I think I understand this and what power supply i need to purchase, but would like someone to look over my idea.
- NEMA17 SY42STH33-1504A stepper motor rated for 2.8V 1.5A (datasheet)
- Chinese a4988 driver (R100 sense resistors)
- 12V 30A Power Supply
- Arduino Mega
Measurements (when driver is powered but not stepping):
- PSU output: 12V 70mA
- Single Motor coil: 3V 120mA
- VRef: 0.4V
So my power supply is outputting 0.84W and my motor is drawing 0.72W. Which is I guess expected, since some energy is lost to heat. If I'm only drawing 70mA from the PSU for a single motor, if i want to use 6 motors on a single PSU, the total current draw would be 420mA, right? I could potentially just use a 12V 1A PSU? This seems very low powered to me, but maybe it's correct.
Another question is, if my VRef is set to 0.4V (which equals 500mA that can be supplied to the motor [0.4V / (8 * 0.1A)]), then why am i not seeing the full 500mA on the motor when it isn't stepping? I'm only seeing about half of that (120mA * 2 coils = 240mA).
My last question is, I'm using my 5V and GND pins to supply power to the a4988 VDD power pin. My multimeter can only read 10mA or greater, and my multimeter isn't picking up anything. I guess this makes sense since the a4988 datasheet says the logic power draws 5-8mA. The Mega datasheet says a single pin can support 20mA (and other places i've read up to 40mA). Can i safely power 3 driver boards from a single 5V pin (assuming that the max draw is 24mA)?