Picked up a battery charger for my digital camera recently and the
scant instructions suggested that the charging time can be worked out
via the information on the front of the charger. Minor problem - canny
understand the info:
Model - Hama UNI 3AS1
Info- Sec: AA-2 x (2.8V = 170-190mA 0,48 - 0.53VA)
AAA-2x(2.8Vu-85mA 0.21 - 0.24VA)
9V/E-2 x (9.0V-17mA 0.13-0.15VA)
Ok, understand the 3 types of cell but how do I work out the charging
time when using Ni-MH???
noel dot hegan at virgin dot net
NIckel Metal Hydride Batteries need a low, slow charge and are not like the
normal Nickel Cadmium Batteries usually used in recharging systems. The
lowest mA at the voltage of your batteries is what you need, and the NI-MH
batteries should be given twice as long to charge as NI-CAD ones.
I'd need to know if the charger you have is set to give fast charge rating,
or if it is set for a standard slow charge of 8 hours.
Fast chargers for Nicad and NiMh exist, that look for a drop in cell
voltage signifying end of charge. The acceptable 'fast charge' rate for
NiMh with a GOOD delta-peak xcharger is one hour, and 20 minutes for
Nicad. Needless to say I have done a full Nicad charge in 12 minutes
many times, so these are conservative figures.
Charging NiMh faster than one hour tho leads to reduced capacity
eventually and poor lifetimes.
The voltage peak on NiMh is also much smaller than Nicad, which means
the chargers AND THE WIRING TO THE BATTERIES needs to be of good quality.
Yes, that is NiMh to a T. I've bitten the bullet and gone straight from
trusty NiMh to Lithium Polymer. Buit then, my requirements ae more
specialised...you are still stuck with a one hour charge, but the charge
life is in months, not dauys, and teh energu density is far higher...
Fast charging for NiCd should stop when the terminal voltage peaks then
declines. For NiMH, charging should stop when this voltage peaks. The
better chargers will also monitor battery temperature. Although NiMH cells
tend to lose charge faster, the higher capacity and lack of 'memory' effect
more than compensate - the cells can be topped up at any time. Charge life
can be extended by storing in a 'fridge.
The following site has some useful information: http://tinyurl.com/ykku
UL, 'memory effect' in NiCds is very, very unlikely to occur in normal
domestic use. It occurs when NiCd cells are recharged by exactly the
same amount at exactly the same interval several hundred times.
Dead (or dying) NiCd cells supposedly caused by memory effect have
just about always been killed by overcharging.
Fine for something which is in regular use, but for intermittent use the
rapid self discharge is a real PITA - and I thought Ni-Cads bad enough in
Memory effect is an urban myth unless you regularly discharge to a certain
percentage - very unlikely with most things. Overcharging a Ni-Cad is the
usual reason for damage.
*I wished the buck stopped here, as I could use a few.
Dave Plowman firstname.lastname@example.org London SW 12
"Noel Hegan" wrote
| Picked up a battery charger for my digital camera recently and the
| scant instructions suggested that the charging time can be worked out
| via the information on the front of the charger. Minor problem - canny
| understand the info:
| Model - Hama UNI 3AS1
| Info- Sec: AA-2 x (2.8V = 170-190mA 0,48 - 0.53VA)
My charger is a 2.8V 150mA and the box says to use 12 hours for 1800mAh
capacity size AA NiMH.
Yes. I'd go with around the 12 to 14 hour mark from flat. But if the
batteries are only showing a weakened state, then I'd settle for a recharge
of around the 8 to 10 hour duration, making sire to check them at the 8 hour
period to see if they haven't become warm or sweaty.
AA size NiMH have a capacity of between 1500mAh and 1800mAh so
charging at 170-190mA will take about 10hours, add a bit for losses in
charging and 12hours will see them tippy toppy. Best not to leave them on
charge at this rate continuously, my (slow) charger has a cutout at
16hours to stop overcharging.
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