Issue powering two stepper motors and two drivers

[drdelos]

Hello,

I'm trying to run two Nema 14 stepper motors with two A4988 motor drivers (one for each motor) using a Teensy 3.5 (Frtizing only had a 3.1 model). Both motors (VMOT on the drivers) are powered by a 6V (2.2A) power supply boosted to 8.5V. The Teensy is powered from a laptop USB. MS2 pins are pulled high with a Teensy 3V pin to enable 1/4 stepping.

While one stepper motor runs okay with one driver connected from VDD on the driver to 3.3V on the Teensy, when I try to add the second driver's VDD to any 3.3V pin on the Teensy, the power cuts out (the booster connected to the 6V cuts out) and the steppers behave erratically. I've tuned both drivers according to Pololu's current limiting instructions.

This is a (hopefully accurate) Fritzing diagram of the setup:

I've tried a bunch of different combinations because I clearly don't understand what's happening.

Can anyone tell me why this is happening? Thank you.

[Paul_KD7HB]

@drdelos

the power cuts out (the booster connected to the 6V cuts out)

Perhaps a data sheet for the "booster" has a clue to the problem.

[groundFungus]

Monitor the motor supply voltage with your DMM to indure that the motor supply stays above 8V.

[jremington]

If the motors are set to the rated maximum of 0.5 Amperes/winding, each motor consumes 8.5 W (17 W total), so the motor power supply is completely inadequate.

A 20 to 30 W motor power supply should be adequate for both of them. I suggest to use a 12V, 2A motor power supply at minimum.

[drdelos]

Thanks @jremington, that is very helpful. I just tried the 12V supply and I’m in business!

[MicroBahner]

I think 12V is the absolute minimum for the A4988 and these motors. More ( e.g. 24V ) is better. The motors have a coil resistance of 17 ohms, which means 8.5V at the rated current. The A4988 needs a significantly higher voltage than the coil voltage to do its job.