Cheapest solution to prevent electrical damage to AIS?

[Franziska]

Hi,

we got a new navigation laptop and I'd like to make sure I am not killing our AIS again.

Our old computer ran of an AC inverter and that worked fine. When I once tried to connect it with a direct inverter (12V DC to 18V) the computer and most equipment connected via USB hub worked fine, but the AIS which had its own connection to the 12V battery got killed when I plugged its USB into the PC.
Guess there was some sort of back current involved.
The PC ran fine and so did the AIS before plugging in the USB of the AIS.

Don't want to repeat that, but would really want to be able to run the new PC from the 12V to 18V direct inverter and connect all equipment.

What's the cheapest solution to make sure I do not fry(?) the AIS again?

Can I use any fuses or other? Or do I need an expensive optical isolator?

Thanks for your help and input,

Franziska

[AedanC]

Does your AIS support a wireless connection?

[CarlF]

I suspect the USB cable. Most are cheap Chinese manufacture that frequently are wired wrong or develop shorts. I'd buy a new name brand USB cable. Most devices aren't hurt by shorts on the USB cable but perhaps the engineer designing your AIS wasn't very good.

Then plug the new USB cable into the computer and use a multimeter to check the pins. The PC should not put out more than 5 volts on USB regardless of the power source. Try this measurement off both your inverter and the 12v direct. Anything over 5V or not the same between power sources indicates a problem with the laptop.

[billknny]

Originally Posted by CarlF

I suspect the USB cable....

No, it was not the USB cable. It was a ground fault, sometimes called a "ground loop" caused when the "grounds" of the two devices are at different potential and a current flows between them. It flows down the ground wire in the USB cable.

This is actually very common and almost unavoidable when powering devices through DC systems where "ground" can vary in potential for lots of reasons. It is not usually an issue until you connect the grounds of two different devices together (like with a USB cable).

These currents can be dangerous. Sometimes the only thing limiting the current flow is the resistance in the USB wire, which can get hot enough to melt and burn.

And you are right. The correct solution is an optical isolator. They start at $50. Or you can set up a wireless connection. Or make the connection through a properly isolated NMEA0183 or a NMEA2K interface.

If you read your AIS manual, I'll bet it tells you, like mine does, that the USB connection is to be used ONLY for configuration and troubleshooting. Not for routine connections to other DC powered devices. Now you know why...

[Paul Elliott]

I suspect that the DC-DC converter was the problem, putting some voltage on the (-) output with respect to your battery ground. Your computer, USB hub, and USB-powered stuff would have been operating with a voltage offset, but if there were no connections to boat ground then all would seem normal. When you connect the AIS power leads to the battery then you create a path for current to flow between the elevated USB ground and battery ground. This could cause all sorts of trouble.

If you can, using the converter, plug a USB cable into the computer, and measure the current between USB shell and battery ground, but first be sure you have a fuse in the circuit. Measure the voltage between these points if you can't measure current, but if the converter output is truly floating the voltmeter could read anything.

If you can't measure the current you might try connecting the converter (-) output to your battery (-) (or to your boat's ground bus if you have a current-measuring shunt in the battery negative connection.) But be sure the +12V into the converter is fused, since if my guess is correct there may be significant fault current.

But this is just a guess.

[Franziska]

Thanks to all of you. Can anyone be so kind to point me either
A) To a suitable, reasonably priced opto isolator for the AIS USB connector

or

B) A means to retrofit Wi-Fi to the USB out of the AIS, if that exists at all?

Thanks for your replies & help.

[transmitterdan]

To avoid ground loops like this power the PC from an isolated power supply. The regular laptop power supplies are isolated from ground. So when you purchase a DC-DC converter you have to be sure it also has the output terminals galvanically isolated from the DC input terminals. The cheap Amazon Dc-DC converters don’t usually have input-output isolation. Because it costs more $ to add the isolation feature. But with a laptop it’s necessary. You could not only burn up the AIS but also the laptop by using the wrong type of DC-DC converter.

Look into a real laptop power supply or a speciality converter that has DC input. They cost more than $100 but have the required isolation and they can be purchased with the correct regulation feature for your laptop.

Lind Electronics make high quality isolated DC-DC converters for many laptops. There are other brands as well.
https://lindelectronics.com/product-...?orderby=price

If you keep using a non-isolated DC-DC converter things will probably keep breaking.

[daga]

I use a Yakker NMEA to WiFi bridge on a Raymarine AIS650. Works just fine. AUD49. YakBitz

[billknny]

Originally Posted by Franziska

Thanks to all of you. Can anyone be so kind to point me either
A) To a suitable, reasonably priced opto isolator for the AIS USB connector

or

B) A means to retrofit Wi-Fi to the USB out of the AIS, if that exists at all?

Thanks for your replies & help.

This product should break your ground loop: Cablemax USB Isolator for about $50

But... I assume that your AIS outputs 0183 or N2K? Those are the better way to connect, although granted more expensive. Actisense makes a bunch of products that can help, depending on your specific configuration.

[verkerkbr]

Originally Posted by Franziska

Thanks to all of you. Can anyone be so kind to point me either
A) To a suitable, reasonably priced opto isolator for the AIS USB connector

or

B) A means to retrofit Wi-Fi to the USB out of the AIS, if that exists at all?

Thanks for your replies & help.

You can use this on from your home country:


https://pcnautic.nl/nl/usb-accessoir...-to-usb-detail


There is also a magnetic usb isolator, also works well cost around € 10,-.


Regards from Zeeland,


Bram

[Franziska]

Hey guys you are awesome. Thank you! Great hints & suggestions. Will look into these. I'm sure there is a solution amongst those. I like especially the magnetic isolator, or opto isolated cable idea from Bram as they are so budget conscious. The AIS NMEA to Wifi add on mentioned looks also great.

[Paul Elliott]

Before you buy new stuff, go ahead and make a few of the measurements that were suggested. That way you at least know what problem you are trying to solve.

[Franziska]

Thanks Paul,

will do the measures too.

:-)