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Topic: regulating voltage across arduino pins/ladyada motor shield pins (Read 617 times) previous topic - next topic

gatecrasher48

Hi all,

I'm running two 12v 0.3A stepper motors off of a ladyada motor shield plugged into an Arduino Uno. The motors are rated at 0.3 amps each, but they're pulling 1.0 amps EACH. I'm worried that my h-bridges will blow, but they've been doing alright so far (about 2 months of testing, on and off). Is there a way to regulate the current going into those pins? Any theories as to why are the motors drawing this much?


Thanks very much all!

MarkT

What are the motors?  What's the winding resistance?  Carrying more than the rated current is not a good idea for stepper motors, they are usually close to the thermal maximum at full rated current.
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gatecrasher48

I'm using this motor, made by adafruit: http://www.adafruit.com/products/168

The winding resistance is 72 W /Ø for our model. One thing I thought of is that the motor is rated at 0.3-0.4 amps per phase, so maybe I should multiply the expected current draw by 2, since the motor has 2 coils to energize (2 phases). Is this a correct thought process?

MarkT


I'm using this motor, made by adafruit: http://www.adafruit.com/products/168

The winding resistance is 72 W /Ø for our model. One thing I thought of is that the motor is rated at 0.3-0.4 amps per phase, so maybe I should multiply the expected current draw by 2, since the motor has 2 coils to energize (2 phases). Is this a correct thought process?


72 what? Ah, I see the datasheet - the problem is there are 4 different motors in that table, unipolar and bipolar, 12V and 5V.  Have you _measured_ the resistance of the windings?

If they genuinely are 72 ohm then the H-bridge is misbehaving, but I think its much more likely you have a 5V 12ohm motor.

Yes if you use full-wave drive then two windings are on at once.
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