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Constant current circuit help

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diegomaradona

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I need constant current of 1 mA in destilled water. Two electrodes are sink in the water and durring the process small particles of anode are dropping in the water and because of that water resistance is dropping and current is going up. I need to current stay constant (1 mA) and voltage must going down. Input voltage is about 30 V. Enybody have sulution for this problem?? Please help!!

thanx
 

you may use a constant current diode which has very less variation of output current and would be very helpful in your case....


also check this site for other constant current source circuits...
**broken link removed**

also visit this post.......
 
Thank you for your answer. I need in the beginning of the process all voltage I can get because the destilled water is high isolator. So if this diode can operate on 50 volts maximum can you tell me what maximum output voltage i can get, will it work?
 

the current diode is nothing but a JFET with its gate shorted to the source... so Vds depends on the current that you use... i think the drop across this diode would be that pretty low... what is the voltage level that you would be needing... if you can specify that maybe i would be able to find a solution....
 
I need that voltage in the beginning of the process be about 30 volts.
 

then using a current limiting diode is not that big a problem... the drop across the JFET that is Vds would be very less and i dont think it would exceed 20 volts i.e.that 50-30 you need.... so you better google and find the current diode for the current that you need...
 
Anand helped me with his answers but diode that he mentioned are very hard to get ( there is no distributors of that kind electronic part in my region) . You can find almoust anything but current regulation diodes are not available!? Can anyone make other way to solution of my problem? I am not that good in electronics so best way to help me is posting electronic sheme of solution, and I will be able by that make a board, but if you tell my solition by the "words" I probablly would not understand.
 

well view this link....


this posting has some discussion of constant current source using commonly used ICs.... which would be easily available...
 
If you do not need high precision current source you may use this circuit.
 
Thank you for your help.

The current must be constantly less than a 0.1-0.15 mA per square cm of anode. So because of that I calculated that current in the water must be max 1 mA.
 

hi, please what exactly are you doing here?

What solution do you place the electrodes and what exact electrodes are you using?
 
I am trying to make collodial silver, so electrodes are pure silver. Collodial silver particles must be nano size . Nano size will be if the current is under 0.1-0.15 mA per square cm of anode.
 

OK you are making collodial silver with electrodes been pure silver. So how do you plan to achieve Collodial silver particles of nano size
 
As I say before if the current in water is smaller than 0.1-0.15 mA per square cm of anode particles of silver dropped in the water will be nano size. Because destilled water has great electric resistance, voltage in the beggining of the process must be as higher as you can get.
 

changing the distilled water at intervals will maintain the water high resistance.

If you are ok with this approach then, calculating the ratio at which water losses its resistance to intervals of changing the water would help in a new design.
 
yes i know you want distilled water, but you said you want to keep the high resistance of the distilled water.

Am i right ?

so if i am then my earlier post is the way out, which is developing a system that can automatically pump in new distilled water to replace the one whose resistance is dropping.

if i am wrong, tell me exactly what you want i,am sure there is a way out.

cheers
 
No I don´t want to keep resistance of destilled water. What I need is that when resistance of water is dropping because of silver particles is "ripping" from anode in to a water than voltage must start dropping, not current! Process if finished when voltage is to low and at that point silver from anode can´t be dropped into wather any more. Thats all!
 

Borber said:
If you do not need high precision current source you may use this circuit.
Click to expand...

What happening with voltage in this circuit afther that R1 resistor? Will I have big dropping of voltage before it came to the electrode? Because R1 resistor is about few kohms and input voltage is max 30 V (jfet can handle) does it mean that voltage on the electrode will be in mVolts? If it is the thrue that this circuit can´t help me,because I need in the beggining of the proces that voltage od electrodes be about 30V.
 

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