Changing torque and power consumption

By default the dispenser is set to draw 1.0A maximum current when the motor is in operation. However there’s some scenarios where you might want to change that.

If you’re dispensing low viscosity fluids you don’t need a lot of torque, or the opposite could also happen you have a thick paste that requires more force.

The unit has an internal current sense resistor for this purpose so there’s no need for an external amp meter, all you need to do is measure voltages with a multimeter.
First open the dispenser: unscrew the four nuts at the bottom, don’t turn the screws themselves.

Remove the bottom part and then lift the top:

eDispenser disassembly

Now plug the motor, power cable (USB or DC jack) and turn on the dispenser.

Press and hold one of the knobs to actuate the motor, simultaneously with a multimeter measure the voltage across the following test points Vsen:

Multiply this voltage by 20 and you get the total current draw from the USB port.

In the center of the board there’s a trimmer which you’ll need to turn clockwise for more current or ccw for less. Always adjust while probing with your multimeter to make sure you don’t go over 1.8A (this is Vsen=0.09V). The trimmer is very sensitive, make small changes.

Stay within a maximum current draw of 1.8A if your voltage supply is 5V (regardless if it’s powered via the USB port or DC jack). If you change to a bigger motor you might need to power the dispenser with higher voltages (more info here).

The current limit of the motor can be set by measuring Vref (test point located between the  two knobs) and multiplying it by 2. For example  Vref by default is set to around 0.18V for a motor current of 0.36A

If the screen dims a lot it means the voltage is dropping too much, measure USB voltage in these test points and make sure it doesn’t go below 4.5V

To solve this problem use a shorter/thicker USB cable and a more powerful power supply.

Test the dispenser with your fluid to see if you get better results. You want to make sure there’s no missed steps.

Important!

– Do this at your own risk, always make small changes and do not exceed 1.8A as this could damage the USB connector, overheat the motor and internal components.