can someone kindly explain what I have done and why it works? I am trying to learn.

 

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.

 

What is the part number of the diode you are using?

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Mike ML.

 

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

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Experience is directly proportional to the value of the equipment ruined.

 

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

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

__________________
Ron

 

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.

 

Roff is telling you exactly what is going wrong. You meter, if setup to measure current in the top diagram, is connected wrong.

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Inside every little problem, is a big problem trying to get out.

 

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.