Introduction: Electric Bike to Electric Generator - Simple DIY Mobile Interactive Science Museum

About: Fat, old, and nearly bald, Pat O'Briant bumbled his way through an aeronautical engineering degree at an enormous state university which fortunately had an open admissions policy. I've spent the last 28 years …

I hear and I forget. I see and I remember. I do and I understand.
Attribute to Confucius (~500 BC).  Still true 2500 years later.

When I was 7 or 8 years old on a miserable cold gray day in February my parents dropped my brother and sisters off  at the Center of Science and Industry (COSI) in Columbus.  What a wonderful place!  Our  favorite of all exhibits was the interactive bike generator. Hop on and pedal. Flip on the switches and power your own lights. See how many watts you could make and for how long.  All day long we kept coming back to try it again and again.  We got it.   Work, power, energy, electricity, volts, amps, watts, watt hours, renewable energy, conservation, limitations of the human body it is all included.  Dead simple and yet brilliant.

For science teachers, PE teachers this should be a  simple to build fun educational demonstration that could fit well into many different standards of learning objectives.  This should also be great for anyone who wants to make a fun interactive exhibit or a science project. 

To keep this simple start with an electric (assist) rear wheel direct drive hubmotor bike.  This is a popular version of Chinese electric conversion kits.  (Crystalyte, 9 Continent, Golden Motor (full size not mini)) (Pictured is the Crystalyte Roadrunner - 408  

For this conversion -
1)Place bike on stand (a simple stand for an Xtracycle  - see my previous instructable
2)Remove and Replace battery with Load (light bulbs and switches) (see following steps)
3)Pedal to generate electricity

Starting with another (not a rear wheel direct drive hubmotor electric bike) is likely doable but more complex. I will leave that as an exercise for the reader.  The popular Bionx direct drive may work but as the Bionx motor contains a proprietary internal brushless controller it may (or may not) be more challenging to convert in this way.

Step 1:

Parts needed:
1)Electric assist direct drive hub motor brushles bike
      a)Rear direct drive drive brushles hub motor direct drive hub motor brushles is (comes with the electric bike)

       b) DC brushless controller - black box / white label  pictured above (Crystalyte and Infineon work well comes with the electric bike)

        An electric bike kit can be purchased  kits at or    or (model Model: HBS36R -- Rear Hub Motor)

2)Load (light bulbs and switches) white box pictured above - See following steps for assembly

         a)24 volt 75 watt halogen light bulbs quantity 8  each $1.23
         b) Wire Connector Socket for MR16, MR11 or G4 quantity 8 ($13.49 for pack of 50)

           c)Electrical outlet box 4 gang – quantity 1 – Home Depot / Loews ($4.45)
           d)Household switches quantity 4 – Home Depot / Loews (contractor pack of 10 -$3.89)
           e)Miscellaneous – wire, connectors, ~4” scrap angle, epoxy

3) Bike Stand - For Xtracycle
                           for traditional frame bike remove damper from a trainer such as
4) Optional - Power Analyzer II - small blue box pictured above  (no longer sold by Medusa)  (measures watts/volts/amps/watt hours) This can also be done with a voltmeter  and ampmeter (2 multimeters but is not nearly as simple)

Step 2: Build Electric Light Load - Circuit Design

A simple (if not precisely correct) model of the output from the DC brushless controller attached to a spinning  electric hub motor bike generator is as a 60 Volt (maximum) battery. 
(In order to hit 60 volts a rider has to use a high gear and spin very fast.) 

A nice simple online circuit simulator from Univ of Colorado is here .

Above is the circuit design for the load - 4 parallel strings with (2x 24 volt light bulbs in series).   With internal resistance each bulb is around 25 volts and the circuit is pulling ~10 amps.  Factoring in motor resistance the circuit is pulling ~600 watts.  (Considerably more than most riders can sustain.) 

Step 3: Build the Load

1) Cut off approximately 4 inch piece of scrap angle metal to use as a light base plate
2) Drill 8 ~ 1/8" holes in order to pass the connector base wires out the back
3) Pass the wires through the holes and epoxy the connectors to the base plate

Step 4:

1) Bolt the light base to a 4 gang junction box
2) Connect the wires (2 lights in series per switch) and (four switches in parallel) (see circuit from Image in Step 2)

Step 5:

Screw on a cover plate, add light bulbs, and label (in this case each light bulb =75 watts)

Step 6:

1) Disconnect the battery from the DC brushless controller on the electric bike, connect this load to the former battery connector (see picture from Step 1)
2) Place bike on stand,
3) Pedal
4) Let the user switch on the lights (load) - generate electricity,  learn and have fun.

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