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  • Author Author: jw0752
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Experimenting with Weak Batteries

jw0752

Many of the small electronic gadgets that I use daily, cameras, labeler, and test equipment, do not tolerate battery voltages below 1.4 volts. As a result I have always quickly accumulated a lot of AA batteries with voltages around this level. When I counted the other day I had over 40 such batteries. Traditionally they have gone out with the recycling. This time however I decided to do a little experimenting to see if I could capture and use some of the remaining energy. A wealth of small DC to DC converters are available today with very impressive efficiency. My first step in doing some of my experiments will be to construct a couple of battery holders so I can put 10 of the AA batteries in series. This way I will have sufficient voltage available so that even a cheap 12 VDC to 5VDC converter will have enough room before we approach its drop out voltage. This should occur when the used batteries reach 0.8 volts and are truly ready for the recycling bin.

 

A search of the local hardware store revealed that 1/2 CPVC pipe had just about the correct inside diameter to serve as a battery tube. I also brought home 4 cap ends. Here is the results of a half hour of cutting and drilling.

 

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One pipe cap is fitted with a spring to keep contact on the batteries and the other cap has a terminal that is made of a brass screw that has been flattened. The pipe caps friction fit onto the pipe tightly enough so that they do not have to be secured in any other way. Here are some detail pictures of the internal construction.

 

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This is the negative end of the battery tube.

 

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Here is the Positive end cap of the tube. The finished tubes (I made two) were 54 cm long. I attached appropriately colored test lead wire onto each cap and terminated the wire with a female banana binding post. I have a lot of adapters using banana plugs and jacks so this termination will allow me to easily attach to any test rig that I might set up.

 

The first simple experiment that I had in mind was to use the batteries to charge my cell phone. To do this I took apart a cheap Dollar Store 12 volt USB adapter and wired it so I could plug it into a bread board. I ran some bench tests on the small converter and determined that it was probably designed to deliver 500 mA. Here is a picture of the set up charging my cell phone. I have used one of the small voltmeters to monitor the output of the 5 volt converter. The second picture is a closeup of the small converter circuit.

 

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After my phone charged I hooked up a small rechargeable battery pack. It was noted that the battery pack loaded the converter down more than recharging my phone had. Within 20 minutes the load lighten up and the voltage level came back up to the 5 volt area. Here is a picture of the set up. You will also note that in this photo I have been at work with the label machine as is customary for me.

 

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I am not sure where I will go with this project from here but the continued interest in salvaging energy on the forum made me want to be prepared for a few experiments. I believe that I will use the battery packs to charge my phone for a few days but the size of the battery tubes and the mess of wires makes it unlikely that they will be allowed to stay on my bedside stand for too many days.

 

John

  • in reply to Jan Cumps

    Hi Jan,

     

    Yes, heating the batteries will add energy, but it will also make sure that the last bit of chemical reaction can occur.

     

    I see adding heat the same way that you would if you squeeze the batteries as shown on EEV Blog.

     

    You add energy in both cases so that the chemical reaction can occur at an accelerated rate.

     

    DAB

  • in reply to DAB

    DAB, we should in that case measure if we're not putting more energy in the heating up than what we get out of it.

    It would be a nice test though.

     

    I think I'll have to work on a configurable load with power measurement.

  • in reply to DAB

    They do work a bit better when hotter, but mainly when they get frozen it inhibits the physical movement of ions, at least that is how I visualize it. It seems some areas or paths are not completely locked up when frozen, although some are, so perhaps the electrolyte is not perfectly homogeneous. If you could come up with a way to make the electrolyte more homogeneous you might see a major improvement in alkaline batteries. Even when hot there would be less internal resistance.

  • in reply to dougw

    Hi Douglas,

     

    You just gave me an interesting idea for heating up older alkaline batteries to excite them to produce more current.

     

    DAB

  • in reply to jw0752

    Good work John,

    When designing battery operated devices, it is useful to keep in mind that alkaline batteries supply useful energy down to half their fresh voltage. And when drawing significant current, their output voltage sags.

    Another point about alkaline batteries - when they get cold (below zero C) their apparent capacity drops dramatically (to less than 40% of normal capacity). But a battery that got depleted at cold temperature will regain its normal remaining capacity when it is warmed up.