[SOLVED] Replace linear pot for digital pot

[zip]

Hi all,

I would like to control two 48V DC motors (500W) from electric scooter with my Arduino.

I've bought two pwm controllers from ebay and they work excellent. Issue is that controllers have pot on them (10k linear) and I need to replace that with digital one so I can drive it from Arduino.

I've bought MCP41010 (10k digital) and connected it via SPI, it all works great for one motor. Problems arise when I want to control two motors and connect both digital pots to Arduino. It doesn't work, precisly it burns pots

Pwm controllers are DC6-90V and pot on them is (5V, 0-5V, 0).

Setup is following:

Arduino is powering and controlling over SPI MCP41010. Motors are connected to PWM controller and controller pot terminals are connected to MCP41010. Controller is powered with batteries (48V).

Schematic:



If I connect only one POT and motor controller all works fine, if I connect two, they burn out ?


Could using parallel connection for powering both controllers be problem?

Controller pictures:

 

[FvM]

I can just guess that the common battery of both motor controllers causes voltage differences that superimpose to the digital potentiometer SPI interfaces. The ultimate solution would be an isolated SPI interface for one or both digital potentiometers.

A minimal length, large cross section ground connection between both motor controllers might also help. I'm assuming so far that the control interface are ground referred which must be checked of course.

 

[zip]

FvM excellent remark, it seems that ground loop is cause of problem and possible solution would be to do digital isolation of pot circuit.

Thanks for helping out.