Elmer Night -
External Power Sources for Your HT or
How
long will your HT radio operate on its batteries?
Some
manuals provide estimated battery life on a fresh set of alkaline cells or on
fully charged NiCad or NiMH battery packs of
different capacities. How long a battery
pack will last depends on several things:
1) The capacity of the battery ... AND
… its state
of charge
2) The duty cycle and the output power setting
(Hi, Med, Low)
How much time in squelched receive (stand by) mode
How much time in receiving mode, and its volume setting
How much time in transmit mode
The
Kenwood TH-K2 Manual on the Specifications page says:
For
each minute the Duty Cycle is:
Transmit 6
seconds, Receive 6 seconds, and Standby 48 seconds.
Is this
typical? If there is more Receive time or more Transmit time, the battery life
will be shortened.
With a
BT14 (9 volt battery case) and 6 fresh AA size batteries installed you should
have:
4 hours on
High power
8 hours on
Med power
10.5 hours
on Low power
How
many extra batteries do you have on hand?
Using the
example duty cycle on High Power how long would you be able to continuously
operate if we had an earthquake and you had 6 sets of fresh
AA cells for your BT-14 battery case?
6
cells/set x 6 sets = 36 AA cells… 6
sets x 4 hours/set = 24 hours
…
Then
what? After 24 hours are you still on the air?
How
about an External Source of Power for your HT ?
Your
car battery?
RV/Marine
Such
batteries are heavy, usually contain sulphuric acid
as liquid or gel, and require attention from time to time, but contain a lot of
electrical energy to run your radio(s).
Example:
TH-K2A Duty Cycle:
10 min Standby
at 0.10 amp = 1 amp-minute
40 min Receive
at 0.50 amp = 20 amp-minute
10 min Transmit
at 1.8 amp = 18 amp-minute
You would
use 39 amp-minutes per hour of operation, or 0.65 amp-hours on High power and 15.6
amp hours for a 24 hour day. If your RV/Marine battery has 120 amp-hour capacity it’ll run the HT for more than 7.5
days at that duty cycle before needing to be recharged.
Deep
Cycle/RV
1. Vehicle batteries are
designed for heavy starting current ... but will power radios, too.
2. Deep Cycle/Marine
batteries are designed for lesser drains, over a longer period and deeper
discharge.
3. Keep the battery in an
acid proof battery box for safety.
4. Check electrolyte
levels carefully, monthly or quarterly.
5. Monitor the battery
voltage and record values
6. RV type batteries have
wingnut / screw connections as well as cable
terminals.
7. Emergency recharging
can be accomplished via generator/charger, or using jumper cables from your
car.
8. Normally charge with a battery maintainer (not trickle
charger)
High
Current 12 VDC can be very dangerous. No rings, watches, bracelets or
other metal jewelry should be worn as
you work with a charged battery. Even a
‘discharged’ battery can spark impressively. Watch your metal
tools, they conduct!
Other
The Power
Station has a 6 amp hour 12 volt battery (360 amp minutes) - it’ll run the
TH-K2A for 9 hours at that duty cycle ( 360
amp-minutes / 39 amp-minutes/hour = 9.2 hrs))
Designing
emergency power sources to run your HT, mobile radios and other items is an
area for a lot of creativity.
Designing
a battery pack using ‘D’ Cells
The
capacity of a D cell is substantially more than that of a
AAA or AA cell. D cells deliver nominally 20.5 amp hour of service and AA cells
deliver nominally 2.8 amp hour of service. 8 D cells in series
would
supply 12 volts ... but your radio needs AT LEAST 12 VDC to operate correctly
... so the life of the pack would be significantly shorter if designed to
deliver 12 VDC, than one starting out at 13.5 VDC or 15 VDC.
Both
battery sizes supply nominal 1.5 VDC per cell.
8 D Cells
– 1.5 VDC batteries in series will provide 12 Volt DC
9 D Cells
– 1.5 VDC batteries in series will provide 13.5 Volt DC
10 D cells
– 1.5 VDC batteries in series will provide 15.0 Volt DC
The
Kenwood TH K2A will accept up to 16
Volts.
Starting out at 15 volts, the pack voltage will decline with use. As the
battery pack drops below 12 volts, performance of the HT will become impaired.
Regardless
of how many cells you use in series, a fresh
D cell will provide 20.5 amp-hour or 1230 amp minutes of service. A Kenwood
TH-K2A uses 39 amp-minutes / hour. So the D cell pack would be expected to run
the radio at the design duty cycle for about
31
hours
Be Sure to Check Your Manual BEFORE You Start
Make sure
you know the voltage requirements for your radio - check your Manual to be
sure of its
requirements.
