Tesla Roadster PEM Capacitor Failure

September 1, 2017

Our service partner in Europe received what we believe to be the first recorded PEM failure due to capacitor aging.   One electrolytic capacitor, (out of 19 in a PEM), had become resistive, and blew up inside the PEM, sending shrapnel throughout the logic and circuitry.  By a stroke of luck, the conductive debris did not short anything out.

Electrolytic capacitors are an integral part of your Power Electronics Module (PEM). They filter and smooth out fluctuations in the inverter section of the PEM, the part that converts DC to three phase AC, and drives the propulsion motor.  Like batteries, electrolytic capacitors have a service life, and degrade over time.

Electrolytic capacitors last 7-8 years, under ideal and favorable conditions found in temperature controlled Data Center environments.  In a vehicle PEM application, temperature control is nearly impossible due to the location of the PEM and the fact the vehicle is subjected to wide environmental extremes.

Why not wait until they fail?

There are two reasons this is a flawed strategy.

There are high voltages (400 VDC) and high currents involved in the circuitry where these electrolytic capacitors operate as filters.  A failed capacitor does not always go quietly into the night.  Sometimes, carnage results as in this case which can affect delicate logic circuitry, or send damaging signal upstream and downstream taking out other components.  In the critical power market, Uninterruptible Power Systems (UPS), which is a 3 phase inverter just like a PEM, there are commonly logic board failures when caps go, and even multiple reports of Data Center fires resulting from old capacitors.  A building in Texas burned to the ground years ago sparked by a UPS failed capacitor fire.

The most compelling reason for pro-active capacitor replacement however, is the Roadster PEM has not been in production for over 10 years.  It is the lifeblood of your car, and there are a dwindling handful of spares available.  Unlike products or parts still in production, where a reliable supply of spare parts are available, a Roadster PEM is a one-of.  Without spare parts availability, component level repairs, and pro-active removal of wear components is essential and the only solution to keeping a Roadster on the road.

We have been servicing product like this for 4 decades

Our Gruber Power Services (GPS) division is a nationwide Uninterruptible Power System (UPS) service organization.   A UPS in a Data Center is the same technology as a Roadster PEM, a DC to AC Inverter.

Our Field Engineers routinely track capacitor aging in UPS’s, and provide periodic “capacitor refresh” on UPS’s every 7-8 years to avoid catastrophic equipment failures, including not only capacitors blowing up and damaging electronics, but equipment catching on fire due to old, resistive capacitors in the inverter power sections.

The Tesla Roadsters have been around since 2008. Electrolytic capacitors in PEMs have reached the end of their service life, and are often ticking time bombs, drying up, becoming resistive, and placing additional load on the PEM inverter section, making your output power transistors work overtime.

Rather than wait for your Roadster PEM to die or self destruct, potentially taking out other costly components in your car, there are pro-active measures you can take.

During a PEM rebuild/upgrade, we replace wear items including resolving know engineering defects such as undersized connector upgrades, IGBT transistor insulating material replacement.  All relay and contactors are replaced along with, interlock switch, internal logic board cooling fan, and any marginal or failing IGBT transistors.

Firmware upgrades include GPS reprogramming to resolve a week number overflow bug, and a complete VMS backup, placing the firmware “car keys” into safe storage on our server in case of future flash chip failure and or file corruption.




Roadster Brakes

Roadster brakes are undersized, and regenerative braking means brakes do not get enough of a workout.

Go out to a deserted paved road and do several HARD STOPS - Emergency-level stops, hard enough to trigger
the ABS. Do this until the rotor surfaces gleam like mirrors, and then do it periodically to maintain them.
The result will be night-and-day in terms of braking performance.

It might just save you from a collision.