12v question for the gurus

Doryman · Posted: Wed Jun 01, 2011 11:52 pm Post subject: 12v question for the gurus

The 2 Raymarine E-80s on my Tom Cat have been increasingly been refusing to play nice with each other (not recognizing the master/slave relationship, spontaneously rebooting, etc.) The guy who sold them to me (very knowledgeable vendor) told me there were two possibilities that I should investigate as low-hanging fruit:

1. Update the software in both MFDs, and

2. Replace the Raymarine SeaTalk (Ethernet) hub as it has been problematic on several of his installations.

It's #2 that I need help with. I was advised that any good 8-port hub should work. I purchased a D-Link unit that received a great many 5-star reviews. It has an adapter that is marked 5v, 1.2 amps. I can plug the hub into 110v from my inverter but I would prefer to run it off the boat's 12v system and not be dependent on the inverter.

I need to know if it will harm anything if I wire the hub directly to 12v power. My vendor says he routinely wires hubs with 9v adapters into 12v without problems. Is the same true for a 5v device? Is some sort of adapter needed?

I'm trying to avoid going to the vendor and paying for a service call.

Thanks,
Warren

Larry H · Posted: Thu Jun 02, 2011 12:19 am Post subject:

Try a google search on '12 volt to 5 volt adapter'.

I got lots of hits.

jkidd · Posted: Thu Jun 02, 2011 2:30 am Post subject:

You could just build a voltage divider circuit with couple of resistors and connect your power leads across the resistor that measures 5 volts. Or you could use a potentiometer and just adjust it till you get 5 volts. Or you look at other brands that already run off of 12 volts. I don't think you can just hook the 5 volt one up to 12 volts it would just burn up. If it were 9 volts you might get away with it.

potter water · Posted: Thu Jun 02, 2011 10:10 am Post subject: Don't mess about with this

Definitely find a high quality 12 volt to 5 volt converter. There are sooooo many ways to go wrong doing it any other way. You've already said that things are flaky. This would not be the time to Rube Goldberg something together to make the replacement you have in mind work to cure a prior flaky bug. You could easily introduce a new weirdness into the system.

centerisland · Posted: Thu Jun 02, 2011 11:53 am Post subject:

USB voltage is between 4.75 V and 5.25, so any automotive USB adapter should give you the right voltage.

Upon reflection, probably not enough current for your application

Larry H · Posted: Thu Jun 02, 2011 12:36 pm Post subject:

Here is a link to the Serial Gear site. They sell an ethernet hub, and it looks like it has external power. Not much in the way of technical specs shown, but they have a phone number.

Link: http://serialgear.com/USB-PRODUCT-details.cfm?sku=520140&cats=585&catid=%20%2C585%2C%2C672%2C%2C217%2C%2C222%2C%2C225%2C%2C214

Another link for same product: http://www.cablemax.com/520140.html

thataway · Posted: Thu Jun 02, 2011 1:25 pm Post subject:

First try the hub you purchased with its own 110 V to 5 volt adaptor at the dock or on the trailer, to be sure it is working properly.

Then go to Radio Shack and get a 12 volt DC to 5 volt DC adaptor. Pay attention of polarity of the plug--you will also take your hub and adaptor to double check the amount of power necessary -1.2 amps-, polarity, size of plug (both external diameter and internal diameter). Finally wire this into the 12 volt system--again being careful about the 12 volt polarity (center of the cigarette type of plug is positive). I would wire it in, and use the same circuit you use to turn the RayMarine gear on and off with. Since you are replacing a hub, the current draw should be approximately the same, and a fuse size change will probably not be necessary.

One thing I would do before that, however, is to spray some contact cleaner on the cable end fittings, and the current hub. Disconnect and connect several times, then wipe the contacts clean with a soft rag. Then spray a small amount of corrosion block on the terminals. I would also check all of the 12 volt connections. Clean them, spray with corrosion block. It is quite possible that just minor corrosion (you may not see it) on the connectors and a slightly low voltage can cause the entire problem.

centerisland · Posted: Fri Jun 03, 2011 11:07 am Post subject:

This industrial 12v USB hub was just mentioned in a comment on Panbo:
http://www.startech.com/product/ST7200USBM-Mountable-Rugged-Industrial-7-Port-USB-Hub
The comment said that it is: