PMDX134

[san83]

Hello -

I have PMDX134 with 4 Gecko203V, out of which I`m only using 3 of them. I have a 12A power supply. I have one drive that gets 6A and the other two get 5A each. I spoke to Gecko and they said for the power supply, add ampere rating for 3 and then use 4. For example, if I had 4 drives of 4A each - I could do 4A * 3 = 12A, and use it for 4 drives.

Since I`m using 3 drives, I was thinking I can add 6A + 5A and then use another 5A. So 12A for the 3 drives.

Now my question is I have 4 drives on the PMDX, no signal going into the unused drive. Just the ground wire. I do have a resistor for it. Is that okay? Since the drive is not getting any signal it is not pulling any amps. Is that correct?

Or do I have to physically remove the fourth drive?

[Steve Stallings]

For modern stepper drivers like the Geckos, a conservative input current
rating is 2/3 of the motor current rating, i.e. 4 amperes to run a 6 ampere
motor. In many cases 1/2 is adequate.

In your example 6 + 5 + 5 = 16 and 2/3 of 16 is 10.66 amperes. Using a
supply cable of more current is fine, so you 12 ampere supply is OK.

A drive that is installed, but not connected to a motor will draw very little
current. Having a motor connected but no step and direction signals will
result in the driver drawing the same amount of current as if it was running
the motor.

[san83]

@Steve - Very clear answer. Thank you. I will swap the resistors to match 4A for the 6A per phase motor and 3.5A for the 5A per phase motors. I appreciate the clarification.

[san83]

Here is another question. Is there an issue if I supply 6A to the drive connected to the 6A motor and not 2/3 value of it. I`m guessing the max 6A is reached only on full load, and in most situations the full load is never reached? So the 6A is never fully utilized.

[Steve Stallings]

You should select the resistors based on the current that you
want in the motor, not the amount drawn from the power source.

A modern stepper driver behaves a bit like a switching power
supply in that it can consume high voltage at low current and
produce low voltage at high current for the motor. The driver
will regulate the amount of current that actually flows in the
motor regardless of the voltage of the power source.

The 2/3 of motor rated current drawn from the power source is
based on a motor delivering maximum mechanical power. With
a modern driver a 6 ampere motor will never cause the driver
to pull 6 amperes from the power source other than as very
brief pulses. Under most circumstances it will draw substantially
less current from the power source.