# Arduino Controllable Digital Pot for Motor Controller

I have an analog motor controller that has a B10K potentiometer on it. I'd like to be able to swap out the analog potentiometer for a digital one, but I'm not exactly sure what voltage is being sent to the original potentiometer as I don't have the spec sheets for it.

My current specifications, which work as a prototype, are:

- Power supply: 48V 4A transformer, connected to...
- Variable speed DC PWM Motor Controller which controls...
- A 130V 1A max DC motor.


I'm fine with the power and speed that 48V gives me, but do I need to specifically look for a digital potentiometer that can handle high voltages, or would a standard 10K digital pot work?

• It all depends on how the pot is connected in the circuit. If it has an external voltage input option chances are it might work, but in general replacing mechanical pots with digital pots is often not practical. Not only does the voltage across the pot have to be lower than the limits of the digital pot (higher voltage ones are more expensive) but the voltage on all three pot connections must be within the power supply rails of the digital pot, or bad things will happen. – Spehro Pefhany Jun 21 '17 at 18:21
• @SpehroPefhany Might you have any recommendations for an alternative solution for this? I'm not cemented to using this motor controller, it was just a proof of concept. Any better suggestions are more than welcome! – clamport Jun 21 '17 at 18:23

## 2 Answers

simulate this circuit – Schematic created using CircuitLab

Figure 1. Analog input on motor controller.

Many industrial motor controllers are designed to work from a 0 - 10 V signal. To provide flexibility they usually provide a reference voltage - typically 10 V - so that a pot can be used if an analog control signal is not available. If this is the case on your controller then you may be in luck.

• With a multimeter check to see if the potentiometer low-speed end is connected to the controller common. If so ...
• Check the voltage between Node1 and common.
• Check the control voltage between the wiper and common.

These measurements should give you enough information to decipher how the analog input works. If all is good you can control directly from an amplified analog signal with no need for a digital pot.

It is doubtful that the pot has 48 volts across it. But since you have one of the controllers, you should be able to measure the voltage across it and the voltage on each side of it to ground. This will help you with possibly finding a digital pot that will do the job.