Continuing the story of the Windcamp bag for the IC-705, see the report about the ATU-100 build here.
The next step was to make a smaller and lighter battery for this pack, to replace the 7Ah SLAB.
This reduces the weight, and makes some room for a simple wire antenna.
This time I started by looking for a suitable box, rather than make one myself from pieces of PCB.
I found an old TV UHF Convertor in my Junk Box, like this one :
The room inside looked big enough to add
not one, but two battery packs of
8 Li-Ion cells of the 18650 type, in a 4S2P configuration. That makes it a battery pack with a built-in backup battery !
I preferred not to put 4 cells in parallel into one pack, if one cell goes bad in such a pack, you could loose all of your power.
Why not make a 3S2P pack that gives 12.6V ?
As I measured, an IC-705 will only produce something like 8W with 12V, only with 13.8V or more you will get the full 10W out of the rig.
So I selected 16 good cells from my stash of old laptop batteries. Each of those cells has a capacity of 2400 mAh when new, so in theory my pack would have a total capacity of 9.6 Ah (two times 4.8Ah).
Being used cells, this capacity will probably be less than this figure, but should still be useful for powering the IC-705, time will tell ...
Here is an attempt to show a schematic of what is inside the box.
Each pack has its' own charging contact for a balanced charger (the 5 pin blocks in the diagram).
Two switches follow : one for selecting which pack to use, and an ON/OFF switch.
A 14A polyfuse protects the pack when a short circuit or overload happens.
The batteries, when fully charged, can deliver 16.8V, which is just too much for the IC-705. Maximum voltage is 13.8 + 15%, which makes 15.87V.
So I included an
Automatic Voltage Reducer in line with the output, after an idea by Phil Salas, AD5X (his article about that can be found
here).
Finally, a Chinese voltmeter is connected at the output terminals.
I connected one output with PowerPoles, but one could also add a second output to power an extra piece of equipment : an autotuner, an amplifier, a fan, ...
This is the (ugly) inside of the box .... doesn't it look like a bomb package ?
I don't think I would dare to take it on an airplane trip , hi.
This is another view when the automatic voltage reducer is in use, when the LED is on, the relay "opens up" so two diodes are in series, giving an output of approximately 15.5V. This is the highest voltage, which will quickly drop after a short time.
I made a small "quick connect" adapter for the balanced charger.
The standard JST XH connectors that are used on these chargers are difficult to unplug, and a little fragile. So I just used some pins and pinheaders for a simple and quick connection. The adapter can remain connected to the charger. The user only has to remember where to put the "red" wire on the battery pack connector (see front/center on the top picture). It's not foolproof, but what fool would want to use this battery pack anyway? 😊
How much weight is saved ?
The whole box weighs exactly 1 kg.
Compare this to the 2.5 kg for a 7 Ah SLAB !
So we have now room for a 1.5 kg of antennas or other accessories !
73 de Luc, ON7DQ
