# Vref measure A4988 (How to measure)

Hi, I want to regulate the maximum current using the Vref metod but I don’t known how measure that, where I have to connect the wires of the multimeter to measure that? I put positive wire of multimetre in Vref, but where I put the another wire (-)? And to measure that I have the motor connected or I have the motor disconnected?
I have 3 steppers motors with 5.1V and 1A and I have connected them 12V throw ATX. I want to use this formula:
ITripMax = Vref / (8 * 0.05) = 2.5 * Vref
Vref = ITripMax / 2.5
1/ 2.5 = 0.4 V.
And another cuestion: the resistance of sense resistor is 0.05 omh in all cases?
Thanks

Hi.

To measure Vref you should connect the positive lead to Vref and the negative lead to ground. You do not need the motor hooked up to make this measurement.

Also, please note that 1 A is pushing the driver to the limit of what it can handle without external cooling, so you might consider lowering the limit slightly or adding a heatsink.

Lastly, the sense resistors on this board are always 0.05 ohms.

-Claire