Geared or Non-Geared stepper motors for focuser ?

[brown_rb]

Hi

I believe users make a common mistake. They look at current and they say ok, I will select this stepper that has 1.6A current and use that on a drv8825 chip, because this stepper is cheaper and the drv8825 should handle that amount of current.

What is forgotten or neglected to mention is that when a stepper actually steps, there are steps when BOTH coils are active at once, so the current drain can be 2x the stepper current. So instead of  a possible 1.6A max, it is actually 3.2A max.

When using a PG27 rated at 0.4A, this would mean a maximum of 0.8A of current when both coils are active. This means that even with both coils active, the heat generated is still "warm" to the touch, the drv8825 is not overstressed, and everything can operate within tolerance.

Regards

Robert