I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.
Trevor Smith

"Trevor Smith" wrote in message
oups.com...
I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.
Trevor Smith


Surely neon lamps like
http://www.maplin.co.uk/module.aspx?...10&do y=14m11
would be a lot simpler.

david

On 14 Nov, 23:10, "Vortex" wrote:
"Trevor Smith" wrote in ooglegroups.com...

I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.
Trevor SmithSurely neon lamps likehttp://www.maplin.co.uk/module.aspx?TabID=1&criteria=neon&ModuleNo=20...
would be a lot simpler.

david
Thing is I need one blue and one red.
Trevor Smith

In article .com,
"Trevor Smith" writes:
I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.

Firstly, consider a neon indicator -- it's a better fit to main voltage.

If you stick with LED, then 5mA is enough current for an indicator,
or make that 10mA for half wave rectified...

1N4004 LED
---/\/\/\----||-------||---------
24k | |
1.5W --/\/\/\--
10k
0.25W

The 24k resistor drops the mains at 10mA, but gets hot.
The 1N4006 diode rectifies the mains.
The 10k resistor ensures reverse mains voltage is all across
the 1N4006, and not the LED which couldn't handle it.

We could reduce power consumption by dropping most of the voltage
across a capacitor rather than the resistor. Can't completely get
rid of the resistor as the inrush current to charge the capacitor
if swithed on mid-cycle would destroy the LED.

LED
---||-----/\/\/\--------||---------
0.068µF 6.8k | |
400V 0.25W ---||---
1N4001
--
Andrew Gabriel

In article . com,
Trevor Smith writes


On 14 Nov, 23:10, "Vortex" wrote:
"Trevor Smith" wrote in messagenews:1163545188.889959.
...

I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.
Trevor SmithSurely neon lamps likehttp://www.maplin.co.uk/module.aspx?TabI
D=1&criteria=neon&ModuleNo=20...
would be a lot simpler.

david
Thing is I need one blue and one red.
Trevor Smith

Ok, diagram below but please think about safety before implementing this
circuit. Neon cases are designed to be safe when used at mains voltages
but LEDs are not. An LED mounted in a clip and poked through a panel or
even in a panel bezel is not safe when used with this circuit. Unless
you are prepared to totally enclose the LED in something like a salvaged
neon housing then please don't implement this circuit.

Anyway, lecture over:

C is 400V ac rated 22nF for 1.6mA, 100nF for 8mA, 220nF for 16mA

View with a fixed width font:

|
|
|
---
--- C (value)
|
/
\
/ 470R
\
|
-----
| |
| |
--- ---
1N4007 / \ \ / LED
--- ---
| |
| |
-----
|
|
|


--
fred
Plusnet - I hope you like vanilla

In article ,
(Andrew Gabriel) writes:
LED
---||-----/\/\/\--------||---------
0.068µF 6.8k | |
400V 0.25W ---||---
1N4001

Oh, and put a 1M resistor across the capacitor too, so it
can't retain a charge after use and zap you.

--
Andrew Gabriel

"Trevor Smith" wrote in message
ups.com...


On 14 Nov, 23:10, "Vortex" wrote:
"Trevor Smith" wrote in
ooglegroups.com...

I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.
Trevor SmithSurely neon lamps
likehttp://www.maplin.co.uk/module.aspx?TabID=1&criteria=neon&ModuleNo=20...
would be a lot simpler.

david
Thing is I need one blue and one red.

Search for 'neon blue' on rswww.com (Radio Spares)

--

Michael Chare

In message . com,
Trevor Smith writes


On 14 Nov, 23:10, "Vortex" wrote:
"Trevor Smith" wrote in
messagenews:1163545188.889959.308260@k70g2000cwa .googlegroups.com...

I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.
Trevor SmithSurely neon lamps


likehttp://www.maplin.co.uk/module.aspx?TabID=1&criteria=neon&ModuleNo=20...
would be a lot simpler.

david
Thing is I need one blue and one red.

You never did get the hang of rugby songs did you


--
geoff

In article .com,
Trevor Smith wrote:
I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.

Ready made mains LED indicators are available and might be the easy answer
as regards safety etc. I've got some which are identical in diameter to a
normal 5mm LED plus bezel with the electronics mounted inline behind and
the whole lot sealed with flying leads for connections. Overall length
about 1.5 inch.

--
*No sentence fragments *

Dave Plowman London SW
To e-mail, change noise into sound.

