[Elecraft] K2/100 Emergency field battery
George, W5YR
[email protected]
Mon Jun 10 11:08:01 2002
Another use for a large RV battery like that is in the shack.
Connect it via an appropriate fuse to the output of your regular a-c power
supply such that the supply will trickle charge the battery at the nominal
13.8 volts. If you have any line power interruptions, especially the
momentary kind (off and then right back on) the battery will function in
the manner of a UPS to prevent the voltage transients from reaching your
equipment.
There are a couple of gotchas in this arrangement, however, that need
consideration.
First, should the power supply crowbar for any reason, a fuse or fast
breaker must be used to open the battery circuit. Otherwise you will rather
quickly release all the smoke from portions of the power supply and create
a potentionally highly dangerous situation with a shorted battery until
something burns up (or the battery explodes!) to open the circuit.
The second problem area concerns the time during which the supply has its
a-c power removed. The battery could force current back into the supply and
possibly damage the series regulators. To handle this problem, use a large
diode to block current flow from the battery to the supply.
Of course, with a diode in the circuit, the radio equipment must be
connected directly to the battery - again through a suitable fuse to avoid
an external short-circuit from damaging or destroying the battery - while
the supply is connected to the battery through a fuse and the diode. To
compensate for the diode voltage drop, the supply voltage should be
increased accordingly. Note that this arrangement is not suitable for
charging a large RV or marine battery. It should be at full charge before
being placed into this service.
Two excellent references in this area are the three-part series "Practical
Battery Back-Up Power for Amateur Radio Stations" in March, April and May
1990 QST. The April article is especially relevant.
The second reference is a bulletin put out by the CAP, describing the
approved procedure for battery back-up of Astron supplies, which is
available at
http://ntc.cap.gov/comm/ntc/RS_Battmod.htm
The procedure consists of inserting a 1/2-watt 10K resistor in the trace
feeding Pin 4 of the 723 regulator chip to limit current and avoid letting
all the smoke out of the regulator. This resistor is inserted by cutting
the trace between the moving contact of the pot R5 (1K) and Pin 4, and
bridging the cut with the resistor.
I have used such an arrangement for some time now and it is comforting to
know that a shack full of gear is protected from power transients due to
line voltage outages. These occur frequently "out here in the country!"
<:}
73/72/oo, George W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437
Bob Patten wrote:
>
>
> Simple solution.. Go to Pep Boys (or check other stores for sales) and
> pick up a 110 A/H marine battery. About $50 and should easily run the
> K2 for three days.
> No, not recommended for backpacking!