On Thu, 25 Feb 2010 17:58:45 +0000, Fred wrote:

Hi,

I was wondering about using rechargeable batteries for our children's
toys. I know that rechargeable batteries are suited better to some
applications than others; do you think they would be suitable for these?
I think it is only low drain uses, such as clocks, where rechargeables
don't perform well, isn't it?



Rechargeables are not always the best choice.

1) You shouldn't run them flat. They really need to be recharged *before*
they go flat.

2) The terminal voltage is lower. Both NiCd and NiMH are 1.2 volts and
alkalines/ordinary cells are 1.5v (nominal - they start higher than
this). This *can* cause problems in some equipment as they may be
detected as flat when, in fact, they have a lot of charge left.

3) NiCd and NiMH have an interesting discharge curve, where they hold
their voltage up right until the end then go flat quite suddenly, without
any warning.

4) NiCd & NiMH have a low internal resistance, that is they can provide a
very large current for a short length of time. If they are used for
motors, for example, then some protection is needed against the motor
being stalled as the resulting high current could permanently damage the
motor.

5) Nicad & nimh are temperature sensitive. As the temperature falls the
cell *appears* to have a lower charge and will go flat earlier. If the
cell temperature is raised then the full charge reappears!


Choice of chargers can be a minefield. Basically, you exchange charging
speed for cell life. Fast chargers shorten the life of the cells, safe
chargers let the cells last longer. There isn't really any need to charge
cells individually in many cases. A lot of equipment uses 2 cells so you
can charge quite satisfactorily in pairs. There are intelligent single
cell chargers, but they aren't cheap. Look for delta-V (if possible) and
cell temperature termination, probably with a safety timer, in any
charger.

I doubt if Uniross are any better or any worse than any other company!
It's difficult to judge without testing a lot of different chargers with
a lot of different cells.

Cell mAh values can often be taken with a pinch of salt. They are rarely
accurate and much depends on the characteristics of the charger and the
load as to how much useful charge a cell will accept. I've had 1800mAh
cells that outlasted 2200mAh cells in a camera - by a large margin too.
I'm not the exception either.

Having said all that, I would first check the toys' instructions. Some
specifically tell you not to use rechargeables. Sometimes this is for
safety reasons and shouldn't be ignored. Any others would be worth a try,
but you may get less "playing" time between charges than you get with
ordinary batteries.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.