We've had 12 volt and 24 volt systems for so long that few of us remember the days when six volts was the norm. Nor just how quickly was the changeover from one to the other (inside two years).

We are soon to be faced with a far more radical change: to 36-volt batteries charged by 42-volt alternators. This is not conjecture: the first so-equipped vehicles are expected to be on sale within months!

There are various and good reasons for the change. One is that the increasing complexity of motor vehicles is sorely taxing the abilities of present-day alternators (a recent Mercedes Benz has over 75 separate electric motors and at least as much computing power as the early Apollo space craft!)

The demand for power

An automobile's electrical power demand is increasing year by year. In 1970, if everything in a vehicle were turned on simultaneously, the total draw would be 300-500 watts. It's now way passed 2000 watts, and is forecast to be 4000 watts within three more years – and a staggering 10,0000 watts by 2012.

Coping with this already demands alternators of 140 amps and more. This is becoming close to the limits of practicality. A 12-volt system generating 4000 watts requires a 285 amp alternator; generating 10,000 watts requires a staggering 700 amps plus! (The reason the arithmetic seems wrong is because a '12-volt' alternator actually runs at 14 volts.)

Generating such currents is hard enough: moving it around requires enormously heavy and costly cables. Fortunately there's a handy relationship between watts, amps, and volts. One can obtain the same amount of watts, for less current, by increasing the voltage.

By moving from 12 volt to 36 volt batteries (using a 42-volt alternator), generating 4000 watts requires a 95-amp alternator, generating 10,000 watts requires about 275 amps. This can be achieved in a package little or any bigger than the 12/24-volt alternators of today and early interim systems are expected to be larger versions of what we already have.

It's more likely though that by 2005, the power generating devices will be combined starter motor/alternators – that possibly/probably replace existing flywheels. (This is a far from new concept – several cars of the 1920s had just that!). This also enables the unit to provide additional acceleration or hill-climbing ability – and probably also act as a regenerative brake that utilises the otherwise wasted energy for battery charging (again an old concept)

Huge technology changes

This electrical change will result in huge changes in automobile technology. Many functions that are currently performed mechanically or hydraulically will utilise electric motors (including so-called 'linear motors' that pull and push). These functions will include fuel injection (this move has already started), steering, braking, water pumps, air conditioning compressors, etc. Catalytic converters are likely to become electrically heated. Because of decreased energy losses, these changes are likely to reduce fuel consumption by at least 10%.

Unlike the 1960s' six to twelve-volt change, the forthcoming move to 36/42 volts will take many years. It's likely to begin with 12/36-volt systems where the higher voltage is used for starting and the 12-volt system for everything else. The first 36/42-volt-equipped vehicle will probably be Fords' new generation Explorer 4WDs.

The implications for campervans and motorhomes are not yet clear. Campervans commonly use car-derived engines and are likely to be the first affected, but it's unlikely to affect motorhomes for many years. Eventually we are likely to have a whole new generation of 36-volt equipment.

One thing's for sure. I'll have to rewrite 'Motorhome Electrics'.

Next Tech Notes

As forecast in my 'Motorhome Electrics' book, the move from 12/24 electrics, to 36-volt systems charged by 42-volt alternators (or alternator/starter motors), is underway. Ford's forthcoming updated 4WD 'Explorer' is believed to be so equipped. The move copes with the increasing electrical demands of conventional dual fuel hybrid-engined vehicles. It is triggering a corresponding move to electric actuation of (currently) hydraulic functions – and also electrically-heated catalytic converters etc.