USB connections

Ground loop

When a GOcontroll controller is connected to a laptop via USB, a ground loop can occur if both devices are simultaneously powered from different mains sources. This situation typically appears when:

• The controller is supplied from an AC-powered test supply (Or electric vehicle that is being charged) and
• The connected laptop is charging via its AC adapter

Because both devices reference earth or protective ground differently, the USB cable can unintentionally provide a secondary ground path. This may lead to:

• Leakage currents flowing over the USB shield or ground pin
• Disturbance of the USB communication
• Unwanted resets or brownouts
• Potential damage to USB interface hardware (Laptop or controller) in extreme cases

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To avoid ground loop related issues:

1. Avoid charging the laptop while it is connected to the controller over USB.
   Use battery mode whenever possible during development or diagnostics.
2. Ensure only one device is earth-referenced at a time.
   If the controller is powered from a floating supply (e.g., vehicle battery), avoid connecting a laptop that is earth-grounded.
3. Use galvanically isolated USB interfaces if a grounded laptop must remain powered.

You can find a by GOcontroll verified USB isolator here.

Pre-mating ground connection

The M12 USB connector on GOcontroll controllers does not contain a pre-mating ground pin. This means the ground connection is established at the same moment as the data and power contacts.
Without a pre-mating ground, connecting the USB cable while either device is already powered may lead to unwanted current flow or ground-loop effects.

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To avoid damage or communication disturbances:

1. Always connect the M12 USB connector to the controller first and fully tighten it.
2. Only then plug the USB cable into the laptop or PC.
3. When disconnecting, reverse the sequence: unplug from the laptop first, then remove the M12 connector.