Re: 50 Farad Capacitor
Here is an email from the EV discussion list about this topic:
Say you have a 144V pack that sags to 110V under heavy acceleration and
the caps are directly in parallel and you pull that heavy acceleration.
The caps are great at t=0, but the cap voltage decays as they provide
current. As cap voltage drops the current will shift back to the batt.
Eventually- time depends on capacitance- all the current is coming from
the batt, batt's sagging to 110V, and the caps do nothing. In fact the
batt voltage will stay low for an equally long period as the batt puts
out equally high currents to raise the cap voltage on these
Furthermore, at 110V the cap still has 58% of its initial energy, it's
just not usable. It might be desirable if your car can keep moving at
say 70V to disconnect the batt and just run on the caps since they don't
wear out or suffer ill effects from high current charge/discharge. But
that is quite an extra level of complexity. In fact once you separate
them you and let cap voltage drop below batt voltage they can't just be
reconnected, it's almost like a short circuit on the batt and the batt
will see the highest currents possible which isn't improving the lifespan.
Don't forget such a cap bank is, today at least, 1) phenomenally
expensive, 2) very large, 3) very heavy. So adding something similar in
size in addition to the main battery bank to stiffen it isn't currently
reasonable and practical.