Using an indicator lamp with 120v

Discussion in 'Electronic Basics' started by kevreh, Dec 13, 2004.

1. kevrehGuest

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)?

Thanks!
Kevin

2. MikeGuest

Would an illuminated wall switch suffice? Leviton makes these...

Mike

3. John FieldsGuest

---
They can't.
---
---
on some lamps there's a resistor built into the lamp, but not to
pritect it from the amps the load is pulling, it's to keep the current
which is making the lamp light up from getting large enough to hurt
the lamp.
---

4. Robert MonsenGuest

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

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.

5. Bill BowdenGuest

If you use a neon indicator in parallel with the switch
(from one side to the other), it will light when the
switch is off and there is something plugged into the
outlet which is turned on. The neon indicator bulb should
have a 100K resistor in series for 120VAC operation.
Some are built in, others are not.

-Bill

6. kevrehGuest

Dumb question, but would the resistor be before or after the lamp (I'm
guessing before since its their to prevent excess amperage from being
pulled).

7. kevrehGuest

Are you sure? I was planning on taking the hot FROM the switch to one
lead of the lamp and a neutral lead that supplies the outlet to the
other lead of the lamp. My terminoligy isn't all that great so some of
what I'm saying may be misleading )

8. John GGuest

worse.

a novice such as yourself to your DEATH.

I never cease to be worried about the technical and complicated answers
given on some of these Electrical news groups to absolute novices who
are way out of their depth in what they are attempting.

11. kevrehGuest

Not so sure about that. I understand and respect electricity, just a bit
fuzzy on the right words to describe the concept I'm trying to explain.
This is intimidating but not helpfull, especially for a forum about basic
electronics. Am I supposed to give up on this project? Why don't you share
your insight on the SAFE way to proceed raise the bar on the quality of this
discussion.
Again, the group is titled "BASIC"

12. John GGuest

I am sorry, I do not want to be insulting, but you do not have the
remotest understanding of even the most basic electric principles when
you ask questions, as you did above, like, Is the resistor to stop the
load drawing too much power? or Should the lamp be wired in series or
parallel? or Should the resistor be before or after the lamp?

Yes this is a Basic group but it is not possible to teach first
principles of a subject as complicated as Electricity by answering
random questions. Some understanding is first required.

And I repeat, from your very limited knowledge displayed above you hould
stay away from even 120volts, it does kill.

13. Randy DayGuest

kevreh wrote:

[snip]
No, you're supposed to get yourself to a community college,
and take a short course in electric/electronic circuits so
you can understand what we're talking about when we use the
*basic* terminology in the subject. It doesn't get much more
basic than schematic/series/parallel/resistor/ground/hot/
electrocution.
I just did. Find a night course at a local high school
offering a beginner's look at electr(on)ic circuits.

Preferably with hands-on experiments, wiring practice
Just like with BASIC physics, BASIC calculus and
BASIC carpentry, you're expected to have some
familiarity with BASIC math, BASIC equations and BASIC
power tools before you attempt any of the above.

Don't cop an attitude, pal. Get to a beginner's class,
and build the birdhouse before you attempt the
two-storey, split-level bungalow.

120 volts can *KILL*. 120 volts can *burn your house to
the ground.* Or both.

You've been warned.

14. Peter BennettGuest

The traditional 120V neon pilot assembly is apparently obsolete - the
stores group at work used to stock them, but last time I bought one, I
was surprised to find that it contained an LED! for pilot light use,
the LED version works as a direct replacement for the original neon
part, but someone depending on the neon characteristic could be in for
a rude surprise.

(This change was particularly surprising, as my boss and I are
supposed to be consulted for any changes to part numbers or suppliers,
and neither of us new of the change.)

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter

15. Roger JohanssonGuest

It is also useful to know the prefixes in the number system and the most
common units. 975mhz means nothing. 975mHz means 975 milliherz, 975MHz
means 975 million Herz, 1 kHz means 1000 Herz, etc..

Learn the prefixes kilo, Mega, milli, micro, nano, deci, etc.. and how to
use them.

Learn some basics about Ohms law, series and parallell, etc..

Don't touch any voltage above 40 Volt until you know a lot more about
electronics and safety precautions.

It is all available at any public library in the world, or through
internet.

16. petrus bitbyterGuest

Kevin,

Your questions show an extreme lack of knowledge and experience. So to stay
on the safe side do not work directly on the mains outlet of your house. Use
a plug and a cable to connect your signaling outlet to the wall outlet.
Build your lanp, switch and outlet close together and make sure nobody can
touch the live wire when you put your plug into the wall outlet. As for the
switch, lamp and outlet: lamp and outlet parallel, switch in series with
them. If you need the lamp for signaling only, buy a neon type with a build
in resistor meant for your local mains voltage. Does not matter how you
connect it to the outlet. Once more, be carefull. Live wire is killing.

petrus bitbyter

17. Robert MonsenGuest

Actually, the number of electrocutions in the US each year is incredibly
small. Only 140 contractors who work with electricity on a daily basis
(many of whom don't really understand it, above "don't touch that") were
killed by it last year.

It's patronizing for me to say it, and I'm sure you are quite careful,
but remember to keep one hand in your pocket when you are working on
powerline AC.

If you do that, the worst that will probably happen if you get careless
is you'll get your hand burned.

It is probably more likely that an old hand will get zapped, due to
becoming complacent.

--
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.

18. kevrehGuest

Sorry if it sounds like I'm "copping an attitude" (I feel like I'm in
high school or something). Since this forum is titled BASIC I thought
people here would be fine answering what I thought would be basic
questions.

There's nothing wrong with taking classes or reading books as you've
mentioned. But there's also nothing wrong with reading and learning on
discussion groups like this.

19. kevrehGuest

I regret ever posting my question here. The feedback I've gotten has reduced
me to someone who doesn't know anything about electronics- which is far from
the truth.

I'll find my answers elsewhere, as there are many other forums out there
that aren't as antagonistic towards someone. Most forums run on the mantra
of "there's no dumb questions", however this one seems to thrive on telling
people how ignorant they are.

Take care-
Kevin