Battery In Trunk/Boot Install With Battery
Disconnect/Cut Off Switch
The Battery is often removed to the rear of a car for a number of reasons, to tidy up or make more room in the engine bay, or to transfer weight to the rear of the car for better traction etc. Often this is a great time to install a battery master switch, either as per racing regulations or to also help stop thief’s making off with your car.
Battery Disconnect Or Cut Off Switches:
There
are basically 3 types of battery disconnect/cut off switches, however wiring
them can cause a few headaches. Often they are incorrectly wired so I will
explain the correct way to install each one. Note: I will only be working on
the switching off of the “Positive +” side, since this is the side that most
racing regulations recognize to correctly install the battery switch. Some
Classic race cars (and heavy road working machines etc) are switched offline
through the “Negative -” cable and this can be done if need be. However another
reason I am supporting the switching of the positive side is that some ignition
spark boxes will short internally if the battery switch is wired to the
negative earth cable.
(For
further tips on Ignition box protection look up my Ignition article Part 5).
Another
thing the following 3 switches have in common apart from switching the + side,
is that the alternator MUST be wired to shut down or go offline correctly when the
battery switch is used otherwise damage to both the alternator and any other
sensitive electrical devices is certain to happen!
The problem that can happen in many
incorrectly wired switches is that once the battery is switched offline, the
alternator will do one of two things, the engine will still continue to run on
as the alternator is now “back feeding” the ignition, or the resulting spike or
surge caused by the battery being removed from the alternator charging circuit
will blow any sensitive electronic systems e.g. alternator diodes, ignition
spark boxes, hi-fi or computers. Sometimes a 12v 100watt
diode can
be placed in the alternators warning light wire, to stop power back feeding to
the ignition, this does not always work however.
Some
of the following circuits have the alternator feed wired directly to the
battery, this means the alternator cable is live when the car is turned off,
hence I recommend a fuse at the battery end
(or both extreme ends of the alternator charge wire) rated 20% higher
than the alternators maximum output.
The
battery, when wired to the alternator, acts like a huge capacitor that smoothes
out voltage spikes or surges. This is another good reason to have the main
battery connections from an aftermarket spark box, wired directly to the
battery and not a starter solenoid or alternator charge wire instead.
The
Painless wiring company sells a 35-amp relay to switch the alternator (35amp
max) off line as well as a special solenoid for the bigger amp alternators.
Jaycar
Electronics also sell a 60-amp and now a bigger 150amp relay that are both a
lot cheaper that the big Painless wiring solenoid, Here is the 35amp wiring
link from Painless wiring:
http://www.painlessperformance.com/Manuals/50103Instruction.pdf
I
am unsure if the Jaycar relays work the same as the above Painless wiring
relay, however they would be worth looking into.
Battery Switch Types:
The 3 main switch types are:
Battery
master switches are made of either plastic, as in the red removable key type,
or metal as in some of the two and four post. In the US the NHRA only allow the
metal or die cast type. Outside of the NHRA some events allow the use of all 3
types plus the switching off of the earth side of the battery. Do consider
mounting the main switch or a second switch near the driver (that can still be
easily reached while strapped in tight seat belts) as well. The battery switch
can also be remotely operated by cable or a rod linkage as well.
Some place the battery switch behind the rear
number plate and then remove the number plate for full access to the switch for
racing, others have an old tail light housing they fit and run a rod through it
to the switch, replacing the tail light with the stock good tail light after a
race meet. In that case, pushing in the rod should shut the car off. The rod
handle or battery switch handle should also be clearly labeled “Push off“ or
“Turn off” near by.
Because I don’t plan on much racing, I have
my battery switch mounted inside the glove box. First I made the inside of the
glove box out of sheet alloy (instead of the factory cardboard), then the glove
box hinge was riveted on instead of using the factory screws so the glove box
lid could be securely locked over the main battery switch.
One
worth while tip if your car has a computer, a clock or an alarm etc, that needs
to stay on, is to run a short wire between the two battery posts on the back of
the battery switch with an inline 5 to 10 amp fuse. With this wired between the
main two bigger battery posts on the switch, enough power is feed to run the
extras mentioned above, if someone else tries starting the car without the main
battery switch turned on the fuse will blow! A small manual circuit breaker
could also be used instead of this fuse. The Fuse or breaker however may just
let enough power through to prevent the engine switching off at a drag meet, so
remove the fuse/breaker while racing.
Two Post:
This type is wired inline of the positive wire, but to completely and safely stop the car the alternator charge wire needs to run to the battery side of the battery switch. The wire could instead also be run right to the positive post on the battery. Do fuse this alternator charge wire as mentioned above; some drivers fuse it at both extreme ends to be 100% safe.
Another
method designed by MAD enterprises, is to mount a Ford starter motor solenoid
at the rear of the car near the battery, with the two post battery switch
cutting the smaller power feed to the front of the car, not the main battery
cable.
