[Updated October 21, 2011]
NEWS: χ1 is now released and available from AMB audio shop
. Please visit the official χ1 website
for full information about this project.
As mentioned in a post elsewhere in this forum, MisterX and I are working on a LiPo battery board that could be fitted into the Mini³ portable amp. It's called χ1 ("chi 1").
(If you can't see the whole picture, stretch the browser window wider)
This board increases the run-time for the Mini³ high performance edition to more than 23 hours, and the extended runtime edition to over 50 hours. It also reduces the charge time to less than 1.5 hours. Full smart-charging and protection will be included on the board. The nominal battery voltage is 7.4V (two 3.7V 600mAH cells in series). The selected LiPo battery is commonly-available and low cost (they are designed for use on RC helicopters).
To use this board, the charging circuit portion on the Mini³ must be depopulated. The two boards will be mated to each other similar to the γ1 DAC in the Hammond case, the interconnection will be pin header/receptacle through the 7812 regulator's pads on the Mini³.
The "charge" LED on the back panel is bi-color, and will glow green when charging, and turn off when charging is complete. It will glow red if there is a fault. The external wallwart specified for the χ1 is 9VDC regulated, with a current rating of 1A or higher.
The following is the current PCB layout:
The blank board areas are actually "no fly zones" to clear the tall parts on the Mini³ board, such as the volume pot, input /output jacks, DC power jack, and electrolytic capacitors. The usable board space is essentially full.
Here is the schematic diagram:
The selected charge management controller is Microchip MCP73864
and additional battery protection is provided by Texas Instrument UCC3911DP-3
. Both are in SOIC-16 package. The battery is two series-connected 3.7V 600mAH lithium-ion polymer cells (Walkera HM-4G6-Z-37, HM-4#6-Z-34 or equivalent, for Walkera 4#3, 4#6, 4G3, 4G6 RC helicopters). These are commonly available from RC hobby retailers and online. The two cells fit perfectly in the Mini³ Hammond enclosure, where the 9V NiMH battery occupied.
The wallwart for use with the χ1 must be a regulated type, DC 9V output, rated no less than 1A load current. Note that this is different than the 15V-24V 300mA unregulated unit specified for the standard Mini³.