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I need to be able to reverse the direction of a RS-360SH motor

  • The operating voltage is 7.2 volt
  • Current is around 5 A on normal running and
  • around 8 A during stalling.

I tried to use a 2-pole 3-position changeover switch. Is it suitable?

I found that most H-bridges have less current carrying capacity.

What should I do.?

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3 Answers 3

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Two single pole relays can easily be wired to move a motor forward, backward, or stop.

SW1 off SW2 off = stop

SW1 on SW2 off = forward

SW1 off SW on = backward

SW1 on SW2 on = stop

The flyback diode protects against spikes, especially if one is using a microcontroller for switching. In that case, some capacitors across the power source may also be needed.

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ I don't really understand what the diode is doing at all. It should either be across the relay coils directly, or from the motor leads to the power rails (which would require four diodes total). Right now, assuming your power supply has any decent amount of bypass capacitance, it will do exactly nothing at all ever. \$\endgroup\$
    – Connor Wolf
    Aug 9, 2013 at 13:26
  • \$\begingroup\$ @ConnorWolf as the motor leads are flipping polarity you can't put the diode across them. Perhaps redundant in the manner used, it sits across - to + at the closest point to where the relays will drive the motor (regardless of which direction). You're right about the relay coils themselves needing a flyback diode each. I'll try to update the diagram. \$\endgroup\$
    – Ron J.
    Aug 9, 2013 at 19:05
  • \$\begingroup\$ I know you can't put the diodes across the motor leads. That's why I said motor leads to the power rails. You use the diodes to prevent the motor connections from exceeding the power supply rails. \$\endgroup\$
    – Connor Wolf
    Aug 10, 2013 at 2:28
  • \$\begingroup\$ I edited your schematic to show what I mean. Feel free to revert it if you have issues with the changes. \$\endgroup\$
    – Connor Wolf
    Aug 10, 2013 at 2:33
  • \$\begingroup\$ Ah, I see now - good point. \$\endgroup\$
    – Ron J.
    Aug 10, 2013 at 12:01
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You would still use a H-bridge. The difference is that you would have to build one from discrete MOSFETs (including heatsinks) instead of using an IC.

Remember that H-bridges work by channeling power through the motor between pairs of MOSFETs, so you would need to activate MOSFETs on opposite corners to control the direction of rotation.

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  • \$\begingroup\$ how can i activate MOSFETs on opposite corners \$\endgroup\$
    – Cyril Soji
    Aug 9, 2013 at 8:53
  • \$\begingroup\$ Depends completely on what the MOSFETs are. See the datasheet for details. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Aug 9, 2013 at 8:58
  • \$\begingroup\$ Is there a reason why no one mentioned relays? Getting a relay with the required switching/continuous current shouldn't be a problem and its very easy to reverse motor direction using a "Double Pole Double Throw" relay. \$\endgroup\$
    – Rev
    Aug 9, 2013 at 10:07
  • \$\begingroup\$ @Rev1.0 good point, I sketched out a basic 2 relay circuit. \$\endgroup\$
    – Ron J.
    Aug 9, 2013 at 13:15
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You can use two form C relays. Tie the "NC" pole to ground, and the "NO" pole to supply, and tie the "COM" terminal to the motor input, one for each relay. Then pull relay 1 to make it go one way, and pull relay 2 to make it go the other way.

An alternative is to buy a pre-made motor driver with built-in high-current MOSFETs. Pololu.com has some nice ones. Another option is battle-bots style motor controllers, like the RoboClaw or the Sabretooth.

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