KX1 Power options

[n0evh]

Be gentle with me folks this perhaps could be a dumb idea by a certified novice
circuit designer!

Was thinking it would be nice to get a full 4 or 5 watts out of the KX1 at
times, but would like to avoid external power packs of 12 volts.  I am willing
to have less total operating time off the internal AA batteries.  I have
considered Paul's approach of inserting half size AA batteries to boost the
overall voltage of the internal AA battery holders.

Would it be possible to use a dc-dc converter chip to boost the 8-9 volts of the
AA's up to 12-13 volts and keep the circuit internal to the case by heatsinking
it to the bottom of the case near the battery packs and in the small space
below the tuner?

A small switch could also be added to control this feature giving one a quick
way to add or substract 3db of power in the field.

John N0EVH (Every Volt Helps)

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[Mike Scott-7]

John,

I have gotten full power out of a KX1 using 8-AAA cells (12 VDC).
The cells will fit but you would have to install new battery holders. I have
not done this yet because I am still experimenting. At the end of the day I
don't know how hard that will be. The KX1 has nice tapped holes right in the
right places. I probably would have to drill and tap new mounting holes or
maybe there is a way for me to put holes in the right places in the two AAA
battery holders. If I went this way I might see if I could purchase a new
case back from Elecraft so that I can go back if I mess it up.

I also added a super capacitor in parallel with the cells, this keeps the
cell voltage higher during transmit as the super cap has a lower equivalent
series resistance than the 8 AAA cells in series. The cap charges between
dits and dahs.

I am also building a boost converter such as you mention. The chip however
is not the end of the story. A boost converter does use a chip such as the
LM2623 or the MAX1771 but you need capacitors, resistors, a power
transistor, a bulky inductor and a diode. I just don't think what I am
building will fit but I will determine that after I have a working external
prototype and then look into how to scrunch it.

I suggest you look up the National LM2623 and the Maxim MAX1771 data sheets
on the web. Google the part numbers and you will eventually find them. The
data sheets show you example boost power supply circuits. The companies will
likely send you a sample part if you ask. I got a MAX1771 as a sample. I am
going to use the IRF Z30 as the power transistor; it is the same form factor
as the power amplifier in your KX1. I have wound the inductor and it is
about 3/4 inch by 3/4 inch by 3/4 inch, rough measurements. The inductor I
wound may be overkill from a current handling perspective so that could be
my first scrunch attempt. The second scrunch attempt could be to remove one
set of batteries and boost from 6VDC to 12VDC and live with shorter life.

Mike Scott
 
Tarzana, CA
 

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of n0evh
Sent: Thursday, June 01, 2006 11:52 AM
To: [hidden email]
Subject: [Elecraft] KX1 Power options

Be gentle with me folks this perhaps could be a dumb idea by a certified
novice
circuit designer!

Was thinking it would be nice to get a full 4 or 5 watts out of the KX1 at
times, but would like to avoid external power packs of 12 volts.  I am
willing
to have less total operating time off the internal AA batteries.  I have
considered Paul's approach of inserting half size AA batteries to boost the
overall voltage of the internal AA battery holders.

Would it be possible to use a dc-dc converter chip to boost the 8-9 volts of
the
AA's up to 12-13 volts and keep the circuit internal to the case by
heatsinking
it to the bottom of the case near the battery packs and in the small space
below the tuner?

A small switch could also be added to control this feature giving one a
quick
way to add or substract 3db of power in the field.

John N0EVH (Every Volt Helps)

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