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G8MNY > TECH 19.10.26 17:04l 172 Lines 8282 Bytes #4 (0) @ WW
BID : 8472_GB7CIP
Subj: 2nd Car Battery for /M & /P
Path: JH4XSY<N3HYM<CX2SA<ED1ZAC<GB7CIP
Sent: 261019/0756Z @:GB7CIP.#32.GBR.EURO #:8472 [Caterham Surrey GBR] $:8472_GB
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Apr 08)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here are 4 options to consider when adding a 2nd battery for /M or /P work etc.
N.B. steering diodes for charging is not usable due to the voltage losses,
unless you use 15V alternators!
1/ NON SWITCHED SYSTEM
300A start wire (e.g. 60A mains tails)
ﾉﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｻ
Start ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｶ
Relay ｳ50A wire ﾌﾍﾍﾍﾍﾍﾍｻ Fuses
ｺ ｳ ign ign Fuse 50A ｺ ﾇﾄoﾄoﾄﾄ> Rig
ｺ ｳ ﾚﾄﾄﾄﾄﾄﾄﾄ0ﾄﾄﾄﾄo\ﾄﾄﾄﾄoﾄoﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｶ ﾇﾄoﾄoﾄﾄ> PAs
Starter Alternator lamp sw Box Wire ﾄﾄﾐﾄﾄ ﾄﾄﾐﾄﾄ
ｳ ｳ ｰｰｰ ｰｰｰ 2nd Start
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｻ Start ｺ ｺ Battery
Engine Earth _ｺ_ Battery _ｺ_ _ｺ_ 30AH
Earth Strap //// 30AH //// ////
Chassis Earths
There is a problem when joining batteries, as the start battery voltage drops
to 10V or less on starting, any paralleled battery and wiring must be capable
of the start currents, if left connected during starting. Indeed there is some
merit in just going for a cheap identical start battery as a 2nd battery...
Advantages:-
a) Easy to replace/swap start battery as they age
b) Doubles discharge capacity
c) Aids starting, so both batteries can be run flatter and they will start OK
d) Shared starting current gives much longer battery life
e) Simple no switching
f) Second start type battery more easily charged from alternator than a deep
cycle one.
Disadvantages:-
g) Leaving a small load on the system will eventually exhaust both batteries!
h) Thick paralleling unfused lead needed
i) Battery failure detection a problem
2/ CHARGING SWITCHED SYSTEM
300A start wire
ﾉﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｻ charge
Start ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｶ 30A relay
Relay ｳ50A wire ign ign ﾇﾄoﾄoﾄﾄo\ﾄｿ Fuses
ｺ ｳ lamp sw Fuse 50A ｺ Fuse ﾃﾄoﾄoﾄﾄ> Rig
ｺ ｳ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄ0ﾄﾄﾄﾄo\ﾄﾄﾄﾄoﾄoﾄﾄﾄﾄﾄﾄﾄﾄﾄｶ ﾃﾄoﾄoﾄﾄ> PAs
Starter Alternator ﾚﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄｿ Box Wire ﾄﾄﾐﾄﾄ ﾄﾄﾁﾄﾄ
ｳ ｳ ｳcharge relayｳ ｰｰｰ ｰｰｰ Aux
ﾀﾄﾄﾄﾄﾄﾄﾁﾄﾄﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｻ ﾀﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾙ Start ｺ ｳ Battery
Engine Earth _ｺ_ _ｳ_ Battery _ｺ_ _ｳ_ 110AH
Earth Strap //// //// 30AH //// ////
Chassis Earths
This system needs a method to operate the charge relay only when the battery is
being charged. Using the above circuit the alternator function needs to be
checked to see if relay affects the exciting action (it should not).
Advantages:-
a) No high starting currents over charging lead
b) Thinner paralleling charging lead
c) Paralleling lead can be fused
d) Large Deep Cycle Aux battery shown here
e) Relay only operated once per engine start cycle
Disadvantages:-
f/ Electronic Control box may be needed if the relay upsets Alternator
g/ No starting aid, but jumper starting possible if leads are thick enough
h/ Deep cycle Aux battery will be difficult to charge up with long thin lead
and may need proper long refreshing charges to maintain fully charge.
