Here you will find everything you need to for an easy to build, powerful, quiet stationary spin bike pedal generator. I’ll cover tools and parts needed, along with diagrams for wiring and things I’ve learned along the way that can make your build a success. Let me start by saying that I am not an electrical engineer, nor a mechanical engineer, this was just something I was interested in and wanted to go about building. If you have suggestions or a better way to build it, I’d love to get your feedback!
Let’s get right to it! First you’ll need a spin bike, also known as a stationary bike or exercise bike. If you don’t have one already, check eBay, Craigslist or garage sales. Otherwise, there are several models from Sunny Fitness that should work. Be sure to get one with a chain drive (not belt).
The next key component is a e-bike hub motor. Hub motors come in many different models, front, rear, 24 volt, 36 volt, 48 volt, 350 watt, 500 watt, 1000 watt and so on. For this to work, you’ll need a front hub e-bike motor (check eBay if Amazon is out of them), as front hub motors will fit between the typical spin bike front braces. You’ll also need to have a disc brake mount on the hub motor. More on this in a minute. For my build, I went with a 24 volt setup, using a 24 volt motor 500 watt motor. You can use a 36 volt brushless gearless front hub motor with disc brake mount if you can’t find the 24 volt variety.
Now you may be wondering how we plan to drive the e-bike hub motor with the chain drive of the spin bike. This took me a little while to figure out, but it just so happens that some people use the disc brake mount on a bicycle to mount a ‘fixed’ gear. There are a few companies that sell sprocket kits just for this purpose. The one I recommend is the 16 tooth sprocket from Origin8. Just take off the free hub adapter parts (the red things) and bolt the sprocket on the disc brake mount on the motor. Some Loctite might be advised.
Once the sprocket is on the motor, pull the original flywheel off of the spin bike and replace it with the hub motor, ensuring you route the chain over the newly installed sprocket.
When you turn the e-bike hub motor the permanent magnets pass over the the copper coils of the stator in the motor, generating alternating current electricity. To convert to more usable direct current, we need simple component called a 3 phase bridge rectifier – it sounds really complicated, but it is really just a basic circuit which takes the 3 wires of alternating current from the hub motor and converts it to direct current. The fat wire coming out of the hub motor consist of the 3 wires just mentioned, and some thin hall effect sensor wires used by a typical e-bike controller to determine RPM of the motor. These sensor wires can be clipped and/or tucked out of the way. For the remaining thicker 3 wires, we’ll put female spade connectors on the ends and connect them onto the 3 posts of the bridge rectifier marked with the “s” squigglies. The other two posts on the bridge rectifier deliver positive (+) and negative (-) direct current. The side of the bridge rectifier has a map of the posts, click on the image at right for a closer look at the map.
Next challenge – the voltage coming out of the bridge rectifier is anywhere from 20 to 40+ volts. This is assuming a 24 volt hub motor spinning anywhere from a leisurely pace to frantic sprint . We’d like this power to be a steady 12 volts so we can charge cell phones, iPads, and run things like fans and coffee makers. With 12 volts output, we could also use a DC to AC converter to charge our laptops, cordless drills or power a TV. Enter the step down converter! If you go with a 36 volt motor, you may want to get a 36 volt step down converter. This critical component is often used in electric golf carts to “step down” the 48/36/24 volt battery power in the golf cart to 12 volts to run fans, radios, lights and other things that plug into a 12 volt car socket. Here’s a diagram of the wiring, including an optional multi-meter – it really is very simple.
That’s it! Those are your basic components to make it all work.
This really is a fun project. With most of the challenges of how to make it all work spelled out above, what’s stopping you from building your own pedal generator?
Some optional components, basic tools and supplies you may need to complete this project:
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