parnass@ihuxz.ATT.COM (Bob Parnass, AJ9S) (12/11/88)
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BATTERY CONSUMPTION OF THE
UNIDEN/BEARCAT 200XLT SCANNER
Part 2
by Bob Parnass, AJ9S
Some Bearcat 200XLT scanner owners don't get the battery
life they expect. They report having to recharge the
slide on NiCd (Nickel Cadmium) battery pack after as few
as only 3-1/2 hours of operation.
Part one of this article discussed the results of several
tests made on the 200XLT portable scanner to determine
its current consumption.1 Part 2 will continue the dis-
cussion and present the results of additional tests.
Low Battery Indicator
As presented in Part 1, the 200XLT low battery indicator
begins to flash when battery voltage decreases to 7.2
volts or less. This starts a 10 minute timer within the
200XLT. After the low battery indicator has flashed for
10 minutes, the 200XLT display blanks.
o Experimental results show that even after the 200XLT
display goes blank, the radio will continue to draw
approximately 50 mA.
In the author's opinion, the display blanking feature is
a liability, not an asset, of the 200XLT. The owners'
guide claims the 10 minute timer and display blanking
sequence is designed to alert the user and prevent the
batteries from full discharge. But, this assumes the
user will notice the display is blank and take action.
Owners have been known to get up to 2 hours more use from
the NiCd battery pack after the low battery indicator
begins to flash. They turn the radio off, then back on,
which resets the 10 minute timer.2 Uniden should just let
__________
1. See "Battery Consumption of the Uniden/Bearcat 200XLT
Scanner," by Bob Parnass, AJ9S, in The Radio Enthusiast,
December 1988.
2. Be forewarned that turning the radio off and on rapidly
in succession may cause the memory to be lost.3 This may
be due to a transient voltage spike. A note in November
- 2 -
the low battery indicator flash, omit the timer, and let
the user decide what to do and when to do it. This would
permit the 200XLT to be used longer.
Measuring BP200 Battery Capacity
The BP200 battery pack contains 6 cells and is rated at
600 mAh. Ron Smithberg experienced short battery life in
his 200XLT. We measured the capacity of his battery
using a procedure similar to the one recommended by Gen-
eral Electric and Motorola. Basically, we timed how long
it took to discharge a fully charged battery using a
resistor to draw current at its one hour rate. This test
considers NiCd cells measuring 1.0 volts or less as
"discharged."
1. We charged Ron's battery for 16 hours using the
factory supplied wall power supply.
2. We placed a variable power resistor (approximately
12 ohms) across the battery terminals, and kept it
adjusted to draw 600 mA from the battery.
3. We monitored the battery voltage during the entire
test. When the pack voltage decreased to 6 volts,
we noted the time, and stopped the test.
It took only 44 minutes for the 6 cell pack voltage to
decrease from over 8 volts to 6 volts. Thus, the battery
capacity was only:
600 mA * 44 minutes
= 26,400 mA-minutes
= 440 mA-hours
After performing the capacity test, Ron recharged his
battery for 16 hours then used it immediately. He was
then able to get more than 9 hours use, much longer than
before. Apparently, Ron's battery was suffering the
effects of NiCd memory.
____________________________________________________________
1988 Monitoring Times recommended the addition of a 100
uF capacitor soldered across the battery to prevent
transients.
- 3 -
Avoiding NiCd Memory Effect
The owners' literature recommends that 200XLT owners run
their batteries down periodically to avoid a NiCd
"memory" effect.
o Avoiding the effects of NiCd "memory" is perhaps
more important for the 200XLT than it is for other
portable radios.
Owners who always recharge their battery packs at the
first blink of the low battery indicator will not extract
the full capacity of their battery. They will decrease
its capacity.
Cell reversal can occur if NiCd batteries are permitted
to fall below 1.0 volts per cell. There are at least 2
ways to "run" the battery down safely:
1. As described in the cell capacity test above,
discharge the fully charged pack into a 12 ohm, 10
watt resistor until the pack voltage is down to 6
volts. This should take an hour or less. You can
prop the battery upside down on a piece of wood
with with the battery contacts resting on 2 nails.
A 12 ohm resistor and voltmeter should be connected
across the nails.
After discharging, recharge the battery for 16
hours.
2. Leave the 200XLT scanner on after the low battery
indicator flashes and the LCD display blanks.
Periodically remove the battery and measure its
voltage. When the battery pack voltage reaches 6
volts, recharge the battery for 16 hours. This
method will take longer and it is easier for an
owner to forget and let the battery voltage dip too
low (below 6 volts). This may cause the loss of
programmed frequencies, as well as possible NiCd
cell reversal.
For Experimentation:
A 200XLT Quick Charger?
Rather than charge the NiCd batteries through the jack on
the battery case rear, you could try charging them using
the contacts on the top of the pack. This would bypass
the internal charging circuitry. As with the discharging
scheme described above, you could position the pack
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upside down on a block of wood with 2 nails touching the
contacts. Using a constant current, or pseudo-constant
current charger, you could select the desired rate of
charge:
charge duration
_________________
60 mA 16 hours
96 mA 10 hours
120 mA 8 hours
240 mA 4 hours
Of course, the battery pack must be removed from the
200XLT while charging this way.
The author uses this flexible scheme for recharging the
7.2 V 600 mAh battery pack on a Yaesu FT-23R walkie-
talkie.
Conclusion
The low battery alert feature of the Uniden/Bearcat
200XLT is too conservative, and disables the radio prema-
turely. Owners can get longer use from their NiCd bat-
tery packs if they adopt good charging habits, such as
discharging their pack down to 6 volts, and charging for
16 hours just before using the radio.
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Bob Parnass AJ9S, AT&T Bell Laboratories - att!ihuxz!parnass - (312)979-5414