Got 2.5V out of a AAA battery, no Batteri*er involved - Page 1
Forum section: electronics / projects

author: jp430bb
author_rank: Contributor
timestamp: October 29, 2015, 01:46:07 am
content: After having a AAA battery burst and spew its goo inside my every-day-carry LED flashlight, I cleaned it up a bit and tried it out with a fresh battery. The flashlight didn't work, but when I checked the voltage, I was surprised at what I found. 2.5V out of a 1.5V battery?!I figured out what was going on after a bit, and then I shot this short video to show some friends as a puzzler. Maybe some readers here would like it.https://youtu.be/MNFjPa-r3Ho

author: 6581
author_rank: Unknown
timestamp: October 29, 2015, 06:39:17 am
content: There is only one scientific explanation for this phenomenon. Universal Evil Organized Battery Union has been secretly preventing us from tapping into 888% of remaining energy in used batteries, forcing us to buy more and more batteries. If we could use all the energy (also known as voltage) in batteries, you could run an electric car from one AA for a year. What you have there is a super secret prototype of a miniaturized Mr Fusion.

author: LA7SJA
author_rank: Regular Contributor
timestamp: October 29, 2015, 09:28:26 am
content: It may be that a white LED need about 3 volts to light so the torch contains a step up constant current power suply to make it light up correct?Johan-Fredrik

author: crispy_tofu
author_rank: Super Contributor
timestamp: October 29, 2015, 10:35:52 am
content: Quote from: 6581 on October 29, 2015, 06:39:17 amTime to drive everything off a cliff and start a new life in the Pacific Ocean.

author: mij59
author_rank: Frequent Contributor
timestamp: October 29, 2015, 11:49:42 am
content: Coin cell about 1.1V at the bottom of the battery holder.

author: Fungus
author_rank: Super Contributor
timestamp: October 29, 2015, 12:55:03 pm
content: The DC booster is in the base?

author: richard.cs
author_rank: Super Contributor
timestamp: October 29, 2015, 01:23:37 pm
content: DMM internal battery low and giving junk readings?

author: Delta
author_rank: Super Contributor
timestamp: October 29, 2015, 01:27:04 pm
content: Magic?

author: Fungus
author_rank: Super Contributor
timestamp: October 29, 2015, 01:33:36 pm
content: Quote from: blueskull on October 29, 2015, 01:06:32 pmGood point.Are we assuming he's cheating or is this a natural phenomenon?

author: Ian.M
author_rank: Super Contributor
timestamp: October 29, 2015, 02:14:30 pm
content: Its about right for the electrode potential difference between Iron and Aluminium.http://www.engineeringtoolbox.com/electrode-potential-d_482.htmlso the most likely explanation is a weak electrochemical cell between the spring and the housing, with the corrosion damage from the leaky battery forming a porous seperator layer saturated with electrolyte. Due to the very low surface area and probably significantly diluted electrolyte after cleaning, the voltage will collapse as soon as any significant load is put on it. Testing the voltage with a metal rod (e.g a large bolt) to reach the spring surrounded with tape or an insulating tube would provide absolute confirmation.Hook the spring out, clean out the housing and clean up the spring with wire wool and rinse with boiling water, hot air dry, tin the spring's contact surfaces which will otherwise rapidly degrade, and re-assemble with a light smear of dielectric grease to exclude oxygen and moisture from the contact surfaces to prevent further corrosion. Then its got a fair chance of being reliable again.

author: Bud
author_rank: Super Contributor
timestamp: October 30, 2015, 01:05:41 am
content: Quote from: blueskull on October 29, 2015, 01:06:32 pmPerhaps he closed the path Through his right hand, with one finger touching the meter probe and the other two or three touching the flashlight. Much less resistance than the meter's 10M

author: Jeroen3
author_rank: Super Contributor
timestamp: October 30, 2015, 10:55:17 am
content: I once got -0.8 volts out of an AA. Yes, you can invert charge them.

author: jp430bb
author_rank: Contributor
timestamp: October 30, 2015, 12:28:58 pm
content: Quote from: blueskull on October 29, 2015, 05:44:27 amExactly!No trickery, just science!@Ian.M explained it even more fully---dissimilar metals (steel spring and aluminum alloy-of-the-week flashlight body) formed an unintentional galvanic cell. I had likewise ended up atwww.engineeringtoolbox.comtrying to see if the potential I measured is what would be expected for iron (ish) and aluminum (of some alloy). Maybe if I had a meter with gigaohm input impedence, I might have been able to see exactly what potential the cell got to after recovery.After scraping out the crusted goo (sandpaper wrapped around a bolt) and lots of washing, the flashlight is operational again. I might take the advice from @Ian.M and give it some more cleaning and try to tin the spring to prevent further corrosion.@EEVBlog Dave recently talked about how batteries should be checked under load, and this unintentional galvanism shows the behavior he referred to in spades.What sets the time scale for the potential drop under load for this thing? Ion migration in the crusty goo?I could imagine this kind of unintended galvanism would be something experienced EEs would have had to anticipate and design for. Maybe very sensitive circuits could be damaged if such a cell was allowed to charge up a capacitor which is later dumped into the circuit?