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### Topic: regulating voltage across arduino pins/ladyada motor shield pins (Read 758 times)previous topic - next topic

#### gatecrasher48

##### Apr 10, 2012, 10:08 pm
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

#1
##### Apr 11, 2012, 12:09 am
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

#2
##### Apr 11, 2012, 12:36 am

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

#3
##### Apr 11, 2012, 01:30 am

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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