Hi, Troy -
LEDology simple for autos and planes, as you can assume the extra
volts when the alternator is working equals the forward voltage of the
LED. Divide 12 volts, not 13.75V, by .020 (typical current figger),
and that's a 620 ohm, 1/2 watt resistor.
Some LEDs have internal dropping "resistor," and your "12 volt rating"
sounds like just that, and they should take 13.75. No drop resistor,
but I have some suggestions that can deny their use.
Another factor is viewing angle. Too wide are dimmish. Too narrow can
be annoying, esp with clear lens, or miss the warning cue. Color,
too, in sunlight, and there's whites and blues nowadays. LEDs are so
cheap, for sunlight use, I buy an assortment and make them show me
something outside. And there's .4" square, white diffused lens jobs
that can be black-letter, clear-labeled on the face. Real cool are
LEDs with built-in flasher chip.
Alt warning lite may be a problem, as its operation may depend upon
the low resistance
of the incandescent lamp (Tony, Rotax Dealer?). Wouldn't bet what an
LED will do when the "L" line goes low on all faults, thus requiring a
10# sledge hammer to fully test. Safer bet is an NPN transistor
circuit, reverse biased to off at the emitter when that line is high,
like when alternator is OK, equivalent lamp resistance emitter to
ground, unfortunately wasting c. 1/4 amp. LED/dropper in collector.
Further details on request.
For door ajar, you can pop-rivet springy tangs or coils, out of a
battery compartment from junk electronic stuff, to contact each shoot
bolt, wired in series from through the internal metal of bolt
mechanisms, port to starboard, to a ground. You'll need an NPN
transistor circuit to sense an open:
Tie base and collector together to really annoy the transistor. 14V
through LED dropping resistor to base-collector. LED from emitter to
ground. Base-collector to the shoot bolt circuit open end. It's an
unswitch - when shoot bolt switch turned on, grounding base, it
doesn't do anything. The triple-duty resistor also limits current
flowing through exposed door hardware and minimizes effect of
dirt/grease on the shoot bolts.
Further, seems you can take the ground from the shoot bolt circuit
through a lever-type microswitch in the throttle housing, affixed to
close at above runup throttle position. No door alert until plane
thinks you're taking off; could even quick-nudge the throttle in runup
to check the doors. But that could make you insufferable at a fly-in,
showing off features like that.
For oil press, there are oil pressure switches like to fire up a Hobbs
meter. But you don't want to plumb a tee in the Rotax oil pressure
sender, a potential engine failure looking for a time to happen. To
electrically tap the Rotax sender, your oil pressure gauge circuit
would have to see at least .7V there, at alert PSI, and an add-on
transistor circuit must not load or bias it so as to cause inaccurate
gauge reading. A more complex IC comparator circuit may be the only
way.
For "master on," an LED always on, off when shutting down, is not a
good alert. I'd try to invert the logic, with flashing LED (or see
below), by grounding LED circuit through again the "L" thing on the
alt reg. It looks good on paper, and would alert only between engine
and master off.
For vital warnings, there's also "Sonalert" type devices. Whistles,
warbles, buzzers, chimes, sirens, and up to enough decibels to cause
soiling of the shorts. We go to power transistors where needed then,
due to current.
Best,
Fred F.
TroyMaynor@aol.com wrote:
>
> Hi Gang,
> I have searched but can't find it in the archive. Someone mentioned the 12v
> 3w lamp that is the alternator warning lamp being changed to an LED and that
> you had to add a resistor, I think, to make the regulator function correctly.
> Does anyone know what will work for sure on this? I have some nice LEDs that
> are 12 volt rated that I want to use. In fact I want to make a series of 5 or
> 6 warning LEDs on a little panel to operate at the correct intensity with a
> 12 volt input to each. I am planning to use one for oil press./master on; one
> for alternator; one for door ajar; one for engine monitor; and starter
> engaged. The alternator one is the one I was concerned about. Is this no big
> deal to do? I am electronically challenged. Please help if you can.
> Best Regards,
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