Replacing vehicle alternator warning lamp with LED

[Axle Roads]

Sorry for the long post. Do you really need variable illumination? I only recently heard on the science channel that the actor Ed Begley Jr has LED dimmers fitted in his house. Tech exists, but might need reverse engineering.

I get the impression you just want to tweak the brightness during production to a comfortable level and set for end user. For the sake of brainstorming, I'll chip in a few low tech solutions. You might have better luck lowering efficiency with either older style, red LEDs or a filter of some kind. Play with filtering out blue light, I think that's bothersome wavelength. A thin coat of high temp wax or, you can replicate the soft dull light of my '67 Ford dash by scotch taping colored plastic and waiting forty years.

One more thing on the brightness. If I recall, LED are designed and sold to shine light at different angles from center depending on it's application. For example LED flash lights shine straight ahead with out silver reflectors. Perhaps you could use this to your advantage by angling the beam of light in such a way that it strikes the rider indirectly. Just a few thoughts.

I've found two alternative LED alternator indicator designs. The first one here: Led circuits page It's the 14th one down labeled Battery Equal Charge Indicator. I think that could be easily adapted. But, It looks like it's drawling current continuously and it looks too complicated. At some point simplicity = reliability. An reliability the whole reason I'm switching to LEDs in the first place.

The second design I found is simply two LEDs with zener diode in parallel. I found it in this book. The encyclopedia of electronic circuits - Google Book Search
I don't know how to link to it, more directly. The problem I see, is if a shade tree mechanic removes the positive battery cable while the engine is running or you leave your lights on and jump start your car, your alternator might send a current to your battery exceeding 6 amps and burn out your zener diodes. Tell me if I'm wrong.

At this point, I think your LED alt. ind. design + a dash voltmeter would prob be the best most reliable upgrade from stock.

 

[Willbe]

3w incandescent = 3/4w or 3/5w LED?

 

[Axle Roads]

Take a look at this circuit. It give you 0-100% control over dimming LED lights.

 

[MikeMl]

A couple of points:

The last car that I owned that had an alternator lamp was a 1965 Ford. I have owned more than fifteen cars and trucks since then, none of which had the lamp. No current production cars, Japanese or American use the lamp as you guys are discussing it. Some modern cars have a "charging system malfunction indicator", but guess what, it is driven by a microprocessor port pin.

In all modern alternator systems I am familiar with, the field excitation comes from the Voltage Regulator which is fed by the battery via the main power distribution bus. In the very early Motorola Alternator system (which no US auto maker has used for thirty years) used the lamp to initially bootstrap the alternator at startup, but if the bulb burned out after the car was started, then the alternator/voltage regulator kept on charging. Even on a subsequent start, there was usually enough residual magnetization of the rotor such that the alternator bootstapped itself even without the lamp.