On 14 Nov 2006 15:13:25 -0800 someone who may be "Trevor Smith"
wrote this:-

Thing is I need one blue and one red.

Why do you "need" a blue one?


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Trevor Smith wrote:

Thing is I need one blue and one red.

Maplin sell snap-in neons in red, amber, green *and* blue

In article ,
Andy Burns wrote:
Maplin sell snap-in neons in red, amber, green *and* blue

Neons simply don't look as good as LEDs, though. They're also a source of
RF interference which might matter on sensitive equipment.

--
*Re-elect nobody

Dave Plowman London SW
To e-mail, change noise into sound.

Trevor Smith wrote:
I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.
Trevor Smith


Probably the best thing to do is to use a capacitor in series with them
- resistors to get to say 20mA will be large and bulky and get hot (5W).
Then you want a diode across them so they don't get reverse voltage
across them.

Working on 20mA for half the time - so 40mA in all, you need around
6Kohms impedance at 50Hz..I make that about a 0.5uF 400v AC capacitor
you need, and any old diode like a IN4148..

The other otion is an inductor - 50mH..but that is a fairly large chunk
of iron and a lot of fine wire.

fred wrote:
In article . com,
Trevor Smith writes

On 14 Nov, 23:10, "Vortex" wrote:
"Trevor Smith" wrote in messagenews:1163545188.889959.
...
I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.
Trevor SmithSurely neon lamps likehttp://www.maplin.co.uk/module.aspx?TabI
D=1&criteria=neon&ModuleNo=20...
would be a lot simpler.

david
Thing is I need one blue and one red.
Trevor Smith

Ok, diagram below but please think about safety before implementing this
circuit. Neon cases are designed to be safe when used at mains voltages
but LEDs are not. An LED mounted in a clip and poked through a panel or
even in a panel bezel is not safe when used with this circuit. Unless
you are prepared to totally enclose the LED in something like a salvaged
neon housing then please don't implement this circuit.

Anyway, lecture over:

C is 400V ac rated 22nF for 1.6mA, 100nF for 8mA, 220nF for 16mA

View with a fixed width font:

|
|
|
---
--- C (value)
|
/
\
/ 470R
\
|
-----
| |
| |
--- ---
1N4007 / \ \ / LED
--- ---
| |
| |
-----
|
|
|



Ah,. Pretty much what I came up with..except you have forgotten that the
current through the LED is half wave..I made it .5uf for 20mA
average..and I see no need for a high voltage power diode like a
IN4007..it doesn't have to take more than 5v reverse across it after
all..the LED takes care of that and clamps it. The 470R is good to limit
transients.

Dave Plowman (News) wrote:
In article ,
Andy Burns wrote:
Maplin sell snap-in neons in red, amber, green *and* blue

Neons simply don't look as good as LEDs, though. They're also a source of
RF interference which might matter on sensitive equipment.


I had another thought on this..it might be possible to use a triac as a
fairly crude 'chopper' - like a basic dimmer type circuit - and then a
resistor and capacitor to smooth it out a bit. More expensive, but more
efficient.

"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
Andy Burns wrote:
Maplin sell snap-in neons in red, amber, green *and* blue

Neons simply don't look as good as LEDs, though. They're also a source of
RF interference which might matter on sensitive equipment.


I had another thought on this..it might be possible to use a triac as a
fairly crude 'chopper' - like a basic dimmer type circuit - and then a
resistor and capacitor to smooth it out a bit. More expensive, but more
efficient.

That's probably what they use in these
http://www.arcoswitch.co.uk/MainsRat...ndicators.html

I wonder if they do free samples?

dennis@home wrote:
"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
Andy Burns wrote:
Maplin sell snap-in neons in red, amber, green *and* blue
Neons simply don't look as good as LEDs, though. They're also a source of
RF interference which might matter on sensitive equipment.

I had another thought on this..it might be possible to use a triac as a
fairly crude 'chopper' - like a basic dimmer type circuit - and then a
resistor and capacitor to smooth it out a bit. More expensive, but more
efficient.

That's probably what they use in these
http://www.arcoswitch.co.uk/MainsRat...ndicators.html

I wonder if they do free samples?


Probably available from RS components and the like

On Nov 14, 11:50 pm, Owain wrote:
Trevor Smith wrote:
I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.Resistor values (ohms) = (Vs-Vf)/If

where Vs is supply voltage
Vf is the forward voltage drop across the LED
If is the forward current through the LED

Vf and If are shown in the specs for each LED in the Maplin etc catalogue

For AC supply connect a diode eg 1N4148 in inverse parallel with the lED
and halve the value of the resistor

(says the Maplin Catalogue from long enough ago when it contained Useful
Information)

The whole lot will have to be insulated for 240V.

