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exit signs #175847 03/12/08 09:22 PM
Joined: Aug 2005
Posts: 265
S
Sixer Offline OP
Member
Today we were replacing the standard 120 volt incadescent bulbs in some exit signs with LED bulbs. The new LED bulbs wouldn't work, so we went through the typical tests and found a heat-shrinked "splice" that wasn't passing power to the 2 sockets. We cut the splice off and connected the line wire to the 2 socket wires and the new bulbs worked.

What we thought was just a splice contained a diode soldered in line. I've never seen this before. Has anyone else ever seen this and can you explain the purpose of this diode?


Sixer

"Will it be cheaper if I drill the holes for you?"
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Re: exit signs [Re: Sixer] #175849 03/12/08 09:52 PM
Joined: Oct 2002
Posts: 482
Z
Zapped Offline
Member
Diodes are usually put in line to keep the voltage from flowing in the wrong direction, or to keep it flowing in the right direction (DC). You sure it wasn't a resistor (to limit current)?. If it was a resistor, you can expect the led lamps to blow pretty soon with that resistor out of the circuit.

Are the exit signs rated for the supply voltage you are using on this application? If not, would explain why the part was making the exit sign not work.

Good Luck!

Re: exit signs [Re: Zapped] #175850 03/12/08 09:54 PM
Joined: Jul 2004
Posts: 9,547
G
gfretwell Offline
Member
They use diodes to make bulbs last longer. You only get half the wave (without the heat you would get with a resistor). If you had just turned this around your LED light would have worked OK.


Greg Fretwell
Re: exit signs [Re: gfretwell] #175852 03/12/08 10:12 PM
Joined: Aug 2005
Posts: 265
S
Sixer Offline OP
Member
It was definitely a diode, Zapped. Extended bulb life is the only thing we could come up with, Greg, but none of us had seen this done before. It was easier to just remove the diode altogether rather than reversing it.


Sixer

"Will it be cheaper if I drill the holes for you?"
Re: exit signs [Re: Sixer] #175860 03/12/08 11:50 PM
Joined: Oct 2000
Posts: 2,721
Scott35 Offline
Broom Pusher and
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Seems kind of funny to install a Diode in front of other Diodes (the LEDs);)

I am just poking fun here!

Scott


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: exit signs [Re: Scott35] #175864 03/13/08 01:16 AM
Joined: Jul 2004
Posts: 9,547
G
gfretwell Offline
Member
That is an old trick. Those buttons you dropped in an Edison socket that they used to sell to extend bulb life were diodes. Logic would say they reduce brightness by half but it actually works out a little better than that but it does seem to make the bulbs last longer. I have heard theories that it is the DC aspect but nobody has convinced me.
In the case of LEDs it would have virtually no effect if you had it forward biased along with the LED. You would have another .7 voltage drop but that is pretty insignificant at line voltage.


Greg Fretwell
Re: exit signs [Re: gfretwell] #175866 03/13/08 04:24 AM
Joined: Dec 2001
Posts: 2,486
T
Texas_Ranger Offline
Member
Are incandescent exit signs still common in the US?

Austria almost exclusively used fluorescent exit signs for at least the past 30 years I think. Now they're switching to LED. I've seen some of them, and they hurt the eyes. The small LEDs are extremely bright, contrasting with a dark background.

Re: exit signs [Re: Texas_Ranger] #175868 03/13/08 08:03 AM
Joined: Aug 2002
Posts: 402
J
jdevlin Offline
Member
I have seen some exit signs where the two bulbs are in series. They don't glow full brightness but they last longer I presume.

Re: exit signs [Re: jdevlin] #175883 03/13/08 06:41 PM
Joined: Oct 2002
Posts: 482
Z
Zapped Offline
Member
Yes Ranger, they still have them, but they are falling out of favor now that LEDs are more available.

Back a few years ago, when I was putting up movie theaters, we were also using "nuclear" exit signs. The glow was actually put out by some sort of reaction - had no power source. Someone here can probably shed some more light on what the actual chemical process was for those signs. First time I saw them glowing in the back of the truck it kinda freaked me out a bit...

Re: exit signs [Re: Zapped] #175902 03/14/08 03:56 AM
Joined: Dec 2001
Posts: 2,486
T
Texas_Ranger Offline
Member
Ah, yes, those are sometimes used for retrofit jobs here. I've seen them used at an underground railway station where they obviously didn't want to bust up the walls but were forced to put up exit signs. Maybe they also already knew they were going to close down the station in a couple of years and didn't want to put in any money (I think it's going to be closed in 2009 or 2010).

I think I haven't seen any incandescent exit signs newer than some 50 years here... all newer ones are fluorescent, usually one 8W compact fluorescent, older ones mostly with a small battery, power supply and charger inside, newer ones in large buildings tend to be/have to be on a central battery, depends on the size of the bldg.).

3 years ago I did an internship with an electrical company and one of my jobs was running around in the garage of Vienna's court house and prison changing out old exit signs "because the batteries had failed". They claimed they had a power outage some weeks ago and the signs barely lasted 5 minutes. We used a couple of them as portable work lights and 4 hours later they were still going strong... whatever.

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