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current control again!

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

  1. Roff

    Roff Well-Known Member

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    It doesn't matter what's inside the CLD. How is the gate going to know what is external to the CLD? It's still connected internally to the same place.
    It's still a two terminal device. I don't know how else to explain it.
     
  2. ke5frf

    ke5frf New Member

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    I think I know the answer, after some contemplation on the drive home from work. The potential voltage across A-C (and thusly across D-S of the JFET) will be the same no matter where you place it in the circuit, at least given steady state circuit/load resistance...and thus the G-S bias of the internal cathode voltage divider (assuming it is just like the example schematic on that link) will be the same with respect to D-S.

    At least I think this is correct and why you are 100% right. Still, it is worth setting it up that way, just to see what happens.

    And without knowing how to check the forward/reverse bias of this kind of diode with a meter, per the earlier suggestion by another poster, he should set up a 25kOhm load resistor in place of the electrolyte, with the diode properly biased, and read his ammeter to see if it is conducting or if it is open, and to verify it is stable. He might even do it with the suggested potentiometer and vary it to see if it makes a difference.

    >......Post verifying his CLD is functioning, I think he has several options.

    1) Play with the various ideas dicussed here WITH the CLD, shorting it temporarily, placing it elsewhere in the circuit, etc. Those are the only two even REMOTELY viable answers for why this CLD may not work as expected, per the discussion. If we are surprised and see either configuration work where the other didn't, woo-hoo! Move on, live and learn. You have your solution.
    2) If the CLD is functioning, but no configuration of the circuit permits it to work as intended, then it won't work, ever. So give up on it.
    3) Explore other possibilities, the timer/potentiometer is one crude, easy to understand and implement solution. Past that, you will have to seek out a current regulator schematic employing transistors, feedback, possibly op-amps or other ICs and various reference and biasing components. There may be something simple that someone can come up with, but it might take some trial and error that requires some knowledge and planning to execute. I'm not sure the OP is interested in the design process as much as the final product, so a LAYMAN approach with the switch and potentiometer might be easier for him to work with.

    Anyway, I'm all out of ideas. I am beginning to sense his frustration and I have a feeling I understand his urgency.
    2)
     
    Last edited: Nov 15, 2009
  3. plumber

    plumber New Member

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    greatness emerges!

    Can I butt in? In response to the precious few things I did understand in the last few posts.
    I was at a loss as to how to test this type of diode. Based on a Internet diagram, I ignorantly wired the diode with the stripe towards the power supply...I cant believe something on the Internet would be so misleading. The notes actually reiterated "put stripe towards power supply" so I did. 1.5 mA came and went at 6.5 hrs. I then wired it stripe towards ammeter and anode. Same result since. Got on the net, some one said I couldn't have fried it. They are wrong huh? So that is the great unknown...the diodes are cheap, I just wanted to understand and learn through this. And finally, I was told at one point "silly rabbit, it is just a JFET with the drain shorted back to the source" Yeah. Like I know what that means. But it made sense, that a drain is needed...like a resistor shunting current in the form of heat. This is exciting, so the simple way was the right way, I just fried it from the very start! Would all concur? You see, I just don't have the physical time to amass the knowledge needed. But I find this whole field incredibly fascinating and I intend to learn all I can. Oh, yes. All physical components remain the same through each test...water, electrode surface, purity, volume, time, etc. You guys are the greatest! plumber
     
  4. dave

    Dave New Member

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  5. ke5frf

    ke5frf New Member

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    Well plumber, you don't exactly have the construction of the JFET correct, it is more like the Source is shorted to the Gate, not the Drain to the Source. I had to think that one through, myself though.

    Yeah, you reverse biased it at one point, but that might not be destructive unless you exceeded the specified reverse bias voltage and current. Being that the distilled water has infinite resistance, I'm not even sure how a reverse biased condition would ever even get to the point of conducting. Anyhow, given a destructive event, You would expect that the result would be an open circuit, thus NO CURRENT would flow in either direction...but it is possible that the internal diode and D-S junction became shorted. I wouldn't have a clue with this type of device, but if it passes current both ways without limiting in the forward direction something is amiss.

    As was posted earlier, the best thing to do is set up a "dummy load". Somewhere between 25kOhm and 50kOhm would do. This would replace the electrolyte and "simulate" a steady state condition with the solution...You SHOULD get around a mA of current forward biased. I wouldn't even try reverse biased. If you happened to have a 25kOhm potentiometer, when you check the diode you could gradually adjust the resistance to a lower and lower value. If the CLD is working, it should hold at 1 mA or thereabouts.

