[VAC] 12 volt 101

[Jim Bounds <jimbounds@xxxxxxxxxxxxxx>]

I deal with pretty complicated 12 volt systems every day working on GMC 
motorhomes so if you want to talk about 12 volt then lets have some fun.  I 
also rewired ambulances for a while so there aren't many wire wads I'm 
afraid of!

The 63 Tradewind I am working on right now has  pretty simple 12 volt and 
110 AC systems.  The 12 volt system uses a "common ground" circuit.  The 12 
volt negative ground power supply (batter and a 4 amp (Daytron brand) 
charger supplies power through one circuit breaker.  The "hot" or positive 
side of the circuit runs a single wire to each 12 volt accessory.  They are 
connected in parallel which means all the hot wires are connected together 
electrically and the "ground" or negative lead to each  fixture is 
connected to the aluminum of the trailer.  That hook up tells us it is a 
common ground circuit.  Some circuits may supply a ground wire to the 
fixture but still may be connected to ground somewhere else which still 
makes it a common ground system.

There is nothing wrong with a common ground system, actually you will have 
less chance of problems due to corroded cremps and wires using a common 
ground system.  You will also use less wire (1/2 as much) if you are 
looking to rewire your system.   There are sometimes problems connecting 
electronic 12 volt devices due to differential ground potential.  This 
situation can cause a "hum" or some other form of static from the battery 
charger or power converter.

The trailer I'm working with is wired with good hi temp jacketed wire so 
unless you know of a shorted wire issue, I would not go through the hassle 
of replacing the wiring and reuse the original wires.

I am going to install a fuse panel and connect the original circuits to it 
for added protection, the original circuit was lacking in this area.  I 
will fuse each new circuit I run through a separate fuse on the new fuse 
panel.  I will be using "ATC" fuses, those are the colored plug in fuses 
you see in newer cars.  They are easier to see if they are blown and have a 
more reliable contact.  I am going to try and separate some of the original 
circuit, they have them all connected together, it is a better idea to have 
different circuits separated so its easier to trace problems and you have 
the option of installing larger or smaller fuses as each circuit requires 
to protect everything better.

I am also going to take out the battery charger and install a new true 
power converter.  A battery charger is a "dirty" sawtooth voltage while a 
power converter supplies a "clean" stable DC voltage.  This clean voltage 
is much better for the battery and eliminate the "buzz" you get in 12 volt 
electronic devices such as radios, etc.  A 30 amp dual level charge unit 
will work great in this application.  If you look to do more dry camping, 
you may want to consider a 40 or 45 amp converter for a faster charge on 
deep cycle batteries.

Batteries, the original location in the Tradewind I'm working with does not 
hold a very large battery.  I can't see how I would have a fun time dry 
camping with that size battery.  I'm going to install a deep cycle marine 
style group 7 battery to be sure I've got juice.  If you do this, you will 
have to get rid of the old 4 amp charger, it will not be adequate for 
charging a marine battery.  The battery must also be in a sealed and vented 
box to keep acid fumes outside the trailer.  I'll do this by using a marine 
battery box and vent it into the original battery compartment.  The 
original compartment will be used for adapters, extension cables or other 
electrical related accessories.

Hope this helps someone, if you want to hear any more about the electrical 
circuits I like to use, let me know.

Jim Bounds