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current control again!

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by plumber, Nov 4, 2009.

  1. plumber

    plumber New Member

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    can someone kindly explain what I have done and why it works? I am trying to learn. current control.jpg
     
  2. mbarazeen

    mbarazeen Member

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    this diodes may be for polarity protection, not for curent limiting, since diods never used for current limiting in forword biase. it just will show a forword drop only.

    also connecting ammeter as in fig 1 is totaly wrong, normally it has to be connected in series with the equipment. also across a diode???? simply you are by passing the diode by connecting so.
     
  3. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    What is the part number of the diode you are using?
     
  4. dave

    Dave New Member

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  5. JimB

    JimB Super Moderator Most Helpful Member

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    What is the current rating of the diode?
    What is the range of the meter?
    What current do you require?

    The diodes I have seen have a current limit of only a few mA, I suspect that you may need a bit more for electroysis.

    The current meter in parallel with the diode is completely wrong, the second circuit where things are in series makes more sense.
    But what current are you expecting? and yes a resistor would probably be easier to use.

    JimB
     
  6. plumber

    plumber New Member

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    Hi mike, thanks for the reply, I dont have time right now to get the part#, but it is in the mauser catalog, it is in fact a CLD rated for 1mA. it is made by national semi conductor only. My question remains...why is it limiting in that config? I was told it is simply a jfet with the drain shorted back to the source. Could the upper config. be doing this manually? I realize it is easy for a lot here to get side tracked...but it is limiting current up to a max of 1mA in this config. Or at least the meter is reading it that way... if the diode was in fact "bypassed" I would have a typical reading on volts and mA's. I swear, it is slicing the current way back down, and from there it slowly rises up to 1mA and stays there...like I've been wanting it to...I am just trying to understand. I know the meter should be in series to read amps... but the diode simply doesn't work when wired that way. Plumber
    To avoid confusion and off track answers I have avoided mentioning starting voltage and some other things...or my question has always been...why wont it work in the 2nd config.? plumber
     
  7. ke5frf

    ke5frf New Member

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    Plumber,

    can you give us the model and brand of the multimeter you are using?

    I read a thread a few weeks ago that you posted that you were learning on the fly about electronics, or at least that was implied. I wonder if you are using your meter properly or if it has become damaged.

    Using an ammeter can be sort of "dangerous", at least for your equipment. if you are on the wrong range scale, you can easily blow a fuse...or if the measured current is on the "edge" of your meter's ability it can as well.

    Having the leads plugged into the wrong connectors on the meter will mess you up. Most meters have different conficgurations for reading amps vs. voltage or resistance.

    And this can very well effect your circuit. This is especially true with analog meters vs. digital because digital meters have a higher input impedance. Some analog meters can load a circuit if not properly ranged etc.
     
  8. mbarazeen

    mbarazeen Member

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    what i beleive is your ammeter by passes the diode and its showing the current through the electrolysis, whats the type of your electrolysis? just remove the diode and connect it, if you will get the same reading then diode is nothing doing with it. i

    n your second schematic diode may not getting enough forword voltage to conduct thus no reading on the meter. just varify it.
     
  9. plumber

    plumber New Member

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    current control again

    Ok. Thank you for all the concern and the nicer than usual responses. I really need some troubleshooting help. Please try to assume the best of my intelligence...misplaced as it might be. If you reference my top and bottom drawings I posted at the beginning of this thread, I will change my question.
    WHY WONT THE BOTTOM DRAWING CONFIGURATION WORK? The configuration is typical...is it not? What I do know, is that current limiting diodes are not cutting edge...they are old and barely sold. I believe this is why no one has yet to forth straightly tell me either how to wire the diode, or why the schematic on the bottom does not limit current. period. I chose the CL Diode from N. semi conductor because it's application seemed very simple and straight forward. No one yet has told me how to properly wire it...or why the obvious configuration wont work. As for electrolysis, for the sake of finding a solution, please leave that to me and imagine a led or something else at the end of the leads. I don't have a problem "monitoring" the current there. OK? I need to "limit" the current there. So I guess I go back to needing to learn how to build my own current control circuit. In my simple way, the schematics using bi-polar transistors or jfets, capacitors, etc., gates and drains seemed way out of my league. Actually, it was the math needed to determine component values that scared me off. So why not a cl diode? It sounded good. Should I just give up and sacrifice voltage and time and use a darn transistor? I have come so far...I'm dyin here. I apologize for the frustration in my tone.
     
