Quoted post said:Originally posted by Wle
is there any battery system that works for rechargeable lights?
i got a cygolight nicad night rover setup.
i guess one problem is that it has a 'dumb' charger.
you literally cannot follow the directions, or if you do, something will be wrong.
a. don;t let them run all the way down
b. don;t charge them unless they are all the way run down
c. don;t leave them on the charger more than 12 hours.
so, if you follow the rules,
you never know how much charge is remaining
you can;t know if they are full when you set out on a trip
what a pain!
sla [sealed lead-acid] batteries are no better. they get progressively dimmer as they discharge. at
least nicads stay bright til the end.
what about nickel metal hydride? [nimh]?
would a smart charger at least let you leave home with a full tank?
wle.
I wouldn't be overly preoccupied with dumb chargers overcharging NiCd batteries.
Rechargeable shavers, power tools, and flashlights with dumb chargers, emergency lights have abounded for years because NiCd batteries are moderately resistant to overcharging.
If you leave your NiCd batteries on your charger double your charge time every time, you probably are only going cut the number of lifetime duty cycles in half of your NiCd batteries. The emphasis on smart chargers picked up recently due the vulnerability of NiMH batteries to overcharging.
Even with NiMH batteries, a couple hours excess on the dumb charger will only noticeable shorten the number of duty cycles-not immediately destroy them-but certainly don't leave them on triple their designated charge time-that would quickly destroy them. Back around 3-4 years ago, standard practice was to charge NiMH batteries on dumb chargers with shutoff timers. NiMH batteries generally have slightly lower weight and more capacity than equivalent sized NiMH batteries. Since the NiCd batteries have low resistance while the NiMH have medium internal resistance, you ought have a little more lead time on the discharge.
The don't run batteries down all they way is an instruction related to the series wired battery pack, not the individual cells. Running a cell down to zero volts on occasion-but only on occasion-is the optimal discharge level for NiCd (and NiMH batteries) since it breaks down the "memory" of the Cd electrode and the milder "memory" of the Ni electrode (memory being a condition wherein due stable compounds forming and accumulating on the electrodes in which said compounds have oxidation states intermediate that of the electrodes' charged and discharged states, a resistance to full discharge occurs giving a partial loss of battery capacity). However, cells charge, recharge at differing rates. After a few cycles some cells get out of balance relative their neighboring cells in series. If you run the packs low, you get a lower charge/and or capacity cell forced into reverse polarity by its higher charged series neighbors. Dendrite formation results rapidly destroying the cell. If you avoid going down all the way, you establish a margin compensating for a weak cell. Since reverse polarity is so much more significant a problem than memory, .9V-.6V/cell is a typical lower limit for series NiMH/NiCd battery packs as a lower threshold for battery conditioners designed for reducing memory.
I'm not familiar with whether your battery pack is permanently wired together like a computer or R/C car battery pack or if the cells individual pop out of the canister like a flashlight. If the latter, and you don't have a conditioner, get a 10 ohm 1W power resister from Radio Shack, and every so often, short the resister across the leads of the individual 1.25volt cell (optimally, every 10 cycles or 1 a month NiCd, every 30 cycles or every 3 months NiMH). In my undergraduate days when my employ included working on defibrillators, we pulled each NiCd cell out of the banks and resistor shorted each cell periodically. However, if you get a shrink-wrapped hardwired NiMH pack I certainly wouldn't bother opening it up to do this.
NiMH batteries have a very high self discharge rate-the're discharged in 2-3 months if never used. NiCd Batteries have a moderately high self discharge rate-higher discharged after 3-5 months. If infrequently riding at night consider that.
SLA batteries are heavier than the alkalines and have a self discharge rate better than the NiCD & NiMH, but still low relative the alkalines. SLA batteries have only one half to one third the number of lifetime duty cycles relative NiMH/NiCd batteries.
Alkaline batteries have a very low self discharge rate when idle. Consider taking along a spare alkaline battery pack tailored to drop into your canister replacing the dead NiCd pack (don't wire the alkalines to the NiCd) and or (my approach) adding a low end backup lighting system powered by alkaline batteries due the very long alkaline shelf life. Revert to the alkalines after the primary source dies.
