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G8MNY > TECH 28.02.04 09:37l 151 Lines 7277 Bytes #999 (0) @ WW
BID : 45577_GB7CIP
Read: DB0FHN GUEST OE7FMI
Subj: 2nd Car Battery for /M & /P
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<ON0AR<IK1ZNW<GB7CRV<GB7CIP
Sent: 040228/0007Z @:GB7CIP.#32.GBR.EU #:45577 [Caterham] $:45577_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Jan 04)
Here are 4 options when adding a 2nd battery for /M or /P work etc..
N.B. diode charging steering is not usable due to the diode voltage losses.
1/ NON SWITCHED SYSTEM
300A start wire (eg 60A mains tails)
ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ»
Start ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄĶ
Relay ³50A wire ÌÍÍÍÍÍÍ» Fuses
º ³ ign ign Fuse 50A º ÇÄoÄoÄÄ> Rig
º ³ ÚÄÄÄÄÄÄÄÄ0ÄÄÄÄo\ÄÄÄÄoÄoÄÄÄÄÄÄÄÄÄĶ ÇÄoÄoÄÄ> PAs
Starter Alternator lamp sw Box Wire ÄÄÐÄÄ ÄÄÐÄÄ
³ ³ °°° °°° 2nd Start
ÀÄÄÄÄÄÄÄÄÄÁÄÄÍÍÍÍÍÍÍÍÍÍ» Start º º Battery
Engine Earth _º_ Battery _º_ _º_ 30AH
Earth Strap //// 30AH //// ////
Chassis Earths
There is the problem of joining batteries. As the start battery voltage drops
to 10V or less on starting. So any paralleled battery & wiring must be capable
of the start currents, if left connected during starting. Indeed there is some
merit in just going for an 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 & they will start OK
d) Shared starting current gives longer battery life
e) Simple no switching
f) Second start type battery easily charged from alternator than a deep cycle
Disadvantages:-
g) Leaving a small load on the system will exhaust both batteries!
h) Thick paralleling unfused lead needed
i) Battery failure detection a problem
2/ CHARGING SWITCHED SYSTEM
300A start wire (eg 60A Mains tails)
ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ» charge
Start ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄĶ 30A relay
Relay ³50A wire ign ign ÇÄoÄoÄÄo\Ä¿ Fuses
º ³ lamp sw Fuse 50A º Fuse ÃÄoÄoÄÄ> Rig
º ³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄ0ÄÄÄÄo\ÄÄÄÄoÄoÄÄÄÄÄÄÄÄĶ ÃÄoÄoÄÄ> PAs
Starter Alternator ÚÄÄÄÄÁÄÄÄÄÄÄÄ¿ Box Wire ÄÄÐÄÄ ÄÄÁÄÄ
³ ³ ³charge relay³ °°° °°° Aux
ÀÄÄÄÄÄÄÄÄÁÄÄÍÍÍÍÍÍÍÍÍÍ» ÀÄÄÄÄÂÄÄÄÄÄÄÄÙ Start º ³ Battery
Engine Earth _º_ _³_ Battery _º_ _³_ 100AH
Earth Strap //// //// 30AH //// ////
Chassis Earths
This system needs a method to operate the charge relay only when the battery is
being charged. Alternator function needs to be checked to see if relay affects
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
g/ No starting aid, but jumper starting possible if leads thick enough
h/ Deep cycle Aux battery will be difficult to charge up with long thin lead
3/ VOLTAGE SWITCHED SYSTEM
300A start wire (eg 60A Mains tails)
ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ» voltage
Start ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄĶ 30A relay
Relay ³50A wire ign ign ÇÄo-oÄÄÄÄÂÄÄÄÄÄo\Ä¿ Fuses
º ³ lamp sw Fuse 50A º Fuse ³ ÃÄoÄoÄÄ> Rig
º ³ ÚÄÄÄÄÄÄÄÄÄÄ0ÄÄÄÄo\ÄÄÄÄo-oÄÄÄÄÄÄÄÄĶ ÚÄÄÄÁÄÄÄ¿ ÃÄoÄoÄÄ> PAs
Starter Alternator Box Wire ÄÄÐÄÄ ³Voltage³ ÄÄÁÄÄ
³ ³ °°° ³ Relay ³ °°° Aux
ÀÄÄÄÄÄÄÄÄÁÄÄÍÍÍÍÍÍÍÍÍÍ» Start º ÀÄÄÄÂÄÄÄÙ ³ Battery
Engine Earth _º_ Battery _º_ _³_ _³_ 100AH
Earth Strap //// 30AH //// //// ////
Chassis Earths
The relay here has an electronic voltage detector that operated it when the 1st
battery is at 13V & also releases it below 13V! eg 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
f) No starting aid, but jumper starting possible if leads thick enough
g) Deep cycle Aux battery can be difficult to charge up
h) Relay prone to pitting as it will be often switching current
4/ IGNITION SWITCHED SYSTEM
300A start wire (eg 60A main tails)
ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ»
Start ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄĶ Relay
Relay ³50A wire ÌÍÍÍo\Í» Fuses
º ³ ign ign Fuse 50A º ÇÄo-oÄÄ> Rig
º ³ ÚÄÄÄÄÄÄÄÄ0ÄÄÄÄÄÄÄÂÄÄÄÄo\ÄÄÄÄo-oÄÄÄÄÄÄÄÄÄĶ ÇÄo-oÄÄ> PAs
Starter Alternator lamp ÚÄÄÁÄÄ¿ sw Box Wire ÄÄÐÄÄ ÄÄÐÄÄ
³ ³ ³relay³ °°° °°°
ÀÄÄÄÄÄÄÄÄÄÁÄÄÍÍÍÍÍÍÍÍÍÍ» ÀÄÄÂÄÄÙ Start º º Aux
Engine Earth _º_ _³_ Bat _º_ _º_ Bat
Earth Strap //// //// 30AH //// //// 100AH
Chassis Earths
This system has some of the advantages of the above ones:-
Advantages:-
a) Aids starting, so both batteries can be run flatter & 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) Battery failure detection a slight problem
REFRESH CHARGING
With the switched battery systems if the vehicle is not used a lot, & 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 to make +ve connections, as this is safer if using
spanners in confined areas where they are liable to short out. Reprogram car
radio eg make sure U have security Numbers before you start!
c) For your garage, put a sign by the car battery that there is a 2nd battery!
d) Use suitable gauge wire
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 (eg in case of accident)
h) Be aware of explosive hydrogen build up on batteries, always "blow away"
before risk of sparks from connecting leads & crock clips etc!
i) 12V Electrical fires are best stoped with a pair of cutters!
j) Molten copper is HOT.
/QSL
73 De John, G8MNY @ GB7CIP
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