electric circuit for chemical reaction

Discussion in 'Electrical Forum discussion & Blog' started by aeacfm, Jul 12, 2010.

  1. aeacfm

    aeacfm New Member

    Messages:
    42
    Location:
    egypt
    i need help in designing electric circuit for chemical reaction
    the required components are

    DC voltage ( i must control it so that i can see the reaction response to different voltages ) in range from zero to 2.5 volt (the main power in my work is AC 110-220 V)

    current density in range from Zero to 0.2 Amp/cm2 (also i must control it so that i can see the response of the reactin to different current densities )

    thanks too much for any help
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    http://www.testequipmentconnection.com/specs/Advantest_TR6142.PDF

    will this work
  3. aeacfm

    aeacfm New Member

    Messages:
    42
    Location:
    egypt
    thanks alot for reply but how much is it?
    i hope it is not so expensive because i need it only for that purpose and after that no need for it
  4. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
  5. aeacfm

    aeacfm New Member

    Messages:
    42
    Location:
    egypt
    it looks so expensive to me ,iam sorry but if you can help me with samller portale one or simple preliminary circuit like transformer , diode and compose them together

    many thanks again for your reply
  6. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Grandpa always told us young-ens that if we can’t pay the fiddler stay off the dance floor. Is this the case here?
  7. aeacfm

    aeacfm New Member

    Messages:
    42
    Location:
    egypt
    lol!!!
    no it is not the case here but just want to find the alternative when Expenses are limited

    thanks again sir for your time and advice

    also what make me say that some one told me some thing about constructing circuit using transformer 3 Volt , varying resistance , diode and wires but i cant got it completely and didn't know the arrangement of its components did you understand me ????
  8. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    I can help you design something. I need to know the area of your electrodes so that I can convert your current density into just a current.

    Do you need to be able to adjust current and volts at the same time or can they be seperate? If you don't have to adjust both, it might be easier to do two circuits:

    Circuit 1: voltage source that goes from 0 - 2.5v
    Circuit 2: current source that goes from 0 - x.x mA

    Are you doing hydrogen/oxygen out of water or something else? If you are doing hydrogen/oxygen out of water (and even if you are not), this is a very common experiment and you might also be able to find some good ideas online as well.
  9. aeacfm

    aeacfm New Member

    Messages:
    42
    Location:
    egypt
    thank you sir too much

    i want to avoid Hydrogen evolution at first
    also i want to adjust both current density and voltage together

    the area of electrodes are th internal torch battery carbon electrode area (A battery )
    thanks alot again for your time
  10. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    I'm sure you are a future einstein who will probably discover the theory of dark, or something. IF you don't blow up your daddy's house in the present experiment!

    Seriously, you need to find a mentor at school who undertands the electric part of this and can advise you accordingly. It is not quite enough to simply say "transformer...diode...etc"
  11. aeacfm

    aeacfm New Member

    Messages:
    42
    Location:
    egypt
    1st electricity and electrical components is not in my Concerns and is not my job
    i need the above circiut i described above in an experiment and The case ended

    do you know the conditions !!!!!!!!!!!!!!
    finally what i write about diode and transformer not from my own knowledge but electrical engineer who told me that

    many thanks
  12. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    I understand what you mean on that part. He is telling you how to convert from the AC to DC. Normally, to get DC, you do this:

    AC --> Transformer --> rectifier (can be built with 4 diodes) --> capacitor (for smoothing the waves).

    This gives an unregulated DC supply. If the transformer is say 12v, then the output would be a bit under 12v (change due to diodes). However, since it is not regulated, if the AC voltage changes a bit, the output will also change.

    To fix this, you can do like above and then add a voltage regulator at the end (5v, 12v, etc.) The input voltage from the transformer has to be higher than the regulated voltage. For instance, if you wanted 12v out, then you might need 16v at the transformer.

    A cheap/easy way to deal with this part of the circuit is with a computer power supply (from a desktop). These are cheap and easy to find used. They have regulated 5v, 12v, and -12v output and are able to provide a good amount of current. This is what I would use as a starting point for your circuit.

    Maybe you can explain the experiment better or perhaps you can give we what the current (not current density) is. Also, how accurate do the values need to be? What I mean is this: say you want 2.5v, does it have to be 2.500v (almost exact) or can it be around 2.5v (say between 2.45v and 2.55v)?

    How precise things need to be make a big difference on how the circuit is made. I assume that you don't need things that exact. When you run the experiment, you can use a digital volt/amp meter to see what the values are actually getting.

    Controlling the volts and current make things a little more complicated, but it can be done. If you only needed to control voltage, all you would need is the computer power supply, a fixed resistor, and an adjustable resistor. It is about the easiest circuit that can be made (called a voltage divider). It won't work for you since you need to adjust the current too.

    Anyway, give me as much information as you can about what you need and I'll see what I can come up with.
  13. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    In his original post he asks for help with a generator that he can control both voltage and current and know the amount of both.

