# LED overvoltage life expectancy ques.

Discussion in 'Electronic Design' started by frenchy, Mar 23, 2007.

1. ### frenchyGuest

If an led lamp is rated at 6 vac, and it's put in a circuit that duty
cycles regular incandescants - it has a peak of 18 vac but the result
of the cycling is the regular bulbs light as bright as if they were on
pure 6 vac - question, roughly what percentage of life would be
expected to be lost on that led over time? I mean, cut it in half, or
more, or (?) Same question for a led rated at 12 volts too...
thanks!
Frenchy

2. ### D from BCGuest

Amazing..It's english and I didn't understand anything in the first
pass.
D from BC

3. ### Guest

Light Emitting Diodes aren't rated for AC at all, being diodes.

If you're talking about a lamp designed as a direct replacement for
an incandescent lamp except it has LEDs instead of a filament, it has
other circuitry within that will strongly influence the answers to

Mark L. Fergerson

4. ### frenchyGuest

Yes these are direct plug in replacements for 44 and 555 bulbs. So
they have built in resistors or whatever else is necessary in them.
They are specified for 6 vac and I put them in a pinball that runs
44s, but later found out the pinball doesn't run pure 6 vac to the
bulbs, it duty cycles them with a peak of 18v. For a 44 the result is
it still looks the same in brightness as pure 6 v, but sounds like the
led is being overdriven in this cycling. So have gotten various
answers from pinball folks that this will reduce the life of these
leds.
Thanks!

5. ### Rich GriseGuest

If the peak voltage across the LED is greater than the LED's absolute
maximum rated voltage, then its life expectancy is zero.

Cheers!
Rich

6. ### Rich GriseGuest

If you plug one in and it works, it will probably continue to work for
the rated life of the LED. If you plug it in and it blows, then its
life expectancy was zero.

Hope This Helps!
Rich

7. ### frenchyGuest

If you plug one in and it works, it will probably continue to work for
Yes they are working just fine. When I plug the same one into the
pure 6vac section of the pinball (one used for general illumination
that's straight off the transformer) it's actually a little brighter
than the ones I have put into the voltage cycled 'feature lamps'
section. So I guess I'm ok. I don't know what the maximum rating of
the leds in these plug-in bulbs are, they are only rated for 6vac use
so that's all I know, they are putting unspecified leds inside of the
lamp casing. Thanks!
Frenchy

8. ### Rich GriseGuest

Well, it's apparent they already have their own limiting resistor, and
a reverse-polarity protection diode, so you should be fine.

I've found that doing an experiment like this can be the quickest way

Cheers!
Rich

9. ### Guest

Agreed, particularly when the mfgr doesn't/won't say what can happen
in these circumstances.

Frenchy, if I were you, I'd worry about it and contact the mfgr.
Plain incandescents are cheap and can handle spikes that kill LEDs,
but LED bulbs are still kinda spendy to take chances with. For all you
know the "feature" supply can also supply spikes that will kill your
LEDs.

If they won't say and you're confident the PS is safe, never mind.

Mark L. Fergerson

10. ### jasenGuest

that depends on the lamp.

-

Bye.
Jasen

11. ### frenchyGuest

I'm only using a few of these leds in spots where vibration is killing
the bulbs and/or where a lot of stuff on the playfield has to be
disassembled to replace them. Bulbs are about a dime, and these leds
are a buck, so not talking large \$. The encouraging thing is that the
color and brightness seems to be the same on the pulsed leds as when
they are placed in the straight 6v. If they were a lot brighter or
the color was being screwed up I'd worry more. They are still
working.

12. ### Terry GivenGuest

I have worked on a number of LED replacements for halogens and
incandescents. These have had little SMPS inside them, providing
constant current drive (unless they had to be dimmable). and would work
just fine in your app. Smash one to pieces, and see whats inside it. If
its a rectifier and a resistor, there will be trouble. If there is more
stuff it will work, and Rich's comment is spot on. A less destructive
test is to run it from 6V and use eyeometry to measure intensity. then
stick in pinball using HAM (Hairy-Assed Mess) "6Vac" and do comparitive
eyeometry; if they look the same then its probably a constant-current drive.

Cheers
Terry