2016-06-15, 03:09 AM
(2016-06-14, 08:30 PM)Kraavok Wrote: I tried with ground and without when I was testing originally but good news is I solved it today by switching the positive and negative terminals as suggested in another thread on these forums. Seems maybe that the device is labelled incorrectly. Works fine now, even without ground - would you recommend I ground it still?
If you are using the same power supply for all equipment, then you dont need a ground.
A common problem on boats and indutrial sites is not having a common voltage reference.
For example, 5 volts is only five volts with reference to ground or 0volts. If you have two power supplies isolated by transformers then connect the two communications cables together, you can get what is called a ground loop The potential difference can damage the device at chip level. An RS485 and RS422 driver chip, has a maximum voltage input of 12volts. RS422 standard is 5 volts. D+ sits at 2.5 volts going to five lolts, and D- sits at 2.5 volts going to zero volts. If you have these ground loops, then voltages can get up to 80 volts.
The NMEA standard calls for optically isolated inputs to stop damage from these loops. As i dont have isolated drivers, i just make sure, all my equipment uses one power connection point on the boat. Each item of equipment has its own fuse.
As a side note, the most common cause of damage to AIS devices is the use of the USB cable to a laptop, where the ground of the laptopis not the same as the AIS unit. This where i first found OpenPlotter, as i can use the RS422 output from my AIS transponder and keep all the ground planes at the same voltage. I no longer need my laptop..
Whilst on a boat, we use our house batteries as common power, so long as there isnt much resistance in joints, most of us wont have problems.