On Sun, 06 Sep 2009 15:52:22 +0100, John Rumm
wrote:
Dave Liquorice wrote:
On Sun, 06 Sep 2009 04:36:03 +0100, John Rumm wrote:
One solution you could try:
R1 LED1
-\/\/\--|^---
| |
| D1 D2 D3 | /
Live in ------|--|--|------o o---------- to lamp
| | sw1
| D4 |
-----|-------
Interesting idea. An improvement might be to use back to back zeners
in place of D1 to 4.
On a quick search I can only find 5v1 ones at 5W dissipation so the
upper limit on the lamp load would be 230W (ish) and you'd have 10W
of heat to get rid of at 230W load. Now if there are some 2v zeners
out there at 2W dissipation...
I had thought of using a zenner but as you say there are difficulties
finding suitable devices, and bog standard rectifier diodes are dirt
cheap and robust. I used a version of this circuit on a battery charger
I built for an "on charger" light. It was a wide ranging charger that
might be dealing with anything from a single 1.2V cell up to about 30V
and currents from 9mA through to over an amp. The circuit above (without
D4 since this was DC) works flawlessly. Three diodes seemed to get
ample voltage to light the LED even if it was a bit below the 2.5V spec.
In the end I opted for simplicity and used the Maplin panel mount red
neon (BK52) which cost 99p, and took the return to earth; it works fine.
Here's the details...
1 Solder flex tail to neon, insulate with heat-shrink, and fit in 6.5mm
hole
http://img35.imageshack.us/img35/760...nthewiresz.jpg
2 I soldered the fine wires to the switched load and earth of the mains
cable to guarantee a lasting connection
http://img142.imageshack.us/img142/7...redthefine.jpg
3 Reconnect mains cable to switch and the earth contact of back-box
http://img36.imageshack.us/img36/484...ecttoswitc.jpg
4 The re-fitted switch with its new red neon
http://img42.imageshack.us/img42/373...ittedswitc.jpg
5 Success!!
http://img178.imageshack.us/img178/3...861success.jpg
Thanks for all the input and neat LED ideas, but its hard to beat the
neon for simplicity, cost, very low current draw, no visible flicker
(100Hz), all round visibility, and ready availability in panel mount.
Phil