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Reversing polarity for electrolysis project

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by BHinote, Jun 16, 2011.

  1. ronv

    ronv Well-Known Member Most Helpful Member

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    Ahhh. Remove the cap from pin 5 of the 555.
     
  2. BHinote

    BHinote New Member

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    If I understand your question, I only need the PWM pulse once the motor has started.

    So far with the 100 Ohm resistor in line with the 100K Ohm Pot the motor always starts. However because I have a magnet sitting on top of the motor I want to ensure that it starts before dropping back to a slow or very slow speed. (There should not be enough resistance with the size Magnetic stirring bar that I am using, but if this is ever increased I do not want to take a chance...)

    Using a similar technique as was done with the Reversing Circuit, to lock left, normal or right, I found that setting the Trigger to Ground forces the circuit to full power on the motor. Removing the Ground lets the timer resume the PWM operation. This is why I was thinking I could use the High Output as a switch for the second timer trigger to ground. I am experimenting with a ULN2003A since Power to A will drop B to Ground. I a hoping that this will act like a Relay and not inter fear once the power to A is dropped...
     
  3. BHinote

    BHinote New Member

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    I must have done something wrong...
    When I removed the Cap from pin 5, the timer never started pulsing.

    I am attaching a zip file containing both of the designs I am currently working with.
    The Fan PWM Control - Best Design_Extra Parts is the one using a 555 and has the Reversing Transistor included.
    The Fan PWM Control - Best Design_Final is the one using the 556 and does not use the Reversing Transistor but is currently testing the use of a ULN2003A. (I found one on the Alarm circuit, if it will do the trick.)

    BHinote



     

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  4. dave

    Dave New Member

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  5. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I've used this http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_120539_-1 kit and was very happy with it. Is it an almost ready made solution for you?
     
  6. BHinote

    BHinote New Member

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  7. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I thought the PWM thing actually worked?
     
  8. BHinote

    BHinote New Member

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    KISS,

    Ok, go ahead…. Give me a hard time… I guess since you and Ronv have helped out so much both of you are entitled to knock me around on this… :(

    To clarify, the PWM circuit has been working and I only posted the PWM Circuit on Wed. to see if I may have overlooked something. Ronv kicked back a couple of suggestions and I gave them a try.

    However after working with some of the things you guys have been showing me I took a closer look at what I though was working and found my startup circuit was not doing what it was suppose to. (i.e. Start 2 seconds on full power then drop back to whatever the pulse was last set at.)

    I mentioned this and Ronv gave me a few additional things to try and I have been working on it every since.

    Sorry…

     
  9. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    OK! 2 seconds is a long time for a power on reset signal. I spent a long time getting an elegant delay design to work. You didn't buy and J174 Fets did you? I have an idea that should work on power up, but once it has been running all bets are off because the reset time would be long. The 555, in my opinion, is glitchy on power up especially if you want it to "one-shot" type things.
     
  10. BHinote

    BHinote New Member

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    No I did not buy the J174 Fet yet.

    Yes I agree that 2 seconds is definatly over kill, but I wanted to see it work and knew that I could always turn this back with diffrent Resistors and/or Caps...

    BHinote

     
  11. ronv

    ronv Well-Known Member Most Helpful Member

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    555 Reset

    Sorry, I'm to old to wait for that simulation to finish.:)
    So I ran it in Spice. The only thing I see is that the 10K on the base of the 2N2222 should be between the base and the output of the 555.
    Remove the cap on pin 5 and use the 220 Ufd as the power on reset cap (In place of the 47Ufd.) It simulates a ok now. I'm not sure of the condition of the 2N2222, but probably ok.
     

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  12. BHinote

    BHinote New Member

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    Ronv.

    Thank you.

    I am between Softball Games with my daughter and will need to take a closer look at this, in the evening.

    Thanks again for you assistance.

    BHinote
     
  13. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Here is my suggestion for a "force PWM to 100%"

    Unfortunately, haven't learned to simulate things yet. The R1/R2 divider must be greater than Vgs.

    It is possible to use lower values for R1/R2 and a high series resistor to the capacitor as well.

    The idea is that when power is off, the cap will discharge through J1. A small series resistor to limit the current to about 100 mA could be usefull 12/0.1 or 120 ohms.

