Forty or so years back, 6-volt systems were the norm. Increasing engine size and compression ratios, plus the need for amp-hungry headlights that one could see by, necessitated a change to 12 volt and 24 volt systems. The change from one to the other was swift and painless - within two years hardly a 6-volt equipped vehicle was being made.

Now we are faced with a far more radical change. The shift is 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 - starting with the 2003 Ford Explorer 4WD!

There are various and good reasons for the change, particularly 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 an 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 past 2000 watts, 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 watt is one volt times one amp. So by increasing the voltage, one gets the same number of watts, for less current.

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 only a little bigger than the 12/24-volt alternators of today. Early interim systems are expected to be larger versions of what we already have, plus much heavier drive belts.

It’s more likely though that by 2005, these 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 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%.

It will also enable diesel/petrol engines to shut down completely whilst, say, at traffic lights - as the new alternator/starter motors will bring the engine back to life silently and within fractions of a second (as did the 1920s versions!). Forthcoming hybrid fossil fuel/electric vehicles may have 36/42 volt systems. Theoretically it makes more sense to go higher, but higher voltages require considerable electrical knowledge, as the risk of electric shock is introduced.

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. It’s forecast however that over one third of all new vehicles will be using 36/42 volt-electrics within three years, and it will be virtually 100% by 2010.

The implications for caravans, campervans, and motorhomes are not yet clear - although it will slash voltage drop (which is always useful).

The most probable scenario is that three-way fridges will continue to be 12/24-volt operated for many years, and that 36-volt/12/24-volt dc-dc converters will become available to reduce the alternator output. But as yachts will also be affected it’s likely that fridges (and a few other portable appliances) will be available in 36-volt form, as may halogen and fluro tubes etc.

Campervans commonly use car-derived engines and are likely to be affected within a few years. It’s unlikely however to affect motorhomes for many years. Eventually we are likely to have a whole new generation of 36-volt equipment. In the meantime one really does not need to do anything about it - it is absolutely certain that 36-12/24 volt converters will be readily available soon.

One thing’s for sure. I’ll have to rewrite ‘Motorhome Electrics’. Oh yes - remember you’ve almost certainly read about this here FIRST!

Collyn Rivers