# Thread: Drive current to low?

1. ## Drive current to low?

I was wondering if possible i have my current set to low. I'm trying to isolate the cause for lost steps on my x travel. it does it at random, and its always a very small amount and in both directions. Always on a straight cut. When I up'ed the feedrate it went away. I ran the machine for 25 mins straight at feedrate and rapid at 100 with a back and forth x travel (no cutting) and it never missed a beat, but the steppers were cold to the touch. Shouldn't they at least be warm?
I have a 48vdc, 25 amp power supply and the max draw with all 3 axis jogging at max is .38 of a amp.
My x and y are rated at 4.8 volt @ 2.53 amps. I'm running them at full winding.
My current set resistor is 10k. Should i give them more juice?
Chuck

2. If my calculations are correct, you need ~26K resistors to get 2.5a. So your getting less than 1/2 the rated torque of the motors. You might also want to look at increasing the voltage, but it's a lot easier to increase the current first. Double check my calculations, though.

3. 48 Volts / 26K = 2.? milliamps

You'll need something like 22 ohms at 150 watts.

4. The formula in the Gecko docs says (47*2.53)/(7-2.53)= kohms. This is the resistor that sets the current on the Gecko, not current limiting resistors.

• Okay, didn't notice he was using Geckos.

• The docs said that if a motor is connected at full winding, the motor's phase current rating is half of its parallel or unipolar rating. I guess the motor label spec's are written at full winding.
My calculations gave me a 11k resister, I went with 10k cuz thats what i had at the time.
Ohm's law says your right so i will stick a 22k in there and see what she can do.
At half the torque it's possible the motor stalled and the result was missing steps.
Thanks again Gerry

• The Gecko white paper (I think the last one on the site) said the calculations were for full windings.

• I ran the numbers also and came up with what ger21 came up with, 26.6K ohms for the resistors.