Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Lead acid (wet and SLA) don't seem to have problems when put in parallel and series-parallel configurations, but other types will just discharge into each other and severely shorten the life of the cells.
Like I mentioned before, I learned this the hard way...
Couldn't you simply use a diode on each positive lead? As long as the packs have similar performance I would think that would work. The current load could still be a little uneven, but the diodes would prevent the stronger pack from charging the other, wouldn't they?
The diodes would make an OR gate. One battery OR the other battery would power the load. The battery with the highest voltage. They won't be in parallel so their currents are not added.
When the battery with the highest voltage discharges down to the voltage of the other battery then they will be in parallel only for a moment.
Perhaps one has to use schottky diodes to reduce power wastage. then the supply to the load will be reduced by the voltage drop of the diode .
thus there will be reduction in the effective working time of the battery.
I dont see anything wrong with using two diodes one for each pack. When one pack
drains the other pack will take over, if it does in fact have a lower characteristic
voltage.
The real question though is whether or not you want to lose the voltage drop of the
diode, which will typically be 0.4v or so with a good Schottky, and that's a lot of
voltage at 2.4v nominal.
You could recharge using two more diodes with series resistors to limit current to
each pack, and that would also allow some voltage variation so both packs can
fully charge.
A better idea though is to go out and purchase some higher capacity batteries.
That will give longer run time and eliminate any voltage drop (or other) problems.
Tipsy, I think you might be talking about 'shocking' a battery. I'm not sure what the voltage is but it involves apply a very high (relative to the cells voltage) to the battery for a very brief period of time, which supposedly causes the oxides in the battery to be burnt off. It can temporarily revive dead batteries, I'd never do it though. If a cell has oxidized to the point where it won't retain a charge any longer the chemistry has either destabilized from over/improper use or just age, it should be removed from regular service and never used in a pack with other batteries.
I've done this several times myself and always found that the cell does revive for a while, but then soon the
same thing happens again. It's not worth the trouble unless you are really in a pinch for a cell (emergency or
something).
I used a large capacitor and wall wart. The stored charge zaps the cell back into operation.
Supposedly it breaks up the larger crystals that form.
Yeah, I'm of the same mind MrAl, I'd be more inclined to pop in a fresh set of Alkaline in a pinch. The crystals you're talking about is the oxide layer I believe. It does break it up, but it doesn't eliminate it, it reforms, you can't just get rid of the byproducts they're there forever unless it's treated chemically.
Use modern Ni-MH cells instead of antique and poisonous Ni-Cad battery cells.
A Ni-MH battery has 4 times the capacity of an old Ni-Cad battery. Somebody should tell the Chinese.
They're not that antique audioguru, they're still used in RC applications because they're cheap, good cycle capabilities and low series resistance. They likely will be for some time. For the cost/benefit analysis they still have their place. The Cadmium itself is irrelevant if the cells are disposed of properly.
Yes i have read about the crystals and whatnot, but never studied it in great detail.
I have also found that NiCd's are needed sometimes when NiMH wont do as well,
as in very high current hand power tools like drills.
Lithiums are taking over in that department, primarily because of the major advances in lithium batteries over the last few years. Between more advanced construction/chemistry and paralleling packs with smarter chargers Lithiums are drop in replacements for almost all battery technologies nowdays.
I'm mainly thinking of legacy/custom rechargeables as they are invariably expensive, the common ones are cheap enough as you say, just bin them and buy new at first sign of failing.
Has anyone heard of reverse charging a certain type to revive it? I've read it on two seperate websites/forums (but failed to bookmark them for further reference). It would be great if I could revive some of these dearer batteries!
Well, NiMH cells are now available in >2AH AA, although sometimes the rating is exaggerated when you get much above 2AH, and a common complaint is that the types which high AH capacity have high self-discharge rates.
You can't parallel NiMH/NiCd in any practical way except in large industrial strings with some fairly advanced circuitry. Been through this. There is no practical way on a small scale.
The "memory effect"- that if you don't run it down all the way before recharging, the capacity is reduced on all later cycles- often cited as a problem with NiCd, it never really existed.
NiCd/NiMH can be run all the way down to 0V without causing significant harm to the cells. However, REVERSING a cell will most definitely permanently damage a cell. Unfortunately, that's what happens if you have a multi-cell battery and run it all the way down. One cell in a 6v pack will be lower than the others, reach 0v first, the pack still develops 4.8v and you keep using the drill. Several amps is forced through a 0v cell the opposite direction as charging, and it'll actually show a negative voltage when taken out. Permanent damage.
The common method of cell death is separator failure. "zapping" a cell breaks the dendrite or whatever is pushing through the broken separator, but it's quite short term since it does not actually repair the separator- the cell will fail again in a few cycles or a few days.
For about one year, Energizer Ni-MH cells that are made in Japan are "pre-charged" and a charge lasts for 6 months or more. Sanyo also has Ni-MH cells that hold a charge for a long time. Maybe Sanyo makes cells for Energizer. The AA cells are 2450mAh.
I cracked open a laptop battery once and noticed it was just an array of C-cell type rechargeables - about nine IIRC. Pity that just one cell can take out the rest. I did plan on trying to replace them but re-assembly looked like a nightmare with various diodes, temp sensor and press-welded terminals threaded through layers of insulative card/plastic.
TBH, I am sick and tired of buying rechargeable devices with short-lived batteries as it invariably proves very difficult to obtain replacements, if not impossible.
Specifically in my collection, I have two laptop packs, one satnav, one mobile phone, one home phone, two one cordless dremel packs, one cordless drill and a pair of PMR two-way radio packs that all use properiatory rechargeables. Asking the retailer that sold the units usually results in shrugs from the poorly trained assistants.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
