In a message dated 6/21/2001 5:13:29 PM Eastern Daylight Time,
CraigFaubel@aol.com writes:
> I'm installing electric water pump, fuel pump and cooling fans in my B with
> 302 Ford, and I'd like to have indicator lights showing green when they're
> operating and red if one of them goes out of service while the power is
> being supplied to them. I went to Radio Shack and the guy told me their
> bi-color LEDs (#276-210) would do this. They have 3 leads, and can glow
> either green or orange, depending on how the circuitry is done.
> Unfortunately, he had no idea how to hook them up nor where to look for
> information. These are nominal 2.1 volt units, and they'd need to work on
> 12v, but I dont know how they'd be wired. Does anyone have electronic
> knowhow or can point me to assistance for this?
>
Craig,
Typically, multi colored LEDS consist of two LEDs in one package. When one
led is lit, you get one color, when the other is lit, you get the other
color, when both are lit, you get the combination of colors, just like mixing
paint.
To use 2.1 volt LEDs on your 12 volt system, you'll need to add resistors in
series with each lead. The value of the resister will be determined by the
current draw of the LEDs. You want to drop app 12 volts, so the resistance
would be 12 divided by the LED current.
That's not your real problem, though. Your real problem is finding a way to
know that the fans/pump *should* be working, but aren't. It can be done, but
it will take a great deal of work. One way would be to use a current monitor
- if they have power applied, but not drawing current, then you have a failed
unit. Another way would be to use a photo cell, and monitor the rotation of
the fan blades. If the pulse count drops, the fan isn't working. Or, you
could use pressure sensors, one in front of the fan, and another in the back
of the fan. If the fan is operating, the difference in pressure will be
higher than if it is not working. Easier said than done.
Probably the best way to monitor them would be to use a voltage sensor on the
temperature sensor. It the temp gets high enough to be a problem, then the
voltage sensed at the temp sender will be low. There are commercially
available sensors that monitor this voltage, and turn on a light if the temp
gets too high. They are typically sold for fuel level monitors, turning on a
dash light when the fuel level dropps below a preset point, but they should
work for temp monitoring as well. They cost about $50.00
Or, you might be able to find a temperature switch from a "civilian" car, one
that operates an idiot light if the temp gets too high, and use the output of
this to operate your LEDs.
For your application, temperature monitoring is just about the only viable
option. If the fan/pump is supposed to be on, but your water temp is still
too high, you have something amiss.
I spent 28 years doing just this sort of design for nuclear power plants, but
in that case, the needed hardware was readily available. Or, if it weren't
available, we just sent someone a suitcase full of money, and they made it
for us. For a car, any time you get away from the norm, you will have a
difficult time finding suitable hardware, especially if you want to retain
the automobile "look" and don't want to clutter up under the hood with
industrial looking junk.
Dan Masters
Alcoa, Tennessee
Triumph TR 250 - TR6 Electrical Maintenance Handbook:
http://members.aol.com/danmas6/
Stuffing a V8 into a small British sports car:
http://members.aol.com/danmas/
British V8 Newsletter:
http://members.aol.com/danmas4/mgv8.htm
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