wiki/ avionics/ av3-battery-pack

The AV3 battery pack was originally picked during the 2009 capstone project.

Battery Pack Requirements

Chosen Battery Cells

We're using a 4S2P pack of "AA Portable Power Corp" PL-5467100-2C (2.75,3.7,4.2) V at 4.250 AHr Li-polymer cell.

Battery pack enclosure

The pack should be held together by double-sticky adhesive-only (thin) tape. It can also be held in the battery box this way, but it will make it essentially impossible to take out if we go this route.

The thermisters for the ?battery sensor board need to fit in the pack; I'm thinking it's a thin SMT part that gets inserted between cells 2 and 3 and between cells 6 and 7, probably in between two strips of tape.

Battery cell boards

In order strain relieve the battery tabs, we're going to solder them down the tabs to small, thin PCBs that will live on the small thin shelf of each cell, like a battery protection circuit. The shelf area is 65 mm wide, 4-5 mm deep, and about 4 mm high.

What we want the PCB to be < 60 mm x 4 mm, and have an area to solder the tabs, and an area to solder two different wires for each tab. Thus we'll have four wires coming off each cell, two for B+ and two for B-.

We have 22 awg high quality wire (it's pre-tinned, high-temp insulation, 32 strands). After some experimentation, we decided 0.35 inch hole works for this wire.

Battery Prep Instructions

  1. CAREFULLY remove the masking tape from the cells. One of the tabs is sandwiched between the tape, so you have to be really careful.
  2. Tin the bottom of the battery tabs.
    1. Clean the bottom of the tabs with acetone and put on lots of flux.
    2. Put a bunch of solder on the tabs, spreading it out with the iron.
    3. Suck off the excess solder with the vacuum desoldering tool.
  3. Flip the battery right-side up, and put the PCB under the tabs. With about 2mm of gap, mark off the tabs.
  4. Cut the tabs with the CERAMIC scissors. Did I mention CERAMIC? DO NOT USE METAL SCISSORS for the love of god.
  5. Now solder down the tabs to the PCB, centering the PCB on the battery (not the tabs necessarily).
  6. Cut 4x 5 cm long 20 awg wires (the brown/red wire is best).
  7. Strip about 4 mm of insulation off two of them, and tack solder them (with lots of solder) down to the PCB facing off the end.
  8. Do the same on the other side.
  9. Using 1.5 cm mylar tape, put strips of tape over the board and wires.
  10. Flip the battery over, and bend the leads around the narrow end of the PCB.
  11. Tape that wrapped-around end to strain relieve it.
  12. Bend the wires at 90 degrees on the underside of the battery towards the back of the battery.
  13. Tape everything down.
  14. CAREFULLY and SLOWLY bend the tabs so that the PCB flips around and lies in the "battery protection circuit" area in the front of the battery.
  15. Tape the hell out of it to protect the leads and the PCB.