# electric bike questions



## evolutioneng (Jun 29, 2011)

since im not ready to spend alot on battery pack. i would like to build a dirt bike with a electric motor.i would like to go 70+ riding miles and about the same speed.if i can go way more that will be great.how much volts am i looking to power it.also will it be hard to make it street legal im not going to tell the department of transportation its electric dont want to bother.everything i hope will be covered with the plastic panels.


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## evolutioneng (Jun 29, 2011)

http://cgi.ebay.com/Maxwell-350-Far...213?pt=LH_DefaultDomain_0&hash=item45fa4bb5fd

how many of these would i need to get 70 miles to charge and 70 mph?


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## Semper Vivus (Apr 13, 2011)

Hi,
I don't know how much energy is exactly needed for that speed and distance. But you will see that the exact number doesn't matter in this case ;-). Let's assume you need 3kWh of stored energy (3000Wh):
The formula for the stored energy in a capacitor is E = 1/2 * C * U^2.
So with that capacitor you will get 1094Ws or 0.304Wh from one piece as it is also written in the article description (1 Joule = 1 Ws).
That results in about 10 000 pieces (3kWh / 0.304) and nearly 600kg of weight! ...but with the power you will be able to udraw from that caps the weight won't be a problem .

Kind regards,
Tom


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## frodus (Apr 12, 2008)

good luck getting 70miles per charge if you're not willing to dump A TON of money into the bike.

Keep it gas and enjoy it.


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## x88x (Aug 19, 2011)

70+ miles at 70+mph is going to take a big, expensive battery pack no matter what vehicle it's in. Even if you got 100Wh/mi, that would still require at least a 7kWh pack...which even with the cheapest Lithium at the moment would cost you almost $3k and weigh at least 150lbs. ...oh, and good luck not getting it impounded if you're doing 70+mph on public roads with a clearly not licensed vehicle...


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## leonheart (Mar 2, 2011)

Look at this motorcycle:http://www.youtube.com/watch?v=Ae8uOz5PnRM
this guy used the original transmission to have more top speed and a few more autonomy. In my honest opinion, is a great idea even if a electric bike doesn't need a reduction gear.


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