Need help connection DPDT Replay

Discussion in 'General Electronics Chat' started by mpcotuong, Jun 8, 2011.

  1. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    Hi All


    I have seen SgtWookie post this circuit for connection of relay. My question that one DPDT relay can connect it? If yes, please specifice how to connect them.


    Thanks,
    Kevin
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    With DPDT you have to use another relay or switch to turn off the motor. So it is better to use two relays to reverse direction. when relays are off, so is motor. With a single DPDT, motor will always rotate in one way. besides u will need time to brake the motor.
     
  3. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    It mean I can't use one DPDT relay? yes, I will have switch to brake the motor before revert direction.

    Thanks,
    kevin
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    No, it would be a bad idea to use a DPDT relay instead of the two SPDT relays.

    I used the pair of SPDT relays for a reason. Connected as shown, it works as an H-bridge where the motor control has three modes:
    1) Off (braking)
    2) Forward
    3) Reverse

    A single DPDT relay would only have Forward and Reverse, and you would not have a pause in between. This would be very hard on the relay and the motor.
     
  5. mpcotuong

    Thread Starter Member

    Aug 26, 2010
    170
    0
    Hi SgtWookie,

    If I need it forward and reverse, the brake will use switch to brake before it go other direction. Can I use single DPDT? If yes, how can I connect to your circuit? I have this relay KS2E-M-DC12 from KEST. Please let me know

    The reason to use one DPDT is for cost saving of the project.

    Thanks,

    Kevin
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    How are you going to switch off the motor.
    There are two ways to do this.
    1. A single pole relay or
    2. A MOSFET power switch in the supply line of the motor.

    Provision has to be made to time the OFF duration before switching direction.
     
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  7. SgtWookie

    Expert

    Jul 17, 2007
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    No, that won't work well at all.
    If you want a relay in a single package, you need a 1 form C x 2 arrangement, such as in this relay:
    http://www.worldproducts.com/pdfs/ep2.pdf
    Mouser stocks relays like that one:
    http://www.mouser.com/ProductDetail/NEC/EP2-3N1S/?qs=sGAEpiMZZMtSzCF3XBhmW7Rmwp1m9ujJ%2bH0Q0/2ZXro=
    That one is wired as an H-bridge. This one is wired as two independent SPDT relays:
    http://www.mouser.com/ProductDetail/NEC/EP2-3N1ST/?qs=sGAEpiMZZMtSzCF3XBhmW04pOILXk9qkZykDmaAXvsQ=
    Either could be used; you would need to make the H-bridge connections external with the 2nd relay, but that is no problem.

    The KS2E-M-DC12 relay you indicated that you wanted to use has a low current rating; 1A @ 125v and 2A @ 28v. The contacts would probably not last very long. The relays I linked to have contacts rated for 30A @ 16V, which is much better for a battery powered application.

    I am not willing to go through the time and effort trying to adapt a DPDT relay to an existing circuit that calls for two individual Form C relays. You would not save any money; the circuit would be unnecessarily complicated and the reliability would suffer. If you tried to simply turn on an internal brake with the power still applied to the motors' windings, the motor would be in a stall condition, and the switch current would be very high.
     
  8. mpcotuong

    Thread Starter Member

    Aug 26, 2010
    170
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    Hi SgtWookie ,

    Your relay is the one I am looking for. I will use your relay instead of mine. Can you please let me know how to connect t it to you exit circuit? After that we can close this case.

    I will check back again for your connect relay to circuit.

    Thanks, so much for your help.

    Kevin
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    For the H-bridge type relay EP2F-B3G1S:
    The motor terminals connect to relay terminals 1 and 8.
    +V connects to relay terminal 4.
    GND connects to relay terminal 5.
    +V also connects to relay terminals 3 and 6.
    One diode connects from relay terminal 2 to relay terminal 3, cathode on terminal 3.
    The other diode connects from relay terminal 7 to relay terminal 6, cathode on terminal 6.
    The two transistors' collectors get connected to relay terminals 2 and 7.

    The relay is designed to be mounted on a circuit board, which you will either need to make yourself, or have made for you.

    The pad layout for the relay is shown on the left side of page 5.
     
  10. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    Thanks so much SgtWookie. I will try it out as your suggestion. We can close this case. if there any question, I will ask you again.


    Kevin
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Threads are not typically closed. If you have more questions on this topic, just reply to this thread.

    It is not a good idea to specifically address a certain member in a thread/topic, as the person being addressed may not see the thread, and others may be discouraged from replying. I am not on the Board nearly as often as in times past; maybe for just a few hours a week now.
     
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  12. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    Hi SgtWookie,

    I have ordered this part EP2-3N1S you recommended. When I connect to wall adapter the motor is working as expect. But once I use 12VDC battery, the motor automatic running for a while and stop. Why battery make the automatic motor run? I have not triggered on 555 yet.

    Please let me know how can I prevent the motor run once I furst turn on battery power?

    I am using the sam circuit on very first page.

    Thanks,
    Kevin
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    So, it works just fine when you are operating it from a wall adapter.

    However, it does not work properly when you connect it to a 12v battery.

    Are you attempting to use that circuit in an automobile or truck? There is a lot of electrical "noise" in automotive environments which can cause false triggering.

    I am not online very often anymore. It may take several days for me to respond.
     
  14. mpcotuong

    Thread Starter Member

    Aug 26, 2010
    170
    0
    Hi SgtWookie,

    I am planning use for moving 12VDC motor same as your circuit. Why the battery make motor run without trigger? How can we prevent this issue?

    Thanks, again

    Kevin
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    What else is attached to the battery besides this circuit?

    And, what kind of battery is it? Is it a lead-acid battery, or something different?
     
  16. mpcotuong

    Thread Starter Member

    Aug 26, 2010
    170
    0
    Hi SgtWookie,

    Yes, it is lead-acid battery for operating power. It ;s only have 556, 12DC motor and NPN. It worked ok with Wall adapter.

    Thanks,
    Kevin
     
  17. SgtWookie

    Expert

    Jul 17, 2007
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    Well, then you have changed something between operating it on the wall adapter, and operating it on the battery. Perhaps the battery is dead? Perhaps the connecting wires are faulty? I don't know.
     
  18. SgtWookie

    Expert

    Jul 17, 2007
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    It may have to do with "switch bounce" when you connect it to the battery, or turn the switch on. When you plugged the power adapter into the wall, it didn't have the switch bounce.

    Once the first cycle is done, it should act normally.
     
  19. mpcotuong

    Thread Starter Member

    Aug 26, 2010
    170
    0
    Hi SgtWookie,

    if that is the case. How we prevent that and fix the issue?

    Thanks,
    Kevin
     
  20. SgtWookie

    Expert

    Jul 17, 2007
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    You might try increasing the size of the 220uF capacitor; something much larger.

    Or, use a semiconductor to switch power to the battery on and off; like a MOSFET.
     
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