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Charging "nonrechargable" batteries

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LAN_403

Avalanche

Wed Feb 22 2006, 03:30PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

I can confirm ordinary Alkaline cells recharge very well, because I have been doing it for years.

I don't tend to bother with other types. I recharge ordinary Alkaline AA cells in a charger built for that purpose, and I have found that the cheaper 'supermarket' type AA cells recharge best of all. Duracell do not charge so well, I would suggest testing different types of Alkaline cell to see how well they charge. Other types, like cheapo zinc-carbon batteries tend to just leak, these truely are 'single use' cells. It makes me sad to see so many perfectly good alkaline cells being thrown away though!

I usually ditch a set of AA cells after about 20-30 recharges. They hold more than ni-cads, and I would safely say that they aren't too different from those so called 'rechargeable alkaline' cells - I just guess the battery manufacturers don't want you to know that!

Electroholic

Wed Feb 22 2006, 09:19PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

in a ZnC cell, it generates H2 around the carbon rod, and when that happens, internal resistance increase.
all you need is to let them sit and wait for the MnO2 to them into H2O, and the battery will work again.
well, until the Zn cup finally get too thin...
But putting them in freezer will slow the process
down.
however freezer is a very good place to store fresh batteries, as it will slow down the self discharge.
Now, a better project would be to reverse engineer the "special" charger that you have and see how it's different from the "normal" charger.

IamSmooth

Wed Feb 22 2006, 11:00PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

As mentioned above, freezing batteries slows down the reaction, preserving battery life.
Heating batteries speeds up the chemical reaction to get a short-term boost in current output at the expense of longevity.

cjk2

Thu Feb 23 2006, 12:51AM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

Well thanks for all the help guys. I will test at least 3 different types of batteries. I think I will end up using a 555 set for about 2 seconds on and 15 seconds off per cycle. Ill use a dralington transistor to switch a 4700uf cap charged to around 5 to 9 volts into two AA batteries in series. How does this sound?

Bjørn

Thu Feb 23 2006, 03:33PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

I had a discharged 9V Duracell Alcaline battery on my desk. For fun I set it to charge at 30mA for some hours, Just now it went bang and cracked the bottom. It was lound enough that I am not going to risk that again. Buying a new battery is a cheap way to avoid a heart attack.

cjk2

Sun Feb 26 2006, 11:47PM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

Well thanks for the advice all. Just to let everyone know, it is now built and seems to work well. The only strange thing I have noticed is that after the batteries are charged, they seem to slowly lose some of their charge and tend to go back to being "dead" after like a day or two. I guess this just means I will have to charge them to a higher voltage to compensate. As for the issue of exploding batteries, I have pluse charged them at up to an average current of 150ma and I have seen no problems. They dont even get warm!

Pictures to come soon.

Part Scavenger

Mon Feb 27 2006, 03:32AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Yeah, I tried afro's circuit (with a microwave time circuit and a blast chamber just to be safe) and I was able to revive 4 9V batts! They work great, and they didn't get hot or buldge! I set my charge current to 40mA and used Duracell as well as Energizer. I had better luck with the latter, but I only had one Duracell and three Energizers so this might not be a fair statement. I just got better results with Energizer. I think Avalanche said something about Duracell not charging too. I plan to try AA's soon.

thom

Tue Feb 28 2006, 07:15AM

Registered Member #239 Joined: Thu Feb 23 2006, 03:15AM
Location: canada
Posts: 23

I tried this with 9V batteries and didnt have much luck.

A few that were already completely dead (around 7V) would charge and then very quickly lose their voltage over a day or so.

The ones that were not fully discharged (8.5V ish) seemed to take a charge much better, and stay stable at 9V. I used around 60-80mA, they got a little warm at the upper limit.

Didnt try AA's because I think its pointless. Nimh are so cheap and have a decent capacity (compared to 9V nimh which are expensive and have very little capacity).

Avalanche

Tue Feb 28 2006, 11:25AM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

regarding charging up 9v batteries, some cells will be weaker that others, and therefore charging them in series is probably not a great idea - especially when the battery has been allowed to go completely flat!

Best results are obtained from recharging batteries / cells before they are completely dead. I find that if you discharge them completely, they will not hold a very good charge at all.

I had 2 sets of alkaline AAs a few years ago for my pocket TV, and I would put them on charge after watching TV and swap to the other set. Those cells lasted over a year like that! I'll try and reverse engineer my charger some time, it does monitor the voltage carefully as you get a digital readout, and a bar graph indicating the sucess of the charging cycle (not sure how that works).

Mr_T

Tue Feb 28 2006, 01:15PM

Registered Member #137 Joined: Sat Feb 11 2006, 09:52AM
Location:
Posts: 2

"BjÃ¸rn BÃ¦verfjord" wrote ...
I had a discharged 9V Duracell Alcaline battery on my desk. For fun I set it to charge at 30mA for some hours, Just now it went bang and cracked the bottom. It was lound enough that I am not going to risk that again.

Hehe.
My mother put a 9V battery on my desk and wanted me to check it (it was built in in a remote control for about one year).
Suddently it explodet but it was not connectet to anything. I almost fell from my chair.

Someone kow why it exploded?

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