Elecraft KBT2 - Manual (Page 9)

9
Using The Internal Battery
Operating Considerations
With a full charge, the 2.9 AH battery will power the K2 receiver continuously for over 20 hours (at 150
mA--see the K2 manual for current-reduction strategies). Transceive-mode operating time at 5 W (CW) is
about 6 to 12 hours, depending on how well the antenna is matched, whether you’re mostly listening or
calling CQ, etc. To extend operating time, use the lowest practical transmit power. If you use 5 W or less
exclusively, you can wind T4 differently to further reduce transmit current drain (refer to the K2 manual).
You should check battery voltage often using the K2’s built-in digital voltage meter. If the voltage reading
is starting to dip below 10 V on transmit you should reduce power output and recharge the battery as soon
as possible. The K2 uses a low-dropout 8 V regulator and will operate down to 8.5 V if necessary, but
discharging the battery below 10 V will reduce battery life.
When operating in the field, we recommend setting a fairly low current limit level using the CAL CUR
calibration function. (This is available only with firmware revision 1.02 and up.) When the current limit is
reached when transmitting, you’ll see a “HI CUR” warning on the LCD, and power will be scaled back as
needed. Often this happens when your antenna changes impedance (due to wind, etc.) or if you change
bands and forget to re-tune your antenna tuner. The current limiting feature will prevent excess drain until
you figure out what happened.
Charging
You can recharge the battery and operate the K2 from the same power supply simultaneously. Even if the
K2 power switch is in the OFF position, the battery continues to charge as long as the power supply is
turned on.
For charging purposes, the power supply must be set for 14.0 V +/- 0.2 V as measured at the transceiver’s
DC input jack (13.7 +/- 0.2 V as indicated by the K2's internal voltmeter, which includes the drop across
D10). Voltages slightly lower or higher than this can be used, but battery life may be reduced.
The 6.2 ohm resistor supplied with the battery limits charge current to a safe level, typically 250 mA,
tapering off to about 30 mA as the battery comes up to full voltage. This eliminates the need for a current-
limited power supply for charging. You can remove the diode and resistor if you plan to use a two-step
lead-acid battery charge controller. Faster recharging is possible in this case.
CAUTION: If you connect an external battery or a power supply of other than 14.0 V to the K2, you must
disable the internal battery using the battery on/off switch. Otherwise, the external battery or low-voltage
supply will charge the internal battery to an inadequate voltage, greatly reducing the internal battery’s life.