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Discussion Starter #1
Well i dont have any questions about building it ha ha, its already done...
pics here:
www.educationaltoolz.com/ebike

It's simple, very fast, and pretty unsafe...gone through 3 or so chains and
a derailer...
clocked at 57.7mph, goes from 0-top speed in one gear, tons of pull all the
way through.
My friend wanted to build it, i had the motor and controller laying around
and a welder so here it is now.

Anyhow i was thinking of upgrading to a dirtbike frame and larger batteries.
Besides the bike not falling apart, i can hold larger batteries leading to a
much higher power/weight ratio.
But i ran into some issues i wanted to see if anybody had advice on while
planning it. First is...is the motor pulling all the CCA out of the
batteries? if so, optimas would easily go over the motors max load.
The batteries we have seem to be dying already, i'm assuming from drawing so
much out of them in such short bursts, is there any way to prevent this
besides....
Capacitors, if my physics calcs are even remotely correct, even a farad
could give you enough juice to go for a second, offloading the batteries in
that time period. Yes i know it would be over $600 to get 75v
capacitors....But still howcome i don't see anybody else using banks of
caps. Seems to me like its not alot of weight and it could greatly aid the
batteries...Maybe too much discharge capacity to safetly power the motor?

To break it down...looking for a way to make the batteries last a bit
longer.

and... could an etek motor handle 4 50ah batteries @48v or maybe like 6 of
lesser ah @72v.

any advice welcome!

-Marc
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70 Posts
Discussion Starter #2
Hi Mark,

We put about 450 Farads on my friend's bike.

http://tinypic.com/view.php?pic=68aoz12

Just a 14 volt system. A bunch of NiCad C-cells.
Basically just playing around with left over parts.
Never serious enough to take data or make scientific
test. But the ultracaps did stiffen up the battery
quite a bit.

I have also done battery/cap combos on larger hybrid
vehicles. My feeling is that the use of ultracaps in
conjunction with batteries is only of real benefit
when you have regeneration available. Otherwise the
battery has to charge the cap. You do get some load
leveling, but probably not enough to justify the added
cost and mass of the cap. You'd be better off
spending that on a better or bigger battery.

Be careful with that thing!!!!

Jeff


--- Marc Breitman <[email protected]> wrote:

<snip>
> Capacitors, if my physics calcs are even remotely
> correct, even a farad
> could give you enough juice to go for a second,
> offloading the batteries in
> that time period. Yes i know it would be over $600
> to get 75v
> capacitors....But still howcome i don't see anybody
> else using banks of
> caps..
<snip>
>
> any advice welcome!
>
> -Marc




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