    In order to do this he will need some pretty precise adjustments as well as a display for each. I don’t think this is something that someone without some formal training is going to be able to accomplish without spending some money. The Generator I posted is ready for the job at hand. One does not have to buy the unit and can rent one for as long as it is needed,

    http://www.tucker.com/java/jsp/product_partnoR6142_invid28544_condR.htm
  14. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    He is best off using a multimeter to display the volts/current. You would have a very hard time matching what even a cheap DMM can do on your own. If he needed something more compact/portable, he could work it into the design.

    I don't think that the actual output needs to be all that precise. Normally, in an experiment, you'll adjust one thing at a time and see the outcome as you change the input. For instance, say you wanted to look at the hydrogen generation rate by placing a DC current through water and looking at what the rate is for different current levels. Say your current supply can do 0-10A. Maybe you'll break up that range into 10 or 20 points. 1A, 2A, etc. The actual current in each step doesn't matter much as you can choose your steps to be whatever size you wish. The important thing is to record the actual current (say it was 0.95A instead of 1A). Then plot hydrogen generation rate vs. current and fit a line through it. Then you have an equation where you could put a different current in and estimate the generation rate.

    Since you normally control one thing at a time, that is why I asked about doing two circuits (one to sweep the voltage, one to sweep the current). Do two separate experiments. The voltage source is easy and the current source is easy. One circuit to do both is a bit harder.

    Another option is an adjustable power supply (basically like what you show, but more basic/cheaper). Something like this:

    http://www.web-tronics.com/00addcreposu.html
  15. aeacfm

    aeacfm New Member

    Messages:
    42
    Location:
    egypt
    i will use the above described circuit in electrolysing or electrochemical reaction .
    1-if you have chemical back ground i will electrolyse aqueous acidic solution in which i dont need the hydrogen to evolve with me ok!!!! thats first
    2-this would achieved using carbon electrode (internal graphite in A battery )
    3- this electrode would be of high hydrogen over potential to prevent the evoultion of hydrogen
    4- the best conditions to aciece the abone conditions are as follows
    voltage v current density Amp/Cm2 efficiency of reaction (%)
    1.5 0.017 60
    1.6 0.024 61
    1.7 0.055 63
    1.8 0.076 67
    1.9 0.147 80
    2.0 0.247 61
    2.1 0.846 23
    2.2 1.456 15

    from the above data you can see how i really need it precise as the efficiency decrease from 80 to 61 by increasing the voltage by 0.1 v !!!!!!!!!
    but if it went like what you noticified 0.05 increments so it may work i think !!!!!
    Last edited: Jul 13, 2010
  16. aeacfm

    aeacfm New Member

    Messages:
    42
    Location:
    egypt
    you can see how i need the precision from the above data
  17. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    Okay. That helps some. It looks like you need something with precision to 0.01V or better. In the table that you listed, I assume this is taken from another experiment. To me, it looks like they controlled the voltage (0.1V steps) and the current density and reaction are just measured. Normally, you control one thing (volts, amps, or resistance). Ohm's Law relates everything to what you did change. For the current density, it was likely calculated be measuring the current (amps) and dividing that by the electrode area.

    I do have a bit of a chemistry background. It is not my specialty, but physics/engineering undergraduate and graduate work had me involved to some extent in all of the physical sciences.
  18. aeacfm

    aeacfm New Member

    Messages:
    42
    Location:
    egypt
    you looks Professional!!!! aha In my opinion, at least
    this is for acid i want to reach them then i will try them for different acids ok!!!

    so in your opinion what you suggest to do but Taking into account that iam not electricity man iam only chemistry man and you make me like electricity
    thanks again
  19. aeacfm

    aeacfm New Member

    Messages:
    42
    Location:
    egypt
    hey
    no body here i really need what i posted it is my last chance in my work !!!!!!
  20. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    Try the 1st page of this pdf. See if that helps.

    http://www.edn.com/contents/images/6598370.pdf

    This is a 0-3v adjustable voltage source built around the LM317 (very common device). If the voltages you were working with were higher, the circuit could be made more simple (especially if you needed say 3v and larger). The only trick with this circuit is it calls for (5-10v) on the positive side and (-5 - -10v) on the negative side. So, you couldn't use the +/- 12v on a computer power supply. However, there is also a +/- 5v on a computer power supply that would work. Take a look at this:

    http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

    So, the combination of these should be able to do what you need for a small cost. On the output, you would add a current meter (inlne between the circuit output aand the electrode) and a voltmeter between the output and ground.

    This circuit should be able to provide 1 amp or so. I don't know the exact electrode size becuase when you say "A battery", I don't if you mean "A" in terms of cell size (like AA, AAA, etc.) or if you mean (a battery) like saying it is a battery but not saying what size. Anyway, if you know the electrode size (in cm^2), mulitply that number with the maximum current density that you need and that will tell you the maximum current that is needed. If you need more than 1 amp or so, then we'll have to go for a different design.
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