Four types of Lead-Acid batteries concern us for vehicular purposes,
automotive starting, low antimony deep-cycle, high antimony
deep-cycle, and gel-cells. I'll go over characteristics of each.
Generally, the storage capacity (ampere-hour rating) of a battery
is a function of the surface area of the plates exposed to the
Automotive Starting Batteries
It has one job only: to start your car. An average car uses more than
300 amps for a few seconds in order to start. The batteries are
constructed with a large number of thin plates of lead sponge. This
provides maximum surface area. The batteries handle only very shallow
cycling, on the order of 1% in normal use. The starting battery will
fail after approx. 100 cycles of 50%. Complete failure at 200 cycles.
The sponge disintegrates with the repeated full charge and discharge
chemical reactions. Lead particles separate from the plates and form
micro-short circuits inside the battery. This highly increases the
self-discharge rate. Maintenence-free batteries have added calcium to
the lead sponges to harden them and reduce water loss. The calcium
also increases the internal resistance, hence slowing self-discharge.
The expected lifetime of a starting battery in true starting use is
3-5 years. In deep-cycle service, expect less than 2 years.
Low Antimony Deep Cycle Batteries
These are run-of-the-mill "marine/RV deep-cycle" batteries. It's a
compromise between a starting battery and a true deep-cycle battery.
They are much closer to starting batteries, however. The plates are
somewhat thicker than starting batteries and have some added antimony.
It is not designed for powering large loads for a long time.
Deep-cycling will damage it, over time. In RV use, with usually no
more than 20% discharge, the battery should last 200-400 cycles. If
cycled 80%, expect a lifetime of less than 200 cycles, or about the
same as the starting battery. The thicker plates and antimony add a
bit of mechanical strength over the standard starting battery. In
float service, the battery will last 5-10 years, much greater than
starting batteries used in float service.
High Antimony Deep Cycle Batteries
This type is designed to be 80% cycled repeatedly for 5-15 years.
There is almost no mechanical similarity between this battery and a
starting battery. They are massive and huge. There are very few true
deep cycle batteries with greater than 6 volts, as they would be too
heavy to move by hand. The grids are over 4 times thicker than a
starting battery's grids. And there is several times the amount of
antimony in the grids. The plates are thick to add lifetime, not
capacity. The plates are not constructed of sponge, but of
scored sheets of lead with up to 16% antimony. The thickness of the
plates combined with the high antimony content lowers the energy
density, so this battery is heavier, larger and much more costly per
kilowatt-hour. The case is also much thicker, and the plates usually
leave a 1-3 inch space at the bottom to allow for accumulation of lead
particles, so that they don't cause micro-shorts. The top of the case
also has more space to allow for expansion of the electrolyte. Plates
can be removed and serviced. As the cell interconnect straps are
exposed, each cell's voltage can be measured individually. This
allows the user to determine when an equalizing charge is necessary.
Some batteries have "wrapped" plates, where perforated plastic is
wrapped around the plates to keep the lead on them longer. Such a
configuration add 25-35% to the lifetime of the battery. Such
batteries are mostly used for electric vehicles, which force a fast
80% or more discharge. They are then recharge much more slowly. A
350 amp-hr 12 volt battery weighs 250 pounds and contains 4.5 gallons
of sulphuric acid. They can be cycled 80% between 1000 and 2000
times. Lifetime should be 5-15 years.
This type is designed for portability. They are small and have a
jellied electrolyte. The case is sealed. The jellied electrolyte
allows the use of this battery in any orientation. They are used
often in aircraft and electronics. They are supposed to be clean and
usuable where acid vapors and spills are unacceptable. They can be
deep-cycled over long periods. They must not be charged or discharged
too rapidly, otherwise it can gas, possibly blowing the sealed case.
They are prone to sulfation if left discharged for a long time. With
proper care, a gel-cell will deliver 1000 cycles over a period of 5
years or more.
Batteries and Temperature
As temperatures are lowered in a battery, ion mobility (the carriers of
charge) and electron reaction rates are reduced. Thus most liquid
batteries cannot produce the same amount of energy at lower
temperatures. If the electrolyte freezes then ionic mobility will be
lowered to the point that the battery is basically useless. This will
probably not happen too often because batteries have awfull thermal
conductivity so they never reach the ambient temperature unless of
course you live in Alaska and leave it parked on a glacier the entire
winter!! The other interesting thing about batteries is that at lower
temperatures there is increased internal resistance. If you leave
something small plugged in (like a radar detector) it will draw current.
