|
Site Navigation:
| |
|
When dealing with PDAs and Windows CE,
the choice of the right energy source can be crucial!
BATTERY
TYPES |
There
are basically 4 ways to power a PDA on the road.
(Everything said in the following text refers to AA-cells,
as they are most common in PDAs)
 | Alkaline batteries (non-rechargeable) Capacity: depending on make and model, the available capacity varies between
500mAh and 2800mAh (Conrad Electronic part number: 61 38 27-44). Typical voltage: 1,5 V
Alkaline batteries do not self discharge too fast. They can
typically be stored for years. It is usually worth to spend the money for quality cells,
as the capacity varies too wide.
Alkaline batteries are often not a good choice to power Windows CE
devices. My Velo1 just makes it to a maximum of 4 hours with a set of two
AA-Alkaline-cells.
Alkaline batteries shall never be recharged! Danger of explosion!
Latest development are Alkaline batteries that can be recharged a
couple of time. They are still quite rare and you should have a special charger.
|
| NiCd cells (rechargeable) Capacity: depending on make and model, the available capacity varies between
500mAh and 1100mAh. Typical voltage: 1,2 V
NiCd cells are capable to deliver high currents, can be fast loaded
and are relatively cheap. They have got a certain self-discharge rate. Cells should be
reloaded after weeks where they were not used.
Disadvantages: contain heavy metals and they have got the so called
'Memory-effect' (more about that later).
|
| NiMH-cells (rechargeable) Capacity: depending on make and model, the available capacity varies between
900mAh and 1500mAh.
The 1500mAh type is quite new to the market and (in March 1998) not
yet available everywhere.
NiMH cells are easy to recycle and do not contain any heavy metals.
They do not suffer under the Memory effect.
Disadvantage: NiMH cells can deliver as high currents as NiCd cells.
NiMH cells have got a high self-discharge-rate.
The NiMH cell is probably the best choice to power a PDA in the
field.
My Velo does run for about 11 hours with a set of 2 NiMH cells (1500mAh).
|
| Lithium-cells (non-rechargeable) The Lithium battery is probably the strongest battery available! With a
capacity of 3000mAh it is the leader of the range.
Lithium cells must be recycled, as they contain highly toxic
substances.
They almost don't self-discharge. After being stored for 10 years a
Lithium cell will still have about 85% of it's original capacity.
Lithium batteries shall never be recharged!
|
|
The
Memory Effect |
| Especially from NiCd cells
we know an effect called "The Memory Effect". This
basically means that the cells remember when they are reloaded before they have been
completely discharged.
A cell that is always used to (for example) 70% of it's capacity and
than reloaded will after a while have no more than these 70% from it's original capacity.
If you happen to find the capacity of your NiCd-cells having
reduced, you have still got a chance to revive your batteries if you have not treated them
bad for too long. The process is called
Reinitialisation
Reinitialising a NiCd cell means to discharge and charge the cell in
cycles a couple of times. After a while the cell will remember it's original capacity if
it has not been maltreated for too long. There are automatic loaders available that
discharge NiCd's completely before they charge them. This is the best way to load NiCd
cells. |
Recharging
NiCd and NiMH cells |
| Even when it is possible to
charge these batteries manually it can not be recommended. You would need a special power
supply where the current can be fixed to a certain limit. Also you would need to keep an
eye on the charging time. Today quite cheap and simple chargers are available for both,
NiCd and NiMH cells. NOTICE: The standard charger you
buy in the supermarket is designed for NiCd only! Don't use it for NiMH cells! NiMH
chargers are well marked as such. Chargers are available that work with both, NiCd and
NiMH. It is important that the charger is certified for NiMH cells!
If possible buy a charger that has got a maximum time limit. Better
charger discharge the batteries before they start charging them. This makes sure not to
overcharge and heat up the batteries.
Even when discharging is not so important for NiMHs as it is for
NiCds it is still worth having such a charger as it will treat your cells smoother. If a
set of batteries is getting really hot while recharging it is quite likely that there is
something wrong. Check your batteries and your charger for correct function.
There are computerised chargers available that do real analysis on
the cells. If you tend to use NiCds or NiMHs more often it may be worth thinking about
buying one of these better chargers as they may extend the lifetime of your
cells dramatically. |
BATTERY
TYPES |
The size of these
batteries is usually referred to as 'AA' or 'AAA'. In PDAs we usually find AA-cells:
| Name |
Type (A...) |
Same as... |
Diameter (mm) |
Height (mm) |
| Micro |
AAA |
LR03, R03, AM4, E92 |
10.5 |
44,5 |
| Mignon |
AA |
LR6, R06, AM3, E91 |
14.5 |
50 |
| Baby |
C |
LR14, R14, AM2, E93 |
26.2 |
50 |
| Mono |
D |
LR20, R20, AM1, E95 |
34.2 |
61.5 |
| Lady |
N |
LR1, E90 |
11.7 |
30.2 |
| Special |
AAAA |
LR61, E96 |
8.3 |
42.5 |
|
|
| |
|
