Read some of the other answers, some of them are not easy to read (I'm not a specialist), some others do not fit my application.

A pretty simple system

  • two brushed motors, each takes between 12V to 20V
  • each consumes 5A at 12V
  • both are driven by the same "smart" controller

However, the load (attached to the motors) may have at times (especially when a motor power gets down) a reverse move that induces a reverse current back to the controller. This disturbs the behavior of the system, and I'd live to prevent such a reverse current to flow back to the controller.

My idea is to serial branch (after checking polarity) a diode between one of the two motor legs and the controller (for each motor).


  • the power (voltage) drop should be as minimum as possible
  • the two diodes should bear the 12-20V (5A) as described above

What kind of diode would you advise for such system?

  • 2
    \$\begingroup\$ I the controller is a smart motor controller, that can control the current in the event of stall, then it should not be driving two motors in parallel, one per motor please. If it is a dumb power supply that provides a fixed voltage, then any kind of diode is OK, big silicon rectifier diodes are fine, cheap, easy to get in sufficient current and voltage ratings. Your voltage is low enough that power schottkies are also feasible, which would lose slightly less power. \$\endgroup\$
    – Neil_UK
    Jan 18, 2016 at 6:54
  • 1
    \$\begingroup\$ ...and what do you mean by a reverse move?. If it's reverse torque with the same rotation direction, so developing the same motor voltage polarity, that's OK. If it's the motor being reduced to a standstill then driven backwards, the terminals will be drawing a large curretn and collapsing the supply voltage, a diode will not help at all here. \$\endgroup\$
    – Neil_UK
    Jan 18, 2016 at 7:19
  • \$\begingroup\$ @user44635 That's a reverse move, meaning the motor turns in the reverse direction (creating a reversed polarity current). \$\endgroup\$
    – Déjà vu
    Jan 18, 2016 at 7:20
  • \$\begingroup\$ torque controls the current in a PM motor, direction controls the terminal voltage (and vice versa). So a diode will not help. Use a different system topology. \$\endgroup\$
    – Neil_UK
    Jan 18, 2016 at 7:21
  • 1
    \$\begingroup\$ You might find, if the motors are PM type, that putting them in series can acheive your system goals better. If you use a diode in parallel with each motor, that will impose a large torque on the load when it tries to turn it backwards, but allow the motors yo have different speeds. Then again, controller per motor will be more controllable. What are you trying to acheive at the system/application level???? \$\endgroup\$
    – Neil_UK
    Jan 18, 2016 at 7:40

1 Answer 1


Schottky diode is probably your best option. They are designed to have a lower forward voltage drop and fast recovery. A quick peek at DigiKey shows that they'll probably cost less than a dollar each.

  • 1
    \$\begingroup\$ The OP says this: "However, the load (attached to the motors) may have at times (especially when a motor power gets down) a reverse move that induces a reverse current back to the controller. " but the trouble here is that reversing the motor mechanically produces a current in the same direction as would normally happen when the power is applied. This is not catered for by a simple diode. \$\endgroup\$
    – Andy aka
    Jan 18, 2016 at 14:11

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