Why install a rear solenoid? Well then the
main battery starter cable through the car is “Dead” after start up, a good
safety idea. The alternator feed goes to the battery side of the solenoid as
usual. Because the smaller power wire going forward to the front of the car
from the solenoid is a smaller gauge cable (often 4gauge), it can be easily
fused as well as the alternator feed (2 or 4 gauge, depending on alternator
size) at the battery end of the charge wire.
If
your starter is fitted with the solenoid mounted on it, a small “jumper” is
added to it from its usual solenoid battery cable post to the small (S)
terminal the keyed ignition switch wire went to before (this keyed wire is now
feed back to the rear mounted Ford type solenoid). With later ‘93 on Ford
permanent magnet starters this “jumper” method may cause the starter pinion to
drag, thus instead a Relay should be fitted on the keyed wire to trigger both
starter solenoid functions at the same time, email me if you need further
advice on this: avocalea@clear.net.nz
Two
Post, With Two Small Posts:
This
type is nearly always the metal type of battery switch.
This is often called a four-post switch .The big posts are wired the same as in the two-post switch but with the other two terminals being used for switching the Alternator offline. Now this is one switch I see wired incorrectly all over the internet in private installs. The smaller two posts are not designed to break the main charge wire from the alternator. Rather they are designed to take the alternator off line through the “Field” wire, two different wiring methods are used depending if your alternator is fitted with a internal regulator or has a separate regulator fitted. You see the smaller posts in the battery switch are only designed/rated for 20 amp max, not 100 + amps! (I saw mention of at least one over heating switch in a car forum on the net). Another method is switching the “Sense” wire instead of the field wire.
Some methods use a special solenoid (NOT a
Ford starter type) or the above mentioned Relay at the alternator cable to
switch it offline, Painless wiring sell these items plus some forklifts also
use this type of continuous duty relay, it must be rated high
enough to cover the alternators maximum output. All of this ends up with what I
consider a complex set up, remember the KISS method: (Keep It Simple Stupid) .
Also
some have had the expensive solenoid fail more than once.
Instead wire the switch the same as the two
post install diagram (alternator to the battery side of the master switch) and
use the smaller two terminals to break the feed to the ignition power (never a
coil wire in a electronic ignition as there is often very high voltage present
at the coil, break instead the small keyed red wire going to the MSD type
ignition box). Or outside of NHRA events, run the proven 6-pole Battery switch
covered next.
Two
Post, Four Terminal:
This
is a switch approved by the FIA and used mostly outside the US Drag racing
scene. The reasons being the NHRA don’t allow the use of a plastic key type
switch.
This
battery disconnect switch shares the same common use of the main two big posts
by firstly breaking the main positive cable.
The
lower four spade terminals then work in the following series:
The two spade terminals (W or 1) switch on
any residue currant to earth through a ballast resister.
And
at the same time the power to the ignition is switched off through the other
two spade terminals ( Z or 2 ).
A
very fool proof method, however these switches are more expensive than the
basic two post battery switch.
NOTE:
If you are
running a CDI or “MSD” ignition type box, wire the “small” red 12v keyed power
wire to the spark box, not the boxes “Bigger” red battery wire. Also always
wire the boxes two main battery cables directly to the battery as per the
ignition boxes manufactures instructions.
NOTE: Care should also be taken to mount
the 3 OHM 11 Watt resistor away from other wires as it produces heat as it
releases residue power.
Fusible
Links, Circuit Breakers And Fuses:
First
up, the main reason a lot of cars have fusible links from the factory is
because they are cheap… but they do work!
I
don’t advise installing them when a better MAXI type fuse could be fitted. One
of the main US wiring companies has a series of stills showing a fusible link
doing its thing, it looks like the 4th of July with sparks
everywhere, just what you don’t want near battery or fuel fumes in my opinion.
One reason some like the fusible link is that the fault has to be located and
fixed instead of just resetting a circuit breaker or installing a new or bigger
fuse without looking at why the fault happened in the first place.
Next
are the manual reset able circuit breakers. Because of all the hi-fi companies
for car installations today, these have got more common. They are available in
many amp ratings too (house breakers are NOT suitable even on the main battery
cable). I feel they are fine in the respect that if someone is going though the
work of this rear battery install, they are the type of person (hopefully) who
would look for a fault and correct it if the breaker is triggered anyway. The
main downside to breakers is they do wear out and they can also be triggered by
a hard knock. I can direct anyone interested to a companies test between fuses
and circuit breakers that show fuses clearly out perform circuit breakers. In a
race type car, breakers can be quickly reset thus no time lost finding a fuse
etc, its actually not uncommon for top race car builders to wire a basic race
car with NO fuses or breakers, feeling a fuse etc could cost a race. Early
Shelby race cars were one such car often wired this way.
