# Flywheel capacitor/battery bank?



## kennybobby (Aug 10, 2012)

Dembones said:


> Could one arrange each series set of cells around a shaft, balance it, sleeve it with a tube for safety, and attach it to a small dc motor?


Flywheel energy storage is a great idea. The difficult part involves the conversion of Kinetic (flywheel) to Potential Energy (storage battery) or other useful forms of energy in a timely manner (quickly). 

For example i have conducted tests on a 1350 lbs flywheel connected to a generator and driven by a heavy-duty 5 Hp dc motor. It takes about 20 minutes to get the flywheel up to 800 rpm with this motor drawing 150 Amps. The generator makes 800 volts that is fed into a 300 Hp inverter to drive a 3-phase linear induction motor. When i fire the induction motor it pulls 300 Amps in 4 seconds and slows the flywheel down to 400 rpm, which now requires 10 minutes to get back up to speed again. A huge amount of very heavy equipment is needed just to provide a 4 second burst of useful energy. 

So like anything else you can imagine it can be done-- can useful energy be extracted in a timely manner for an EV is the big question.


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## Ziggythewiz (May 16, 2010)

I wouldn't want my cells kept in a centrifuge...pretty sure they weren't designed for it. Even if it were okay I doubt the cost/effort would be worth it. There's a reason KERS runs in an F1 and not a Prius.

I think there was a MIT team that had an e-bike with the cells in the wheel, I wonder if they had any issues because of that.


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## Dembones (Apr 22, 2013)

Thanks for sharing your experience. For a 144v system, each series bank of cells weighs approximately 32 lbs (45 @330g each). The spin-up time will be very fast as each of these in parallel has its own motor/generator, but again it comes down to how LiFePo4 cells react in a centrifuge. I don't believe I saw centripetal force yield ratings anywhere on the website.
A system like this could be 100% modular and factory made, each series "spinning battery" could be built for the specified voltage. 
I wonder about the gyroscopic effect, how would this affect handling even if the cells can withstand enough centripetal force to be efficient.


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