Maker Pro
Maker Pro

LED Installation question

C

Chevguy

Jan 1, 1970
0
Hello all.

I have (hopefully) a simple question.

I wish to install a basic LED in an extension cord to tell me if it has
power or not.
The cord will be used in standard 110-120 volt applications.

Can this be achieved with just resistors?

I can plug an LED straight to 120 volt a/c if I use enough of them. Is this
correct to do? Is this safe? Is there a better way to achieve this?

Thank you.
 
C

Costas Vlachos

Jan 1, 1970
0
Chevguy said:
Hello all.

I have (hopefully) a simple question.

I wish to install a basic LED in an extension cord to tell me if it has
power or not.
The cord will be used in standard 110-120 volt applications.

Can this be achieved with just resistors?

I can plug an LED straight to 120 volt a/c if I use enough of them. Is
this correct to do? Is this safe? Is there a better way to achieve this?

Thank you.


You'll need a diode to half-wave rectify the mains, and a series resistor.
Like this:

.. ___
.. o------>|------|___|------>----.
.. 1N4004 R I |
.. | /
.. 120VAC LED V /
.. RMS -
.. |
.. |
.. o------------------------------'


The half-wave rectifier protects the LED from excessive reverse voltage, and
R limits the current. For 120V RMS, there will be about 170V peak across R.
So, for I = 20mA peak, you'll need a 8.2 kOhm resistor. Because of the
half-wave rectifier, there will be about 85V RMS across R, so it will
dissipate about 0.9 Watts. Note that the average LED current will be much
less than 20mA, but most LEDs will light up just fine. You can also use
low-current LEDs to minimise heat dissipation across R (in which case you
need to recalculate R). Finally, BE EXTRA CAREFUL, you can get killed by
directly handling live mains like this!

cheers,
Costas
 
S

Stefan Heinzmann

Jan 1, 1970
0
Chevguy said:
Hello all.

I have (hopefully) a simple question.

I wish to install a basic LED in an extension cord to tell me if it has
power or not.
The cord will be used in standard 110-120 volt applications.

Can this be achieved with just resistors?

Yes, but the correct resistor will dissipate a fair amount of heat. You
also need an antiparallel diode to protect the LED (or a second LED).
I can plug an LED straight to 120 volt a/c if I use enough of them. Is this
correct to do? Is this safe? Is there a better way to achieve this?

No, LEDs are constant current devices. And you would need quite a lot of
them in series.

What's wrong with a small neon lamp and a series resistor? You can even
buy neon lamps with the correct resistor for 120VAC built in. They're
built for exactly the kind of job you got. LEDs are not the *only* light
emitting device around...
 
C

Chevguy

Jan 1, 1970
0
Costas Vlachos said:
You'll need a diode to half-wave rectify the mains, and a series resistor.
Like this:

. ___
. o------>|------|___|------>----.
. 1N4004 R I |
. | /
. 120VAC LED V /
. RMS -
. |
. |
. o------------------------------'


The half-wave rectifier protects the LED from excessive reverse voltage, and
R limits the current. For 120V RMS, there will be about 170V peak across R.
So, for I = 20mA peak, you'll need a 8.2 kOhm resistor. Because of the
half-wave rectifier, there will be about 85V RMS across R, so it will
dissipate about 0.9 Watts. Note that the average LED current will be much
less than 20mA, but most LEDs will light up just fine. You can also use
low-current LEDs to minimise heat dissipation across R (in which case you
need to recalculate R). Finally, BE EXTRA CAREFUL, you can get killed by
directly handling live mains like this!

cheers,
Costas

Is it possible to not use a half wave rectifier? I don't exactly have a
Radioshack nearby.
I hooked it up with 10.82 k?

I ran it for about 15 min. with no real apparent heating.
What do you think?
 
C

Chevguy

Jan 1, 1970
0
Stefan Heinzmann said:
Yes, but the correct resistor will dissipate a fair amount of heat. You
also need an antiparallel diode to protect the LED (or a second LED).

How would I go about hooking a second LED to protect the other one?
No, LEDs are constant current devices. And you would need quite a lot of
them in series.

What's wrong with a small neon lamp and a series resistor? You can even
buy neon lamps with the correct resistor for 120VAC built in. They're
built for exactly the kind of job you got. LEDs are not the *only* light
emitting device around...

How small is the light you are referring to?
 
J

Jim Thompson

Jan 1, 1970
0
Is it possible to not use a half wave rectifier? I don't exactly have a
Radioshack nearby.
I hooked it up with 10.82 k?

I ran it for about 15 min. with no real apparent heating.
What do you think?

