Battery Charger Times For Ni-MH???

[Noel Hegan]

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(2.8V=75-85mA 0.21 - 0.24VA)

9V/E-2 x (9.0V=14-17mA 0.13-0.15VA)

Ok, understand the 3 types of cell but how do I work out the charging time when using Ni-MH???

Many thanks

Noel

noel dot hegan at virgin dot net

[BigWallop]

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.

[Fred]

That means my 2 hr charger is no good then :)

I have to say, these batteries are hopeless if you charge them and expect to use them in 2 weeks time. They'll be flat.

[The Natural Philosopher]

Not necessarily.

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...

[Owain]

"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.

Owain

[Terry D]

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:

D.

[usenet]

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.

[fred]

In article , Noel Hegan writes

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.

HTH

[Bob Smith]

Also, only charge them that long if they are empty. Better to use a smart charger.

Bob.

[Bob Smith]

NiCd do not have memory effect. They just get fried by people with timer or manual chargers.

From your own tinyurl:

[Bob Smith]

As in a battery pack on board a satellite.

If it gets warm when you are charging it, you are killing the batteries.

Bob

[Dave Plowman]

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 this respect.

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.

[BigWallop]

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.

[Noel Hegan]

People,

Many thanks for answering my post and providing plenty of useful information on the topic.

Rgds

Noel

noel dot hegan at virgin dot net