Separate Power and Logic Grounds on motor driver

Hey guys

I’m using one of your excellent dual VNH5019 shields in an automotive application - I’ve tapped into some of the sensors which are connected to the ECU so therefore I wanted to ensure my Arduino shared the ECU signal ground, to ensure I’m not getting any offset in my measurements and am seeing the same sensor values as the ECU. I started wiring it up thinking in my head your shield offered the option of powering the Arduino or running off the Arduino logic supply and having a separate power supply for driving the motor(s). Now that I’m looking at it more closely I’m a bit bummed to find the ground needs to be shared - I obviously can’t run 10A or so motor current back through the ECU ground. Is there any way (trace I can cut or anything) to use a separate power ground for the motor drivers? If not do you have any driver boards (doesn’t need to be a shield and I only need a single VNH5019 driver - not making use of the dual) that would support this or is it just physically not possible (I’m only learning)?



I think you are confused about something.

Why would the motor current run back through your ECU ground? Can you post a diagram of how you have everything connected?

- Ben

Hi Ben

Thanks for the reply - I’ll try and draw a quick diagram up tonight, but basically the idea was to tap into the ECU signal ground (between the car’s ECU and sensor grounding point - this ground current flows back through the ECU itself) - this is the best spot to take the Arduino ground from as all sensor values are measured relative to this in the ECU so I can be sure the Arduino is getting as close as possible to the same reading for the same sensors. This is only suitable for low current though as it sinks through the ECU and I don’t want to cause noise and voltage drops on this line as I believe that’s why the car designers have separated the low current sensors to their own ground in the first place. So I don’t want to connect the motor driver shield’s ground to this wire for this reason as that will cause the motor current to flow back through the car’s ECU.

I wanted to connect the driver shield’s ground to the existing ECU’s power ground wiring - the grounds are all connected at the block anyway, but this ground wire will take higher current, does not pass through the ECU itself and noise/voltage drops on this line wont affect the sensor measurement. If I connect the motor driver to this wire, but have the Arduino connected to the ECU signal ground, since the motor shield appears to connect the two grounds together I’m worried I could end up with ground loops/stray ground currents flowing through the Arduino should an offset ever develop between either ground (due to corrosion, wire aging, other currents flowing or whatever)…

That’s my understanding anyway - maybe I’m barking up the wrong tree. If it’s not clear what I’m trying to do, I’ll try and draw a diagram up tonight…

Thanks again


A diagram of how you have everything connected would be helpful.

- Ben

Hi Ben - here you go - this should give the basic idea. Black is existing wiring, the blue is what ideally I’d be adding in…

Ok, I better understand your concern now. Unfortunately, we do not carry any motor drivers or controllers with isolated motor power (though that is a feature we would like to offer on some future controllers). If you wanted to try to implement such isolation yourself, the best place to do it would probably be between your sensor and the Arduino.

- Ben