current limiting, you won't have 24V.Reduce the sodium carbonate concentration instead: this reduces conductivity of the solution. Merely monitor current flow using a multimeter.Tim

author: ScottK
author_rank: Contributor
timestamp: February 20, 2017, 04:33:32 am
content: Here's a simple constant current sink. At 1-5mA, you can use almost any little NPN transistor.Regulation won't be as good as the three terminal regulator method mentioned by another poster, but it'll do for your niece's needs. You do need more than 24V to accommodate the headroom for the regulator, but that's true of any method you'd use to achieve constant current. If you don't have a pot, replace the combination of R3 and R4 with a single resistor that gives your desired current with 5.1V across it.You can probably use three 9V alkaline batteries to power the experiment. Current will fall with battery voltage, but that may not be an issue over the duration of the experiment.ETA: How do I get the attached image to show full size in the post? I'm new here!ETA2: Thanks for the tip, Brumby.

author: mtdoc
author_rank: Super Contributor
timestamp: February 20, 2017, 06:35:22 am
content: Quote from: Trailboss on February 20, 2017, 02:24:13 amPlease tell me no one is planning to ingest this colloidal silver.

author: george.b
author_rank: Frequent Contributor
timestamp: February 20, 2017, 06:38:27 am
content: Quote from: mtdoc on February 20, 2017, 06:35:22 amI was about to ask what his niece wants the colloidal silver for. I, too, hope nobody's planning to ingest it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 20, 2017, 07:00:16 am
content: Meh, it's not really toxic or anything. Not that it's particularly useful, either.Doing it regularly, not a good idea for other reasons:https://en.wikipedia.org/wiki/ArgyriaTim

author: george.b
author_rank: Frequent Contributor
timestamp: February 20, 2017, 07:38:51 am
content: Well, precisely. Who wants to end up looking like a smurf?

author: JoeN
author_rank: Frequent Contributor
timestamp: February 20, 2017, 08:19:05 am
content: Quote from: george.b on February 20, 2017, 07:38:51 amCould be useful if you are into cosplaying, Smurfs™... Just sayin'...

author: Trailboss
author_rank: Contributor
timestamp: February 20, 2017, 02:44:50 pm
content: Quote from: evb149 on February 20, 2017, 03:24:25 am

author: Brumby
author_rank: Unknown
timestamp: February 20, 2017, 02:55:05 pm
content: Quote from: ScottK on February 20, 2017, 04:33:32 am1. Prepare your post with the attachment.2. Post it.^-- This much you have already done --^3. Click on the attachment thumbnail. The full sized image will appear.4. Right click on this full size image and click on "Copy image address" (Chrome) or the equivalent in your browser. This will put the URL of the full sized image on the clipboard.5. Edit your post and add the image tags where you want the image to appear and then paste the URL in the clipboard within the tags.6. Click "Save" and you're done... and it will look like this:

author: Trailboss
author_rank: Contributor
timestamp: February 20, 2017, 02:59:54 pm
content: Quote from: T3sl4co1l on February 20, 2017, 07:00:16 am

author: mtdoc
author_rank: Super Contributor
timestamp: February 20, 2017, 05:54:42 pm
content: Quote from: Trailboss on February 20, 2017, 02:59:54 pmNo. It's quackery.The harm comes if you're using itinsteadof real, proven treatments.And the there's the whole smurf thing..

author: Benta
author_rank: Super Contributor
timestamp: February 20, 2017, 08:09:56 pm
content: 1...5 mA is actually the sweet spot for JFET-type current regulator diodes.My favorite was always the J500 series from Vishay-Siliconix (2-pin TO-92), working voltage up to 50 V, and more important: operation below 1 V.They're unfortunately obsolete.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 20, 2017, 08:45:21 pm
content: Quote from: Trailboss on February 20, 2017, 02:44:50 pmDo you mind editing that to unquote your responses? It's hard to read.I guess you used the  markup, so you can see how this stuff works... just change the  to end-quote and the end-bold to start-quote.Tim