Deals On Wheels Australia – September 2019

Have you ever stopped to wonder how

healthy the heart of your electrical system

is? Many of us are guilty of ignoring the

need to calculate the total power usage of

our vehicles and make sure we have the

right alternator.

The electrical system of your vehicle

finely balances energy demands with

energy production and when this balance

is disturbed, subsequent failures may occur

in various components, causing expensive

downtime and mechanical repair. This

electrical balance is often disturbed by the

addition of driving lights, marker lights,

cooling systems, refrigerators, microwaves,

etc. These products draw additional current,

placing more load on a system. The outcome

can present itself in premature battery

failure, damage to starter motors or the

alternator itself.

PACCAR Parts senior product manager

Rekha Mohan shares some key points with

us to help us better understand the need to

assess the vehicle’s electrical demands and

how the next generation of alternators can

reduce the risk of system failures.

A truck’s electrical system is a basic

one that uses the alternator to convert

mechanical energy into electrical energy.

This supports the primary electrical

loads of the vehicle and also maintains a

healthy battery. If your electrical system is

underperforming then chances are your

current alternator may not match your

vehicle’s demands. Please be mindful

that variables such as temperature, cable

condition and battery condition can

impact the charging system.

A typical prime mover requires 65–75

amps to cover the bare minimum electrical

load of the vehicle’s systems. This includes

engine management, internal and external

lighting, heater and air-conditioning fans,

gauges, UHF and radio. When you install

extra accessories to your prime mover

such as driving lights, additional trailers

requiring marker and rear lights, fridges,

electrical cab cooling systems and so forth,

the total electrical load can exceed well

over 100 amps.

Table 1 lists the electrical requirement of

some common accessories that are fitted

to trucks.

If a truck had all of these installed, the

current requirements to cover these

electrical loads are:

• Electrical accessories: 80A


• Engine control system: 65–75A


• Total current requirement: 145–155A
  Any alternator’s advertised output
  rating is at a stabilised 24°C (SAE J56
  standard). The alternator output achieved
  at the normal under bonnet operating
  temperature of the truck (~125°C) will be
  considerably less than the advertised
  rating. It is important to ensure the output
  of the alternator at operating temperature
  will exceed the combined electrical loads of
  the truck and the electrical accessories that
  are installed.
  Using an example of a road train
  departing at 6pm from Townsville to
  Mount Isa, let’s assume the electrical
  accessories listed in Table 1 are working
  for the majority of the 10-hour trip. The
  electrical requirement at this stage is
  approximately 155A. When the truck

The electrical system of your truck could be

overloaded. A timely reassessment can help

improve productivity and save you a bundle

on repairs of damaged internal components

ALTERNATORS

at low engine

speeds

output

IdlePro

alternators

by Prestolite

Electric deliver

industry best

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12 Volt Device Power (Watts) Current (Amps = Watts/12)

Electric Cooling System 240 20

LED Driving Lights x 4 660 55

Clearance Lights x 16 10 0.8

Additional Fridge 55 4.6

Total Current Draw 80.4

Table 1:

182