Just to get everyone reading this on the same page:
Electricity is the flow of electrons, and the flow of electrons through the motor is what makes the IMA work. current is how many electrons/second are passing through the circuit.
The major electrical difference between caps and batteries:
A cap is a tank to store electrons, it does not produce them, so it can be charged almost instantly, with the main limit being the resistance of the leads, and also discharged almost instantly.
A battery generates electrons from the plates chemical reaction, so it can produce electrons as long as the plates can be reformed and the electrons stripped off.
The main difference in capacity comes from the cap voltage dropping continuously as the electrons are sent into the load, since the cap does not make electrons, only store them.
The battery keeps making electrons while the plates are charged, and the voltage produced is very flat while as electrons are readily produced fast enough to satisfy the load, with little voltage drop during the whole process.
Since the insight was designed to use batteries, and batteries need to not be over discharged, the useable voltage range the inverter will accept is between ~110 and 190VDC, and the batteries are nearly fully discharged when the pack is at 120V.
To get the full capacity out of a supercap pack, one would need to discharge it to zero V, but the car can olny use > 110V, so one would only be using a portion of the capacitors energy before the cap dropped below the useable voltage.
In most full capacitor drive systems, dc/dc converters are used to take the dropping voltage of the caps, and dc/dc convert it so the output is always in the 110 to 190V range.
It gets more interesting when one considers a cap/battery parallel combo.
Here we use the cap to impruve the high current pulse performance of the battery, but since the battery volts only drops a bit when a big load is applied, it will only draw current from the cap as the battery drops in voltage, so one may see the 150V pack drop to 130 under a big power pulse, but the cap only helps keep the battery volts from dropping as fast as it would if the cap was not there, the caps will hold the voltage up longer, but will eventually drop to the battery V, but once the cap is at the lower loaded voltage of the battery, it is dead weight. Electrons can only flow when there is a voltage difference.
When the load is removed, the battery volts wants to jump up to its unloaded value,
but the battery now has the additional task of recharging the cap as its unloaded volts try's to rise to the batterys unloaded state, so the battery also needs to produce the recharge current for the cap, so its load continues compared to what it would have did if the cap was not there, so the cap boost was not free.
So the bottom line is that with cap in parallel with the batteries, one would not have a substantial performance improvement unless the car was driven hard, and for hypermiling where we try to minimize the load, it could be a liability due to the increased weight and complexity.
Supercaps are also low voltage devices,with most being 2.7V max per cap.
We can only store the max energy if we charge them up to nearly the max volts.
2 cells at the highest V we have seen. under heavy regen, packs can reach 190V
This works out to 1.58V/cell so even with 2 cells/cap, under heavy regen, we could see over 3 V with 2 cells in series, which exceeds the safe operating V of the single cap.
If we use 1 cap/cell, then we are not fully charging the cap, and will need twice as many.
No matter how you look at it, supercaps in a insight will probably not be a cost effective way to get better MPG.
My 48V booster battery that charges the main pack on the fly 5through a step up dc/dc converter worked pretty well, and that may be most cost effective way to boost the cars MPG.
