Sorry if this is Electrical Engineering pre-school. I'm a software guy that hasn't taken a class involving voltages for 10+ years.

I'm working on an Arduino project that will have to be fairly mobile. I'm using a Nema-17 stepper motor that is rated at 12v 1.2a (link to specs). I'm looking for a suitable battery to power my motor for around an hour. I found a 12v 2000mAh battery (link to battery). This (according to my knowledge) means this battery should be able to power my 1.2a motor for around 1.6 hours.

My question is; will my motor only draw what it needs(assuming I don't short it) or will the battery pump too much power and fry my motor? Any help Would be great!

  • \$\begingroup\$ That is a fairly high amount of power. Steppers generally perform better when low voltage winding motors are used with several times rated supply voltage using a chopping current regulator, to overcome winding inductance which would otherwise severely limit the current (far below rating) as stepping speed increases. \$\endgroup\$ – Chris Stratton Nov 20 '13 at 15:24

As the battery is the right voltage for the motor, the motor should not draw more than its rated current, unless mechanically overloaded.

  • \$\begingroup\$ Thanks. Is there any way I can prevent it from drawing more than its rating? In some situations I may be taking it close to its mechanical limits. \$\endgroup\$ – Bms85smb Nov 8 '13 at 4:38
  • 2
    \$\begingroup\$ There are four things you could do - but three of them do complicate the circuit. In order of simplicity - 0) just depend upon the internal resistance of the battery + motor to limit the current to some level - 1) Put a 2A fuse between the battery and the motor. - 2) Use a resettable polyfuse between the motor and the battery to open the circuit above some current level although tolerances may be tough in your specific scenario. - 3) Add in a series FET to switch off the circuit when driven by a sensor circuit that measures the current across a very low ohm resistor as an overload. \$\endgroup\$ – Michael Karas Nov 8 '13 at 5:26
  • \$\begingroup\$ open cct the stator windings is a bad idea \$\endgroup\$ – JonRB Nov 8 '13 at 10:29

The batteries can handle a high current load for less than a second even a dead short. If the battery is only a 2AH battery nothing will happen other than shorten the life of the battery. This is ok as long as the motor starts turning and current drops to no more than twice the AH rating of the battery, for a lead acid battery, the surge current is higher for other chemistries.


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