New in CT

Discussion in 'Introduce Yourself' started by veloman, May 31, 2008.

  1. veloman

    veloman Member

    Hi there. I found this site in my pursuit to build an electric assisted bike.

    Some backround on me: I've been into cycling/racing for the past 9 years since I was a teenager. I do a lot of road biking and some mtn biking now. I finally made the jump to tinker with an old mtn bike and strap on an electric motor, to save some gas going to work and mainly to just have some more relaxed fun.

    For some of you unfamilar with power/speed requirements, I can tell you that if you get aero/lightweight, you can go 25mph or so on ~350watts. Well, that''s for a road racing cyclist. 35mph takes me about 800watts once I get up there. 6% grade uphill at 30mph = only 1400watts. I have a powertap powermeter that accurately measures watts. This is all dependant on an efficient gear ratio though. If you have a 2hp engine, it's not going to put out 2hp at lower rpms up a hill.

    Point is, if you get light and aero enough, and are on an efficent machine like a road bike with high pressure tires, you can go considerably faster that what most of you are familar with. Comfort is an issue though.

    Anyway, my project I am starting when the parts arrive is this. Bought 2 12v 17ah SLA batteries and a small 24v 350watt motor. With proper gearing this motor will perform better than what most people would expect.

    (For example, if I put out 100% effort sprinting in a huge gear on my road bike, I might only produce 1000watts. But if I am in the correct gear, that same effort will get me 1700-1900w. With this in mind, you can see how important gearing and possible multiple gears are.)

    I plan on doing a straight up circuit with an on/off switch, no controller. Since the motor is only 350watts, I really hope this is not a problem, concerning the electrics? (I have no problem with ride/speed wise with this type of on/off function.) I would think that a controller would end up soaking up power and decreasing efficiency.

    My total cost should only be $150, (excluding the bike which I already have.) I going for pure simplicity and low cost on this setup. I will still pedal the bike on hills and starts, but I wanted the electric motor to take the bulk of the work on my relatively flat commute to work. I can't wait to get started on it! :grin:
    Last edited: May 31, 2008

  2. Accender

    Accender Member

    Hiya Vel, nice to have you here!
    What type of battery are you lookikg at?
    Or, what is SLA?

    edit: Oops, sealed lead acid. I looked it up. might be heavy

    Last edited: May 31, 2008
  3. veloman

    veloman Member

    Yeah they are a bit heavy, 13lbs for each, so 26lbs in batteries. But I got them cheap, for $80 shipped, on ebay.
  4. crabdance

    crabdance Member

    Hi Veloman,
    Welcome to the forum. This is a nice place with plenty of nice people here. Hope you enjoy your stay and feel free to ask questions when you like.
  5. veloman

    veloman Member

    Okay, doing some calculations on I determined that the additional power requirement of 26lbs for the batteries will cost me only 80 watts more up a relatively 'steep' hill of 8% at 18mph. At 22mph, the total battery weight will cost an additional 100 watts of power on the same hill.
    So a switch to an advanced lightweight battery system would likely only yield a 1 mph increase on a typical hill. With a weaker rider/motor combination, the difference would be even less between heavy/light batteries.

    In my opinion, that's not too too bad. For an economical setup, lead acid batteries still seem viable.

    One very critical component to my setup that I am going to try very hard to do is give my bike the ability to coast without the motor turning.
  6. dbigkahunna

    dbigkahunna Guest

    And put a friction drive on the back with a 35cc 4 stroke and you have the ultimate hybrid.
    Welcome to MBc from the Giant Side of Texas!