Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Electric Bikes Here's a place to discuss ebikes, from home grown to high-tech.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 07-10-12, 07:01 PM   #1
built
Junior Member
Thread Starter
 
Join Date: Jul 2012
Bikes:
Posts: 6
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
250w 24v ebike and 24v alternator

im looking into getting the hill topper kit from clean republic for my trek 4300. i'm not looking to make a perpetual motion vehicle but rather create a charging system for when the ebike's 250w motor is not in use. with a 24v 40amp alternator using a bicycle peg running on the rear wheel of my mountian bike in place of it's pulley the alternator should be capable of producing 960w of charging power. i'm thinking if this is used while the 250w hub is drawing from the battery the drag on the alternator would most likely prevent the bike from moving. my idea would be to have some sort of switch used to excite the alternator when the hub motor is not in use. there are other things i would need to get this to work but this is just a rough idea. any thoughts or imput would be great
built is offline   Reply With Quote
Old 07-11-12, 09:36 AM   #2
crackerdog
Senior Member
 
Join Date: Mar 2008
Location: Port Townsend, WA
Bikes: xtracycle, electric recumbent, downtube folder and more
Posts: 982
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Off the top, you can't generate 960 watts unless you are Superman. The record for an hour is 430 watts. Trained athletes in the Tour de France put out about 400 going up steep hills and about 250 on the flat. So figure maybe 200 watts. Then there is the 50% loss from converting to electric.....

Last edited by crackerdog; 07-11-12 at 09:38 AM. Reason: more info
crackerdog is offline   Reply With Quote
Old 07-11-12, 11:55 AM   #3
built
Junior Member
Thread Starter
 
Join Date: Jul 2012
Bikes:
Posts: 6
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
A 12v 40a alternator can put out 480w
A 24v 40a alternator can put out 960w

With the smallest peg I can mount on the alternator to run on the wheel I would be able to turn the alternator approximately 50 times for every one rotation of the crank. Here is an example, he isn't using anything to store the power he is just using it to power a 220w food processor:
built is offline   Reply With Quote
Old 07-11-12, 07:22 PM   #4
crackerdog
Senior Member
 
Join Date: Mar 2008
Location: Port Townsend, WA
Bikes: xtracycle, electric recumbent, downtube folder and more
Posts: 982
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Yes, the alternator can put out that much but a bicyclist can't. Did you notice how his legs slowed down when the button was pressed on that little tiny motor on the food processor?
crackerdog is offline   Reply With Quote
Old 07-11-12, 07:22 PM   #5
DAME
Senior Member
 
Join Date: Jun 2011
Location: Norfolk/VA Beach
Bikes: '08 Trek 6500, '10 SOMA Double Cross, '12 Brompton M6R
Posts: 97
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Sounds interesting. I'd love to see a prototype.

Possibly get on endless sphere and ask the same questions for some possible inputs.
DAME is offline   Reply With Quote
Old 07-11-12, 07:35 PM   #6
Allen
Senior Member
 
Join Date: Sep 2005
Bikes:
Posts: 4,758
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Entropy and drag. It will take more energy to charge the batteries and run the motor than it would to just power the bike on its own. Quite a bit more.
Allen is offline   Reply With Quote
Old 07-11-12, 11:35 PM   #7
SpecialX
Senior Member
 
Join Date: Apr 2012
Bikes:
Posts: 162
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Your original hypothesis is correct, the SECOND you would energize the alternator, you'd get ENORMOUS drag, and at BEST (this has been tested before), you'll get 100w from it (at a speed of about 6 mph - and that's pedaling as hard as possible--if you try to go faster the resistance will preclude you from being able to pedal more)...
There is no reason to do this, when just pedaling the bike yourself will net you more speed, better efficiency and no need for the added weight and complexity of a motor/recharger system..

You'd be better off just buying a bigger battery and pedal with the motor.

This has been discussed ad naseum.. If you want to do it as a "fun project", then good.. But it won't work well (if at all) in practice.
SpecialX is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 04:06 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    get answers from real people!
Click to start entering your question.
I HAVE A QUESTION