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re:Window Switch Lamp Repair for Archives - Long
... much usefull stuff deleted ...
<< In the switch I just repaired, the
LED was in series with a 270 ohm resistor. This would allow 50 mA to
flow with 13.5 volts across the switch. I don't know if this was a
fabrication error or Audi uses particularly robust LEDs (evidently not
given their propensity to fail), but for the new Radio Shack lamp, a
larger resistance is called for. Replace the resistor with a 1 kohm
0.25W resistor, or thereabouts (up to 1500 ohms would be fine). >>
I don't mean to be quarrelsome (there's enough people on this list
for that!), but a 270 ohm resistor won't give you 50ma. An LED has a
voltage drop of around 1.6 volts. The actual current is then:
i = (13.5V - 1.6V)/270ohm = 44ma.
I do agree that this is quite a bit. You can find bright LED's that
can handle this much, but for the common 10-20ma LED you would want
a larger resistor:
R = (13.5V - 1.6V)/10ma = 1200 ohms - 1/4 watt. So anywhere from 1K
to 1.5K would work, like you said.
Thanks for your procedure. This is something I plan to tackle on my
'88 90Q soon...
Steve Valin http://reality.sgi.com/steve_engr firstname.lastname@example.org
"Time wounds all heels" -Crackerbash