Auto dimmer for LEDs

Why don't you replace the traic ;-)

Probably. I can't imagine it being worth doing. Tungstens have zero output at near half power, LEDs have zero output near zero power, hence the behaviour you see.

NT

This sounds like a simple circuit charging up a capacitor to bias on a transistor. The problem probably is that the settings used assume a lower resistance load than the led. It depends if its using someform of feedback to achieve the more smooth gradual illumination. Brian

'cos car electrics are dc

Except for Ford model T.

NT

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

Yes.

not very relevant in the contexct of a Merc's interior lights.

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

Quite so. The Ford T had nothing powered by the battery bar the trembler co il, and its ac system was unable to charge the battery. In fairness with no electric starter, and no load bar briefly the trembler coils at start time , it didn't need much charging, so plugging it in on occasion was workable.

NT

True, although early cars had no starter motor (and therefore needed no battery). Were there any other pre-starter-motor cars that had AC electrics?

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

Nowadays such things are more often done with a microprocessor. It is probably actually cheaper than the high value stable capacitor you would need tor the analogue timer. My bathroom fan does its timer this way, making modifying its behaviour a work in progress.

You will however need a magneto

On cars that used a magneto and which therefore generated alternating current at HT voltage, was the phase of the magneto "hard-wired" to that of the crankshaft (eg by gear/chain/toothed belt drive), so each pulse of the magneto corresponded to the instant when a spark was required in one of the cylinders, or was it totally asynchronous, with it being a matter of luck whether the magneto was outputting maximum voltage at the instant when a spark was required? Or did they rectify the magneto output and smooth it slightly with a capacitor to keep the HT at a high voltage irrespective of the phase of the magneto?

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

The T was handle start, carbide lights, magneto ignition & no electrical accessories. But it still needed a battery, the magneto couldn't generate a spark at crankhandle speed.

Start sequence: Switch to trembler coil ignition Crank Switch to magneto ignition

- Or shout for assistance if it just ran you over.

NT

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.

Magnetos have the magnet in the edge of the engine flywheel, producing one timed spark per rev.

Trembler coil ignition ran all the time, resulting in very ropey spark timing & rough running. Hence it was just used for starting.

NT