And
fuses? I prefer the recent MAXI type fuse for heavy amp use, they are very easy
to find and buy, including the fuse holder, and they respond quickly to faults.
They are colour coded and also come in lots of amp ratings; some also have a
small light that goes on when the fuse blows.
For
smaller applications the ATO type fuse is fine, there are also manual reset
able circuit breakers that fit in like a fuse to both Maxi and ATO type fuse
holders as well.
MEGA fuses can also be used but they are not
always as easy to find in shops and cost more, do buy the correct fuse holder
that fully encloses the fuse whatever type you go with.
Note: For any original Mklll Zephyr and
Zodiac car with the owner keeping the battery in the original position, I feel
a short length of heavy 4gauge wire with a Maxi fuse in line at the Mklll
factory engine bay solenoid terminal to the main wiring harness feed, is a very
worthwhile mod (you can buy an enclosed plastic MAXI fuse holder that only
needs a terminal post fitting at either end of the cut loop of the wire that’s
already fitted to the fuse holder).
Battery
Install:
Normal
lead batteries were once said better to be placed with their inside plates
going lengthwise with the centre line of the car, thus under very hard
acceleration the plates couldn’t touch each other. However with most better
batteries, including those Gel filled, this is rarely a problem. I advise
mounting the Battery as securely as possible and to still allow easy access and
use of the boot/trunk. The rear mounted solenoid (if fitted) and a
non-conductive material should also cover the back of any battery switch.
Battery
boxes can be of the plastic marine type, however those of you in the US need a NHRA certed box with a
sealed lid (The NHRA sets these standards for the US tracks, I feel they are
good standards wherever you are). The box should be vented through at least a ½
“ hose to the outside (through the floor) of the car, this stands for even a
sealed battery according to the NHRA.
Some mount the Solenoid and/or Circuit
breaker to the battery box to keep things tidy. The box could also be made of
alloy or stainless plate, however I would then advise lining it and its lid
with a non-conductive material.
I
also recommend an alloy or steel sheet metal firewall be fitted to the area
behind the rear seat (don’t forget the speaker shelf above it) and use RTV
sealant to seal the sheets edges to the inner guard area etc. This 100% stops
fumes or acid leakage coming through in a bad smash. This however is your choice.
The Battery box should be firmly bolted down with grade 8 fasteners with thick large washers both in the box and under the trunk/boot floor. Make sure the bolt heads cannot wear into the bottom of the battery. Tie down the battery inside the box as well (no factory type “J” bolts as they open up). Remember batteries make for a heavy missile if they detach from their mountings in a collision.
Battery
cables:
I
recommend Marine or Welding cable, the thickest you can afford. Normal car
battery cable does not lead itself to bending through the many contours of a
car while welding cable is much more user friendly. Some buy extra long
“Jumper” cables and use them after cutting the ends off. Never use the fancy
fluro type coloured type stereo cables in the cars main wiring as the vinyl
covering is not as abrasive or heat resistant as normal battery cable, a lot of
this type of cable is of very poor quality.
I recommend crimping the terminal ends on
battery cables or using the screw type that tighten fully around the cable. Do
use heat sink as well to seal the cable ends. I am more in favour of running
the cable within the cars interior, encased inside the proper flexible plastic
conduit (then its fully away from any road damage and garage jacks that can cut
underneath mounted battery cables). I then secure the cable every 300mm with
plastic clamps, rubber lined Adel clamps are great here too. I run my cables up
the side of the transmission tunnel however the area near the door sill is also
fine.
Do
use thick rubber grommets when a cable runs through sheet metal and run cables
away from moving, hot or chafing areas.
I
fully recommend running a dedicated earth cable right up to an engine or
starter motor mounting bolt with another cable then going from the engine to
the chassis/body. Braided flat type earth cables are best here.
Earth leads running from one cylinder head to the other cylinder head (V8) to the chassis are also recommended by ignition companies as is an earth from the alternator housing and distributor housing to a good common earth fixing, these can be of 4 gauge cable.
The
above earthing methods will correct a lot of hot start, ignition and charging
problems.
Also
to add a couple of notes, sitting a battery on a concrete floor will NOT
discharge it! Often it’s a layer of dust over the top of the battery that may
do this. One of the best chargers for cars that sit for months at a time is the
12v Battery Fighter, both the 750ma model and the bigger 1.25 model are perfect
for our cars and do not damage the battery overtime like trickle chargers.
Jaycar electronics, Supercheap and many other part stores carry these well
priced battery chargers.
Any
questions or comments contact me at: avocalea@clear.net.nz
Disclaimer:
The advice and guidelines given in these articles are given in good faith.
The owners and managers of the Galeforce Zephyr site will take no
responsibility for any injuries or loss sustained while carrying out the
described tasks and procedures or any consequences arising. Please read
the Safety First
Article