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I have a 8HS11-0204S stepper motor and need to match a driver to it. HERE it says that the recommended voltage for driving it is 12-24V. But if you open the (feeble) DATASHEET, it says that the rated voltage is 4.8V, which is confirmed by multiplying the operating current with phase resistance. If this is true, then as I understand any driver that requires higher minimum input voltage than 4.8V is unsuitable.

Which value should I look at when choosing a driver? Is looking at the rated voltage enough?

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  • \$\begingroup\$ I would trust the datasheet. But remember, rated voltage is just the voltage used to rate the specification, but not a maximum. \$\endgroup\$ – Eugene Sh. Nov 11 '15 at 16:08
  • \$\begingroup\$ But anyway motors are driven by current, not voltage. A driver should supply as much voltage as needed to achieve the required current. \$\endgroup\$ – Eugene Sh. Nov 11 '15 at 16:16
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    \$\begingroup\$ The first link (HTML) also says " Each phase draws 200 mA at 4.8 V, allowing for a holding torque of 1.6Ncm(2.3oz.in)." So the 4.8V seems to be just for that. \$\endgroup\$ – Fizz Nov 11 '15 at 18:40
  • \$\begingroup\$ Note that both answers below are correct. You need to pay attention to the current. More at geckodrive.com/support/step-motor-basics.html \$\endgroup\$ – Fizz Nov 11 '15 at 18:47
  • \$\begingroup\$ See also en.wikipedia.org/wiki/… \$\endgroup\$ – Fizz Nov 11 '15 at 18:55
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There are 2 approaches to driving a stepper motor.

The simplest is just to connect DC to each winding in turn, via switches (FETs, driver ICs). And in that case, use 4.8V (5V - switch losses) as you confirmed from current and resistance. This is fine at low and medium speeds.

If you need maximum performance, you'll find the motor's inductance attenuates short pulses, so running the motor faster reduces its torque. You can overcome this with a more complex stepper driver, supplying pulses at the recommended 12-24V, to maintain current and torque at higher speeds.

Each pulse is maintained at a high voltage for long enough to build the rated current in the phase, then it should reduce in voltage to the safe level of 4.8V for the remainder of a slow pulse or steady state. This reduction in voltage can either be timed, or achieved by monitoring and limiting the drive current.

So both voltage ratings can be correct : 4.8V continuous, and 12-24V for an optional boost to high speed performance.

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  • \$\begingroup\$ For OP's benefit, the 2nd method is called a "chopper drive[r]", More details at ST or adafruit. \$\endgroup\$ – Fizz Nov 11 '15 at 19:10
  • \$\begingroup\$ I can imagine other ways of implementing it' but a chopper is certainly the usual one. \$\endgroup\$ – user_1818839 Nov 11 '15 at 20:24
  • \$\begingroup\$ Much clearer now! However I have one question. Let's say the page does not provide a recommended voltage range but I know the phase voltage and I want to use a stepper motor at a certain RPM and torque with a chopper driver. How do I know what voltage to connect to my driver? Marko in the other answer proposed a method with inductance, do I simply calculate the minimum voltage for that speed from the coil inductance using the formulas in that page, and if I find the torque is insufficient - increase the voltage more? \$\endgroup\$ – I have no idea what I'm doing Nov 13 '15 at 15:45
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    \$\begingroup\$ Yes I would use the calculator as suggested by Marko. As for increasing voltage, I would watch the real power (I^2*R) dissipated in the motor winding resistance and not exceed the (0.2A) rating. \$\endgroup\$ – user_1818839 Nov 13 '15 at 16:52
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The important data for stepper motor is rated current and voltage factor Kv [volts/krpm]. Now lets assume the motor winding is made of superconductor, this implies that at zero speed and current 0.2A (holding torque) the voltage is 0V. If the speed is 1000rpm and it has data Kv=35V/krpm, you can guess it generates 35V herfore you need more than 35V drviver voltage to feed it with 0.2A.
Now the real world scenario. The winding has 24ohms: at zero speed, current is 0.2A you need to supply 4.8V. When you spin it up to 1000rpms, there is no data about Kv, neither the nominal power power of the motor, the only data is inductance 8mH.
From this approximative calculator: http://www.daycounter.com/Calculators/Stepper-Motor-Calculator.phtml you will get 2200rpms at 24V and power 5W, if you trust this. Good luck.

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  • \$\begingroup\$ I'm really not sure about your answer. The Kv ratings belong to brushless DC motors, often used in RC vehicles. And the unit is not volts/krpm, it's rpm/volt. A 1250 Kv BLDC motor, when supplied with 12V and no load, will spin at 12*1250=15000 rpm. Those motors are three-phase motors and need special drivers called ESCs (electronic speed controllers) to operate. As far as I know, none of this stuff applies to stepper motors. The speed of a stepper depends on how fast the driver is stepping it. You can spin at 50 RPM regardless of the supply voltage. \$\endgroup\$ – Gene Pavlovsky Nov 20 '20 at 12:43
  • \$\begingroup\$ However as the speed goes up (step duration becomes shorter), there is less time available to pump current into the coils. Coils have inductance, which means they resist fast changes in current. Raising the supply voltage allows to pump the current into the coils in shorter time. Once the coil is saturated, the driver "chops" the current to the rated value, so higher voltage doesn't lead to currents above the motor's rating, as would happen with a simple (non-chopper) driver. GeckoDrive has nice articles on stepper basics - geckodrive.com/support.html \$\endgroup\$ – Gene Pavlovsky Nov 20 '20 at 12:48
  • \$\begingroup\$ The calculator you suggested seems reasonable. I wish it would provide rpms, not just revs per second. Although somehow when I plug in my NEMA 34 stepper's data, it tells me max rpm is ~350 at 48V, while the manufacturer's torque curve suggests the motor was successfully tested at up to 900 rpm at 48V. \$\endgroup\$ – Gene Pavlovsky Nov 20 '20 at 12:51
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I suspect the 12 volts references the input voltage to a PWM stepper controller. For such a controller, it's useful to run at a higher voltage than the motor nominal, and current control is used. So, as long as the controller is set to no more than 0.2 amps the motor will be happy.

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