Ground loops - using one isolator and usb hub with two odrives

Hi,

I want to use two odrives with one power supply, controlled by one PC, with the PC connected via a usb isolator and a usb hub (see pic). Will this protect against ground loops?

Thanks,

Luke

Yes, you should be ok. There is still a possible ground loop between the two ODrives via the USB hub, but this is a much smaller loop - just make sure that your power cables are both low resistance and low inductance. Keep the positive and negative wires close together or twisted to minimise inductance, and wire them as a bus, rather than a star.
If you get USB comms issues, I would recommend CAN. e.g. with one of these isolated USB-to-CAN adapters: https://www.amazon.co.uk/USB-Converter-Module-Raspberry-Zero/dp/B07Q812QK8
I’d also recommend using ferrite rings on your motor wires.

Ok, thanks for that. Can I check that I’ve understood what you mean by a bus (vs a star)?:

2 Likes

Hi Luke,
I have used ODrives in a very similar topography as you and have now fixed all communications problems

I spent a LOT of time trying to fix what I thought were ground errors and random but frequent USB communications errors. I solved these issues by adding ferrite rings to the motor controller phase cables. seem to have solved my problems. After introducing the ferrite rings I have been able remove the three USB isolators from my project.

See this link for my solution:

USB comms going down with 48V power supply

Good luck and let us know how you go with this fix.

Cheers, Tim.

2 Likes

Hi,

I can confirm I’m having no issues using two odrives with my original scheme as per my first post. The power input cables are laid out in a bus pattern.

-Luke

1 Like

Hello!

Im thinking this might help me with my connection issues but Im still not sure how to wire the odrives in a BUS pattern. Does it mean connecting the negative from the first odrive to the second and the negative from the second back to the power supply?

Thanks very much!

TBH, I think the main reason that this problem was solved, was because of the use of ferrite rings on the motor outputs. Definitely use ferrites.

But as for your question “what does a bus pattern mean?” I mean:
Connect + on the PSU to + on the first ODrive. Connect + on the first ODrive to + on the second. ...
Connect - on the PSU to - on the first ODrive. Connect - on the first ODrive to - on the second. ...

Electrically, this is identical to wiring all of them separately to the PSU. But it reduces the resistance & inductance (slightly) between each ODrive.

1 Like

Im already using ferrite rings that match the ones in the odrive store, I have braided the motor wires and looped them around the rings 3 times. The connection problems are less frequent but not fully gone. Because of the layout of my build I have my power supply about 2ft away of three odrives that are layed out side by side, this will reduce my wiring by quite alot!

Thanks very much for taking the time to answer!

1 Like