  10. plumber

    plumber New Member

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    current control again

    If no one knows the answer, would anyone be willing to help me actually design a current limiting circuit? I mean actual component values and part numbers? I am pretty dense and obnoxious but I would need that kind of help, if I cant have my beloved current limiting diode.
    If there are any takers, then I will explain one more time exactly what I am working with. What the heck. 30vdc, current at electrodes 24u. STARTING.
    I need the voltage in the beginning!!! As conductivity increases through the electrolyte, the amperage climbs...very slowly at first. I need this!!! However, at around 800u (6 hours) the current begins to climb too fast. The current cannot go over 1.25 mA period! I'll settle for around 1 mA. At 1 mA, I am willing to let go of my 30vdc and begin limiting the current. I need to hold the process there...at 1mA at the electrodes until the process is complete. Anything over 1.25 mA causes irrevocable problems and the process must be stopped. So there it is. I don't think I can be any clearer than this....but what about my current limiting diode? I miss it already.
     
  11. plumber

    plumber New Member

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    current control again

    Thank you mbarazeen. If I read you correctly, you described what it is supposed to do. This is wonderful news if I am understanding you correctly. I am in fact monitoring the current across the electrodes. It is the configuration or wiring I dont understand. And why The diode works in this configuration. I wired it this way trying to figure out why the diode wouldnt limit current...while I monitered the effects on the current across the electrodes. No one else seems to think it possible, or they cannot explain why it is in fact limiting the current wired this way. The lower schematic config simply didnt work. But I dont know why the other config does work.
     
  12. mbarazeen

    mbarazeen Member

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    you are working on very low current, 1. mA even less at the begining. if you select a propper diode for your second schematic it may work, current limiting by a transistor circuit is very easy to assemble, if out of home until saturday and i can help you after that, or any one can post to you the dagram, the basic of a transistor is to set a certain current (limit it) proposanal to base current, you can have a variable control upto 1mA as you needed.
    i hope some one will post it before me, dont worry transistors are so good for the purpose and you dont want to bother, for the problems and the answers you need for your circuits , let me analyze it and come to you later.
     
  13. Roff

    Roff Well-Known Member

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    The simplest explanation that comes to mind is that you are using a multimeter in voltmeter mode instead of ammeter mode. That would explain why the top circuit works and the bottom one doesn't.
     
  14. plumber

    plumber New Member

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    current control again

    Roff, I lived in Idaho for a while...I can read too. Please leave my meter alone and help me understand what is going on. If you know. I have never had a problem monitoring the current. In fact it is the only way to know when the process is done.
     
  15. kchriste

    kchriste New Member Forum Supporter

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    Roff is telling you exactly what is going wrong. You meter, if setup to measure current in the top diagram, is connected wrong.
     
    Last edited: Nov 5, 2009
  16. mbarazeen

    mbarazeen Member

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    did you try your 1st circuit without a diode? and compare it with the one with a diode??

    if you assume the diode has a open circuit (due to faulty or wrong selection) then as you said your 1st circuit will work and not the 2nd one. you do the experiment 1st as i told above.
     
    Last edited: Nov 6, 2009
  17. Roff

    Roff Well-Known Member

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    I'll ignore your rudeness and suggest that you make sure the meter probe wires are plugged into the current jacks and not the voltage jacks.
    BTW, the ability to read, or previous residence in Idaho, does not preclude improper use of a meter. I'm a retired EE, and I've done it a few times.
     
  18. ke5frf

    ke5frf New Member

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    Mr. Plumber...

    About 5 or 6 posts up, prior ro Roff's, I suggested the same scenario as he.

    You have drawn us a picture of two circuits, where you claim the first one is working and the second one is not. The first one had the meter parallel to the diode and the second one in series with it.

    Both configurations will read current as long as there is no failed or improperly biased component creating infinite resistance, as long as the meter is on the proper range, the fuse is not blown, all function switches on the meter are properly set, and the leads are connected to appropriate terminals.

    However, the parallel configuration, which you say is working, will bypass the diode. There will be no current limiting. You might as well remove the diode from the circuit and make it a Christmas ornament.

    The SECOND configuration, as long as YOU are doing everything correctly with your meter and components, all setting correct and components properly biased, assuming the components are suitable and properly functioning, and furthermore assuming this circuit is a proven design, SHOULD WORK.

    If it isn't working as you expect, those of us on this end HAVE to assume either you are doing something wrong, your equipment is faulty, or the design is bogus. Exploring any of these possibilities is not an insult.

    After all, you came to this site asking questions and as far as I can see some knowledgeable people have done their best to help you. My suggestion is that you take a deep breath and explore the possibility that you are doing something wrong per our suggestions.

