On 23/05/2013 10:20, Arfa Daily wrote:


"Nightjar" wrote in message
news
On 23/05/2013 01:27, Arfa Daily wrote:


"charles" wrote in message
...
In article , Nightjar
wrote:
...
In the legislation they are called position lights, a name that
probably
dates back to when you could have the headlights close together, as in
Mk1 Land Rovers. To anybody in the habit of using them by
themselves in
a built-up area, once a common practice, a parking light probably
means
a single bulb lamp, showing white in one direction and red in the
other,
that you clipped over the top of the door window when parking at
night.

my father's one had an electromagnet, so it stuck to the side of teh
car
when plugged in.


And the battery wasn't flat in the morning ... ?

That was the point of having a single 5 watt bulb. You could run that
off a battery for a couple of nights and still have a good chance of
starting the car, even with the measly batteries used in the 1950s and
dynamo charging.

Colin Bignell



You miss my point. He said that it hung there by electromagnet when it
was plugged in, and no electromagnet strong enough to hold a small
parking light, is going to be down at 5 watts on its consumption. And
even if it was, that, plus the 5 watts of the bulb, would still be the
better part of one amp, and given the small size and lack of
sophistication of car batteries back then, and the fact that they were
charged by a dynamo barely adequate for the job, I would think that a 14
hour (6pm until 8am) overnight operation of such a light, would leave
the battery seriously depleted.

Why wouldn't it be possible to put the coil in series with the lamp?
Its DC so it wouldn't affect the lamp if it were thick enough and
doesn't need to dissipate power if the field is static.
The only loss would be the coils resistance.
I doubt if you would need many turns as you have about half an amp of
current flowing.