240v LED for bathroom fan

[David W.E. Roberts]

Hi,

I have discovered the fatal flaw in my pull switch and humidistat bathroom fan.

I cannot tell if the humidiatat is on or the pull switch is on.

I have worked out the wiring (which is how I first proved that the humidistat was on most of the time) but I would like to fit a small LED which only lights when current is passing through the switch.

To do this I need a 240v LED which can be mounted in a small hole in a plastic casing.

Looked in Maplins but can't find a 240v LED - although most don't seem to have a voltage rating.

Any ideas/sources?

TIA Dave R

[Tim Mitchell]

In article , David W.E. Roberts writes

use a neon, not an LED. You can wire up LEDs to work at 240V but it would be far simpler to use a mains neon, which would give a very similar effect.

[Sean Delere]

Try looking for Neon rather than LED

Sean

[David W.E. Roberts]

Thanks guys - will do

[Dave Plowman]

That's because an LED is a DC current operated device. For normal DC operation they require a series resistor the value of which depends on the voltage it's running off and the current you wish to drive it with. For AC use, you require a diode as well.

It's more normal to use a neon indicator, but if you'd prefer the look of an LED it's easy enough if you can solder.

I *think* RS components do mains LED indicators ready made - they certainly exist, I've got some.

[Mike Ring]

"David W.E. Roberts" wrote in news:bgrdcp$rkf0d$ [e-mail]:

Wire a mains neon ie one *with* a series resistor, between the switched contact and neutral; connect the series resistor end to the live (switched wire) side. Modify the case so you can see the neon, obseve safety at the live end.

A LED would have to have 228V dropped across it's resistor, at about 10 mill thats about 2.3 watts - definitely not the way to go

mike r

[John Rumm]

You could use 3 or 4 series rectifier diodes and wire the LED + resistor across these - that would give you a suitable voltage drop to power a small LED. You would also need a reverse diode to bypass the LED so that when the reverse phase comes along your LED does not go pop!

[Tim Mitchell]

In article , Mike Ring writes

Not true, LED's are only tolerant to a small reverse voltage, much less than a normal diode. If you are working from a 9 volt PP3 then they will be OK connected backwards. At 240V mains they will be destroyed by the reverse polarity.

[MarkM]

If the electrical option is too complex for this reason, there may be a mechanical solution. The last time we were in the US, the ceiling fans had a little mechanical doodah on the pull cord to show what state the fan was in. Although now that I think about it, the fans (and the doodahs) were designed with 1 off state and 3 on states for the different speeds. So even if you could find them here (unlikely) they probably wouldn't be much use for a 2 state device... Sorry!

[David W.E. Roberts]

I already have an external on/off switch with both neon and mechanical indicators. The issue is the internal switch (tiny) within the fan body. I need a very small indicator light to show if power is coming via the switch or the humidistat - both of which are built into the compact fan body. So the indicator has to be integrated into the fan body.

[MarkM]

Maybe I didn't explain myself well... The mechanical indicator is attached to the pull string of the internal fan switch, so that it would track (and indicate) the state of this internal switch. So it would indicate whether the humidistat was being over-ridden by the manual switch. Sounds very clunky, but actually worked fine on the overhead fans. I expect these are an over-the-counter accessory sold in the US, but may not be available in a two-state on-off form.

[David W.E. Roberts]

Things become clearer :-) Does this replace the plastic toggle at the bottom of the pull cord? I guess I could always order one from the US.

Cheers Dave R

[MarkM]

The ones I saw were fitted about half way up the pull cord, around eye level. I have no idea if these came as standard with the fans or were after-market.

[Abdullah Eyles]

Did you get your answer yet, David W.E.?

I read most of the thread but couldn't see any simple answer...

As far as I am concerned, you need to look at the *current* flowing through the switch (or the humidistat), as I guess they are connected in parallel...

I saw a circuit using a LED and a few diodes, which in effect will monitor the current. It was used as an indicator for a normal (no neutral) 240V light switch.

Quote: (for 'Lamp' read 'Motor')

fixed width font LED ----RES180R---|>|---- | | SWITCHED-FEED----|>|--|>|--|>|--|>|------LAMP | | ---------||-- = DIODE

A bit heavy on component count but lights evenly independent of lamp load, choose diodes to match full lamp current. LED is low current (5mA).

All parts are live, including the LED. For safety don't poke the led thro the panel, use a plastic holder.

Extra components would be required to meet BS/VDE safety.

Unquote... (from uk.diy - "Power an LED from a light switch?")

[David W.E. Roberts]

Main answer I got was that I asked the wrong question.

The lights in switches are apparently neons not LEDs.