The writer prepared a BLOG in August 2009 discussing the pros and cons of various means of recovering and reusing the energy normally dissipated as heat in friction brakes in the operation of HYBRID cars. The ULTRACAP was known at that time but was not widely available and range of product was restricted. Well that has changed and the BLOG will reconsider the ULTRACAP potential use. There are also other contributory factors.
Of these contributory factors the nagging problem is that Li-ion batteries in mass production are not following any reasonable learning curve and the cost are staying very high and in fact the writer suspects that there is more than a little connivance in maintaining the high cost for marketing purposes. Particularly in the of the EV, Electric Only, the cost of a 24Kwh battery, is about $700 per Kwh resulting in battery pack of nearly $18,000 and is a major portion of the car cost as delivered.
What Toyota has apparently done with its very successful PRIUS is actually reduce the Li-Ion pack cost and size and works this smaller battery harder to behave almost as a ULTRACAP to provide the electrical acceleration power and provide the load for regenerative braking and in so doing appears to achieve about a 60% recovery of the braking energy normally lost to heat. What is being suggested here is using the ULTRACAP to augment the smaller Li-ion pack to raise the recovery to nearer the 90% level-----a very nice increase. This will very directly improve the MPGe performance---always desirable.
What is proposed here is to operate in parallel; a ULTRACAP pack with the Li-ion battery pack in such a manner that the peak current sources and sinks are handled by the ULTRACAP while the average current requirement will be handled by the Li-ion.
SIZING THE ULTRACAP PACK----
Calculating an ULTRACAP’s energy use the formula (½ xCxV^2) where the energy will be in watt-seconds; C will be in Farads and V will be in volts. It is an interesting point that Ioxus ULTRACAPS have stamped on the case side a Wh (watt-hour) value, as well as the voltage and the capacity. For example a 2.7 V, 3000F has a 3.042 Wh specification. So to estimate how many ULTRACAPS, you first need to calculate how much energy will have to absorb to decelerate from what design speeds and how quickly. BTW the Wh figure on the Ioxus units is based upon total discharge of a fully charges ULTRACAP cell in this case to 2.7V. In actual practice you can operate the ULTRACAP over a (2.7V to 0.9V) range and achieve 90% of the Wh figure printed on the case. The necessary calculations are tedious but straightforward.
CONCLUSION----
It seems like that ULTRACAPS will soon find their way into the acceleration/deceleration system certainly for HYBRID cars and it is the writer’s guess that even now Toyota engineering people are experimenting on how to incorporate into the next generation PRIUS.
INTERESTING----