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After connecting the usb lead on a GME AIS transponder to the raspberry Pi3 I noticed the lights would light up on the AIS as soon as i put power onto the Pi.
This will damage the AIS unit if left like that.

GME sugested i buy a isolation unit for the usb port.
They also advised that blowing up USB ports is commin when powering up a laptop with mains adaptor connected.

Anyway, I was wondering if anyone has one of these AIS units and has cut the 5volt line comming out of the Pi to fix thier own problem.
"This will damage the AIS unit if left like that" - What's the evidence for that unequivocal statement?

In providing a USB intended to be connected to, for instance, a PC, then I am sure GME were aware that the device it was being connected to was going to provide a 5V supply. It is part of the USB standard(s).

My AIS also has a USB connection and that is used by the AIS so that it can be configured at home without being provided with 12v that is required to deliver the full functionality of the device. You couldn't do that without the unit getting a 5V supply from the USB connection.

I don't know what model you have but, for instance, the manual for the GME T120 says a similar thing. You connect the AIS to your PC/laptop and use the software provided by GME to configure it. It is working as GME designed it. They are relying on the supply from the PC to provide sufficient power to do that configuration. If you placed an isolator in there then there's no way the AIS could get the power. Once configured then you could argue that the 5V from the PC/Laptop/Pi is no longer required and yes you could put in an isolator but why? If GME have done their design correctly then there is no risk, especially from a puny Raspberry Pi.

As for laptops blowing up USB ports, I'm not sure I'd set much store by GME's "wisdom"
(2016-09-06, 04:44 PM)baltika_no_9 Wrote: [ -> ]"This will damage the AIS unit if left like that" - What's the evidence for that unequivocal statement?

In providing a USB intended to be connected to, for instance, a PC, then I am sure GME were aware that the device it was being connected to was going to provide a 5V supply. It is part of the USB standard(s).

My AIS also has a USB connection and that is used by the AIS so that it can be configured at home without being provided with 12v that is required to deliver the full functionality of the device. You couldn't do that without the unit getting a 5V supply from the USB connection.

I don't know what model you have but, for instance, the manual for the GME T120 says a similar thing. You connect the AIS to your PC/laptop and use the software provided by GME to configure it. It is working as GME designed it. They are relying on the supply from the PC to provide sufficient power to do that configuration. If you placed an isolator in there then there's no way the AIS could get the power. Once configured then you could argue that the 5V from the PC/Laptop/Pi is no longer required and yes you could put in an isolator but why? If GME have done their design correctly then there is no risk, especially from a puny Raspberry Pi.

As for laptops blowing up USB ports, I'm not sure I'd set much store by GME's "wisdom"
Hi,
To be brief, I am an electronic Engineer. When i was looking at making my own instruments, the first thing i looked as was the communication hardware. Whilst there is a lot of talk of serial, RS422, RS232 and NMEA0183, this wording is only partly correct. NMEA is actually serial data sent via an opto isolator to stop ground loops. The D+ is the feed for the anode on the opto, and the D-  is the cathode
Whilst we can use other hardware, they only survive because of viltage and current limiting protection circuits.
Asfor the GME AIST120 (2016 model) thereis a USB port with the AIST configured as a downstream module. By plugging in your laptop, you can configure the device. 12 vilt power is required to operate the tranciever. The tranceiver is transmitting a radio signal which requires much more voltage and current than a usb port can supply.
Because there is minimal protection on USB ports,  when a laptop is plugged in and is being charged at the same time, you can get voltage differentials and ground loops via the usb port.. After some initial testing, i notice the 5volt rails were tied together and only TXout, RXin and ground, and no specifications asto what voltage the serial port put out, i needed to know more before hooking up my expensive chart plotter. I spoke to GME techical support, advised of my situation and what information i needed. As this was above the tier 1 support guys, they patched me through to the next level. We spoke about power railts tied, RS422 and opto isolation and what the internal electronics could do. The USB port was discussed and that my findings were correct. GME confirmed that damage to the USB driver chips can and does occur when hooked to laptops and other devices when a galvanic USB isolator is not used. They will replace the unit ine time only under warranty, provided you porchase an isolator from someone. The preferred method for getting data from the AISTis via their serial ports. The serial ports only out our AIS data. The usb port adds GPS minimal data.
Feel free to contact GME support to have my findings confirmed, and ask the question about blowing up usb ports when a laptop that is being charged is plugged in. It's not an everyday event but it is a commin fault.
There is my evidence with references to qualified confirmation contacts. Feel free to call them
I think they recommended "actisense' or something like that.q
I will certainly ask the same questions of the manufacturer of the AIS I use that you've put to GME.

Thank you
(2016-09-07, 08:43 AM)baltika_no_9 Wrote: [ -> ]I will certainly ask the same questions of the manufacturer of the AIS I use that you've put to GME.

Thank you

 1300 463 463  make sure you talk to the AIS specialist I have the AIST120. 
Let us know how you went. I last spoke to them about a week ago.
Cheers.
I use a Digital Yacht AIT2000 so will get in touch with them. In fact on just browsing the support documentation on their site they do indeed sell a (rather expensive) cable to provide exactly the isolation you refer to.

Thanks