EMC198  Battery Thoughts 1/2     Release  8/23/98
    
By Paul Christensen WA6TIL
    
"Providing battery power to equipment is a function of what it is
used for, where it is located, and what connectors are available.
Most equipment can accept external power; the down side is the
need for cables with specific connectors and the correct voltage.
Where you have a choice, standardize on equipment that can run
from the same voltages and connectors. Consider current rating,
size, and durability when selecting connectors. Which connector
to use can be a subject by itself
    
Rechargable batteries are economical for day-to-day operations,
and are environmentally friendly, but consider:
    
1. Equipment in operation that is also charging batteries
dissipates additional heat, which can degrade performance.
    
2. Nickel based rechargables tolerate deep discharging well. Lead
based rechargables can be adversely affected by deep discharging.
Auto batteries may be affected if discharged below 75% of their
total capacity.
    
3. Battery packs that supply 12 volts may not fully charge from a
car outlet even with the engine running because of diodes or
other voltage drops within the pack.
    
4. All batteries self-discharge over time. Nickel rechargables
tend to discharge faster (1 percent per day) so you can't just
charge them up, and forget them.
    
5. Over charging is detrimental to most rechargable batteries,
Some chargers prevent overcharging and some rechargable
batteries are more tolerant of overcharging (NiHm). Lithium
based batteries have special needs for safe recharging.
    
6. Remember that using a couple of rechargable packs just
postpones the eventual need for external power, whether by
recharging or by directly running from an alternate source.
Multiple rechargable packs can compound battery maintenance
issues as well as be a useful tool.
    
7. Batteries have internal resistance and the total amount of
usable energy is less at higher current draws.
    
8. Low temperature typically reduces the available battery power.
    
9. Nickel and Lithium batteries typically can supply more current
for a given size than Alkaline or Lead
    
10. Alkaline Rechargables seem to be able to supply less current
than a comparable sized Alkaline disposable.
    
Equipment that can accept both rechargable and disposable AA or
D batteries can be quite useful because many agencies (private
and public) stock these sizes of alkaline batteries. The Nickel
based rechargables provide a slightly lower overall voltage and
are used for day-to-day operation. A stock of disposables
(because of their long shelf life) can be kept nearby in case an
emergency runs longer than your rechargables do."
    
Continues in part 2, next week

EMC199 Battery Thoughts 2/2              Release 8/30/99

There are many possible sources of battery power. A flashlight,
tape recorder, or other battery-holding piece of equipment may be
modifiable to provide power. This has the added benefit of having
equipment that does double duty. Broken equipment may provide the
parts for a power supply..... W6WWW modified a broken electric
drill handle to provide an ICOM HT with 9.6 volts from a Makita
rechargable battery, while I to get power from a modified Maglite.

There is also the time honored method of building from scratch.
Battery holders comes in different shapes and sizes. An eight
cell AA holder makes a very compact 12 volt supply using alkalines,
a ten cell AA holder is available for making 12 volts  with Nickel
based batteries.

Consider how to power each item of equipment based upon how you
will likely be operating. A Shadow has different needs than a
Mobile OR Portable station. Also consider the battery needs for
personal pagers, test equipment, hearing aids, etc.

Consider the range of power each piece of equipment will
tolerate. Some RF power amps shut down at about 10 volts, some
will continue at lower total output when input voltage drops as
low as 6 volts. An ICOM 706 mobile that I use will distort audio
when powered from a car outlet if the engine is off.

In an emergency, supplies may consist of what you have
'in-hand'. When caught with limited power resources consider
these aspects:

1. Keep the cell phone off and use a radio or pager to alert you
when someone wishes to call in to you. Most cell phones will
still transmit covertly while in standby. This is the reason they
are banned in some RF sensitive environments.

2. When using packet or other forms of digital communications
that require a computer having limited operational time, use a
packet MAIL indicator, paging, or voice contact, to determine
when the computer needs to be activated.

3. Use the minimum amount of RF power that is reasonable, perhaps
even relaying through a station that is not strapped for power.

4. Use a HT rather than a mobile to monitor. The mobile can be
activated for actual contact if the HT is not strong enough.

5. Be conscious of keeping transmissions short. Rather than
saying the message at handwriting speed, use bursts of 3 words
then drop carrier while the receiving station is writing it down.
This is good practice in any event as it has the added benefit of
giving more room for emergency break-in.

6. Audio uses power. Lower the volume and/or use earphones.

7. For low light conditions, LEDs can be used for lighting. A two
cell mini MagLite will operate continuously for days if the bulb
is replaced with a small  high efficiency LED. A new "white" LED
(blue tint) is available that makes the  high efficiency yellow
look dim.

8. Let others know of your needs. There may be a mobile passing
through that is carrying more than enough power to share.

Paul Christensen, a long standing member of ARES and RACES,
can be reached via
wa6til@amsat.org.