How it's powered (one paragraph)
A commercial USB-C PD power bank supplies the system — never raw lithium cells, because the bank's built-in BMS provides cell-level protection (over-charge, over-discharge, short, thermal). A small "PD trigger" cable negotiates a fixed 12 V from the bank to feed standard 660/850 nm flexible LED strip. Total draw is about 15 W / 1.3 A: a slim 10,000 mAh bank runs roughly eight 15-minute sessions. Sessions are supervised, so the bank does not need to ride on the dog — keep it beside the dog or in a leash-side pocket, with the magnetic breakaway taking up any snags.
Buy list
| # | Item | Spec to look for | Qty | Est. |
|---|---|---|---|---|
| 1 | USB-C PD power bank | 10,000 mAh, 18 W+ PD output, slim. (20,000 mAh if you want ~16 sessions per charge) | 1 | $25 |
| 2 | USB-C PD trigger cable, 12 V | "PD decoy/trigger", fixed 12 V, bare leads or DC5521 plug, ≥3 A | 1 | $9 |
| 3 | Red/NIR LED strip | 12 V flexible strip, 660 nm + 850 nm mix (sold as "red light therapy strip"), ~14 W/m, 2 m reel — cut three ~370 mm rows | 1 | $25 |
| 4 | Countdown timer relay | XY-WJ01 or equivalent: 6–30 V supply, 5 A relay, settable 1–999 min, auto-off | 1 | $10 |
| 5 | Thermal cutoff switches | KSD9700, 40 °C, normally-closed (45 °C only if the array has a spacer layer); metal face | 2 (5-pk) | $7 |
| 6 | PTC resettable fuse | 2 A hold / 4 A trip, radial lead | 2 (pk) | $6 |
| 7 | Magnetic breakaway connector | 2-pin magnetic pogo, ≥3 A rated (e-textile / drone style) | 1 | $10 |
| 8 | Master rocker switch | SPST, panel/inline, ≥3 A @ 12 V (optional — the timer's button can serve) | 1 | $4 |
| 9 | Silicone hook-up wire | 22 AWG, red + black, 3 m each (silicone stays flexible) | 1 | $9 |
| 10 | JST-SM 2-pin pigtail kit | Male/female pairs — one pair per strip row, rows replaceable | 1 kit | $8 |
| 11 | Heat-shrink + fabric tape | Assortment; every joint gets shrink, every run gets strain relief | 1 | $8 |
| 12 | Clear TPU / vinyl film | 0.5 m — wipeable skin-side cover over the strips | 1 | $8 |
| 13 | IR thermometer | Any basic unit — first-run skin-temperature checks | 1 | $15 |
| Jacket fabric: neoprene/softshell 0.5 m ($15) · 2 in hook-and-loop 1 m ($8) · edge binding tape ($6) | $29 | |||
| Total (approx.) | ~$170 | |||
Wiring schematic
Block-level schematic — order matters: bank → trigger → breakaway → timer → fuse → thermal cutoffs → strips. Everything downstream of the breakaway lives on the jacket; everything upstream sits beside the dog.
The safety layers (what "automatic safety switch" means here)
- Thermal auto-cutoff (primary): two KSD9700 normally-closed bimetal switches in series in the +12 V line, taped metal-face-down onto the LED strip at zones C and D (the hottest spots, mid-array). If the array reaches 40 °C they open and power drops — no software, no battery, purely mechanical. They self-reset once cooled ~10 °C. Two in series means either one can kill power.
- Session auto-off: the countdown relay cuts power after the set session (start at 10 min). Prevents overdose and prevents an unattended forgotten jacket.
- Overcurrent: the 2 A PTC fuse trips on a short (e.g., chewed or chafed wire) and self-resets when the fault clears.
- Mechanical breakaway: the magnetic connector separates if the dog snags or walks away from the bank — no yanked wires, no dragged battery.
- Cell safety: the power bank's internal BMS. This is why the design uses a retail USB-C bank and not bare 18650/LiPo cells — never put unmanaged lithium cells on an animal.
Assembly order
- Cut three strip rows ~370 mm (only at the marked cut points). Solder JST pigtails; heat-shrink every joint.
- Tape the two KSD9700s face-down onto rows at the C and D zone marks; wire them in series in the +12 V feed.
- Mount rows on the pattern's LED grid lines, cover with clear TPU film (wipeable, keeps fur out of the LEDs).
- Build the inline harness: breakaway → timer → PTC → array. Fabric-tape every wire run to the panel; leave a service loop at each strap.
- Bench test before the dog wears it: full session on a towel, IR thermometer on the LED face every 2 minutes — it should plateau well under 40 °C. Hold a hand under the array for the final 5 minutes.
- First on-dog sessions: supervised, 5 minutes, check skin temperature and skin condition after. Work up to the vet-agreed dose.
Dose & disclaimer. At typical strip output (~13 mW/cm² at
contact) a 10-minute session delivers roughly 8 J/cm² at the surface — inside the commonly
cited 1–10 J/cm² PBM range — but fur attenuates strongly and published veterinary dosing
varies by condition. Agree wavelengths, dose and schedule with your veterinarian. This is a DIY
aid, not a certified veterinary medical device. Never run it unattended, and stop at any sign of
discomfort, redness or heat.