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RE: TR2 - converting to negative earth

To: Doug Hamilton <douglasehamilton@shaw.ca>, triumphs@autox.team.net
Subject: RE: TR2 - converting to negative earth
From: Randall Young <ryoung@NAVCOMTECH.COM>
Date: Wed, 27 Mar 2002 09:24:05 -0800
> I'd be very careful with one of these converters they don't
> address the real problem of installing a negative ground radio in
> a positive ground vehicle. And that is your antenna still grounds
> to the body thus creating a dead short between the positive earth
> car chassis and the negative earth radio chassis.

Doug, I'm sorry, but that is simply not correct.  The converters work by
generating +12v relative to your car's ground, which is what the radio
requires to work.  The radio chassis and antenna are both still grounded to
the car, no short exists.

A lot of people seem to find this concept confusing, there's nothing magic
about connecting a "positive ground" to a "negative ground" as long as the
opposite terminals do not touch.  A better way to look at it is that the
car's chassis is zero volts (0V).  A "positive ground" system has the
battery positive terminal connected to ground, hence the other terminal
becomes -12V.  But, there's no reason you can't connect a second battery
with it's negative terminal to ground, which would make it's other terminal
+12V.  And, you'd get 24V between the two battery terminals.  This is
exactly the way the "ground converters" work, they create a "virtual
battery" with it's negative terminal to ground.

It's actually a very common configuration in electronics, your PC (or Mac)
for example most likely has both +5v and -5v voltages (along with a host of
others).

Randall

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