2024-2026 Custom Supplemental Battery

Project Overview

This project entails the creation of a custom 24v nickel metal hydride battery pack for the Power Distribution Enclosure. The pack will be 20 cells spot welded in series and will have active charge and discharge protection. The supp-mon PCB will monitor voltage, current, and temperature. This supplemental battery is integral to the ignition sequence.

Project Owners: @Leo Block , @Jingyuan Wang (Abel)

Resources:
Current OTS Supp. → https://power.tenergy.com/at-tenergy-24v-4200mah-nimh-rechargeable-battery-pack-20s1p-100-8wh-30a-rate-standard-mini-tamiya-connector/

Electrical Counterpart

Power Systems -> LV Subsystem.

OBBB Project → Supplemental Monitoring Board Subproject

Electrical POCs:

• @Frank Li - Electrical Lead

• @Abigail Parsons - Supp. Mon. Board Project Owner

• @Ravi Shah - Power Systems Lead

• @Surabhi Karighattam - LV Sublead

Project Requirements

• 20 NiMH Cells

• 24v nominal

• Size constraint → similar to current OTS supplemental battery

• Thermistors

Subtasks

1. Cell Selection

2. Connector and Harness Selection -> Contact Electrical

3. Design and Packaging

   1. Bus Bar Design

   2. Cell Holder Design

   3. Cell Protection

   4. Harness

4. PDE Integration Design

5. Manufacture

6. Test

Documentation

1. Cell Selection:

Selected Cell: Tenergy 10505 Sub-C 4200mAh Flat Top

Spec Sheet

Reasoning: To mimic the Tenergy sup as closely as possible so it can be swapped at a moment’s notice.

2. Connector and Harness Selection:

• xt30 (Already selected)

  • Revision: two are needed because 2nd (parallel) set may be needed for voltage sensing

3. Design and Packaging

   1. Bus Bar Design R1 (Cell formatting is same, busbars & terminals have changed since then)

      1. Open

         

         *Note: Sheet metal in SolidWorks to curve bus bar
      2. Open

         

         Bus Bar Layout/Cell Holder Design - Side View

      3. *Material: Use nickel

      4. Open

         

         *Realized that because we are only connecting, at max, two cells, there’s no need for the spilt connector faces, so drew up 3 designs.

      5. Chosen Design: Upper Right

         1. Reasoning: Because w/ right degree bends, any misgivings in the manufacturing process will lead the cell to put stress on the entire push bar when inserted, instead of a angled bend, like how it would be w/ the spilt connector face.

      6. Open

         

         *Realized that for simplicity reasons, a straight rectangular bus bar is the most optimal solution.
      7. Open

         

         ~2x the chart below (link)
      8. Open

         

         by a Matador(aura) from a forum (link)

         1. R[wire] = ρ[Ni] * (L/A) = (6.99E−8 Ω/m) * ((.03711 m)/(2.0E−6 m^2)) = 0.0012969945 Ω

         2. P = R[wire] * I^2 = (1.2969945E-3 Ω) * (15 A)^2 = 0.291823763 W

      9. Power loss @ 15 A & [0.15mm * 10mm * 37.11mm] = ~0.389 W

      10. Power loss @ 15 A & [0.15 mm * 12mm * 37.11 mm] = ~0.324 W

      11. Power loss @ 15 A & [0.2mm * 10mm * 37.11mm] (link) = ~0.292 W

      12. Power loss @ 15 A & [0.2mm * 12mm * 37.11mm] (link) = ~0.243 W

      13. Dimensions for bus bar strips: 0.2mm x 12mm (link)

          1. Open

             

              

   2. Cell Holder Design

      1. Optimal cell layout: something like 4*5 rectangle of triangular circular layout

         1. Make sure + and - end up on the same side for the connector

      2. ~100mm x ~150mm

      3. Stuff to fit into it (ov uv oc ot protection):

         1. 12A Fuse (between + and output, easily accessible)

            1. *Note: do the fuse mount

         2. 2 thermistors (flex pcb temp sensors)

         3. Bus bar guides (so placement is easy and reduces shorting)

         4. Panel mount connectors to case?

   3. Cell Protection

      1. *Note: Aside from temp. sensing, also will add voltage & current monitoring if implementing active charging from the main battery.

      2. *Note: Thermistors, connect to the SubMon PCB in OBBB

      3. Thermistor Selection:

         1. NTC (Negative Temperature Coefficient Thermistor) vs. RTD (Resistance Temperature Detector) vs. PTC (Positive Temperature Coefficient Thermistor)

         2. *Note: We need probe thermistors to attach to the exterior of the cells

*Reasoning: Cheapest, Smallest, Very accurate, and Quickest.

