[VAC] Re: Why Car & Trailer Battery to Univolt?

["Weimers" <mweimer@xxxxxxxx>]

Right now, I'm using the diode system.   A couple of months ago I wrote
about my ammeter not working in my Airstream because I didn't have a shunt
in the line. I had mentioned that my old Chrysler tow car has an ammeter
that works on the shunt also. After considering what was written here, I'm
wondering if the diode on my dual battery set-up is what might have goofed
up my shunt type ammeter in the Chrysler. It quit working years ago
...probably about the time I put the diode in.

The Chrysler has two batteries. One, the accessory battery, is hooked to the
trailer line and the car electrical system. The other, the engine start
battery, is hooked ONLY to the starter motor. The diode is right next to the
alternator. The main (common) wire from the diode goes directly to the
alternator. One of the anode posts of the diode is hooked to the wire that
originally came off the alternator, and the other is hooked directly to the
engine start battery (through a circuit breaker).

I have had trouble with the car on occasion when the accessory battery was
severely discharged while the engine start battery was fully charged. There
seemed to me to be some kind of strange back flow through the electronic
ignition  (probably through the ballast resistor) that caused my ignition to
NOT fire (no spark). Once the batteries equalized, the spark was back and
the car started.   That's just a theory, however!

Maybe this relay you are talking about might create a better isolator.
What if I put a relay between the two batteries so that they are hooked in
parallel while the car is running (and charging). When the car is shut off
then, the relay would open and the engine start battery would be isolated
from the trailer line. The accessory battery WOULD be connected to the
trailer line.

I hope I'm making this understandable:  there would be a cable (heavy gauge)
between the two positive posts on the two batteries. The relay would be in
the cable between the batteries.  The trailer line is hooked to the
accessory batteries positive terminal and the engine's starter is hooked to
the engine start battery's positive terminal.

Does this sound like a good arrangement?

I can see an advantage in this. With the relay, while the engine is
cranking, the two batteries should be in parallel giving me more cranking
amp/hours.  In the diode system, the starter is running off the engine start
battery only.

Actually I'm considering all this because I am hooking up a two battery
system in my other tow car and am wondering if I want to buy another diode
system.

I had a relay to try, but when I tried it (by leaving it on for several
minutes) it became rather warm. I'm afraid it wasn't continuous duty. Do you
know specifically a relay that IS continuous duty?

MARC WEIMER
Punxsutawney, PA  -  Home of the Groundhog
#15767
1963 Globe Trotter
1971 Globe Trotter
http://users.penn.com/~mweimer