Ext. Power Supply and Motor Shield

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ktorimaru
 
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Joined: Mon Sep 12, 2011 5:09 pm

Ext. Power Supply and Motor Shield

Post by ktorimaru »

Hi

I'm an electronics newbie so this question maybe obvious to most but here goes.
I've bought two stepper motors from you, the specs read:
"12V rated voltage (you can drive it at a lower voltage, but the torque will drop) at 350mA max current"

To run both and maximise torque what are the specs for the ideal power supply and why?

I'm guessing 14V because of the 2 volt drop I just read about but I'm very vague on how the amps figure into the equation.

Thanks ahead!

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adafruit_support_bill
 
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Re: Ext. Power Supply and Motor Shield

Post by adafruit_support_bill »

The voltage drop is more like 1.2v but 0.8v over voltage is not going to kill anything. (It will give you slightly more torque at ~75 more current draw and slightly lower motor lifetime.)

Steppers are pretty much 'constant current' devices in that they draw the same current at all loads and all speeds, even standing still. That makes them somewhat less efficient, but it sure makes the math easy. :D

Each motor will typically have 2 phases (coils) energized at a time. At 350 mA each, that is 700mA per motor or 1.4A for two motors. Adding another 7% for the over-voltage gives you pretty close to 14v @1.5A.

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ktorimaru
 
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Re: Ext. Power Supply and Motor Shield

Post by ktorimaru »

Thanks!

Any source suggestions?

Also, just to clarify, I want something that puts out 1.5A and no more.
If I'm only using one motor 1.25A or do I not understand how amps work?

I'm trying to understand so I don't need to ask every time I get a new motor.

Thanks again!

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adafruit_support_bill
 
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Re: Ext. Power Supply and Motor Shield

Post by adafruit_support_bill »

I want something that puts out 1.5A and no more.
More is generally not a problem. The motor(s) will attempt to pull what they want to pull from your supply and no more.
If I'm only using one motor 1.25A or do I not understand how amps work?
Amps are additive. At 12.8v, you will need ~750mA for one motor or ~1.5A for two.

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