This current will flow through this internal resistor creating heat.
This in turn will keep the battery warm. But it will drain some juice
out of your battery.
Heating a battery produces the opposite effect. The battery will yield
more. The only problem is the electrons tend to go crazy and cause the
battery to self destruct. I had the unpleasant experience of having a
battery that was boiling BLOW UP in my house garage. Luckily the hood
was up and I was behind my CJ. There was acid everywhere and my ears
were ringing for about an hour. A boiling battery can produce a
substantial amount of Hydrogen gas. Thus creating a small non-nuclear
H-BOMB capable of burning you, your vehicle, and anything in its path.
Avoid a boiling battery at all costs...........
The battery material was written by Michael Naum, July 93 adn
Daniel I. Applebaum October 94.
Some of the information was obtained from "The Complete Battery Book"
by Richard A. Perez. Copyright 1985. ISBN 0-8306-0757-9.
All of us are concerned about wiring our car properly. So much
so that I'll bet most of you engineer to overkill. What are the
issues you need to be concerned about?
1. Use the smallest reasonable wire size for the required current.
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.
- Wire is expensive and the larger you go, the more expensive it
- 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.
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
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
the chart on the next page. Using the 10 Amp column you'll find
that you can run 10 Amps on 15 feet of 18 AWG with only ½
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.
Is your Alternator big enough for all your electrical equipment?
Each 100 watt lamp is going to draw about 9 amps so six of them
is going to suck up about 55 Amps. The other accessories on your
car - cooling fan, heater fan, ignition, fuel pump, running lights,
etc. - are going to draw roughly another 30-40 Amps - your total
power requirement will reach about 90-100 Amps.
It's impossible to compensate for a small alternator by throwing
in a bigger battery as the battery will just be drained and the
voltage will suffer, affecting your light output and overall performance.
Your best solution is to go to a modern, high output alternator
of at least 100 Amps or more. If you are really worried about
weight, you're better off with a smaller battery. All it really
has to do is start the engine if the alternator is large enough
to carry the rest of the load after the car is running.
|Maximum Current load in AMPS @ 12 Volts DC
|Wire Length in Feet|
|Maximum Current load in AMPS @ 12 Volts DC
|Wire Length in Feet|
|12|| 15|| 20|| 50|| 100|| 200|
Calculate the current load and find the next highest on
the top row. Go down that column until you find the length you
need to run. The wire gauge required is shown in the far left
The maximum lengths are based on a ½ volt drop over the indicated
To be safe, always choose one or two wire sizes larger than you
need for the indicated current carrying capacity and length. For
example: You've calculated a 10 amp load over a length of 15 feet.
The chart shows that 16 AWG is suitable (12A column). Choose 14
AWG to allow an adequate margin for safety.
|Current-Carrying Capability of Some Common Wire Sizes
|Wire Size (AWG)||Continous-Duty Current *|
| 8 || 46 A|
| 10 || 33 A|
| 12 || 23 A|
| 14 || 17 A|
| 16 || 13 A|
| 18 || 10 A|
| 20 || 7.5 A|
| 22 || 5 A|
|* wires or cables in conduits or bundles|
|Resistance of copper wire per 1000 Feet at 25C|
|Gauge ||Diameter || Ohms|
| 20 || 0.032 ||10.35|
| 22 || 0.025 ||16.46|
| 24 || 0.020 ||26.17|
| 26 || 0.016 ||41.62|
| 28 || 0.013 ||66.17|
| 30 || 0.010 ||105.2|
Most of the wiring information in this wiring section was provided
by Ken Beard.
This page covers a ton of electrical information as it pertains to jeeps. I have found that sometimes people have a difficult time understanding electric information in relation to cars. A great resource to help build a solid foundation can be found here. Now home systems aren't quit the same, but it will help build a strong knowledge of electrical systems.
CJ Gauge & Sender Diagnostics
Finding documentation for diagnosing CJ gauge and sending unit problems
is next to impossible. John Foutz pulls together all the required
information and makes it easy.