Last
month I squeezed two Black Panther BP1000?s into my TJ, and installed
a 175A Wrangler NW alternator into the stock location. While these are
all very nice to have, the new components won?t be able to fully
perform without the correct size and type of wiring.
First, you must decide how you want the batteries
to operate together. They can be hooked up in parallel or with a battery
management system. I decided, due to my shrinking engine compartment and
dash area, that a simple parallel hookup would suit my needs.
Parallel
hookup means you connect the positive terminal of battery 1 to the
positive terminal of battery 2, and also connect the negative terminals
of the two batteries together. This type of setup basically allows the
rest of the electrical system to see the batteries as a single,
higher-amp battery. The voltage output of the batteries remains the
same, but the Amp-hour (Ah) rating is doubled. Essentially, my dual
batteries look like a single, 1300 CCA battery to the vehicle. This
allows the Jeep to draw from the full potential of both batteries
whenever necessary. The downside to this type of setup is that if you
run accessories with your engine off for extended periods of time, the
batteries may completely drain, leaving you stranded. The Black Panthers
can run over three hours at high draw before losing their charge.
Battery managers provide a relay and switching
system that usually connects a single battery to the electrical system,
and allows you to jump start with the second battery, or connect them
together when more amps are needed (such as winching).
NOTE: Never hook batteries up in an automotive
electrical system in series. Series wiring doubles the voltage output
(24V) but retains the Ah rating. You will damage your car?s electrical
system!
When
I ordered my alternator, I also ordered the parallel hookup battery
cables. These were custom made to length by Wrangler NW. They are 2
gauge cables, terminated with rings and fully weather sealed with
weather-resistant heat shrink. The two cables also came labeled POS and
NEG, even thought the flexible jackets were bright red and dark black.
After buying four 3/8" side post studs to
install on the Black Panther battery terminals, I began to connect the
batteries. The end result looks like an octopus (or 3) but is organized
with correct size and length wiring.
Wrangler NW also sent a new 2 gauge charging
cable. This is the cable that goes from your battery to the alternator
(in the Jeep TJ?s case, it goes to the main fuse block and then to the
alternator). Because the alternator can put out 175 amps, the small
stock charging wire has to be replaced, or you will risk damaging the
alternator, batteries, or wiring. Wrangler NW also recommends a
similar-size wire from the negative alternator terminal directly to a
battery negative post.
The stock ground wires to the engine block, frame
or body, and starter can be retained. As well, the stock positive wiring
to the starter and fuse block can be retained. Also visible in the
battery octopus are :
Winch leads + and ?
Painless Wiring Auxiliary Fuse Block +
Painless Wiring Auxiliary Lighting Relay + (2)
So what wiring should you use when upgrading
batteries and/or alternator? With primary circuit components like these,
you should be safe running 2 gauge wire between them. Of course, using 2
gauge wiring for every accessory you install is not practical. Here are
some guidelines:
1. Use the smallest reasonable wire size for the
required current.
- Wire is expensive and the larger you go, the
more expensive it is.
- Wire is heavy and the larger you go, the
heavier it gets.
- Mechanically, smaller wire is easier to route,
easier to protect, easier to fit connectors on and therefore, more
reliable mechanically - up to a pratical limit - see below.
2. Use a large enough wire so there is no voltage
drop. We want whatever it is we are wiring to operate at top efficiency.
3. Maintain an adequate safety margin. We don't
want to melt any wires.
The first thing you have to do is determine the
current you have to carry. For DC circuits, that's relatively easy. Some
equipment on a car is rated directly in current draw. Auxiliary fans,
fuel pumps and things like that are rated in current draw - Amps. Some
equipment is rated in Watts - mostly the lighting equipment. The power
requirement in Watts will be printed right on the bulb or stamped in the
base. To come up with amps use one of the formulas shown.
Current in Amps = Watts/Volts
Current in Amps = Volts/Resistance (Ohms)
Current in Amps = Square Root of (Watts/Ohms)
Watts = Amps x Volts
Volts = Watts/Amps
In an automotive electrical system, these formulas
are easier since a constant of 12V is always present.
Let's calculate for a typical 100 watt driving
light - the power required is 100 Watts and the voltage is 12 Volts - so
the current requirement is 100 Watts/12 Volts = 8.33 Amps.
Let's assume you have to run a wire 6 feet from a
relay to the lamp and look at this chart.
Using the 10 ft. length column you'll find that
you can run 15 Amps on 10 feet of 18 AWG with only ? Volt drop. Go to
the next size larger for safety margin and you're at 16 AWG.
Now in reality, you have to balance the
mathematical results with mechanical reliability and efficiency. For
lighting, the rated output is figured at 13.5 volts, not 12 volts. With
the 0.5 volt drop shown in the chart, you have 13.0 volts available at
the lamp - and at that 95% rated voltage, you are only going to get 80%
of the rated output - or the equivalent of 80 watts from a 100 watt
lamp.
In our example, I'd go to 14 AWG as the wire and
connectors are physically stronger, easier to work with, and there's no
voltage drop - plus I only buy three sizes - 14, 12 and 10 AWG. Those
three and crimp-on connectors are readily available just about anywhere.
And except for primary circuits, those three sizes will cover just about
anything you want to wire in a car with an adequate safety margin.