Use TWO LEDs in anti-parallel.....
___
o--------------|___|------>----o-----o
R I | |
| / | /
120VAC LED V / - /
RMS - A LED
| |
| |
o------------------------------o-----o

or the second LED can be a diode. The series diode approach is
dangerous because it doesn't account for leakage effects.

...Jim Thompson
 
J

James Meyer

Jan 1, 1970
0
You can also use
low-current LEDs to minimise heat dissipation across R (in which case you
need to recalculate R). Finally, BE EXTRA CAREFUL, you can get killed by
directly handling live mains like this!

cheers,
Costas

I would use a neon bulb, NE-2 or equal, and a current limiting resistor.

I heard of someone getting killed by 12 volts DC. A truck battery fell
on his head.

Jim
 
S

Stefan Heinzmann

Jan 1, 1970
0
Chevguy said:
How would I go about hooking a second LED to protect the other one?




How small is the light you are referring to?

You mean how small mechanically? They come in various shapes, but the
smallest ones I know are glass bulbs 10mm long with 4mm diameter.
 
S

Stefan Heinzmann

Jan 1, 1970
0
James said:
I would use a neon bulb, NE-2 or equal, and a current limiting resistor.

I heard of someone getting killed by 12 volts DC. A truck battery fell
on his head.

Ouch!

That is the smallest of dangers from a truck battery, I reckon.
Witnessing a spanner evaporate that has been put across the battery
poles is more fun...
 
A

Active8

Jan 1, 1970
0
Use TWO LEDs in anti-parallel.....
___
o--------------|___|------>----o-----o
R I | |
| / | /
120VAC LED V / - /
RMS - A LED
| |
| |
o------------------------------o-----o

or the second LED can be a diode. The series diode approach is
dangerous because it doesn't account for leakage effects.

...Jim Thompson

I want some of those 10.82 k resistors ;)
 
A

Active8

Jan 1, 1970
0
Hello all.

I have (hopefully) a simple question.

I wish to install a basic LED in an extension cord to tell me if it has
power or not.
The cord will be used in standard 110-120 volt applications.

Can this be achieved with just resistors?

I can plug an LED straight to 120 volt a/c if I use enough of them. Is this
correct to do? Is this safe? Is there a better way to achieve this?

Thank you.
You kinda hinted that you want something small, but those surge
supressor strips have built in neon lights and sometimes an LED.

What is the end use of this thing, anyway? If you turn on a lamp
and it doesn't light, for example, you either try a new bulb or
start probing with a neon voltage tester if that's all that's
available. With a 3-prong extension, you can use an outlet tester
and verify the the house wiring is right at the same time.
 
B

Byron A Jeff

Jan 1, 1970
0
-
--> -> > Hello all.
-> >
-> > I have (hopefully) a simple question.
-> >
-> > I wish to install a basic LED in an extension cord to tell me if it has
-> > power or not.
-> > The cord will be used in standard 110-120 volt applications.
-> >
-> > Can this be achieved with just resistors?
-> >
-> > I can plug an LED straight to 120 volt a/c if I use enough of them. Is
-> > this correct to do? Is this safe? Is there a better way to achieve this?
-> >
-> > Thank you.
->
->
-> You'll need a diode to half-wave rectify the mains, and a series resistor.
-> Like this:
->
-> . ___
-> . o------>|------|___|------>----.
-> . 1N4004 R I |
-> . | /
-> . 120VAC LED V /
-> . RMS -
-> . |
-> . |
-> . o------------------------------'
->
->
-> The half-wave rectifier protects the LED from excessive reverse voltage,
-and
-> R limits the current. For 120V RMS, there will be about 170V peak across
-R.
-> So, for I = 20mA peak, you'll need a 8.2 kOhm resistor. Because of the
-> half-wave rectifier, there will be about 85V RMS across R, so it will
-> dissipate about 0.9 Watts. Note that the average LED current will be much
-> less than 20mA, but most LEDs will light up just fine. You can also use
-> low-current LEDs to minimise heat dissipation across R (in which case you
-> need to recalculate R). Finally, BE EXTRA CAREFUL, you can get killed by
-> directly handling live mains like this!
->
-> cheers,
-> Costas
-
-Is it possible to not use a half wave rectifier? I don't exactly have a
-Radioshack nearby.

No. LEDs have a very low reverse breakdown voltage. The opposite swing of
the AC presents a reverse voltage of up to 170V. Way to high. Eventually
it'll burn up.

One simple way to resolve the problem is use a bi-color LED, which consists
of a red and green LED in antiparallel configuration. So on the positive
swing one conducts, and on the negative swing, the other does. So each of the
LEDs protects the other from reverse breakdown.

-I hooked it up with 10.82 k?

As long as it's 1W or more it should be fine. if you only have 1/4 watt
resisters you can parallel two 5K 0.5W resistors to get a 10K 1W type.

