[Elecraft] KX1 Battery Modifications.. Rev.A

[W0rw@aol.com]

Here is the  KX1 - 1/2AA NiCad battery modification...Rev. A..Added Note 
below..

Originally i had 6  'AA' NiCad batteries in the KX1 but i needed more power 
for pedestrian mobile operation.
i removed 4 of the 'AA' NiCad batteries and added 8 - 1/2'AA'-250 short type
NiCad batteries to boost the voltage to 14 VDC. 
That raises the output power to 3 Watts.
The operating time is about 3 hours on a full charge (depending on your speed 
and number of "Q's)..
These batteries are available from Batteries Plus.
They have flat contacts so they need to have a little
solder blob added to the + terminal so they will touch each other when in 
series.
These 1/2 AA 'short' NiCad batteries (250 mAH) are 7/8 inch long. There is a 
longer 
1/2 'AA'  battery that is 1.2 inches long and it won't fit the battery holder.
ps: If you make any modification to your KX1 it will void the warranty...
---------------
Here is a how you can charge the 1/2AA NiCad's without taking the KX1 cover 
off.
(This is not suggested if you are only using primary L91 Li batteries).
Here is the modification i made to my KX1.

i installed a small 2.5 mm mono phone jack to the lower corner of the battery 
chassis. You have to drill hole in the chassis.
The jack goes right below the auxiliary DC connector J1.
Rev. A...Note: For the J1 power switching modification to work correctly this
jack must be isolated from the chassis. That requires a few mica or thin fiber
washers and a small piece of tubing.
This jack has a NC switch built into it so when you plug in the charging plug
the batteries are disconnected from the radio and the charging voltage only 
goes to the battery even if the radio is turned on.
The connections are: black wire to the jack ground pin, red wire to the 
center pin and the NC switch wire to the red wire of J5-1.
Now you can operate the KX1 from the auxiliary DC connector while charging the
internal batteries through the new charging jack.
This modification allows charging internal batteries without taking the unit 
apart. You can also monitor the battery voltage through this connector.
The charger can be any wall transformer that puts out about 18VDC open 
circuit.
The charging current for the 1/2AA NiCad batteries is 50 ma for 5  hours.
You will need to insert a resistor in series with the transformer to limit 
the charging current.
---------
Here is another  KX1 battery switching modification.
The current design "AND's" the internal battery and external battery sources
together using 2 diodes.
If your external battery voltage goes below the internal battery 
voltage, the internal batteries will start draining.
i left my KX1 on for a few days and after i ran down the external battery and
the internal batteries took over and became discharged.
These were the expensive Lithium "AA" Primary batteries (L91's).
i wanted to save the use of these Li batteries for special uses
like Pedestrian Mobiling: See the w0rw/pm KX1 report on the Adventure Radio 
Society web site at:
http://www.arsqrp.com/ars/pages/back_issues/2004_text/0204_text/W0RW.html

Here is the DC J1 switching Modification:
The DC Power connector has an unused (normally closed) switch.
This modification will use that switch so that when an external power source 
is connected the internal batteries will be disconnected, and conversely when
the DC power plug is removed the internal batteries will be reconnected.
Open the unit on an ESD grounded work station.
Separate the battery compartment by pulling the battery connector (J1) out.
Cut the 2 traces that ground P1-2 "-" (getting scary now)...Top Side..
Now add an insulated jumper wire from P1-2  "-" to the side contact of J1
(J1 is the power connector), The unused switch contact is soldered to an 
isolated pad just the left of the marking 'Z2'...
That's it....
Now you can protect those internal batteries.
One other thing that you can do is to set the LED Display Control to "INF"
then the LED display will act as a pilot light.
72  de w0rw
Paul w0rw@aol.com