For
example:
Kenwood
TH-79 specifies:
External
Power, DC jack 5.5V – 16 V (13.8 V)
Kenwood
TH-KT2A specifies:
Operating
Voltage, DC IN jack DC 12.0 – 16.0 V (13.8 nominal)
Connections for External DC
Considerations
1. There
is often a coaxial outlet is on the HT (check size
and polarity) most commonly
the center
pin of the plug is + and the ring is -.
2. Connect
to a regulated power source. (Batteries not connected to chargers
qualify if the
voltage is within the specified range) e.g. Kenwood ‘s PG-2W DC Power Cable
3. Many
manufacturers make cables to use auto cigarette lighter outlets. These
contain circuits that
ensure voltage spikes or overvoltages are not applied
to the
radio. e.g. Kenwood’s PG-3J Cigarette Outlet Power Cable
4. Check
all disclaimers and warnings - the manufacturers are relatively conservative
about their warnings regarding connecting HT’s to
auto batteries installed in a vehicle.
About
Connectors
If everyone
utilized a similar connector for external power input for their radios, and if
our emergency power sources used the same connector, then it would be easy to
swap in fresh power sources for our radios ... or to change radios if someone
wishes to take theirs with them when they go off shift or go to another
assignment. Quick for station set up, take down as well.
Is there a
power connector standard ? Yes, there is. Meet the
Either
the 15-ampere or 30-ampere sizes may be used, and both
sizes mate with each other. The plastic parts are the same for both sizes. The
connectors dovetail together as a compact unit.
Identical
connector halves are genderless—making assembly quick and easy and
reducing
the number of parts stocked. When connections are disconnected, no metal
parts are exposed. The 15-ampere contacts are designed for 16-20 AWG wire and
the 30-ampere contacts are designed for 12-16 AWG wire.
The
contacts can be soldered or crimped to wires. The
contact lugs are designed to be crimped and non uniform crimping can distort
the barrel fitting so that the contact will not fit in the housing however soldering
can be done if the
solder is applied sparingly.
There
are a variety of devices on the market using Powerpole
connectors ... e.g. RigRunner. The wire from your
battery or power supply to a RigRunner or ‘Y
connector’ power distribution network should be heavier gauge and use the 30 A connectors.
OK ... How About a
Example: A Kenwood TM-731... an elderly dual band mobile transceiver.
Power
required: 13.8 VDC +/- 15% (calculated: 11.7 to 15.8 VDC)
Current
Drain High Power < 11 amps
Receive
w/ no signal ~0.6 amp
Output
2 Meters: High 50 Watts, Low 5 Watts
Output
440: High 35 Watts, Low 5 Watts
Fuse
15 amp
A Kenwood TM-271 - a current model 2 meter mobile transceiver
Power
required: 13.8 V DC ±15% (11.7 ~ 15.8 V)
Current
Drain High Power 13 amps or less
Receive:
2 Watt output - less than 1 amp.
Output
2 Meters: High Power 60 Watts
Low
Power: 25 Watts
Fuse
15
In mobile
installations Kenwood’s recommendation is to connect the radio directly to a
nominal 12 volt vehicle battery using the supplied wire (#16 or larger gauge)
with fuses on both positive and negative sides. Red wire connected to positive, and black wire to negative.
The same
120 amp-hour battery will run one of these radios at the 40/10/10 duty cycle
for about 40 hours. (Assumes 13 amp drain in transmit, and 1 amp drain for standby
and receive.) There is no apparent warning about overvoltage
conditions for connection to the vehicle battery in the manual for either of
these mobile radios.
Grabbing
power from other places?
What to do? ... ‘my batteries are all
flat and I ran out of replacements and no chargers are running’ With a power
cord with heavy battery clips on one end and Anderson Powerpoles
on the other, you can connect to any 12
VDC auto battery that you can borrow. Caution:
you must watch polarity.
Brush or
wipe down ‘borrowed’ batteries so that chemical crusts or drips don’t come into
contact with your
skin or sensitive components. (A box of sodium bicarbonate can
neutralize any small
spills.) This solution also allows quick connections to power supplies that may
be available when your wrench, screwdrivers, or other tools aren’t at hand.
Clip onto the terminals, plug in the Powerpoles and
you’re in business. These are a bit more vulnerable to jostling which may cause
short circuits or other interruptions. Position them safely out of harms way.
Further
The
ARRL Handbook for Radio Communications has
information about discharge planning, battery charging, sample projects and
more in Chapter 17.