led questions

[redls1bird]

thank you all very much for the info, this is exactly the kind of
stuff i was looking for. i posted ona few other lighting specific
forums and got absolutely nothing. appreciate all the help and
advice. you just made my job alot easier.

 

[redls1bird]

well, here is my thoughts. i have a set of non functional vents on
the quarter panel of my car. asthetically they are nice, but i would
like to make them have a function. my thought was to set up a small
led array behind each one (orange in color) and use them as a side
parking/turn signal indicator. looking at the links i got some great
info, including how i could create just a park light, but how could i
turn it on and off with the blinkers? optimaly, i would like to
change the intensity of the lights to indicate a turn. i read in a
few places about 555 chips, but i dont know what they are or how to
use them. any more ideas or links? like i said i appreciate all of
the help!

 

[JeffM]

I was originally responding to somebody who said
they THINK that Christmas lights are available
as LED's wired in parallel. My point was that IF that is the case,
they would each need a separate series resistor.
And of course run off a low voltage DC source.
redbelly

I'm pretty sure that is the case.
Tom MacIntyre

Not the ones I've seen. Transformers increase cost.

..
..

The new ones can have a few bulbs fail and the string still works.

That part is true,

http://66.102.7.104/search?q=cache:A7dE6OHLIB0J:www.cityoftemecula.org/events/Holidays/xmas/howlights.htm+the-new-bulbs-contain-an--internal-shunt+The-shunt-wire-contains-a-coating-that-gives-it-fairly-high-resistance-until-the-filament-fails
but now you've switched from LEDs to bulbs.

 

[Jasen Betts]

In article <cmahg1tr860kl72btr4akipjmu6l9eb483@4ax.com>, Tom MacIntyre wrote:

I don't know either. I was originally responding to somebody who
said they THINK that Christmas lights are available as LED's wired
in parallel. My point was that IF that is the case, they would
each need a separate series resistor. And of course run off a
low voltage DC source.

I'm pretty sure that is the case. The new ones can have a few bulbs
fail and the string still works.

They've invented bulbs that fail with a short circuit for that purpose,
you get a string of series wired christmas lights with 39 fail-short bulbs
and one (regular) fail open "fuse" bulb to stop a cascade failure from
starting a fire.

the fail short bulbs seem to have somethin wrapped around the terminal wires
inside the envelope, I'm guessing it's some sort of wire with poor
insulation that the mains voltage can punch through if the filament fails.

Bye.
Jasen

 

[ehsjr]

Kitchen Man wrote:

On Fri, 19 Aug 2005 23:14:00 -0700, "Rodney" <rdavies@okanagan.net
wrote:


It does happen to be in parallel with the other lights. Just had to
solder a 220 ohm resistor to it.


Right, I think that's the source of the confusion in the discussion.
You are wiring resistor-LED-pair series circuits in parallel with
other devices using the same source, and I think the ehj-someone is
implying that non-current limited LED's should not be paralleled.

What is confusing about "Do NOT wire LEDS in parallel." ?
I am not implying that non-current limited LED's should not
be paralleled, I am stating it, forcefully:
Do NOT wire LEDS in parallel.

In pictures:

+V--[R]--[LED]--Rtn
|---[circuit]---|

and not:

+V--[R]---[LED]--Rtn
|-[LED]---|
|-[LED]---|

which would probably be ok *if* R is chosen for the current used by
the parallel group, and the LED's are closely matched for voltage
drop.

Wrong. Do NOT wire LEDS in parallel.

Ed

 

[ehsjr]

redls1bird wrote:

well, here is my thoughts. i have a set of non functional vents on
the quarter panel of my car. asthetically they are nice, but i would
like to make them have a function. my thought was to set up a small
led array behind each one (orange in color) and use them as a side
parking/turn signal indicator. looking at the links i got some great
info, including how i could create just a park light, but how could i
turn it on and off with the blinkers? optimaly, i would like to
change the intensity of the lights to indicate a turn. i read in a
few places about 555 chips, but i dont know what they are or how to
use them. any more ideas or links? like i said i appreciate all of
the help!

Find the + and - wires wire that connect to the existing
turn signal bulb, and the + and 1 wires that connect to the
running light bulb. You can connect them directly to the
two identical circuits below that you will build that feed
your led array(s).

From Turn Bulb + ---[R1]---+-----+--- To LED Array TURN+
| |
[TVS] [C1]
| |
From Turn Bulb - ----------+-----+--- To LED Array TURN-


From Running Bulb + ---[R2]---+-----+--- To LED Array DIM+
| |
[TVS] [C2]
| |
From Running Bulb - ----------+-----+--- To LED Array DIM-



LED Array:

D1 D2
From TURN+ ---[Rled]--->|----+---|<---[Rdim]--- + To DIM +
|
[LED1]
|
[LED2]
|
[LED3]
|
[LED4]
|
From TURN- -------------|<---+--->|------------ - To DIM -
D3 D4


C1,C2 = .1 uF 100 V
D1-4 = 1N400x diodes
TVS = 18 volt TVS diode such as P6KE18CALFCT-ND from Digikey
R1 = 10 ohm, 5 watt

Rled = 220 (assuming 2V drop for each LED, and 4 leds in the array)
or compute as Rled = (12.6 - Vledtotal)/.02 where
Vledtotal = Vled1 + Vled2 + Vled3 + Vled4
(The D1, D3 pair, or the D2, D4 pair drop the nominal
voltage - 13.8 - by ~1.2 volts)

Rdim is found experimentally. You use the value of
resistance that dims the LEDS to the brightness you
want.

The purpose of the TVS, R1 and C1 is to reduce transients
that might otherwise damage the LEDs.

Ed