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Old 01-17-2014, 02:00 PM   #1 (permalink)
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Super-capacitors instead of a battery?

Happened to see the following video on Youtube... Just wondering if their would be any worth-while efficiency benefits by using capacitors instead of a chemical battery??

Towards the end, he talks about being able to quickly recharge the caps using a solar panel, when the car is stationary.

Could you perhaps uses a smaller and lighter battery - with the main whack of starter current provided by the charged capacitor bank??


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Old 01-17-2014, 02:43 PM   #2 (permalink)
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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.
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Old 01-17-2014, 03:00 PM   #3 (permalink)
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Another discussion on this topic:

Supercapacitor Battery Replacement
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Old 02-20-2014, 10:11 PM   #4 (permalink)
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I asked around about this a couple months ago and along with what UFO said, the computers on modern really need the constant full power a battery provides. With the capacitors dropping down to 10 or 11 you could possibly get voltage spikes that would destroy the sensitive computers. However, if I had a cheap old CRX or something of the like I wouldn't hesitate to give capacitors a try.
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Old 02-21-2014, 03:47 AM   #5 (permalink)
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Quote:
Originally Posted by Daox View Post
Another discussion on this topic:

Supercapacitor Battery Replacement
several threads on this. still try to sort out if their is some benefit..........
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Old 02-21-2014, 03:52 AM   #6 (permalink)
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fyi
the youtube 4 lasersaber boostpack has been updated....clearly ultracaps have a higher cycle life and store/release dc power differently than agm battery
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Old 02-21-2014, 02:39 PM   #7 (permalink)
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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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Old 05-05-2014, 05:10 PM   #8 (permalink)
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If you want a light weight battery, have you guys considered a Dyna-Bat from Performance Distrubutors? Weighs 13 1/2 pounds.
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Old 05-05-2014, 11:35 PM   #9 (permalink)
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Some motorcycles have alternators. Solid state components have a working range of voltage between the indeterminate condition and burn through. A small battery is used in a computer to maintain a voltage while the power supply is off. Dampening capacitors are used in circuits to prevent spikes in voltage or current. Regulators can control generator output by limiting current to the field windings. Old tractor generators had a cut out switch to do this. A heating element could be used with the LiFePo4 battery to bring it to temperature and act to limit current as well. Time to do some electrical engineering homework.
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Old 05-23-2014, 12:29 AM   #10 (permalink)
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Quote:
Originally Posted by redpoint5 View Post
I'll be updating my post on this soon...

My motorcycle, with its very low 1.25mA parasitic drain, only takes about 5 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.



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.
sub'd for results

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