Long low-level LED light output

[Dave_H]

LEDs sometimes show amazing ability to deliver low-level light over long periods with very low current, including from cells which are considered otherwise dead.

I've been running string of 50 "microdot" multicolour Christmas lights from two NiMH AA for six months continuously, since Christmas. The LSD Duracells are getting low, total around 2.3-2.4v. Light output has become faint, but visible night and day; a sort of "perpetual nightlight" . I measured 70 microamps total (for 50 LEDs!). The blue ones seem brightest.

Dave

 

[Dave_H]

I should add that very cheap 12-LED 3AA lantern from Dollar Tree has been running overnight for weeks on its low setting with cells at 1v or below. Light is dim but sufficient. At this rate I will have difficulty using up all those "free" alkalines.

Dave

 

[Dave_H]

Another example is a set of two 1-foot orange LED strips which run from 12v. Each SMT LED is a triple wired in series with dropping resistor so there is lots of overhead, each LED typically 2v. At 12-14v it is quite bright. Run from one partly-used 9v battery it is not nearly as bright, and brightness decreases, but it runs several nights as a kind of novel night-light.

"Demo mode" of the package uses two 9v zinc-carbons series-wired which drops under load. I can run from two used cells below 6-7v in series to the point they are no longer usable, then off to recycle.

Dave

 

[thermal guy]

Yep the battery drainers “vampire” that you can get on a CPF are great for this.

 

[Dave_H]

I took a 1AA solar garden light having colour-changing RGB LED, whose battery terminals had corroded (difficult to repair) and wired it to a 2AA cell holder with switch. Series cells run until total drops below about 0.7v. It's amazing to sometimes get several nights worth of nightlight with cells at those levels. Then they are truly ready for recycle.

Alkaline leakage at those levels...can happen. If not caught soon enough, it's contained by plastic cell holder taken from a dollar-store LED string (whose LEDs went to repair a lighted solar planter, story in itself).

Dave