Dead AA Batteries - They are full of energy!!!

[schuler]

  Hello Experimenters! 

I would like to share an experiment.

I've got 4 so called AA 1.5V dead batteries. They were batteries used in a wireless mouse and keyboard. Both mouse and keyboard stopped to work because the voltage wasn't enough. My multimeter shows 1.2V in each battery. Before throwing these batteries in the trash bin, I decided to connect these 4 AA batteries in series, use a 680r resistor connected in series with 16 water clear/white 5mm LEDs in parallel. The current is around 1.5 to 1.7 mA. I found interesting how much light I can get from just 1.5mA.

This little experiment makes me think how much energy is sent directly into the trash bin. My experiment is now running for days using so called dead batteries.

It seems that the smaller the current, more energy you can get: http://www.powerstream.com/AA-tests.htm .

Have Fun 

[TinselKoala]

You are totally right.

Many consumer gadgets like cameras, mp players, mouses, etc. have "low voltage cutoffs" and either tell you to replace the battery when it hits 1.2 v or simply stop working at that voltage.

This is to prevent erratic behaviour as voltage drops below reliable levels. But there is still plenty of energy in the batteries!  (This is also why many of these devices won't run on NiCads for very long: the cell voltage of a NiCad is too low even when fully charged, so the device thinks it should stop working at 1.2 volts.)

Circuits like the Joule Thief in all its variants will allow extraction of this "throwaway" energy down to an indicated voltage of less than 0.5 volts in some cases. The simple series resistor that you are using is actually wasting power itself: it is dissipating P=I²R Watts while you are running your light string -- over 1.5 mW going to heating the air around the resistor.

So... we need a battery charger, that will take these used alkalines and suck the energy out and put it into a rechargeable battery like a LiPo at higher voltage. Even if the overall efficiency of such a charger  might be low, it's still going to be better than tossing the batteries into the recycling bin when they are still indicating 1.2 volts.

[Pirate88179]

TK:

Yes, i have many friends that save their "dead" batteries for me and i light most of my home using them and some JT circuits.  I always use the "" when saying dead batteries because, as you point out....they just have dropped below the threshold of whatever device they were being used in.  There is a lot of useful energy left and I have 3 gallon freezer bags full of "dead" batteries to help light my home for some months to come.  I hate to see anything wasted.

Bill

[schuler]

Hi Pirate,
What kind of LEDs/resistors/current are you using? Any current/voltage measurement? I've found that white and blue LEDs are the most energy efficient.

[Pirate88179]

Hi Pirate,
What kind of LEDs/resistors/current are you using? Any current/voltage measurement? I've found that white and blue LEDs are the most energy efficient.

I am running mostly modified Fuji circuits outputting around 400 volts.  I have several lights consisting of 2 Lights of America chip LED bulbs (each bulb has like 24 chips I think)  I have no idea what the amp draw is but I run these almost every night and a "dead" AA battery lasts for many evenings.  I am working on lighting up some Cree type LEDs now to see what happens.

Bill