Coin Batteries that won't die!

AlbertHall

Joined Jun 4, 2014
10,258
Also, the lower the drive current, the more efficiently the LED operates.
Curious. I have heard the opposite. Feeding the led with 50:50 pulsed 10mA gives more light than running it at a steady 5mA as the LED is more efficient at the higher current.
Which of these is correct?

[Edit - I see this was answered before I had written it. Very crystal ball!]
 

dl324

Joined Mar 30, 2015
11,317
Feeding the led with 50:50 pulsed 10mA gives more light than running it at a steady 5mA as the LED is more efficient at the higher current.
Most datasheets should have a graph showing relative luminous intensity vs forward current.

Here's one for a green LED, chosen because it shows that efficiency isn't linear and trails off at higher current:
upload_2016-12-15_11-28-30.png

I have a book written by engineers from HP's Optoelectronics Division back in the late 70's that described the effect in more detail. I'd quote it, but it's not handy...
 

dl324

Joined Mar 30, 2015
11,317
That graph seems to show efficiency rising all the way, not trailing
My bad. It actually shows efficiency continuing to increase to the highest current shown.

The phenomenon that reduces efficiency is essentially current crowding in the junction. I'll look for my book and quote the section.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,929
12/20/2016 and one red LED still glows on. I was certain it would have gone out a long time ago. If anyone is still following this thread - I'm just about ready to toss the battery regardless of whether it's glowing or not.

Go figure.

BL3 voltage reading: 1.674 (that's with the LED glowing)

If I don't see you before then, have happy holidays.
 

AlbertHall

Joined Jun 4, 2014
10,258
My battery capacity tester has arrived and is presently employed on the task I bought it for. When it has a slot in its diary, I will be repeating the experiment and I will report the results.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,929
FYI: I've started a new test using a CR2032 out of my wireless doorbell.

It's standing voltage (unloaded) is 3.008 volts (3.01). Shorting the battery with a 100Ω resistor (actual value 101.3Ω) for 2 seconds, battery voltage drops to 2.10 volts. At an ambient temperature of 72˚ F, the battery voltage with a SUPER BRIGHT RED LED (typical Vf of 1.95v) is 2.00 volts.

I will be charting my measurements as the days go on.

Hope everyone had a good New Years Eve celebration. We were up till 3:30 AM.
 
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