Owain

Thanks for the advice and I have decided to go for ready made
indicators.
Trevor Smith

In article ,
Owain wrote:
Resistor values (ohms) = (Vs-Vf)/If

Doesn't work for AC.

--
*24 hours in a day ... 24 beers in a case ... coincidence? *

Dave Plowman London SW
To e-mail, change noise into sound.

In article , The Natural
Philosopher writes
fred wrote:
In article . com,
Trevor Smith writes

On 14 Nov, 23:10, "Vortex" wrote:
"Trevor Smith" wrote in messagenews:1163545188.88995
9.
...
I'm not sure if this is the right group but here goes, I want to use 2
led's as indicators but they will be on 240v ac and I don't know how to
work out the resistance needed or what size or type of diode I would
need. I have looked at different site that sell them but they are too
large for my requirements which rules out using transformers to drop
and rectify the voltage, and I can't find any other information on how
to wire them.
Trevor SmithSurely neon lamps likehttp://www.maplin.co.uk/module.aspx?Ta
bI
D=1&criteria=neon&ModuleNo=20...
would be a lot simpler.

david
Thing is I need one blue and one red.
Trevor Smith

Ok, diagram below but please think about safety before implementing this
circuit. Neon cases are designed to be safe when used at mains voltages
but LEDs are not. An LED mounted in a clip and poked through a panel or
even in a panel bezel is not safe when used with this circuit. Unless
you are prepared to totally enclose the LED in something like a salvaged
neon housing then please don't implement this circuit.

Anyway, lecture over:

C is 400V ac rated 22nF for 1.6mA, 100nF for 8mA, 220nF for 16mA

View with a fixed width font:

|
|
|
---
--- C (value)
|
/
\
/ 470R
\
|
-----
| |
| |
--- ---
1N4007 / \ \ / LED
--- ---
| |
| |
-----
|
|
|



Ah,. Pretty much what I came up with..except you have forgotten that the
current through the LED is half wave..I made it .5uf for 20mA
average..and I see no need for a high voltage power diode like a
IN4007..it doesn't have to take more than 5v reverse across it after
all..the LED takes care of that and clamps it. The 470R is good to limit
transients.

Yes, quite right the current would be a bit low, on reflection I thought 470R
might be a bit low as that is a 0.5A limit and LEDs are a bit peak sensitive.
I chose the high voltage version of the diode because they are cheap and
because I didn't want a failure of the LED to ripple through and cause the
failure of the diode (single fault safety principle & all that) but wasn't clever
enough as failure of the diode will result in the LED popping.
--
fred
Plusnet - I hope you like vanilla

In article ,
Owain wrote:
Resistor values (ohms) = (Vs-Vf)/If
Doesn't work for AC.

Not even where it says "halve the value of the resistor for AC"?

Ah - missed that bit. You should have included it in the equation. ;-)

--
*If Barbie is so popular, why do you have to buy her friends? *

Dave Plowman London SW
To e-mail, change noise into sound.

The Natural Philosopher wrote in
:

Ah,. Pretty much what I came up with..except you have forgotten that the
current through the LED is half wave..I made it .5uf for 20mA
average..and I see no need for a high voltage power diode like a
IN4007..

I'd have used a 4006, perhaps I never got as far down the list as 1N4007.

Any how, I use a 4006 for absolutely every general purpose silicon diode,
I'v used zillions (nearly)

Perhaps I lack imagination

mike

In article ,
Andy Burns writes:
Trevor Smith wrote:

Thing is I need one blue and one red.

Maplin sell snap-in neons in red, amber, green *and* blue

Maplin's green neons are an amber neon with a green lens.
It gives a sort of dim **** colour, literally.

Real green neons used to be available (actually, they were
fluorescent, utilising the UV lines from a discharge).
Not seen them for some time, and they didn't have the
same life as regular neons.

--
Andrew Gabriel

In article ,
fred writes:

Yes, quite right the current would be a bit low, on reflection I thought 470R
might be a bit low as that is a 0.5A limit and LEDs are a bit peak sensitive.

If you connect at peak (340V), it's 0.7A, which will damage most
20mA LED's eventually.

--
Andrew Gabriel