There are special chips for the purpose, inverting dc/dc isolators. They
are expensive; $10 a piece as I recall.

I had a lot of trouble with this whole setup; you need a separate isolator
for each panelmeter [volts, amps] I had a meter for each of several
alternators.

a loose connection on a heavy user [DC air compressor powered by a starter
motor] caused a spike that blew 2 isolators and panel meters. I added more
protection, reverse diodes and clamps; a few months later, again some
distant fault blew a couple of my panelmeters, even though I had bought more
expensive ones this time that were supposed to be internally protected as
well..

I'm not sure that the idea is at all practical in reality, these meters seem
just too delicate for our world.

I'd love to hear from people who have successfully installed a bunch of
panel meters on a boat or similar system. I have a couple set up to read
temperature as well, one for the engine room in general and one for the
house batteries [you need to adjust the charging voltage for battery
temperature].

regards, Mark Holden



"stefanhanoi" wrote in message
oups.com...
Date: Mon,May 2 2005 8:01
From: "Glenn Ashmore"

The power to run the meter has to be isolated from the circuit being
measured.
They need either a battery or an isolated dc/dc converter to power them.

After some search it looks like the typical 200mV digital meter modules
take about 1 to 2 mA.
Even if I use a couple of them, for voltage and some currents (to
trolling motor, other loads), I need max. about 10 mA. For this low
current, a transformer to isolate the DC seems to be overkill.

I am considering to take a simple 555 and insert a capacitor not only
in the output signal line, but also the return (no common 0V anymore)
line. On the "secondary" side would be a simple bridge rectifier, a 9V
Zener diode, and a capacitor to smooth the ripples.

Did anybody try something like that already? Other simple solutions?

TIA,

Stefan