White Leds can be reversed EASIER

[**DONOTDELETE**]

in my psudo relistic experimentaions here
i have been running White Leds off of a AC circuit, WHY cause i can

actually because i would have to make a full rectification for it and it wont fit in the halogen lamp with the capaciters too

the white leds are coping continuously with the reverse current, but i have tested cyan time and time again , using more per bank and everything , and they just dont do it.

so i thought that was interesting to point out
also the cyan lexeos(sp) star was the first to go in a microsecond from reverse currents

strange seeings the two of them basically use the same technology

mabey Whites are for newbies

 

[Silviron]

Interesting. I'm glad I'm not the only one...

I know I burned out my Cyan LS (Luxeon Star)with just a tiny little mis-application of electron flow.

Still, I think I'd at least try to figure out some way to give them ALL DC.

 

[**DONOTDELETE**]

well i could drop a diode in on each side
then it would be pulsed dc instead of reverse pulsed dc
a led is a diode , just not a powerfull one
but to rectify without capaciters would just give me pulsed dc

but along them lines i can diode the cyan and reds, and see if it was the pulsing or the reversing for sure.

(picture of lightbulb over head)
i think ill try that , there must be something in this big box of garbage parts that will fit

the other desk lamp which has less voltage is doing wonderfully, but this one on my desk was giving me he!! even with the halogen in it, it would burn out once a month
course it never gets turned off


*rummage scrounge rummage scrounge*

 

[Silviron]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Video Guy:
well i could drop a diode in on each side
...<HR></BLOCKQUOTE>

Don't forget about the ~ .7V voltage drop from each diode.

 

[JoeyL]

Hi folks!

I wonder if you could help me since you're on a similat topic.

I tried to run two white LEDs in series off a 12 v transformer with a single diode. The voltage ac was measured at 12v.
The pulsed dc voltage with the diode in place was 7.1v.
When I put them in the circuit, they lit fine, no brighter than usual, but got really hot in about a minute and one fried out.
Is it because the voltmeter only registered an average voltage and the pulsed dc voltage with the diode in place is much higher?

Any thoughts would be welcome.

Thanks,

 

[Silviron]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JoeyL:
I tried to run two white LEDs in series off a 12 v transformer with a single diode. ...I put them in the circuit, they lit fine, no brighter than usual, but got really hot in about a minute and one fried out.<HR></BLOCKQUOTE>

Several of the other regular posters are more knowledgable on this subject than I, but here is what I think:

You should have been reading AT LEAST 11 volts with just one diode. It may be as you surmised, you were only getting an "average" reading on your meter (was it analog or digital?)and your peaks were MUCH higher.

All of the 12 V transformers & unregulated wall warts that I have tested put out 14 - 20 V under no or very light loads.

Anyway, Sounds like "thermal runaway" to me.

The hotter they get, the more power they draw, the more power they draw the hotter they get. . . and on and on till something burns out.

I wouldn't even try to run LEDs off a transformer without a regulator in place. Voltages in plain old transformers is remarkably unstable depending upon the draw of the device hooked to them, so thermal runaway is even more likely than with batteries. You MIGHT be safe if you used a transformer that was rated at under 50mA. (and if you find any 12 V with < 50 mA ratings, let me know, I've been looking for some)

Plus voltage spikes coming down the AC line can kill your LEDs too, even if you don't have thermal runaway.

 

[e=mc²]

Silviron, I know you said 50ma @ 12 VAC, but this one at Hosfelt is pretty close, and I have used these successfully in my white LED night light projects.
Hosfelt PART # 56-217
They are only $1.49 USD. I typically use a miniature bridge rectifier (DIP packaging) to provide full wave rectification so the flicker rate is 120 Hz rather than 60 Hz on a single diode rectifier. I don't bother to filter it since it is only a nightlight for those "nightly trips" around an otherwise dark house. Hope this helps.

Edwood.

 

[**DONOTDELETE**]

JoeyL
from what i know
yes it is an average
and completly dependant on LOAD
put a capaciter on the circuit to see the accrued into a capaciter voltage from the pulse, and i bet your no load reading goes way up

ALL
i might note that these desklamps are on semi regulated UPS's for the computers so they arent likely to have huge spikes