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From February 2005 QST © ARRL
Figure 5—The Computerized Battery Analyzer consists of a heat sink and small fan
sitting on top of a plastic tray.
mertime Scout operations—not good for
winter months.
While looking through a recent issue
of QST, I noticed an ad for the West
Mountain Radio PWRgate PG40. The
PWRgate can handle up to 40 A continu-
ously, either from a power supply or bat-
tery. That makes it a perfect match for
my 40 A switching supply, and will
handle the current requirements of my
Elecraft K2/100 HF rig, KAT100 antenna
tuner and a VHF FM transceiver and other
station accessories.
The PWRgate PG40 looks like a small
heat sink with three sets of Anderson
Powerpole connectors on top. The Power-
pole connectors follow what has become
the common standard for ARES and
other emergency operators. The compact
PG40 package is about 4×5×1
5
/8 inches
(H×W×D), and has mounting holes on
each end. Connect your 13.8 V dc supply
supply to the
PS input and your 12 V bat-
tery to the
BAT input. Then connect your
rig or dc distribution panel to the
OUT con-
nector and you are ready to operate.
When the ac supply is on, your sta-
tion power supply powers your equip-
ment. If the ac supply goes off for any
reason, the PWRgate instantly routes the
battery voltage to the output connector.
My radios didn’t even blink when I tested
the operation by pulling the
PS connec-
tor out of the PG40. With my K2 display
set to read applied voltage and current I
could see the supply change instantly
from 13.8 to 12.0 and back again when I
unplugged and reconnected the ac sup-
ply to the PG40. With a PG40 connect-
ing my ac supply and back-up battery, I
may not even know the commercial power
went off until it gets dark.
What’s Inside?
The PWRgate uses two 80 A Schottky
diodes wired to isolate the battery and
power supply from each other. The input
with the higher voltage automatically
connects to the output. The Schottky di-
odes have a forward voltage drop of about
0.4 V that should be considered during
a PC running Windows 98SE or higher
with a Pentium 233 or faster processor, at
least an 800×600 display and an avail-
able USB port.
The warnings about heat build-up
when charging and discharging the bat-
teries point to the value of the optional
temperature probe. This optional device
plugs into the side of the CBA. When
connected, the software will display the
temperature. You can set an automatic test
cut-off temperature, so if your battery
becomes too hot the test will stop. The
default temperature is 140°F, but you can
change that in the software.
Setting Up a Test
Before you are ready to start a battery
test, take a few minutes to read the safety
information file on the CD, as well as the
CBA owner’s manual and the battery in-
formation and FAQ files. Then double
click on the software icon and a test win-
dow will open. Type a descriptive name
into the
TEST NAME box. Next you will
have to select the battery type from a drop-
down list that includes most battery types.
Enter the battery capacity for the battery
you are testing. When you connect the
battery to the CBA it will measure the bat-
tery voltage and take a guess at the nomi-
nal battery voltage and the number of cells
in the pack. The software usually defaults
to a test current equal to the capacity of
the battery. The software also sets a de-
fault test ending voltage; in the case of the
12 V gel cell, the default is 11.4 V.
If you want to use these software de-
faults, simply click the
START button. If
you want to find out how long the bat-
tery will run your equipment, set the test
end voltage to the lowest battery voltage
at which your radio will still operate
(taking into account all voltage drops be-
tween the battery and radio) and the cur-
rent to correspond to the drain of your
your dc wiring design.
5
The PWRgate
also uses a diode and resistor to provide
up to 1 A of charge current to the battery
when the ac supply is operating. When
the ac power comes back on, the PG40
will switch back to your power supply
and your battery will start to recharge at
up to a 1 A rate.
It will take a while to recharge my 100
Ah battery if it is completely discharged.
After a relatively brief operating period
on the battery, though, the PG40 will top
up the battery and keep it fully charged
and ready for the next emergency or
weekend campout.
How Do You Know That Battery is
Taking a Full Charge?
As any battery ages it will tend to lose
some of its ability to take a charge and
return the energy as useable current. This
is where the West Mountain Radio Com-
puterized Battery Analyzer (CBA) be-
comes valuable. The CBA looks like a
large heat sink and top-mounted fan at-
tached to a small plastic tray. It measures
about 2
3
/4×3
1
/2×3 inches (H×W×D). See
Figure 5.
An 8051 microcontroller measures
current, temperature and voltage, in three
automatically switched ranges to 10 bit
resolution. The microcontroller operates
a pulsewidth modulated power MOSFET
load for the battery under test. A plug-
and-play USB interface to your computer
allows software control of the load cur-
rent, temperature sensed cut-off (with the
optional temperature probe) and also al-
lows the computer to collect data about
the battery discharge characteristics.
The user interface to the CBA is via
Windows software that installs from a CD
included with the package. You will need
5
J. Hallas, “Emergency Power at W1ZR,”
QST
,
Dec 2003, pp 41-44.
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