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Old 02-21-2014, 01:39 PM   #7 (permalink)
redpoint5
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I'll be updating my post on this soon...

My motorcycle, with its very low 1.25mA parasitic drain, only takes about 3 days until the 400F capacitors discharge to the point that it won't start the bike. Using the 3000F capacitors in the video would be very expensive, but would likely give about 3 days of sitting time before they failed to start a vehicle. Combining the "Boostpack" with a small LiFePo4 battery is certainly the proper way to eliminate the lead-acid battery.

My hesitation with the LiFePo4 battery is that charging them in sub-freezing conditions will cause permanent damage. To extend the life of the battery, one would need to either ensure it's warm enough to accept the rapid charge an alternator would supply, or limit the charging to a sufficiently low amount as to avoid damage. I have not found a source of info that lists the safe C-rate to charge.

My question is-

Could a power resistor be put between the LiFePo4 battery and the capacitor to limit the rate of charge/discharge to the battery? Would this still allow the battery to eventually come up to full charge, and maintain the charge of the capacitors when the car is idle?

The goal is to get the car to rely on the capacitors for starting/charging, but have the battery maintain the capacitor when the car is off for extended periods of time.

Quote:
Originally Posted by UFO View Post
To take advantage of any improved efficiency in recovering stored energy, the electrical system of the car would have to be changed. Your alternator would not work very well without a battery any more, as you cannot charge a capacitor without the voltage rising and alternator regulators are designed to maintain a constant voltage.
I'll post another video of my motorcycle starting, charging, and then maintaining the voltage of the capacitors. Correct me if I'm wrong; my understanding is that motorcycles use a generator instead of an alternator, and the generator outputs full power all of the time, with the excess not absorbed by the battery being converted to heat in a voltage regulator.

I would imagine that in a car, the alternator would detect full voltage and then turn charging off until voltage sagged below a certain threshold... another thing for me to test.

I'll buy that LiFePo4 battery today so that I can test, and answer some more lingering questions on this topic.
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Last edited by redpoint5; 10-02-2014 at 03:54 PM..
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