    When power is first applied,J1 will be shorted (and shorting a pin on the 555) moves it to 100 duty cycle.

    R1 charges C1 until it exceeds Vgs, then the JFET opens. The "to power" should be after the power is switched to turn on the motor.

    ronv:
    Want to have at it for simulation?

    BH:
    Can I apply the racing stripes?
     

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  14. ronv

    ronv Well-Known Member Most Helpful Member

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    KISS
    I couldn't get it to switch clean. Did you mean to use a JFET transistor?
     
  15. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Yep, a P channel JFET, p/n J174 http://www.electro-tech-online.com/custompdfs/2011/07/J174.pdf

    For the power pin use a triangle source. (0 to 12 and back down to 0). A ramp would even be better

    At the Top of the JFET, use a LED and resistor to ground. It can sink 100 mA when Vgs is 0V and it woul d have an 85 ohm resistance. Probably could add about 22 ohms in series with the + of the cap.

    Try 100K for the top resisr to +12
    1 Meg for the resistor across the cap
    Make the cap 100 uf.
     
    Last edited: Jul 3, 2011
  16. BHinote

    BHinote New Member

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    A little confused

    I am a little mixed on this one. I kind of understand what both of you are saying about the PWM idea, but I am also a little confused.

    I will see if I can do some research, for a better understanding tomorrow after noon. (i.e. Sunday)

    By the way, “…Racing Stripes”, sure why not.

    I also received the parts from Mouser’s, so I am going to try to assemble the Silver Generator over the next couple days…

    Best Regards,

    BHinote
     
  17. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  18. BHinote

    BHinote New Member

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    Special Thanks

    To both RonV and KeepItSimpleStupid,

    Before I let too much time get away from me, I wanted to take this opportunity to say “Thank You” to both of you for all the help that you gave me. Without your efforts I would not have been able to complete the circuit using the proper components and/or tolerances… Considering the number of people that appear to visit this website, the two of you were the only ones that took the time to help. Thank You…

    I have been testing the circuit from the project board and all appears to be working as intended. If all continues to work well, I will build a PCB from the design in the near future.

    Thanks again for all your efforts.

    Best regards,

    BHinote :D
     
  19. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Congratulations! You did most of the work.

    Did you try both output circuits (Transistor based H-bridge, SSR based H-Bridge)?
     
  20. BHinote

    BHinote New Member

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    Yes I have tested each of the designs using either Transistor Based or LM317 Based Constant Current Regulation circuits. At the moment I am using the SSR Based H-Bridge with the Transistor Based CCR circuit. Although the LM317 appeared to work well, subsequent reading indicates that the LM317 should have a minimum load current of 10ma and I did not know how reliable this would be over time. I would have tried the LM334, but did not have one available. So with that said, I opted to use the Transistor Based CCR circuit.

    When I tried the Transistor Based H-Bridge, it appeared as though I was getting different Current values from one side to the other. I switched the various transistor and resistor locations in the bridge, but the difference appeared to follow the condition of the 4001BP. (i.e. Power supplied by on vs. off condition of the 4001BP.) After switching to the SSR Bridge and ULN2003, I discovered that my Multimeter was not providing a true reading based on it’s settings and connections. After making some adjustments with the multimeter, I am now seeing expected readings. I believe that the Transistor Based Bridge would now also provide consistent values from either side, but I have not elected to switch back to prove this yet…

    As was indicated early in this thread, Steam Distilled Water has a very high resistance (i.e. Somewhere in the neighborhood of 10M ohms), so it takes a while before I start seeing any type of reading on my multimeters.

    Question: When using the Transistor Based CCR, why does the Voltage steadily drops when the mA reading has not reached the adjusted value desired? (i.e. High Resistance requires High Voltage to achieve the same Current Value. Whereas Lower Resistance requires Lower Voltage to achieve the same Current.) So as the resistance starts to drop why doesn’t the Voltage remain High until the current reaches the preset value and then drop accordingly to maintain the desired Current Value.

    Best Regards,

    BHinote
     
  21. ronv

    ronv Well-Known Member Most Helpful Member

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    :DGlad you got them working.:)
    Not sure why the voltage would drop. Is it by any chance the one using the 317?
     

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