Eternal led 'on' ?

[marseye]

Hi Guys,

Just a quick note, but kind of food for thought : to my surprise, a tiny (white) led attached to a big capacitor doesn't seem to shut off completely. Not a bright or in any way convenient light (it's veeery dim), but it feels like 'ON' !

Mesured voltage : 0.000v current : 0.000A (my DMMs are not pricey ones). But after 1 hour, still 'on' !!! I'm just curious to see how much longer that's gonna last. The setup will rest attached.

The bigger the capacitor, the better. Observable from a 470µf (extremely dim though, but still 'something'...), but best seen with a 47000µf (and while it's dark of course ; mine is rated for 25v. Still a nice chunk !).

Wanna try ? Just hook a led to a big polarized one, feed that group briefly with 3v, then observe.

The capacitor discharges first because of the led closing the circuit. But there's a point when there's nothing left enough for the led to fire anymore. The capacitance only seems to be enough to keep the led barely 'on'. That's why I'm advising around to use a big capacitor (the remaining 'pressure' inside is bigger (larger/wider/whatever), and permits a much visible effect).

Searching about that phenomena, I found a relevant advice adressed to electricians. They are advised to install a resistor in parrallel to avoid such domestic problems :
https://www.lightrabbit.co.uk/cable-...blem-led-lamps

But food for thought, as I said....

[ricards]

Hi marseye,

The big capacitor serves as your power source, That high Capacitance can really power a Led at it's dimmest for days.., but that doesn't mean It's eternal, It's going to be discharged sooner or later.

If your led goes brighter If you ground 1 Lead, you probably are in an area where there's good electromagnetic activity. your big capacitor is being charged by it and If you would look at the way capacitor's are constructed, they are really like pancake coils extruded. If this is the case and the electromagnetic energy your capacitor gets is higher or equal than that Led takes, congratulations you may have had an eternal LED.

But It might not work in other locations.

just a theory though..

[marseye]

I understand perfectly. 'Eternal' was just provocative (with a question mark).

It's just proof that diodes can be active on such few energy levels... They won't fire from an original undervoltage. But it seems they keep conducting after having been fired correctly if a capacitance is still present.

I just found that was interesting. Not sure about what to do with that. But it's now in a corner of my head. There may be an application to it. One never knows.