DTM7000
6
Doc.: 00293978-v1
Vehicle power supply
Vehicles are fitted with batteries, which work as chemical storage devices for the electrical energy
produced by the vehicle's generator (alternator). The batteries must be capable of providing rapid high
current supplies (above all, at low temperatures) when starting the vehicle cold and providing partial or
total supply to the other major loads throughout the vehicle's electrical system for a limited period, above
all when the vehicle's engine is running at idle or has been stopped. This requirement is generally met by
a lead-acid battery (sulphuric acid).
The normal voltage for a battery fitted to a private vehicle is 12V.
The requirements imposed by each of the vehicle's circuits, in terms of starting power, capacity and
charging current, apply for a temperature range of between -30 and +70 °C.
The various characteristics of vehicle batteries:
Voltage - generally 12.5 V for private vehicles.
Capacity, in Ah (Ampere-Hours), i.e. the number of amps which can be consumed for a period of
one hour before the battery is fully discharged (Caution: with a half-charged battery, it may prove
difficult to start the vehicle).
The number of amps supplied at start-up - depending on vehicle type and engine.
The size and height - different for each vehicle.
Location of positive and 0 V terminals.
Standardised terminal IDs (taken from DIN 72 552)
A few examples of markings:
1
Ignition - low voltage
15
Positive when ignition is turned on
Battery
Starter
30
+ Battery
50 Starter motor control
31
Ground 0v
Relays
85 & 86
Relay control
87
Working
87b
At rest
30
Common
Connections
Definition:
Connections are used to link two or more components, with the option of disconnecting the link,
maintaining a good electrical contact and even waterproofing the connection.
Several different types of shapes exist, all of which are easy to remove.
The best connections are those with the lowest possible electrical resistance.
Be aware of current restrictions!
Examples of types of connector:
Female flat-lugged connector.
3-way female flat-lugged connector.
+
0V
0V
+
