Greetings, all. Let me tell you about my latest disaster.
My 30-yr old beaut was designed with rice grain bulbs for the instruments - mostly T3.5, but some are T10. The T3.5's installed were originally 0.5W, but the only ones I can get these days are 1.2W. Twice the brightness, twice the heat... so these end up melting the buttons.
So I decided to replace these with LEDs. And they look
a-MAZE-ing!
Unfortunately, I picked up an unforeseen problem.
My alternator is not even two years old. I had it replaced shortly after installing the LEDs. But I discovered that, while previously the charging light would die as soon as the engine started, now I have to rev the poor engine to redline to get the charge going. I checked the voltage regulator, the slip rings, the ground cable, everything recommended by motor forums and auto electricians.
A study on how these self-excited alternators work has led me to conclude that the LED I use in the charging circuit is to blame: the alternator requires the indicator lamp to provide exciting current. But the LED draws much less current than the alternator requires. So I could put back the incandescent lamp and watch the plastic melt, or I can keep the LED and ruin my engine.
Or could I perhaps take Option 3?
If I could design a circuit, connected in series with the alternator, to provide the alternator with the required current, which relies on the indicator but boosts the current up to a limited point. In other words, if I could install an incandescent bulb, the current would be limited (as would the light - but really, it's a tiny indicator, nobody's going to miss half of twice the light) to what the alternator needs, but if I install a LED, the current would be boosted to what the alternator needs.
Transistors are used to provide current gains. But what would limit the current? What would this circuit look like?
FWIW, the alternator requires 10A of exciting current.
Thanks
P.S.
If the ON times were shorter, there'd probably be less of a problem. But this is not always possible. The diesel has to glow, sometimes for up to a minute, to get the engine started. And some of the electric features only work when the key is in the ON position (not the ACC position).