I’m using the DRV8825 (md20a) controller and a #1206 stepper (4.5V/670ma) and am trying to setup an appropriate current limit for it. I have a 12V power supply and will be using the controller in micro-step mode (but I’m unsure exactly which mode I’ll be using at this point).
I understand there are 2 ways to set the current limit: measure specific coil current or use Vref. Here are my questions:
Do both of these methods result in similar results? Is there any benefit to measuring the specific coil current vs. using Vref?
If measuring specific coil current, the stepper needs to be hooked up which may result in the stepper getting too much current (since I have no idea what the pot is set for at this point). Should the pot be moved to a specific position before starting the measurement? When doing this, only 1 of the coils should be connected, correct? Should the A or B outputs be used, or does it not matter? Just so I can keep the motor safe, can you list the specific steps to use to do this measurement without damaging the motor?
Also, when doing a specific current measurement the product page states that this value will be 70% of the full current, so for my motor (#1206) I’d be trying to set the pot to give a current of approx. 470ma (0.7 * 670ma), correct? Should the full rated current value be used or should something a bit smaller be used?
When doing the Vref calculation, should the published stepper current (670ma for the #1206) be used as the current limit value or should that be set somewhat lower? Assuming I should use the published stepper current, the Vref I should set the pot for would be:
Vref = (current / 2) / 0.7 = (.670 / 2) / 0.7 = 0.48V Correct?
When I try to measure Vref with a 12V source, the smallest value I can get with the pot is 0.85V. Obviously doing something wrong … any ideas?
- The current limit calculations outlined on the product page (and several other sections of the provided information) state everything with respect to full-step mode. If intending to use the driver in a micro-step mode, do you have to do anything different when calculating the current limit?
Appreciate any help.