parnass@ihuxz.ATT.COM (Bob Parnass, AJ9S) (12/11/88)
x-------------- CUT HERE --------------------------------------x 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 - 4 - 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. x-------------- CUT HERE --------------------------------------x -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Bob Parnass AJ9S, AT&T Bell Laboratories - att!ihuxz!parnass - (312)979-5414