The Roadster’s Auxiliary Power Supply (APS) is a custom DC-to-DC converter that steps the ~400 VDC propulsion main battery pack voltage down to 13.8 VDC for the entire 12-volt system, headlights, audio, VMS, window regulators, and door & trunk actuators, and it charges the 12-volt battery (in the passenger-side fender on 2.x cars).
Two main APS variants were used in Roadsters: Martek and Delta (with some early Eaton lineage).
All variants are no longer in production and were engineered specifically for the Tesla Roadster.
The APS is an electronic assembly buried deep inside the 1,000-lb ESS battery pack and shares the same coolant plumbing and thermal potting conventions as the battery sheets. Access requires a battery pack pull. With the global Roadster fleet now well past a decade old, these converters commonly suffer from aging electrolytic capacitors throughout these units, providing filtering for the inverter stage. This mirrors known PEM electrolytic capacitor aging. Typical capacitor service life is 8–10 years.
We have reverse-engineered the Roadster APS (Martek & Delta) and provide full board-level repair and upgrade services. Since new units are NLA and donor parts are aging, we replace and uprate the electrolytic capacitors, address heat-stressed solder joints, service high-voltage input components, and verify regulation, ripple, and load response on a bench harness. Units are reassembled with long-life capacitors and protective measures to reduce
future thermal and electrical stress.
| Applies to | Tesla Roadster 1.5 & 2.x – Martek and Delta APS (DC-DC) variants |
| Function | Converts ~400 VDC to 13.8 VDC; powers all 12-V systems and charges the 12-V battery |
| Known issues | Aged electrolytic capacitors, heat-stressed joints, donor unit unreliability, NLA status |
| Service | Reverse-engineered rebuild with uprated capacitors, HV input refresh, ripple/load testing |
| Access | APS is buried inside the ~1,000-lb ESS; requires battery pack removal for service |
Offered as a pack-out, bench rebuild during in-shop ESS service, or as a ship-in sub-assembly when feasible. Turnaround time depends on variant and condition. We can coordinate APS rebuild alongside battery upgrades/sheet replacements and BSM board service to minimize duplicate labor.
With ~2,000 Roadsters now beyond a decade in service, proactively rebuilding the APS/DC-DC protects the 12-V system and overall vehicle reliability, avoiding unexpected shutdowns and preserving safe operation for years to come.
Ship your failed APS unit to:
Gruber Motor CompanyQuestions or Roadster tech support: 623‑433‑8500
Maintenance Tip:Low coolant levels don’t just reduce ESS pack cooling and cause pump cavitation, they also compromise cooling of the DC-DC converter, sometimes leading to failure of this vital and hard-to-access component. Keep your coolant level properly maintained.