    After all, if you are claiming the first drawing is "working" but do not realize that it CAN'T be working per the design of the circuit (ie no current limiting from a bypassed diode), then we MUST explore any and all possibilities.

    As Roff said, and I can personally attest, even the most skilled and experienced craftsman can have a brain glitch and improperly use the tool of his trade.

    Please offer us, as I asked previously, the make and model of your meter. Is it analog, is it digital? What is the min/max current range, etc.

    And if you have a digital camera, a detailed photograph of your experiment MIGHT shed some light.
     
    Last edited: Nov 6, 2009
  19. Roff

    Roff Well-Known Member

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    Excellent post, ke5frf! I think you've said it all.
     
  20. ke5frf

    ke5frf New Member

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    TY Roff. Don't mean to sound rude myself, but he keeps asking us to not question his intelligence when asking someone if they are using their equipment correctly has no bearing on intelligence whatsoever.

    I have a feeling that he IS using his equipment correctly but the diode simply isn't conductiong when he has it set up "correctly",

    Going back, he said he refuses to tell us his starting voltages, etc because he doesn't want us to "go off track" with our suggestions. In a way, that is an insult to the person from whom you are seeking advice! In fact, all the voltages and specifics of the circuit very much have a bearing on the outcome. He may not even be applying enough voltage to produce a current through that particular diode for all we know.

    In one of his first posts, he said he didn't have time to look up the model number of the diode, which is extremely relevant! Yet he has time to post questions, defend his intelligence, banter, and OUR time is of no consequence.

    OK, Mr. Plumber I am sorry for getting testy myself. I truly am. I think you are sincere, but you have to give us ALL pertinent information in order for us to help you, willingly and without hostility.
    _________________________________________________________________________________________________________________________________________________________________________________________________________________________

    EDIT: As an aside comment...if the current measurement with the meter parallel to the diode is not exceeding a milliamp in that configuration, per your observations, a few things you should consider and understand...

    First, conceding that I am no expert with electrolysis, it MUST be concluded that the conductivity of the electrolyte solution along with your battery voltage and the resistance of your conductor are the ONLY FACTORS limiting the current in your experiment (in the parallel meter configuration) according to Ohm's law. This is pure Physics 101 and unless you are the discoverer of a new Earth shattering phenomen this conclusion is all that is left.

    What you have is two parallel conductors. IF ANYTHING is certain, your actual current is MORE than your measured current, because the forward biased diode (probably) offers only a little more resistance than the meter and leads, and the overall current will be the sum of the two branches according to Kirchoff's current law. It is entirely conceivable that you have as much as 2 mA of current passing through the circuit but will never know it because to detect it would require two ammeters.

    This doesn't seem likely, however, because you say the series configuration isn't working. I would be interested to know how you define not working. In other words, is there NO measured current, or is the current more simply LESS than you expected it to be? If there is no measured current, the only reasonable conclusion is that the battery voltage along with the conductivity of the electrolyte is not enough to properly forward bias the diode and get it to conduct. If there is a current but not what you expect, the only reasonable conclusion is that the overall conductivity of your circuit and the voltage supply is not permitting the current you desire, in part because of the current limiting of the diode.

    Are you an actual plumber? OK then you should be familiar with pressure regulators. Think of them for a moment. A 10 lb pressure regulator cannot regulate 5 lbs of water pressure. The supply pressure has to be more than the desired output. You need headroom. This may be the case, in terms of current, with your experiment. By pure coincidence, the electrolyte solution may offer just enough conductivity to permit 1 mA of current with no diode in place (bypassed), but with the diode in place, you simply do not have enough current for it to perform as you desire.

    At any rate, without knowing the EXACT performance specifications and conditions of every component in the circuit, there is no way to give you the exact answer you are looking for, only guesses and speculation. But one thing is for certain, your "working" set-up is not working.
     
    Last edited: Nov 6, 2009
  21. kinarfi

    kinarfi Well-Known Member

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    Your diode, a CLD or CRD as I learned them many years ago, will pass 1 ma regardless of applied voltage. Look at my drawing and A1 will be 1ma, A2 will be your electrolysis current, and A3 will be the same as A2 minus 1 ma. In your lower drawing, your current is limited to 1 ma by the diode. It may be the diode keeps the emulsion ready to work when the voltage is raised, don't know why it's there, but that's how the diode works. I think CLDs are so cool, if in series with a capacitor, the voltage will rise in a straight line instead of the usual 5 TC curve.
    Enjoy,
    Kinarfi
     

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