    I would at least try this while you wait on your new mail order diodes. You can also experiment with the other suggestions I posted, bypassing the diode temporarily etc.

    HINT: When you call companies like digikey and mouser, talk up your "upstart company" and tell them you are looking for samples for testing. They often will be happy to oblige a few free components thinking you are a potential mass-purchaser.
     
  6. plumber

    plumber New Member

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    I have a couple of pots, I'll see if one will work. The diode has always allowed
    voltage and current to pass to my meter, and that is where the confusion begins. Because of the different nature of this non- typical diode, I have always wondered if my meter is where it truly should be, and does it's position effect how the diode functions. The Tyndall effect through the distilled water is what tells me I am going past 1.5 mA. This is irrefutable proof of what is really going on at the electrodes. The meter also concurs with this. So I am still haunted by a photo of the red test probe being attached between the dc source and diode, the black probe being attached after the diode before the electrode. Very frustrating, I have searched for the the photo on the net but could not find it. And why would a seemingly reputable source emphatically state that the diode stripe should face the power supply? Misdirection perhaps? I don't think it would be an honest mistake. I know I have burned a lot of your time, and I thank you. I'll check back when the new diodes get here. plumber
     
  7. Roff

    Roff Well-Known Member

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    Plumber, the diode stripe (cathode) has to be more negative than the anode. Whether it "points to the power supply" or not depends on where the load (in your case, the electrolysis cell) is in the series circuit. The load can actually be connected to the anode or the cathode, as long as you get the polarities of the power supply, the CLD, and the electrolysis cell correct.
     
  8. kchriste

    kchriste New Member Forum Supporter

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    You should always check the datasheet for the device you will be using. People do make mistakes. Sometimes different manufacturers do things differently too.
    Here is a excerpt from a Motorola datasheet for the same current regulator diode. In their documentation, the current is regulated in the forward direction. ie: the band away from the + of the power supply. There is no current limiting in the reverse direction and destructive currents can flow:
     

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    Last edited: Nov 15, 2009
  9. kinarfi

    kinarfi Well-Known Member

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    What is your emulsion and what is it for? Just curious, if neat, it may be worth play with myself.
    kinarfi
     
  10. Roff

    Roff Well-Known Member

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    OR - what are the anode and cathode materials? We know the "electrolyte" starts out as distilled water.
     
  11. plumber

    plumber New Member

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    Get two cheap stainless steel teaspoons but any metal spoons will work. Bend the round part over the handle to form a hook. For a quick rendition use a small glass container(4" dia. opening). For a longer more accurate rendition use a wide mouth glass container. The farther apart the electrodes are the longer it will take to establish an ion stream. I'm using two liters of distilled, deionized water(ionized is fine). Electrodes are 5 1/2" apart. The ionized water only has to do with the finished process. It doesn't matter. Some alligator clips, 12-35 dc unregulated power supply(wall rat or batteries), 1 ammeter capable of reading micro and milli amps and 1 CLD or CRD. For experiment any mA rating will do. Keep in mind that I need the process to be slow, so I use mechanical stirring to keep the ion stream from becoming condensed. For test purposes, don't stir it, and you wont have to wait 6 hours to reach 1mA (2 liters, electrodes 5.5'' apart). At 1.5 - 2 mA, a weak Tyndall effect can be seen in the water with a laser pointer or led flashlight. The cathode's only role is to impart hydrogen ions and s.s. is well suited for this. The anode on the other hand will impart metal ions causing the Tyndall effect after 1.5mA. If you have some platinum or palladium lying around great. Otherwise a spoon will suffice for test. Metal type will only affect time. Not current control test results. Stainless steel will go a bit quicker. Hope I didn't lose any friends on this one, I really do appreciate it. plumber
    (my dc supply is a 30 vdc unregulated power supply, puts out 34.5 dc consistently)
    foot note: wired a pot and got no current limiting it was only 10kohm with a 30v rating. Off produced 3mA, on produced 3mA up to 3.86 mA as I turned the dial. I know I needed 25k, but with diode in place, it still read 3+mA.
     
  12. Roff

    Roff Well-Known Member

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    Can we ask what your goal is?

