I need a simple Polarity Reversing Circuit

Discussion in 'The Projects Forum' started by GuitarZombie, Oct 31, 2014.

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  1. GuitarZombie

    Thread Starter New Member

    Oct 31, 2014
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    I need a simple Polarity Reversing Circuit. It can be adjustable or can cycle on and off equally for a minimum of 60 seconds to a maximum of 5 minutes. I am alternating + and - on two 30V DC electrodes.

    I have a DPDT 12 v relay RS 275-0206 that I would like to use.

    Basically all I have to do is cycle the relay on and off automatically. I do not need an on switch. I have a variety of wall power supplies ranging fro 5 to 18 and 30 VDC.

    I do not necessarily need a timing adjustment.

    Given a reasonably simple circuit, I can build one. If I only had a party light that strobed in the time range I need, I would use that (LOL). [​IMG]
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    all you need is a 555 timer in astable mode,set to the desired delay,to operate the relays.
     
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  3. GuitarZombie

    Thread Starter New Member

    Oct 31, 2014
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    I know about the 555 chip, but I'm not an electrical engineer. I kind of need a circuit.
     
  4. Alec_t

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    Sep 17, 2013
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    This should give you about 2.5 mins on, 2.5 mins off. Change R1 to adjust the timing.
    Note: long delays like this with a 555 are subject to errors in timing due to electrolytic capacitor leakage current (which can vary with age and temperature).
    RelayDriver.gif
     
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  5. GuitarZombie

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    Oct 31, 2014
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    That's great! is there a chart or something where I can get all of the values of the diode? Plus I am assuming the voltage of a 555 is 5 volts. is that correct?
     
  6. ISB123

    Well-Known Member

    May 21, 2014
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    From 5V to 15V.
     
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  7. GuitarZombie

    Thread Starter New Member

    Oct 31, 2014
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    Thank you all! I didn't see the value of the diode and I had no idea a 555 worked on 5 - 15! Thanks again! I'll et you know how it turned out.
     
  8. GuitarZombie

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    Oct 31, 2014
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    One more question, can I get rid of the diode if I use the circuit like this? [​IMG]
     
  9. ScottWang

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    Aug 23, 2012
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    Don't use it that way, it may destroy the 555 somehow, just using the circuit from Alec_t .

    The diodes you can use 1N4001~1N4007.
     
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  10. Alec_t

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    The diode (just about any silicon diode will do) is there to supress the high voltage spikes which would otherwise occur when the relay coil switches off. If you omit it the 555 may die.
     
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  11. ScottWang

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    If using a light current relay around 30mA then 555 is ok, otherwise using a transistor to drive the relay is better, and I like to do this way.
     
  12. GuitarZombie

    Thread Starter New Member

    Oct 31, 2014
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    OK I got the diode, and the 555 will be only pulling the coil. The relay is 12V so According to ISB123 it should work (5-15V). The current of the coil is ? But I have found sites that say Nonmetal Current: 75mA - but I am thinking it is a typo but I have seen this on several sites. The relay will fire a separate power source. At $1.00 per 555, I'll probably try it as drawn, seeing I just got the components.
     
  13. ScottWang

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  14. GuitarZombie

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    Oct 31, 2014
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    Well it didn't work. I am thinking that the current of the relay killed the 555. (It is a 555CN - but the pins are identical). I also used a microsoft wall supply that said 12V DC but when I metered it, it read 15.7 (within the spec of the 555). Can someone show me how to add a transistor to fire the relay - I'll need a schematic and component numbers (values). Thanks so much, when finished, I'll share my cool application. Oh and the 555 never heated up that I could feel.
     
    Last edited: Nov 2, 2014
  15. GuitarZombie

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    Oct 31, 2014
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    Here is my circuit. [​IMG]
     
  16. ScottWang

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    Aug 23, 2012
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    You may choosing the Fig-01 diagram as below, same Rb or less that it depends on the current of relay, two pins of +V and Q1_C connecting to the coil of relay, and the diode(1N4001~1N4007) in parallel with relay, the negative of diode connecting to +V, the positive connecting to Q1_C.
    +V → (-)diode(+) → Q1_C.

    Or to google "ne555 pwm bjt drive relay", or to see the second circuit as this.


    [​IMG]
     
  17. Alec_t

    AAC Fanatic!

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    It may have. And any spikes above 15.7V wouldn't show up on a conventional DMM.
    Is it a LM555CN, or a LMC55CN? The latter has a 15V absolute maximum rating and certainly can't provide enough current to drive a relay.
    Here's a mod of the circuit to use a transistor to drive a relay.
    RelayDriver2.gif
     
  18. GuitarZombie

    Thread Starter New Member

    Oct 31, 2014
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    Thank you for being patient. [​IMG] I apologize for not being electrical literate. I can follow directions, but one should not assume that I know anything other than figuring out the orientation of diodes and capacitors and how to solder and follow directions. I have incorporated figure 1 as you mentioned. Does this schematic look correct?
     
  19. ScottWang

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    Aug 23, 2012
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    I'm not sure why you always forgot the diode, the diode is to protect the bjt for back emf of relay, just remember to in parallel a diode with the coil of relay, and the negative of diode connecting to Vcc.
    The Rb is connecting to Pin 3 of ne555, and the (+) of relay is connecting to Vcc.
     
  20. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    "The diode, the diode," says Tattoo!
     
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