Out of the blue LED experiments

[micropv]

Long story short, found in our yard a marker light, kids?


pulled the LED and hooked to 2 junker low capacity batteries 3+ days ago, LED fv unknown, batteries known capacity of only 235mah with a starting voltage of 2.7v



at nearly 60 hours continual run time, voltage under load is down to 2.59v(?)

so, did some digging in my junk drawer (I bet I am the only one who has a junk drawer) and rounded up two more white LEDs (fv unknown) that came out of broken solar lamps.  Hooked to known capacity batteries this morning.  The 2.4v setup had a starting voltage of 2.7v, capacity of 1830mah.  The 3.6v setup had a starting voltage of 4.0v, 1355mah. 



It will be interesting for me to see run times on these as I have never really played with individual LEDs even though I have used LEDs in fixtures for many years now.  And of course I had to order some more to play with as well as some resistors.  The above LEDs have no resistors.

[southpaw]

I once connected a yellow led to 2 double A alkaline batteries in series just before Thanksgiving .
It was still glowing at Easter.

[DamonHD]

My little LED nightlight went the best part of a year between its last two charges.

http://www.earth.org.uk/LED-homebrew-nightlight.html

It does have a little solar panel in there, but I'm not at all sure how much difference it makes.

The key improvement I made was to use the 'hybrid' NiMH cells, because normal ones nominally self-discharge in 3 months or so.

Rgds

Damon

[micropv]

My little LED nightlight went the best part of a year between its last two charges.

http://www.earth.org.uk/LED-homebrew-nightlight.html

It does have a little solar panel in there, but I'm not at all sure how much difference it makes.

The key improvement I made was to use the 'hybrid' NiMH cells, because normal ones nominally self-discharge in 3 months or so.

Rgds

Damon

Hey Damon,

Thanks for the link!  At 4.7kΩ that is really choking down on the battery drain for sure!

I have ordered both 250Ω resistors (7mAh-8mAh current draw) for running off of 4.8v packs, as well as 100Ω resistors (10mAh current draw) from 3.6v packs.  Hopefully I have done my math correctly.

For the night lights, for now, I will continue as is using 2.4v packs as it is really simple.  My little blue LED up top is now on day 5 continual run time and voltage is only down to 2.57v (235mAh capacity pack), just slightly better than a 1/2wh pack (finally a use for these cheap batteries labeled "3000mAh"!!!).

I wonder what the bare minimum voltage is that is required by a 3.1v LED to display any light?

[tanner0441]

Hi

I have a little LED torch while tracing cables at my old work place I dropped it down the side of an RSJ into the void at the back of the wall cladding. I was prepared to leave it there but a week later it was still glowing at the same level as when  I dropped it. So after a little bit of measuring I cut a hole in the plasterboard and retrieved it. out of curiosity I put it in my toolbox still on another week later I had to use it and took it out but it was still as bright as when I lost it.

My yards back and front are now lit with LEDs two ten watt units and one 7 watt unit down the side of the house, I also have a seven watt bulb on a dusk till dawn sensor in a bulkhead fitting lighting the area where we park the cars and the drive from the road, also I have replaced all the lighting in my motor home with LED lighting and apart from the main living area throughout my house use LEDs. As long as you look for colour temperatures around 3000 to 4000 Deg K then it is a comfortable light to live with.

LED lighting.. I am definitely a convert, for main living areas CFLs still have the edge on lighting level but the difference is a lot closer, If I was building a house now I would definitely  wire the lighting circuit for low voltage and put solar on the roof and batteries in the loft. A big plus, LED down lighters don't need fire screens over them like halogen.

Brian

[micropv]

After 7 days on the cheapie "3000mAh" batteries, the ones advertised on epay from China (300-600mAh in reality), voltage is at 2.55v.  Cut off for the LED is 2.5v where as no visible light will be detectable as far as I can tell. Blue LED is still emitting light, albeit a very tiny amount.

Next test will be to charge 4 batteries of similar capacity, then 2 on the LED and 2 just resting.  I wonder if the resting batteries will hold voltage longer with no load, or visa versa?

Kinda fun stuff.