-
-I ran it for about 15 min. with no real apparent heating.
-What do you think?

See above

BAJ
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Byron A Jeff <[email protected]>
wrote (in said:
if you only have 1/4 watt
resisters you can parallel two 5K 0.5W resistors to get a 10K 1W type.

Where you from? Not in this Universe.(;-)
 
C

Chevguy

Jan 1, 1970
0
Active8 said:
I want some of those 10.82 k resistors ;)

Yes, I should probably explain...

I am using 2 resistors in parallel ( I think they are supposed to be 21.5-22
k)

I just measured with the meter to get the "actual" reading of 10.82.
 
C

Chevguy

Jan 1, 1970
0
Active8 said:
You kinda hinted that you want something small, but those surge
supressor strips have built in neon lights and sometimes an LED.

What is the end use of this thing, anyway? If you turn on a lamp
and it doesn't light, for example, you either try a new bulb or
start probing with a neon voltage tester if that's all that's
available. With a 3-prong extension, you can use an outlet tester
and verify the the house wiring is right at the same time.

I want to mount in the male end of the plug for the blockheater in my
vehicle. Then I will always know if the various outlets I plug in to have
power or not.

In my last vehicle, I made an apparatus that sat inside the engine
compartment. If the blockheater would draw enough current, it would light
the led in the plug end. That was hard to make and expensive. I can't
believe I forgot to take it out when I sold the truck!
 
C

Costas Vlachos

Jan 1, 1970
0
Chevguy said:
Is it possible to not use a half wave rectifier? I don't exactly have a
Radioshack nearby.
I hooked it up with 10.82 k?

I ran it for about 15 min. with no real apparent heating.
What do you think?


As others have posted, standard LEDs have very small reverse voltage ratings
(in the order of a few volts). Your LED will probably get damaged soon if
not protected. Anyway, it's just a diode that you need... 1N4003 and above
will do it. Or use a bi-colour LED in which case your resistor will
dissipate twice the power than the half-wave rectifier approach, as the LED
will light up during both half-cycles (and will be brighter too).

Costas
 
A

Active8

Jan 1, 1970
0
I want to mount in the male end of the plug for the blockheater in my
vehicle. Then I will always know if the various outlets I plug in to have
power or not.

In my last vehicle, I made an apparatus that sat inside the engine
compartment. If the blockheater would draw enough current, it would light
the led in the plug end. That was hard to make and expensive. I can't
believe I forgot to take it out when I sold the truck!
Oops.

That's interesting. I designed a pager activated block heater relay
for a guy with a hobby farm so his tractor would be ready to rock
when he got there from the home or office. He can set it to stay on
for a preset time and hit it again with the pager to extend the
timing cycle. I figured with a 800W block heater, the savings of
not having it on all the time paid for the project in just a few
months and he spared no expense on an approved steel electrical box
and one of those high dollar plated-thru Vector boards. A few more
months of energy savings paid for me. Damn. That thing's been
working for 2 yrs now with no problems :)
 
R

Richard Henry

Jan 1, 1970
0
Byron A Jeff said:
if you only have 1/4 watt
resisters you can parallel two 5K 0.5W resistors to get a 10K 1W type.

If I only have 1/4 watt resistors, where do I get the 0.5W resistors?
 
C

Chevguy

Jan 1, 1970
0
Active8 said:
Oops.

That's interesting. I designed a pager activated block heater relay
for a guy with a hobby farm so his tractor would be ready to rock
when he got there from the home or office. He can set it to stay on
for a preset time and hit it again with the pager to extend the
timing cycle. I figured with a 800W block heater, the savings of
not having it on all the time paid for the project in just a few
months and he spared no expense on an approved steel electrical box
and one of those high dollar plated-thru Vector boards. A few more
months of energy savings paid for me. Damn. That thing's been
working for 2 yrs now with no problems :)

How much did that set the farmer back?

Mind you, it wouldn't do me any good. I have no cell. service where I live.
 
A

Active8

Jan 1, 1970
0
How much did that set the farmer back?

Mind you, it wouldn't do me any good. I have no cell. service where I live.
I figure he spent $100 - $150 on parts and hardware plus an e-bay
pager - Motorola Classic. He paid me $75 up front and IIRC, $75
after. If I had to do it over again - he wanted super simple
because of his experience level - I'd just modify a PIC
programmable timer with LCD and keypad that I designed.

It could be set to have the thing warm in the morning. No need for
a pager if it doesn't have to be remote activated.

He also didn't wan't to deal with programming PICs nor a lot of
point to point wiring nor making a PCB. At the time, I didn't have
all my stuff set up nor the space to do it for him.
 
Top