3/ VOLTAGE SWITCHED SYSTEM
300A start wire
ﾉﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｻ voltage
Start ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｶ 30A relay
Relay ｳ50A wire ﾇﾄo-oﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄo\ﾄｿ Fuses
ｺ ｳ ign ign Fuse 50A ｺ Fuse ｳ ﾃﾄoﾄoﾄﾄ> Rig
ｺ ｳ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄ0ﾄﾄﾄﾄo\ﾄﾄﾄﾄo-oﾄﾄﾄﾄﾄﾄﾄﾄﾄｶ ﾚﾄﾄﾄﾁﾄﾄﾄｿ ﾃﾄoﾄoﾄﾄ> PAs
Starter Alternator lamp sw Box Wire ﾄﾄﾐﾄﾄ ｳVoltageｳ ﾄﾄﾁﾄﾄ
ｳ ｳ ｰｰｰ ｳ Relay ｳ ｰｰｰ Aux
ﾀﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｻ Start ｺ ﾀﾄﾄﾄﾂﾄﾄﾄﾙ ｳ Battery
Engine Earth _ｺ_ Battery _ｺ_ _ｳ_ _ｳ_ 100AH
Earth Strap //// 30AH //// //// ////
Chassis Earths
The relay here has an electronic voltage detector that operates it when the 1st
battery is @ 13V and also releases it below 13V! e.g. there must be no
hysteresis.
Advantages:-
a) Very simple to connect
b) No high starting currents over charging lead
c) Thinner paralleling charging lead can be fused
d) Deep Cycle Aux battery
Disadvantages:-
e) Electronic Control box is needed to drive relay, with special attention to
the problem of relay oscillation when the Aux battery is connected.
f) No starting aid, but jumper starting possible if leads thick enough.
g) Deep cycle Aux battery can be difficult to charge up on long thin lead and
may need proper long refreshing charges to maintain full charge.
h) Relay prone to pitting as it will often be switching current.
4/ IGNITION SWITCHED SYSTEM
300A start wire (e.g. 60A mains tails)
ﾉﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｻ Ign on
Start ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｶ Relay
Relay ｳ50A wire ﾌﾍﾍﾍo\ﾍｻ Fuses
ｺ ｳ ign ign Fuse 50A ｺ ﾇﾄo-oﾄﾄ> Rig
ｺ ｳ ﾚﾄﾄﾄﾄﾄﾄﾄ0ﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄo\ﾄﾄﾄﾄo-oﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｶ ﾇﾄo-oﾄﾄ> PAs
Starter Alternator lamp ﾚﾄﾄﾁﾄﾄｿ sw Box Wire ﾄﾄﾐﾄﾄ ﾄﾄﾐﾄﾄ
ｳ ｳ ｳrelayｳ ｰｰｰ ｰｰｰ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｻ ﾀﾄﾄﾂﾄﾄﾙ Start ｺ ｺ Aux
Engine Earth _ｺ_ _ｳ_ Bat _ｺ_ _ｺ_ Bat
Earth Strap //// //// 30AH //// //// 110AH
Chassis Earths
This system has some of the advantages of the above ones:-
Advantages:-
a) Aids starting, so both batteries can be run flatter and still start.
b) Shared starting gives longer start battery life.
c) Fairly simple high current contactor switching.
d) Second battery slightly easier to charge from alternator (less lead loss)
e) Large capacity deep cycle aux battery can still aid starting OK.
Disadvantages:-
f) Thick paralleling unfused lead.
g) High current contactor type relay needed (200A peak rated)
h) Start battery failure detection a slight problem.
REFRESH CHARGING
With the switched battery systems if the vehicle is not used a lot, and if the
second battery is a deep cycle type, then occasional charging with a regulated
mains charger for at least 24 hours is recommended to keep the batteries tip
top. Check acid specific gravity with a battery hydrometer to see condition of
the batteries.
SAFETY
a) Make sure the battery polarity is correct!
b) Disconnect battery earth first to make +ve connections, as this is safer if
using spanners in confined areas where they are liable to short out.
Reprogram car radio e.g. make sure U have security Numbers before you start!
The same goes for some type of engine management systems, read handbook.
c) For your garage, put a sign by the car battery that there is a 2nd battery!
d) Use short runs of suitable gauge wire, remember @ 12V volts are easily lost.
e) Protect wire though bulkheads from chafing damage with suitable grommets.
f) Use suitable fuses. (no nails/ally foil).
g) Make sure 2nd battery fastenings are secure (e.g. in case of accident).
h) Be aware of explosive hydrogen build up on batteries, always "BLOW AWAY"
gases before risk of sparks from connecting leads & crock clips etc!
i) Acid makes holes in clothes, wash any splashes immediately. In eyes wash
immediately and seek medical help.
j) 12V Electrical fires are best stopped with a pair of cutters!
k) Molten copper is HOT and stays hot. Use water on red hot leads.
l) Use RCDs protected mains on outdoor leads for charging/soldering etc.
m) Take extra precaution if gas soldering leads/connectors on/near vehicles!
o) If you are wiring -ve directly to battery then fusing the -ve to rig
protects against faulty battery earth straps!
Why Don't U send an Interesting bul?
73 De John, G8MNY @ GB7CIP
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