Hi all
i looked at this mod
and decided to add a recharging circuit using a BD140 as a constant current source
of about 30-40ma you can use any 100ma sink current pnp transistor like bc557
youll see how the design works
when the falcon is powered the +5v rail runs the nvram and also charges the battery @up to 5v @ 45ma
via the falcons 12v rail when not powered the batteries take over
becouse the batteries will dictate the voltate due to there loading the charger
the voltage wont exede 6v {well 1.2v per cell {more like 1.37 or so when full} X4}
if the batteries fall below 6v then the recharge will allow 40 or so miliamp charge
and the cells will stay put at 6v
this is a preliminary design
and has NOT been tested yet..!and is purly posted for any view and any errors people spot
im making a pcb first for my falcon ill callibrate the R1 current limit to suite
it may turn out to be another value than 15R this is an educated guess
i need to build the circuit add the batteries and measure the current avalible
i recond 10 -45 ma @ ~4v is fine to charge four cells every so often
with nicads etc its the current that matters
as long as its limited By R1 its cool and infact this circuit will output about 6v@45ma
i think this is a better idea for the falcon than batteries that run out and cause boot up problems
and maybe adding a 6.2V clamp zener to the battery pack is a good idea
credit for the diode switching
{ive used this method many times to replace the dodge switches on psu socket on ham radios}
and the 'clear' thinking to realise how the actual ic will use its own internal battery
and resolve
http://www.geocities.com/SiliconValley/6880/phsw.html
a few posts back
pcb board size is 17 mm X 17 mm
its always better to snap off the old cell
'most' of the nvram chips
have the battery in a plasic case mounted above the actual chip
so cut it off and throw away the top bit
make neet the connections
il mod my own falcon tomorrow and post some pics all going well
if a few 'more than 10' pm me
ill make a kit
this will be pcb populated and tested
a holder or cell pack and batteries and instructions
all with plugs and short wired up to suite board
should mount on top of the nvram
especialy if you remove the old cell from it with cutters
dont leave it there even with the other members mod
it may get hot if you used say alakline batteries
and its own diodes have gone short say or leaky
it can explode showering your machine with eating alkalie
its a ticking time bomb much like the amegas batteries
the archive below has the .bmp files if you prefer these when making pcb's
views are needed please !!!

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