Charging "nonrechargable" batteries

[cjk2]

For this years science fair project, I plan on testing standard batteries, and seeing if they will take a charge (I know this is possible). I plan on constructing at least 3 circuits for use in testing. I will build a circuit to discharge the batteries(1.5v cells), a constant current charger with an lm317 regulator, and a "pulse" charger.

My question is this: to build a pulse charger, could I use something as simple a 555 and a transistor/FET to discharge say a 4700uf cap at 1.5v into the battery? Or is something more complex needed to keep the cells from exploding?

 

[audioguru]

About the only way to keep the cells from exploding is to read and follow the advice on their label: Do Not Charge. Keep Away From Fire.

 

[mechie]

Old Battery Charger

I have an old "universal battery charger" which claims to recharge the old zinc-carbon disposables, admitting that you get less from the battery every recharge. It just half-wave rectifies the mains transformer's output to produce the 'pulses' - no smoothing, no fancy control gear ! (No. I've never tried it!)

Be warned - these batteries work by non-reversible chemical reactions (the zinc case is eaten away) so take care - you WILL end up with leaky batteries - and keep the charge current low - less than an equivalent ni-cad and for a shorter time.

There is a risk to this so take care. Be prepared for fire/explosion/chemical leaks :wink:

 

[bryan1]

I made up the smart fast charger kit that siliconchip did as a project back in 2000 that chargers just about all the re-chargeables and lead acid batteries but it states in big plain english Don't try and charge non re-chargables as not only would it kill the charger it WILL kill you in the process. I'm sure I don't want battery acid all over my body just because I want to be different and say hey I can recharge these enigiser batteries.

Just my Thoughts Bryan

 

[chemelec]

Using a Low Current, 10 mA from a constant Current source will usually Re-Charge most Zinc/carbon batteries quite safely, over a 12 to 24 hour period. I have also done this with "Energizer Lithium Batteries".

The biggest problem "May be having the battery leak fluid", but exploding shouldn't be a problem.

 

[Someone Electro]

Some getho guy has tryed to recharge them and he did it.(Ith one of the rare useful things on his website)

**broken link removed**

 

[cjk2]

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.

 

[Oznog]

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.

It's unlikely pulsing would do anything special. I think it'll be less efficient than straight DC because you're either looking at a higher peak rate- which is more likely to cause trouble- or a low peak rate and thus just taking longer because part of the time you're not charging at all.

People have been talking about recharging carbon-zinc batteries. Don't know why this is being mentioned. Long before the "Rechargeable Alkaline" battery type, people have been getting fairly good results with recharging normal alkaline batteries. But there's issues. I heard the charging only really succeeds if the cell hasn't been discharged more than 50%. And it's only good for a few cycles.

LOTS of web pages on recharging alkalines. Just Google for "recharging alkaline" and try to sort it out from the ones selling the newer Rechargeable Alkaline types.

The assertion that you'll kill yourself are way out of order. You want to place the charger and batteries on a nonflammable surface and get a bit of clearance in case they leak- or potentially they can spray a few inches at best, though I've never heard of it. If I recall correctly alkaline electrolyte paste isn't extremely strong anyways, it would probably cause serious injury if you got it in your eye (goggles might be a good idea if you're really close). Recharging can generate flammable hydrogen gas, but only a small amount. Hydrogen, like any flammable gas, is only flammable when a specific concentration is exceeded. So unless you have it in a small enclosure or really high charge currents it's unlikely you'd be anywhere near a combustible mixture.