Auto dimmer for LEDs

Theoretically ac could have been connected to a stepup transformer for long enough to ensure a spark happened. But an LT sliding metal contact timing switch would have worn, oxidised & pitted badly. IIRC reliable distributors came later.

NT

Reply to
tabbypurr
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Not on our Fordson N type tractor , Separate unit just driven from the engine.

Not a coil in sight.

It's nearly 50 years ago but on starting which unless you were built like Charles Atlas was done by winding the starting handle one cylinder movement at a time the magneto had a spring mechanism which wound up and the flipped the rotor fast enough to create the spark. Once the engine fired this was mechanism was disengaged and the rotor run directly. Heck easier to read the Manual

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Could get a good spark just by turning the end of an unmounted unit by hand, Dad did not appreciate this when we connected the output to a wire taped very carefully to the seat of the outside loo where just a couple of strands poked above unseen.

G.Harman

Reply to
damduck-egg

You just use a high enough frequency.

Reply to
Roger Hayter

Not up to you - or me, come to that. It's something the owner wants.

Did you miss the bit where newer cars manage it with LEDs?

Reply to
Dave Plowman (News)

Doubt our Dave knows the difference between a triac and SCR. ;-)

Reply to
Dave Plowman (News)

Could well be. Have looked to see if there are any dedicated chips for this job - but so far no luck.

Reply to
Dave Plowman (News)

No. At the risk of stating the obvious if an analogue fade circuit starts & stops at half power there's a good chance it can be modded by changing a set point.

There isn't really any useful answer to your question unless you can find a stand alone retrofit module or you post the schematic.

NT

Reply to
tabbypurr

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.

Reply to
The Natural Philosopher

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

Reply to
Bob Eager

I don't know what the start point is. All I know is it did what looked to be a perfect fade up and fade down with tungsten.

Very unlikely to find a schematic of such a proprietary part. But do have the connections to it from the car wiring diagram.

I have slung together a lash up using a voltage reg to give a soft start and a simple RC for the fade out. With a small tungsten, it gives a pretty good fade in and out. With a LED, it exhibits the effect I noted. It sort of comes on at about half brightness then fades up to full. It fades out perfectly. Almost as if the LED had a 'strike' current.

Reply to
Dave Plowman (News)

Our car has this also, had a look at the circuit board and as expected it's just a COB. The one in ours also has canbus as well as power, so it's at least possible the dimming is done by the BCM.

I dare say that anyone familiar with a PIC could program one up to do the job of a basic fade in/out in a few minutes. Anyone on here want to offer? :)

Reply to
Lee

I wonder if the tungsten module is doing it by varying the voltage whereas the LED one is PWM/current control? Should be easy to check and then maybe knock up a voltage controlled PWM? I note there are a few old school 555 designs for that :)

Reply to
Lee

I still think you need to PWM it to get the effect you want, simple voltage control is unlikely to achieve that.

Reply to
Lee

That's a good guess, I'd say.

Not seen any that do the fade in fade out when powered up and down, though.

As was said, it might be easier to use a microprocessor for this. Above my pay grade, sadly.

Reply to
Dave Plowman (News)

Not just of WW2 either, most light aircraft still use magnetos today.

And light aircraft.

Reply to
Hankat

Almost as if the LED had a 'strike' current.

`Strike` voltage, bit over 3V usually for white blue and true green LEDs, less than 2 for older colours.

Reply to
Adam Aglionby

PWM won`t quite make it to zero theres a slight step down to zero , but usually close enough, current control is usually smoother.

Arduino and output transistor, cheaper than building it in discretes

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Reply to
Adam Aglionby

Right - which would explain the 'jumping' on, but smooth fade out?

Reply to
Dave Plowman (News)

Thanks, Adam, I'll pass this on.

Reply to
Dave Plowman (News)

Then why did yuo tell me to replace the triac in my dimmer ?

Reply to
whisky-dave

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