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I'm thinking of using two of these motors with this motor driver. However, one thing concerns me: the stall current of the motor is 3.3A, and the motor driver has a peak current output of 3A.

The motor would be used in a robotics situation involving rapid changes of direction, and potential stalling.

Could this cause an issue, and do I need to get a lower power motor / better driver, or will it still work?

EDIT:

What will happen if I DO exceed that thing's current rating, given that it has temperature protection? Will it blow the microcontroller, the motor chip, or the motors?

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2 Answers

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You should not use that driver if you think you'll be pulling that much current. For one, it's rated for 3A for a maximum of 10ms per the datasheet and you'll certainly try to draw for longer than 10ms in a stalled condition. And that is the maximum rating for the device which the datasheet says is not to be exceeded under any circumstance. It sounds to me like you'll be abusing the poor thing. Find a beefier driver, or if you're feeling really adventurous, parallel two of them. Is that a good idea? I've never done it, never heard of it being done, and wouldn't do it myself, but you could certainly try :)

I would just find another motor driver on pololu's site. It looks like there's plenty of them. Make sure their maximum CONTINUOUS current is greater than your stall current.

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sometimes putting semiconductors in parallel works, sometimes it doesn't. the source-drain resistance of a mosfet goes up as the device gets hot; you can parallel mosfets b/c if one mosfet in a the group starts taking too much current, it gets hot, and the resulting resistance rise pushes the load to the other mosfets. BJT's respond opposite to that, and if one gets hot, it just hogs the current until it burns out, then the next one pops, etc. – JustJeff Oct 15 '10 at 22:04
Where are you getting the 10ms from? It says "t w = 10ms Single Pulse", which seems rather cryptic to me... – Eric Nov 23 '10 at 20:03
@AngryEE Your last sentence about the continuous rated current being bigger than the stall current would certainly make things work. At the same time, that may be an over-spec. On a related note, if the motor is stalled for a long time, and it's allowed to pull the stall current for a long time, then the motor can burn out. – Nick Alexeev Mar 15 at 2:13
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first things first. what load does your motor have to move? at what speeds?

knowing the above two pieces of information is most important in being able to correctly work out the rest problem. The load will tell you peak torque, which is directly proportional to current, and later will tell you two things. The first is power output, which is equal to torque by speed (with a bit of a constant), and the second is inertia (with a bit of modelling of your actual load)

Inertia can be a bit of a gotcha is these situations. If you think that the motor has enough torque and power handle the load, you may find you have problems in trying to "control" the load. With more inertia on the load, it will take the motor sometime to ramp up, and the load will continue to drive the motor, on the other hand, having too much inertia in the motors rotor will mean the motor responds slower than needed for the given load. Ideally these need to be matched by circa 10:1 in the motors favour. dont forget that inertia scales by the square of the gearbox ratio!

back to your problem, if you are not interested in precise control, consider, but do not worry about the inertia issues.

What you do need to answer is the questions about your load, speed and gearbox being used.

With the extra information, it will be possible to answer your question about matching the amplifier to the motor!

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