June 8, 2012
about 2 years ago
Since the motor still magnetically holds position when turned off, I’m guessing PM.
Stepper motors draw a fairly constant current when the coils are energized, regardless of speed. This motor contains two-phases. Each phase is essentially a completely separate electromagnet with 34 ohms of resistance. At 12V, when both coils are energized simultaneously, the motor draws 706mA. When only one is energized, the motor draws 353mA.
Whether one or two phases are energized and how often is based on the drive mode. In two-phase on, full-step mode (probably the most common mode), both phases are always energized regardless of speed, and at 12V, this motor draws 353mA per phase - 706mA in total - constantly. Even when it’s not moving and just in a “holding” state.
Half-step mode uses a bit less current, because half of the time, only one phase is one. So in half-step mode, you can expect this motor to draw 530mA at 12V on average. The current it will draw in a holding state depends on at what stage of the drive mode the motor was held. If you are programming your own logic, you can actually control this - which might help prevent overheating.
Now, it’s possible that some motor drivers will switch off all phases in between steps, regardless of drive mode. I have no idea why they’d do that, and mine certainly doesn’t (it’s just an L293D that I control will a shift register), but I’m just covering my butt here. If your driver does this, then it’s possible for speed to have an effect.
For stepper motors, the speed doesn’t determine the current use, but rather, the drive mode does. The drive mode and speed together determine the torque. In general, more torque is correlated with more current.
I’ve got this motor working very nicely with an L293D quad half-H-bridge, a 600mA 12v supply (I might use a higher current supply, as this takes it to its limit), and an Arduino UNO. I’m running it at 120rpm. It also runs fine at 240rpm, although torque is lower, and if you accelerate the motor to 240rpm, there is at least one resonant frequency at which it will skip steps.
Both full and half stepping work well.
It gets comfortably warm, but not hot, after about 40 minutes of continual use on full-step mode (which has both coils energized all of the time, so uses the max current).
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