Connect with us

Regulator to limit 12v DC current

Discussion in 'Power Electronics' started by georgewalker, Feb 24, 2020.

Scroll to continue with content
  1. georgewalker

    georgewalker

    14
    4
    Feb 18, 2020
    I'm interested in a suggestion for a rectifier component or circuit to limit the current in a circuit to between 200mA and 450mA.
     
  2. Audioguru

    Audioguru

    2,725
    614
    Sep 24, 2016
    Why would you use a rectifier to limit 12VDC current?
    What is the load resistance?
     
  3. georgewalker

    georgewalker

    14
    4
    Feb 18, 2020
    Because I wanted to limit current travelling through a12v circuit and while searching for something to do it on a component site, a rectifier was suggested.
    The load resistance is variable (two electrodes in distilled water) and in the process of applying power, the resistance decreases. Controlling the current between 200mA and 400mA will limit the size of the particles emitted into the solution.
     
    Last edited by a moderator: Feb 24, 2020
  4. Minder

    Minder

    2,922
    615
    Apr 24, 2015
    Sounds like you are getting into electrolysis?
    A little more than just a rectifier may be needed!!;)
    M.
     
  5. georgewalker

    georgewalker

    14
    4
    Feb 18, 2020
    Yes, you are spot on. As you have guessed, I should have said regulator and not rectifier.
    I have made and tested the electrolysis process (for Colloidal) simply by directing 12 vdc into two electrodes suspended in distilled water. It works but is problematic for duration and particle size.
    There are two parts of the circuit I am working on.
    1. Controlling the process duration while periodically reversing the polarity in the electrodes to equalize wear. This is progressing and I am waiting for parts (from China) originally due mid March at the earliest. Now Coronavirus will no doubt create further delay.
    2. Limiting the current to the electrodes. Earlier I was under the impression that somewhere between 200mA and 400mA would do this but further research recommends below 40mA. This is the main determining factor in creating nano particles of Colloidal Silver.
     
  6. Bluejets

    Bluejets

    3,764
    781
    Oct 5, 2014
    Pretty simple to knock up a current control using a 317 regulator and a couple of fixed resistors a pot and a couple of caps.
    Plenty of circuits on the web.....look up LM317 variable current regulator circuit.
     
  7. davenn

    davenn Moderator

    13,496
    1,830
    Sep 5, 2009
    This thread looks like a continuation of your last one which was moving into screwball themes and was moved and closed

    are you going down the same path ?
     
  8. georgewalker

    georgewalker

    14
    4
    Feb 18, 2020
    Thank you. I'll look into it.
     
  9. georgewalker

    georgewalker

    14
    4
    Feb 18, 2020
    It is not my intention to do anything but try and create a workable circuit. I tried to change the thread title from Rectifier to Regulator but couldn't fins a way to do that.
     
  10. davenn

    davenn Moderator

    13,496
    1,830
    Sep 5, 2009

    OK .... A simple regulator circuit will regulate voltage, not current. Current limiting requires a bit more work



    No, you cant do that, only moderators can. I have edited it for you :)


    Dave
     
  11. georgewalker

    georgewalker

    14
    4
    Feb 18, 2020
    LM317.jpg
    Am I reading this correctly that I need a 60 Ohm resistor to limit the current to 21mA or have I misread the decimal point. Can I assume this will work with a 12VDC circuit?
     
    davenn and duke37 like this.
  12. duke37

    duke37

    5,297
    739
    Jan 9, 2011
    You need sufficient voltage to run the circuit. 1.25V across the sense resistor and a couple of volts across the 317 plus the voltage across the output. 6V may be sufficient. High input voltage will dissipate power and the 317 will get hot.

    How do you pass current through distilled water? Water cooling of high power valves running at several kV is used, the water needs to be free of ions.
     
    georgewalker likes this.
  13. Bluejets

    Bluejets

    3,764
    781
    Oct 5, 2014
    Calculation is correct.:)
     
    georgewalker likes this.
  14. Alec_t

    Alec_t

    2,757
    733
    Jul 7, 2015
    That's what I was wondering. Pure water is a very poor conductor. I've just tried two multimeter probes about 1mm apart in ordinary tap water (with goodness knows what dissolved in it) and the resistance between the probes was ~200k. It would be a lot higher in distilled water and require quite a high voltage to get even 1mA to flow (at least initially).
    I've not tried electrolysis. Does a tiny initial current lead to increased conductivity and hence rising current?
     
    Last edited: Feb 24, 2020
    georgewalker likes this.
  15. hevans1944

    hevans1944 Hop - AC8NS

    4,376
    2,046
    Jun 21, 2012
    "Electrolysis of water" discussions do indeed often lead into woo-woo "science" that is not tolerated here. What TO DO with colloidal silver produced by electrolysis of water will 99 44/100% (the "purity" of Ivory-brand soap) of the time lead directly into a woo-woo discussion. That is why the previous similar thread was terminated after it wandered away from electronics circuitry. So, please let us keep the discussion limited to electronics circuitry since that is what the ElectronicsPoint.com website is all about.

    The constant-current circuit shown in post #11 is a very simple and convenient way to produce a constant current in a load referenced to power supply common. The only caveat is the regulator output voltage must be sufficiently high to drive the constant current through the load resistance. The LM317 (see attached datasheet) output voltage is adjustable up to 37 volts and requires a minimum 3 volts drop across the regulator (from input to output) to operate properly, thus the maximum input voltage is 40 volts.

    The regulator design is such that it tries to maintain a constant 1.25V reference voltage across the resistance connected between the "output" and the "adjust" terminals. Since the "adjust" terminal is a high-impedance input, the current through this resistance must be supplied from a load connected between power supply common and the "adjust" terminal. This current is supplied by the regulator "output" through the resistance connected between "output" and "adjust," said resistance setting the constant current through the load connected between "adjust" and power supply common. Figure 14 "Precision Current-Limiter Circuit" in the attached Texas Instruments datasheet provides an example of how this is done.

    If there is no load (electrolysis probes removed from the water) the LM317 output voltage will rise to a maximum value determined by the input voltage. There will be no regulation of the output voltage under these conditions, but no harm to the regulator either. If the regulator is supplied with only 12V DC, the output voltage may not be high enough to cause the desired electrolysis current. You can raise the input voltage from 12V up to 40V (well filtered, and this is a maximum value!) or increase the area of the electrolysis electrodes immersed in the water to reach the desired 21mA electrolysis current. If neither approach is feasible for you, someone here at EP will have to re-think the problem and find a higher voltage constant-current solution.
     
    georgewalker likes this.
  16. georgewalker

    georgewalker

    14
    4
    Feb 18, 2020
    I'll build it and try it out with different input voltages and other variable. Thank you for the long explanation.
     
    mnak and hevans1944 like this.
  17. Audioguru

    Audioguru

    2,725
    614
    Sep 24, 2016
    Here is the photo of a guy who ingested colloidal silver which medical experts say is not considered safe:

    ATTACH=full]47174[/ATTACH]
     

    Attached Files:

    davenn and hevans1944 like this.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-