*Ideal Values: R₂₅ = ~10 kΩ | β-Val = ~3400 K to 3950 K | Accuracy = ~±1% to ±3%

*Reasoning: Use old main batt thermistors.

Open

Cut the wires to fit in PDE.

4. Fuse PCB

   1. *Note: Two xt30 connectors, pos. + gnd.

   2. Fuse: 12A automotive blade fuse

Open

R1 KiCad schematic (bad n lame)

*Note: 2x2 for input 1 1x4 for output (Thermistors) --Parthiv

Parthiv mount link

Open

R1 Fuse PCB

Open

R1 Fuse PCB Schematic

*Note: Needa get accurate xt30 and nanofit connector schematics and footprints

Open

Switch to screw terminals

Open

R1 of Fuse & NTC PCB

Open

New sideways orientation

Open

switch xt30 for output

Open

R1 -> sideways orientation

Open

R2 → Reverted to top orientation

Open

R3 → Restructure to better match frame (purple is for lid cutout, and orange is for thermistor connectors)

9/30 Internal Review Notes

• Rename the assembly (spaces lol) Done

• Bigger hole 2.5 mm keep out space (?), 4.5mm diameter, 5.5mm deep Done

• Add handles to frame Done

• Add connection from top frame to bottom Done

• Add attachment point to frame from housing Done

• Make the frame + cells a single assembly (that’s the supp)

  • Allocate space for thermisters and fuses Done

  • DOUBLE thermistor Done

• .5 tolerance between frame and case Done

• Assembly distance mate Done

• PDE mount Done

  • two vert (y axis) on length side

  • two hori (z axis) on top length side

• Assign material properties

• Assign colors make it look pretty Done?

• File edges of bus bar guided

  • bad lame n not cool

  • I’m NOT doing ts vro 💔

  • I think it’ll make cutting the bus bars way harder

  • maybe we should, cause it’ll look pretty

10/7/25 Meeting Notes

• Mech

  • Add rails to the frame to slide into housing Done

  • Add cell to DL Done

  • Hide planes on CAD Done

  • Flip cell models in assembly Done (for cathode and anode)

    • Use linear pattern and instances

  • Suppress text on frame (suppress for processing time of 000) Done (deleted bc unnecessary for now)

• Elec

  • Update footprint on PCB/check 3d viewer is good Done

  • Change up schematics to simplify Done

    • Screw connectors set to one pin Done

      • Change up screw connector CAD to get rid of screw Done

    • Nanofit connectors set to general connector schematic Done

  • Use Github/Sharepoint to get good footprints Done

  • Change planes to be solid (get rid of cross deal) Done

  • Change up thermistor connector directions to match frame (opposite sides) Done

  • Change up bus bar mounts to opposite sides Done

  • Get rid of unneeded traces Done

  • Trace size: at least 0.2 mm Done

  • Make PCB overall smaller Done

  • Round corners of PCB Done

  • Make mounting holes Done

• *Note:Spot weld bus bar to cell terminals then fold over bus bar

  • Adds strain relief and allows us to solder to PCB (can’t solder to cells directly)

• Change + - to .5 mm Done

⭐To do: Case slides into PDE, sliding mechanism, c-shaped rails on the side of PDE

Open

Open

Current Dimensions!!!

10/14/25 Meeting Notes

• Get rid of Cell Done

  • Delete the current one, delete local copy, reference the one from design library Done

• Move PCB to Power systems folder in BILD Done

• Add space to naming of Bus Bar in BILD Done

• Fix mates in assembly (mounting holes) Done

• Lower casing height (so lid goes through pcb) Done

• Make frame attachment screw hole 3.2mm

• Finish rails

  • Make the the c rails (new part) Done

• Change bus bars to local pattern Done

• PCB

  • send for review Done

10/21/2025 Meeting Notes ✨

• Make screw hole 3.2mm

  • Housing to Frame Done

  • Lid to Housing Done

  • Rail to Housing Done

• DCDC Support

  • make 3.5mm thick Done

  • make taller/shorter Done

  • make tolerance tighter Done

    • 0.2mm

  • make triangle brace longer Done

• Lid Lip for DCDC Support Done

  • make thinner

    • 5mm

• Housing

  • Make rails longer Done

  • Make cool pattern to cut extrude Done

    • weight savings

10/28/25 Meeting Notes 🌈

• type shi