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| Stepper motor question. Low voltage, high current vs low current, high voltage |
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| Gibson486:
I have a question about stepper motors. Some manufacturers give you the option to use a high voltage, lower current stepper. This is at the expense of a higher inductor. Is it best to keep everything at a low voltage so we make the inductor smaller? The way I see it, the bigger the inductor, the more time it will take for energy to build up and drain. This means the higher voltage cannot run as fast as a lower voltage one. Is this correct? is there any other reason to not use higher voltage steppers? |
| Benta:
Makes no difference at all. The lower inductance just means you have a lower driving voltage and need to reach a higher current. Same time constant. Even the lower resistance cancels out due to the higher current demand. The relationship between voltage, current and inductance is linear, only copper fill factor can make a small difference. |
| langwadt:
--- Quote from: Benta on January 22, 2019, 05:09:42 pm ---Makes no difference at all. The lower inductance just means you have a lower driving voltage and need to reach a higher current. Same time constant. Even the lower resistance cancels out due to the higher current demand. The relationship between voltage, current and inductance is linear, only copper fill factor can make a small difference. --- End quote --- inductance is turns squared, field is turn*current i.e. a stepper that can be wired in series or parallel, parallel will have 1/4 the inductance and resistance and only need 2x the current |
| Gibson486:
So, in essence, that means the voltage rating on a stepper is kind of useless. It is only applicable for L/R Drivers or any other drivers you cannot adjust the current. |
| T3sl4co1l:
The voltage rating is continuous, only. Typically you'll have a quite high supply voltage, to achieve reasonable torque at high RPM. A stepper motor driver/controller acts as a crude VFD, delivering only the voltage necessary to change current from positive to negative (at whatever the current limit is set to). Because the windings have considerable inductance, this voltage is approximately proportional to frequency. If you don't need fast operation, you can run from a supply of the rated voltage. Torque drops off at a frequency around DCR / (2*pi*L), or (freq * 60 / (steps per rev)) RPM. Otherwise, to maintain torque, voltage must rise ~proportionally above this point. Tim |
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