    Do you mean a current limiting diode, in series with the pot, the power supply, and the electrolysis cell? If it is a CLD, rated at less than 3mA, then it is either damaged or wired incorrectly.
     
  13. Roff

    Roff Well-Known Member

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    Coincidentally, I have been running an electrolysis process for the last few days to remove rust from a railroad spike, just as an experiment. I'm running about an amp in a solution of washing soda (sodium carbonate). Several years ago I used an automotive battery charger to remove rust from some gold rush era tools, and it worked great.
     
  14. plumber

    plumber New Member

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    It was to test the diode, the pot replaced the electrodes, cathode lead, wired to wipe...I think that's how it went. I ordered more CLds.
    You guys have been more than kind, and I wont waste your time by being vague. But I cannot tell you my goals for personal reasons. No free energy device, not for money or hobby.
    ppm metallic mirrors and contrasting background for creating full dimensional photo models of nano mechanisms in action...microscope slide juice that allows 360 degree view angles with stunning contrast.
    Just kidding. plumber
     
  15. Roff

    Roff Well-Known Member

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    Post deleted.
     
    Last edited: Nov 17, 2009
  16. kinarfi

    kinarfi Well-Known Member

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    I was expecting a hydrogen generator.
     
  17. ke5frf

    ke5frf New Member

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    "foot note: wired a pot and got no current limiting it was only 10kohm with a 30v rating. Off produced 3mA, on produced 3mA up to 3.86 mA as I turned the dial. I know I needed 25k, but with diode in place, it still read 3+mA"

    Yes, I would expect a 10kOhm pot to allow twice as much current as your "ideal current controlled" 1.5 mA target, per Ohm's law (E=IxR), that is being that the device is obviously shorted and not working. If the device wasn't there, a 10 kOhm load will draw 3.5 mA, which is what you saw. So, your CLD is most positvely nothing more than a conductor at this point and should be replaced.

    Get your new CLD and a 25 kOhm pot, when you revieve it go ahead and wire up this same test rig, with the diode forward biased as you understand now, and verify under controlled conditions how the CLD works, for your own peace of mind. Then, set up your test and plug away at your experiments. Good luck.

    BTW, if for some reason things still don't work as planned, a lot of good suggestions have still been made here which WILL lead to fruit, so don't give up if some little something still isn't just right.
     
  18. plumber

    plumber New Member

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    nanites

    That it does. The industry from lowly electrowinning and anodising clear up to nuclear projects are now venturing into stainless steel cathodes instead of expensive noble metals. It is based on a brush bristle design that provides lots of surface area compared to conventional cathodes. Surface area means lots of hydrogen bubbles. I still like my nano-photo theory though. Colloids are fascinating, but silver colloids will turn your skin blueish green forever. gold colloids are down right poison. platinum colloids are too expensive, but palladium colloids reflect light in almost the same wavelength...like diamond mirrors floating in pure water...there would be a imaging use for such a thing.
    Don't get me started, and thanks again...plumber (to make straight)
     
  19. kinarfi

    kinarfi Well-Known Member

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    I was working on my project until I fried all my quad op-amps so I pulled out a J310 jfet and hooked it up with 1924 ohms drain to gate. Positive to the source, load on the gate side of the resistor. The load was my Fluke ammeter. At 5 volts from my lambda power supply, I got 1.4 ma, 10 v - 1.43 ma, 15v - 1.45 ma, 20v - 1.46 ma. That's as high as my power supply goes.
    I also put an 820 ohm resistor between the adjust and output of an LM117 and hooked my ammeter to the adjust side of the resistor, at 2.5v - 1.54 ma and it was constant up through about 15 volts, then as I went higher, the current was increasing also, at 20v, I was up to 1.6 or 1.8 and I was worried about frying my LM117 so I quit.
    I found it interesting that the 117 did this, I wonder what would happen to my J310 if I kept raising the voltage.
    Kinarfi
     
    Last edited: Nov 17, 2009
  20. mneary

    mneary New Member

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    J310 is rated at 25 volts, so it should work fine at least to that level. It might work at higher voltages, but the risk of failure increases exponentially.

    The LM117 is still within its ratings all the way up to 40V. It will shut down if it gets too hot.
     
    Last edited: Nov 17, 2009
  21. plumber

    plumber New Member

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    Me?

    kinarfi, you replied to this thread...this is plumber. Please remember.I havent hit novice status yet. I did not understand most of what you just said. Have a good one! plumber
     

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