Jay Summet wrote:
The reason the DC2DC converter does NOT run all the time is that (for
safety) Nissan has chosen to disconnect the HV battery from the rest of
the car (with contactors inside the main battery) whenever the car is
turned off.
Ken Olum via EV wrote:
What danger are they concerned with?
I can't speak for Nissan, but I think they are "just being sure". Their
lawyers could probably imagine all sorts of bad scenarios if they did it
differently.
However, there is no technical reason that EVs couldn't have a tiny 12v
battery (or just a big supercapacitor), and an always-on DC/DC to keep
it charged. Our homes and businesses are already full of "always on"
gadgets. Despite being dirt-cheap, they manage to have enough
reliability, isolation and fail-safes so they don't electrocute people
or burn down houses. The automakers *could* include a small, safe,
inexpensive DC/DC to provide 12v power when parked.
The more likely reasons to keeping the big old 12v battery are cost, and
tradition. Automakers have always done it that way, and don't want to
change. Cars are filled with computers and other vampire loads that
would run down a small battery if the car was parked for a few days. So
they put in a *big* battery. Consumers are used to big 12v batteries
that have to be replaced every few years. The aftermarket is full of
accessories that require substantial amounts of 12v power.
While I'm at it, here's another pet peeve. Car electrical systems are
tremendously inefficient. Everything is designed as if they have an
"unlimited" amount of power. Car clocks, radios, alarm systems, keyless
entry, etc. all consume hundreds of times more power than equivalent
portable devices. There is no reason that cars couldn't be designed to
use microamps on standby, instead of milliamps. That would also solve
the "dead 12v battery" problems.
The system we have isn't ideal; but no one is in the mood to change it.
Lee Hart
--
Ring the bells that still can ring
Forget your perfect offering
There is a crack in everything
That's how the light gets in.
-- Leonard Cohen, from "Anthem"
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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