This Auxiliary Power Supply (APS) sub-assembly is a DC to DC Converter that converts the 400 Volt DC pack voltage to 13.8 Volts DC to power Roadster electronics, headlights, audio, VMS Module, Window Regulators, Door and Trunk Actuators, and charges the 12 Volt auxiliary battery which resides inside the Passenger Fender on 2.x Roadsters.
It was originally made by Eaton, Martek, and Delta Electronics. It is a custom part, made for the Tesla Roadster, and includes the same plumbing as the ESS Battery Pack Sheets. It also incorporates the thermal potting compound found in Roadster ESS Battery Pack Sheets. The assembly is buried inside the battery packs and requires a battery pull for service.
Tesla may have dwindling supply left. Spares are often harvested from donor Roadsters, the supply of which is also steadily declining. Even if a replacement is found, they have aged and are most likely full of deferred maintenance issues. There are 4 large electrolytic capacitors in the 400VDC input section of this assembly. These are the same electrolytic capacitors found in the Roadster PEMs, and like the PEM, this assembly needs a rebuild every 8-10 years since that is the service life of large capacitors.
Fortunately, this part is repairable and rebuildable. We have successfully reverse engineered this sub-assembly, have schematics, and are offering full rebuild services.
Around 2000+ Roadsters are running around with parts aged 10+ years. We recommend rebuild of the electronics buried in the ESS Battery Pack, including the BSM board, whenever a battery upgrade and battery sheet replacement is done.