Sound Devices MixPre-6 LiPo Battery Backpack

thingiverse

Update for v2: June 03, 2020: - New side cleat (mixpre-batt-side-cleat-v2(print2x).stl) is more durable with a larger hook end, allowing the recorder to stand on its end without falling over from the offset weight of the battery pack. Here's my DIY solution for powering the Sound Devices MixPre-6 audio recorder. The official "L Series" battery sled (MX-LMount) works great, but I wanted something that meets my specific use case. It's a flat "backpack" that hooks under the MixPre via claws on the front and back, with a short wiring harness that connects to the existing 4xAA battery sled on the back of the recorder. The design files are included (FreeCAD 0.18). Enjoy! Goals: * Low profile: My makeshift audio bag has limited depth, so I can't really fit the official battery sled. * Capacious: Must be 4.4Ah or greater. * Cheap: The official sled is $65 before you add batteries & charger! * Quick-swapping isn't a priority, but readiness is: I use the recorder for ad-hoc field recording rather than organized paying gigs, so I'd rather keep a large semi-permanent battery attached and charged, rather than swapping multiple smaller batteries. * No fragile external connections: Many people use USB-C power banks for these recorders, but there are currently no low-profile USB-C cables with right-angle connectors. Also, you lose the recorder's battery indicator if you use an external battery. * Reproducible: Should be made of parts that are reasonably easy to source. Parts Required: * 3D printer with > 135mm printable area * 2x "906090" LiPo batteries (90mm x 60mm x 9mm pouch style) I got mine from China via eBay. * Battery wires and charging system (see below) * 6x M3 nuts * 6x M3x10mm allen head cap screws * 6x M3 washers * 2x M3 thumbscrew caps. (I had [these from McMaster](https://www.mcmaster.com/91175a061) laying around, but maybe there's a better printable option?) Wiring & Charging: * The 2 batteries need to be wired in series to create a 7.4v pack. * You'll need to route the cable out of the hole in the main shell and check that everything reaches. Usage: * Hook the LiPo backpack on the front lip of the recorder * Slide the side cleats until the backpack is locked in place, then tighten the thumbscrews. * Plug the battery wire into the sled and you're done! Room For Improvement: * The batteries may swell over time, so the whole thing should probably be a mm thicker to accommodate. * This design attaches to the bottom of the recorder, blocking the tripod mount. The main shell could be modified to add a second flat for the top cleat, allowing it to attach to the top of the recorder if desired. * There's no printed layer between the battery cells and the recorder chassis. I don't need it, but you may feel more comfortable with a hard shell. * To get the power into the recorder, I modified the included 4xAA sled. A custom-printed option would be more elegant. Lot's of tight tolerances to deal with, though. * Battery wiring and charging methods are up to you. It would be nice if there was a more "off-the-shelf" option. (But maybe that's what power banks are for?) * The included FreeCAD design file is not pretty. It's the result of lots of iteration and last-minute adjustments. You can probably figure it out though.