kevreh said:
I want a simple on/off indicator for a switch that's controlling an
outlet. It sounds like a neon indicator lamp is the way to go. What I'm
wondering is if the amps pulled by whatever I have plugged in could fry
the bulb. Or do they have a resistor built in to the lamps to protect
against this? If not, should I include something?
Also, should the lamp be wired in series or parallel FROM the switch?
Btw, would using an LED be more hassle (wiring)?
The indicator needs to be parallel to the load.
You can use an LED by using a diode pointing in the other direction in
parallel with it, and a resistor to drop the current to something
managable...
A 1/2W 100k resistor will drop the current to 170/100k = 1.7mA peak. The
dissipation in the resistor will be 120^2/100k = 144mW.
You also should use a 1/8A fuse. You can get ones that look like little
resistors that will work perfectly for this.
Line --- fuse ---- resistor --- antiparallel LEDs --- Neutral
Line is the little rectangular hole, Neutral is the big rectangular hole.
Make sure Neutral is within 10VAC of the big round hole, ie, ground. If
not, don't do this, and call an electrician.
US 120VAC ONLY WITHOUT EXPLICIT INFORMATION FROM COUNTRY IN QUESTION.
.-------. 100k 1/4W
| | _ ___
-----| | | |-o \_/o--|___|----o------.
| | | | | |
| | | 1/8 A | |
| | o | V - LEDs or Diodes
| | | - ^ One Up
| '-------' | | One Down
| | | |
| | | |
|--------|----------------------o------'
| |
| _ |
| / \ |
----(_/_)---|
\_/
AC Meter Should
Read < 10VAC
Tape everything upstream of the 100k resistor
(created by AACircuit v1.28 beta 10/06/04
www.tech-chat.de)
If the LEDs aren't bright enough, you can use a lower value resistor. Be
careful, however, about dissipation. The formula for heat generated is
V^2/R
So, as R decreases, the heat increased. 1/2 R will double the heat,
meaning a bigger (1/2W maybe?) resistor.
A 47k resistor in place of the 100k resistor would dissipate about
300mW, so a 1/4W resistor wouldn't work.
--
Regards,
Robert Monsen
"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.