[aprssig] APRS In A Car

Dave Baxter dave at emv.co.uk
Tue Jan 24 09:39:09 EST 2006

Did you have a fuse in the Neg feed from the battery?  If you powered
things that way.  If not, there's your problem, probably starting
current passing back to the battery the easiest way, via your kit, not
the battery ground strap.

I just checked another post, and you did make mention of the D700
connected directly to the battery, my guess, without a fuse in the Neg,
or one too big for the job?

Always, take your accessory earths back to a known good ground point,
and preferably in a way that will not suffer huge fault currents if the
battery ground strap fails, and you try to start the engine!

Draw out the starting/charging circuit of your car, and you'll see what
can happen.  Ive seen speedo cables, break cables, throttle cables all
burst into flames when an engine has been started, and something bad has
happened to the engine ground.  (Mechanics don't always do the nut's up
tight!)  If it can "take out" a 1/2" bowden cable in an instant, a radio
and PC is small beer to that sort of fault.

Check all automotive earthing BEFORE you add stuff to your wheels.  And,
either take the Neg feed from the chassis/frame/body ground NOT the
battery, or if you have to use the battery Neg, FUSE it, and make sure
your gadget grounds are man enough to take the fault current, for as
long as is needed for the fust to blow!...  (Made that mistake before!)

Always try to immagine what and where, if a fault should occur, not just
with your radio/TNC/GPC/PC etc, but elsewhere in the car's electrical

Ground straps can and do fail, or go "HR" causing all sorts of odd
electrical problems at best, or a fire as you nearly found, at worst.

Been there had that, I do not want to hear of anyone else having that
experience, it's not nice, and easy to prevent, if you apply the grey
cell before you start hooking up all the gadgets.

Take care..

Dave G0WBX.

> -----Original Message-----
> I pulled over and 
> discovered that the serial cable from the computer was hot to 
> the touch with the insulation at the d700 connection melted 
> and the label on the cable blackended.  I imagine if it was 
> left unattended it would have caught fire.

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