On Fri, 18 Nov 2016 10:15:21 +0000, The Natural Philosopher wrote:

On 17/11/16 23:48, Roger Hayter wrote:
The Natural Philosopher wrote:

On 17/11/16 20:16, Roger Hayter wrote:
The Natural Philosopher wrote:

On 17/11/16 19:40, Roger Hayter wrote:
charles wrote:

In article ,
The Natural Philosopher wrote:
On 17/11/16 18:47, NY wrote:


wrote in message
...
On Thursday, 17 November 2016 18:28:43 UTC, charles wrote:
'cos car electrics are dc

Except for Ford model T.

Is there any fundamental reason why early pre-electronic car
electrics were DC and not AC?

Yes.

to go further, the car electrics rely on a battery - this
inherantly a DC device.

They need not rely on a battery. If, for example, you have a
starting handle and carbide lamps.

You will however need a magneto

AC ignition could easily have been devised. Even if it actually
wasn't.


No, actually it couldn't.

How you gonna time a spark if your AC happens to be zero at that time?

Remember even rectifiers were hard to come by then.

The solution was the magneto. Whether you call that AC or DC is
debatable.

You just use a high enough frequency.


Which the technology of the day wouldn't have been able to generate.

A magneto is AC at crank speed synched to the crank, if that's what you
want to see it as. But its not AC as we understand it today.

And magnetos still had contacts for timing the spark.


My point being that the magneto was at the a time a well used fairly
cheap reliable and well understood beast, and there was no point in
doing it differently until cars came with batteries, and dynamos, which
introduced a whole new level of sophistication. The electric starter,
the electric lights - and the magneto disappeared leaving behind only a
coil, contact breaker and eventually a distributor. And that didn't
really change till the advent of electronic ignition in the 70s.

Note that aircraft engines of WWII used magnetos too IIRC.
Reliable self contained ignition built into the engine was the magneto.

Still used in lawnmowers, and most garden power tools and most
motorcycles.

And aircraft. OK, it's out of production now, but see the Cessna 152.




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