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Old 11-17-2017, 04:43 PM
SamuelA is offline
Join Date: Feb 2017
Posts: 3,369
Originally Posted by jz78817 View Post
it's got to be a bug somewhere, e.g. a module didn't sleep and drained the battery. We have a Fusion Energi in my lab right now and I checked, when you turn the car on (w/o ICE running) the HV system lifts the 12V system to 13.5 volts. IIRC the '13-14 C-Max had some software issues causing 12V system run-down, don't know if the Fusion was affected too.
jz, most EVs have a large parasitic draw from their various computers. Yeah, they should all be sleeping, but features like remote start, remote firmware update, detecting the remote control when the owner approaches all require you to energize some of the electronics. Sloppy optimization on your power states can easily suck a ton of power - apparently Tesla sucked about 80 watts.

So what you just observed in the lab is consistent with what others experienced. The HV system only lifted the battery to 13.5 with the car on. If the battery were left at 13.5, or the HV system were to engage a bypass circuit or something, you could directly power the electronics with HV derived energy only*. Assuming an efficient DC to DC converter and good firmware that will hard kill all the electronics* if the HV state of charge ever gets too low, this would work.

*by opening a relay and having a startup circuit that can only start again if a charging plug is inserted into the charging port and supplying power.
*some lead acid battery chemistries don't do well with being kept at 13.5 all the time. The SLA in UPS batteries seem to do fine, and I think most EVs and hybrids use an SLA, however.

Last edited by SamuelA; 11-17-2017 at 04:45 PM.