Actisense NDC-4 USB - "ground loop"

[cliveshelton]

I am planning a winter upgrade.

The manual for this useful device warns about a ground loop hazard (a new term to me) between the battery and USB power supplies. Apparently "for installs where the NDC-4 must still operate when the PC is switched off, full PC isolation can be maintained by using Port 0 (OPTO IN 0 and ISO OUT 0) as the PC connection". I am not confident that I can ignore the warning.

I intend to use the multiplexer to connect a SH GX2150 to a Raymarine C80 chartplotter and hopefully repeating all NMEA data to a PC through the USB lead and possibly serving this wirelessly in the future to a handheld device (iPad etc.) There will be times when I don't want to use the PC which hopefully can be used also to upload routes and waypoints to the chartplotter. My Raymarine system has heading, speed, depth, wind, autohelm, radar)

If I disconnect the NDC USB lead but then connect a USB-RS232 lead (I have a one already) to Port 0 (presumably not powered) would this solve the ground loop problem? Will I maintain the functionality needed?

Any advice welcomed from those "in the know" here. Many thanks.

 

[cliveshelton]

Bump! No pressure! I've got all autumn and winter. But I know someone knows the answer. I should be more patient I suppose. Trouble is, once I'm off the front page I'll be out of sight.

 

[VicMallows]

The manual for this useful device warns about a ground loop hazard (a new term to me) between the battery and USB power supplies. .

In this context they seem to be implying that a DC potential difference could exist which might then affect the signal levels. In any well designed system/equipment this should not happen. Their solution seems to recommend incorporating an optical isolator.

Ground-loops can indeed be a problem in certain specific circumstances, but very unlikely in the situation you describe.

I would not worry until/unless a problem exists.

 

[mickbond]

It might be something to do with using a 12v converter to power the Pc. This will probably have a dc to dc switched mode converter in it without any connection between the 0v of the input and the output.Not a problem as nmea should be opto isolated to the floating usb port. If however you have a 12v powered usb hub connected to the PC after the nmea interface a ground loop can exist undermining the isolation
On my boat I use a pc powered hub to overcome this issue. This might not be your issue at all just trying to help or prompt other opinions

 

[wizard]

I had this unit attached to a laptop with Raymarine gear, had absolutely no problems in 3 years of use with and without the power supply attached, mains or inverter.

The unit is fully opto-isolated on all inputs and outputs so should not be a problem.

To put your mind at rest why not phone them and describe your setup and get the experts advice.