14.4.
Vehicle Electrical Loads
Other than the battery and starter, the loads placed on an alternator can be considered under three separate headings. These include continuous loads, prolonged loads and intermit-
tent loads. The charging system has to cope with these loads under various conditions. To have an estimation of the required output, the power used by each individual component is added including the power required to charge the battery. The typical electrical power requirements of various vehicle systems are listed in Table 14.1, which also includes the current requirements for 12 V as well as at 24 V systems for comparison. The values are approximated to nearest 0.5 A in the Table.
Figure 14.3 illustrates how vehicle power requirement has increased over the recent years
including a prediction of its continued increase. The Table 14.1 does not include the possible new consumers, to name some are electrically pre-heated catalytic converters, electrical power assisted steering and heated windscreens. It is therefore clear that always some changes are expected to the vehicle electrical system in the future. This section is also intended to discuss some of the possible consequences for the vehicle charging and electrical system as a whole. Most of the intermittent loads are used infrequently and also heated rear windows and seat heaters, are generally equipped with a timer relay. The factor of 0.1 may, therefore, be applied to the total intermittent power requirement, for the purpose of further calculations. This, however, assumes that the vehicle is operated under normal driving conditions.
Thus average consumption of intermittent loads (using a factor of 0.1) is estimated as 170 W. It can be seen from Table 14.1, which includes most of the consumers on a vehicle, that the demands placed on the charging system can be high. The sizing of alternator considering the expected load has been presented in section 14.6.
Fig. 14.3. Power demand increase over recent years and a prediction of its continued increase.
Table 14.1. Vehicle Electrical Components Typical Power Consumption. |
|||
| Loads | Power (W) | Current (A) at | |
| 14 V | 28 V | ||
| Continuous loads: | |||
| Ignition | 30 | 2.0 | 1.0 |
| Fuel injection | 70 | 5.0 | 2.5 |
| Fuel pump | 70 | 5.0 | 2.5 |
| Instruments | 10 | 1.0 | 0.5 |
| Total | 180 | 13.0 | 6.5 |
| Prolonged loads: | |||
| Side and tall lights | 30 | 2.0 | 1.0 |
| Number plate lights | 10 | 1.0 | 0.5 |
| Headlights main beam | 200 | 15.0 | 7.0 |
| (or) headlights dip beam | 160 | 12.0 | 6.0 |
| Dashboard lights | 25 | 2.0 | 1.0 |
| Radio/Cassettes/CD | 15 | 1.0 | 0.5 |
| Total (Average of main and dip) | 260 | 19.5 | 9.5 |
| Intermittent loads: | |||
| Heater | 50 | 3.5 | 2.0 |
| Indicators | 50 | 3.5 | 2.0 |
| Brake lights | 40 | 3.0 | 1.5 |
| Front wipers | 80 | 6.0 | 3.0 |
| Rear wipers | 50 | 3.5 | 2.0 |
| Electric windows | 150 | 11.0 | 5.5 |
| Radiator cooling fan | 150 | 11.0 | 5.5 |
| Heater blower motor | 80 | 6.0 | 3.0 |
| Heated rear window | 120 | 9.0 | 4.5 |
| Interior lights | 10 | 1.0 | 0.5 |
| Horns | 40 | 3.0 | 1.5 |
| Rear lights | 40 | 3.0 | 1.5 |
| Reversing lights | 40 | 3.0 | 1.5 |
| Auxiliary fog/spot lamps | 110 | 8.0 | 4.0 |
| Cigarette lighter | 100 | 7.0 | 3.5 |
| Headlight wash wipe | 100 | 7.0 | 3.5 |
| Seat movement | 150 | 11.0 | 5.5 |
| Seat heater | 200 | 14.0 | 7.0 |
| Sun-roof motor | 150 | 11.0 | 5.5 |
| Electric mirrors | 10 | 1.0 | 0.5 |
| Total (approximately) | 1.7 kW | 126.0 A | 65.0 A |
