# H bridge and polarity in a motor

Hi there, I have a question, I'm working on an own robot, just for fun, and I'm using a h bridge, I realized, that is possible to set both poles of the motor positive (HIGH).

So I wonder what happen to the motor if I do this?.

(I will never do, but I have curosity)

If you study the data sheet for your motor driver, you will very likely find that this case is discussed.

You can also set both outputs low.

Often those two cases have different effects (brake versus freewheel).

OldTatita:
I realized, that is possible to set both poles of the motor positive (HIGH).

Do you mean set both Arduino outputs HIGH (which is what @jremington is referring to)?

OR

Do you really mean "connect (say) 12v to both poles of the motor"?

Connecting the same voltage to both poles of a motor means there will be no current flow. For current to flow there must be a voltage difference.

...R

which is what @jremington is referring to

No, I was referring to the outputs of the motor driver.

The result can be different in the case of motor driver outputs both LOW versus motor driver outputs both HIGH.

But the OP forgot to tell us which one of the tens of thousands of motor drivers he/she is using.

jremington:
No, I was referring to the outputs of the motor driver.

The result can be different in the case of motor driver outputs both LOW versus motor driver outputs both HIGH.

Now I am confused.

AFAIK some motor drivers treat two low inputs differently from two high inputs. In one case they use the MOSFETs to cause a short circuit between the motor pins which acts as a brake. In the other case they cause an open circuit which allows the motor to freewheel.

I don't see how the motor would behave differently if the two motor terminals were connected to GND or to Vmot. In both cases the motor would see a short circuit.

However I have not tested this and I am willing to be corrected.

...R

I don't see how the motor would behave differently if the two motor terminals were connected to GND or to Vmot. In both cases the motor would see a short circuit.

The motor leads aren't connected directly to either GND or Vmot. There are always semiconductors of various types in between.

But this discussion will go nowhere until we know what the OP has.

Robin2:
For current to flow there must be a voltage difference.

...R

That is true for a resistor, but definitely not for a motor. Current and voltage can be pretty independent,
voltage depends on speed principally, current on torque.

If you short the motor terminals together you'll find its harder to turn the shaft and current flows
through the terminals - you are using the motor as a generator into a zero ohm load.