How about a 4 pound "battery"?

[CTScott]

Originally Posted by Amdkt7

Very cool! One of my concerns would be the possible overloading of the alternator due to the very low internal resistance (fast charging rate) of the caps. I don't know if the alternator is self limited in peak output, or if the battery holds it back.

The biggest concern is the possibility of having to charge it after not using the car for a few days. Since mine rarely gets even one day off this should not be a problem.

One other concern would be the possibilities of voltage surges exceeding 16.2 volts. I might consider placing an appropriate sized zener across the caps, but the super caps themselves should help prevent such surges anyways.

I will follow your results with a great deal of interest.

If this seems to pan out I will replace my own battery in a couple of years this way. I'd just as soon get all the use out of the original battery that I can.

Perhaps a much smaller standard battery along with the caps could keep the charge up for several weeks and still start the car.

The voltage regulator module, within the alternator, would be the first to fail if the current draw by the caps is too much. Thus far I have seen a peak current draw of 45A, which is well within the 70A rating of the stock alternator.

The zener diode is not a bad idea to prevent damage from over voltage, but there again the voltage regulators in modern cars generally prevent that type of failure mode. I will eventually add a large rectifier diode to the pack to prevent the possibility of reverse polarity, as that would result in the most catastrophic failure.