By default the dispenser is set to draw 1.0A maximum current when the motor is in operation (or around 0.75A for version 1.2). 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.
Now plug the motor, power cable and turn the dispenser on, go to menu screen #13 “Motor always on” and change the option to YES.
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/DC connector.
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.
Note for dispenser version 1.2 (August ’16 onwards):
-The trimmer has been changed to a multi-turn type.
-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 connector). If you change to a bigger motor you’ll need to power the dispenser with higher voltages, read here for more info.
-The current limit of the motor can be set by measuring Vref and multiplying it by 2. For example a motor rated for 1.2A should have a Vref of 0.6V Vref by default is set to around 0.18V
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. If current was reduced you don’t want any missed steps and if it was increased you don’t want an overheating motor.
When you’re done switch the option “Motor always on” to off and assemble the unit again.
– Do this at your own risk, always make small changes and do not exceed 1.8A this could damage the USB connector, overheat the motor and internal components.
– If total current draw is set to 1A or more, don’t enable the option “Motor always on” for more than a couple of minutes at a time, regularly check the motor temperature and switch off if it gets excessively hot to the touch.