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14181 Views 2 Replies Latest reply: Jun 20, 2012 9:25 AM by MikeWeed RSS
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Jun 18, 2012 11:04 PM

Newbie needs help with simple electric boat joystick control/power

I'm building a simple electric boat out of a salvaged jet ski hull and an old trolling motor with directional control.


The plan is to have a joystick controller for simple on and off (ie no speed control) operation AND reversing of current for reverse and steering.


The kicker is that I was unable to find a joystick that could handle the 35 or so AMPs that would be pouring through it.


I understand that I need a relay. So, I did some chatting with the Digi-Key folks and they sold me these two parts, however, I think the relay needs to be a dual pole.


Anyhow, even if I had the correct parts I don't know how to wire up a relay. Below are the URLs of the two parts I bought.


Attached is my rough sketch of how this will layout - ie two DC motors each needing forward and reverse.


I am a complete newbie. Any help or direction is appreciated.


Thank you in advance I'll look for your response.





  • MikeWeed Apprentice 57 posts since
    Oct 21, 2011
    Currently Being Moderated
    Jun 19, 2012 1:10 PM (in response to lake15)
    try this

    You need a double-pole double-throw relay to reverse a DC electric motor.

    You will also need a SPST (or SPDT) relay to turn the motor on or off.

    Be sure the relay contacts are rated for the motor amperage. The attached

    drawing shows how to hook it up. The diodes are necessary so that the

    reversing relay is not turned on in forward mode.

    • MikeWeed Apprentice 57 posts since
      Oct 21, 2011
      Currently Being Moderated
      Jun 20, 2012 9:25 AM (in response to MikeWeed)
      second thoughts

      It might be hard to find a DPDT relay with the contact ratings you need, but

      you can accomplish the same end using 8 SPST relays like the one you

      already have. Each joystick switch turns on 2 relays that connect the

      battery + and battery - to the motor leads. You should connect

      reverse-biased diodes across each set of relay coils to suppress the voltage

      spike that would otherwise occur when the relays are de-energized.

      The motors will also produce spikes unless you connect a reverse-biased

      diode from each motor lead to the battery + and another reverse-biased

      diode from each motor lead to the battery -. Diagram attached.


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