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How can I reverse polarity to a motor using relays?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Swifty, Sep 21, 2008.

  1. Swifty

    Swifty New Member

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    Hi all,

    I have a motor that has two poles, the direction the motor rotates depends on which way round the polarity it for these two poles..
    Now, I want to control this motor via my PC - I currenly have a parallel relay board which has 8 relays, I have 6 of these relays currently free..

    How can I use the free relays to control the polarity of the motor? (eg. signal relay 1 = motor spins clockwise, signal relay 2 = motor spins anticlockwise)

    I'm sure there must be a way.. but I can't think how I'd do it - The control from the PC must be via the relays though, as this is what my software uses..

    Many Thanks!
     
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,:)

    Your relays need to be of the single pole changeover type, are they.?
     
  3. Swifty

    Swifty New Member

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    Hi Eric,
    Yes they are.. sorry I should have mentioned the relay type.

    I have been searching some more on this myself and found that a 'H-Bridge' is the most common way of achieving what I need.
    The attached image shows one diagram I found which looks really easy to setup... but I am a little concerned about the lack of protection if one of the relays kicked in at the wrong time..

    Thanks
    Neil
     

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  4. dave

    Dave New Member

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  5. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    If you just want to drive the motor CCW and CW at maximum speed you dont need that bridge.

    Consider that you have two relays, one wire of the motor is connected to the wiper of one relay and the other motor wire to the wiper of the second relay.

    You connect +V to opposite ................................

    I'd better do a diagram it will be quicker...:)
     
  6. Swifty

    Swifty New Member

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    Like this ?
     

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  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Like this.

    The CR is for noise suppresion.
     

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    Last edited: Sep 21, 2008
  8. Swifty

    Swifty New Member

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    Hi Eric,

    Thats great, thanks so much.. I don't know why I didn't think along those lines before - but as soon as I read the first line of your reply I had an idea of what you might be drawing :)

    Thanks for your help!
     
    Last edited: Sep 21, 2008
  9. prakhar

    prakhar New Member

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  10. sam288

    sam288 New Member

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    In the circuit posted by ericgibbs...what is the use of the capacitor and resistor across the motor?
     
  11. Hero999

    Hero999 Banned

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    The capacitor and resistor is a snubber network which takes some of the strain off the relay by absorbing the high voltage pulse given off by the motor when it's turned off. It also helps to improve EMC by absorbing the high frequency noise generated by the motor's commutator.
     
  12. tblo163

    tblo163 New Member

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    reverse polarity

    Reversing the polarity with relays is quite simple ,all you need is two 5pin relays(crossover) & a 3 position switch.I've attached a pdf for you,
    Page#1 is reversing polarity & Page#2 is speed controling.
    good luck Terry,:D
     

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  13. fictious

    fictious New Member

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    hi .............can u plz help me wid NC NO and their respective +v $-v.....i dnt know abut dere working........and how they can b used as a switch????????
     
  14. tblo163

    tblo163 New Member

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    reversing polararity

    Hi Ficticious,I will gladly help you,but am not sure what you need to know,you need to be a bit more specific.So I'll start with a few simple basics.A DC motor can run in either direction,by just reversing the polararity.to do this a simple reversing switch is suitable,providing no HIGH Ampage is involved;(you can get a switch from a car breaker's yard or an electric drill)Most circuits will indicate that both the motor terminals are connected to ground,when the switch is OFF,When the supply to ONE of these terminals is supplied with + ,the motor will run.the reversing switch simply changes these connections around.If the motor draws a high current you HAVE to use relays,suitably rated for this.a relay is in fact a switch that can be controlled by a low ampage supply (thinner wiring) it has two seperate circuits,the energising (low)& the high ampage contacts.The crossover relay (CO) is a 5 pin relay,which changes the supply from 30 to 87 & 87a ,it can be seen that 1 of these pins is ON & the other is OFF,when the circuit is at rest.The circuit I've shown is contolled by a simple 3 position switch.which alternates from 1 relay to the other.O.K that's the basics,let me know where you are from,and I will probably be able to comunicate in your native language.Gutten targ TERRY.
     
  15. tblo163

    tblo163 New Member

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    Hi Ficticious, Please tell us a bit more about yourself,don't be shy.We are all here & eager to help,ther are thousands of members all over the world,who want to get to Know you, good luck.
     
  16. tblo163

    tblo163 New Member

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    reversing polararity with relays

    If you are having trouble identifying the suitable relays,check the thumbnail below.There are several types of 5 pin relays,make sure you get the right ones,they don't all do the same function,just check that one of the pins marked 87b is on,& 87 is off.
     

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  17. fictious

    fictious New Member

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    hi tblo163 ....m from paris france.but i cudnt actually understand hw dis 5 pin relay works......plz send me few links
     
  18. tblo163

    tblo163 New Member

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    Reversing polararity

    Bonjour Fictif, un relais est un Interrupteur,Contenant Deux Circuits,ONE est de dynamiser le relais,cela peut se faire avec CABUAGE BASSE AMPAGE,L'autre circuit est capable de faire face A HAUTE CURRENT,qui empeche les contacts de BURNING OUT. 5 PIN LA CROIX SUR RELAIS A DEUX PINS. a DYNAMISER,ET TROIS PINS POUR LA CONECTION DE LA POWER.When Le relais est off,il existe un code pin conection Entre 30 ET LE RELAIS 87a,When ON Est,iL N'Y A CONECTION entre pin 30 ET 87.
    Vous le verrez dans le schea,que les deux terminaux sant relies MOTEUR A QUAND LA NEGATIVE 3 position switch is OFF,By COMMUTATION SUR UNE ALIMENTAION EN RELAIS seqa POSITIVE DE COURIA,PARLA SELECTION DE LA POSITION D'AUTRES RELAYS VARIATION SUR SIMPLE.
    bonne chancel Terry.
     

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  19. kirkhan

    kirkhan New Member

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    Please help

    hello, i was reading this thread and found it very useful for the motor control that i wanted to build. I am fairly new to electronics and was wondering if the 5 pin relays referred to are SPDT or SPST. I know this thread is pretty old but if anyone could please answer, i would be more than thankful.


    Thanks
     
  20. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    Post #6 by Eric uses SPDT two each. Eric's design was based on what the original poster had on their relay card. A single DPDT relay could be used very easily also.

    Ron
     
  21. tblo163

    tblo163 New Member

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    Hi Kirkhan, To identify the 5 pin crossover relay,read my post #15, the circuit is post #17, and a PWM speed control circuit is post #11, if you need any help just ask, good luck.
     

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