Originally Posted by
Brian Hjelm
I well remember 6 volt cars with generators. They were what nearly all of us drove as young shavers. Most of them could barely cover the draw of high beam lights and a long night run using high beams could mean a starting problem in the morning. Many heavy prime movers have been 24 volt for years and most have voltage reducers fitted to supply 12 volts to the trailer/ trailers. The 12 volt bulbs are mechanically stronger and are less likely to fail from the shaking of empty running or severe outback service on our "roads". The operators that can afford them are going to LED trailer lights and prime mover tail lights, but, as most line haul owner-drivers are paid a pittance and operate on a shoestring, a total chabgeover to LED is a long way off.
When cars first started to get electrics around the end of the first world war, voltage was 4, 6,8 or 12 volts, occasionally higher. This settled down to mostly 6v except for a few luxury cars which were 12v by the mid to late twenties. By the 1930s most manufacturers had changed to 12v except for the US and France and a few economy cars.
After WW2 nearly everyone outside the US had 12v with notable exceptions being VW and Citroen, (and some US subsidiaries such as Holden). Landrover for example had 12v from the start as Rover was already 12v.
Holden changed, I think, in about 1960, but most US cars remained 6v well into the sixties. One of the reasons for this was a legal limit on power of lights that stayed into the 1980s at least. But by then, other power demands were growing, and another factor came in - as more and more electrics were fitted, the sheer bulk and weight of wiring became a problem, and the simplest way of reducing this is to increase the voltage. By doubling the voltage, you can halve the cross section of the wire for the same voltage drop - but it is even better than that, because your voltage is twice as high, you can stand twice the voltage drop you could at the lower voltage, which means you can go to a quarter the cross section, not that i can think of anyone who has actually gone quite that far.
But this makes it clear why manufacturers are looking at even higher voltages - the payoff is very good, for the cost of a somewhat more expensive battery - plus all the bulbs, fittings and electrical devices can only be bought from the manufacturer, at least until it becomes a new standard.
If you look at a car of the early 1920s, it probably had two 24w headlights,
plus two 6w sidelights, and a 6w tail light - total 66w.
By 1930, add an instrument light - 6w, and a stop light, 21w, for a total of 93w (OK, I know they would not be all on at once, and I have left the horn out)
By 1950, most cars now had two tail and stop lights, and the headlights would have been 36w - total 138w.
By 1960, add blinkers, car radio, interior light, maybe boot light, some cars heater fan.
By 1970 increase headlight wattage to probably 55w on high beam, and many cars have four headlights, doubling that, but transistors have reduced the drain of car radios. Drain has increased to where alternators are becoming common (although what actually made them standard was when diodes became cheap enough that alternators were cheaper than generators).
By the 1980s ECUs started to appear, and airconditioning with its fans and compressor clutches started to become common, although it did not become almost standard until the 1990s.
In the 1990s, gadgets such as electric windows and central locking, which had existed since the 1930s, became common.
Since 2000, ABs, multiple CPUs, traction control, electric seats
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
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