# Re: OT My simple electric bike

• posted on July 30, 2015, 4:46 am
On Wed, 29 Jul 2015 23:24:58 +0000 (UTC), John Doe

This is really interesting, but I'm having trouble with some of the numbers. Say the "two bars" consumption equals, roughly, 3 A-hr. At 20 volts, we have 60 W-hr. Just guessing here, but say you travelled that 6 miles at 12 mph.
That means the drill was drawing an average of 120 W for a half-hour. Let's be generous and say that the system efficiency is 80% from storage to power at the drill shaft. So, given chain and friction losses at the tire, you have 1/8 hp driving the bike.
Will that be enough to move you at 12 mph? I'm not familiar with the actual power consumed by these bikes, but that sounds low. Am I missing something?
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Ed Huntress
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• posted on July 30, 2015, 4:55 am

Well consider also that the bars may not be an accurate indicator of the state of charge.
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• posted on July 30, 2015, 12:17 pm
On Thu, 30 Jul 2015 06:11:27 +0000 (UTC), John Doe

I looked up some energy research data on bicycles and it looks like you can get just about 12 mph with 100 - 120W. So you're right in there.
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Ed Huntress