If you’re looking for a way to build an inexpensive but powerful and efficient pedal charger, you’ve come to the right place. When comparing bike generator plans, here are some things you may be wondering:
How much will it cost to build?
What tools will I need?
How hard will this be to build?
Where can I get all of the components?
Will this bike generator be efficient?
Will I have to take my bike apart? Can I still ride my bike when not being used on the trainer?
Will this pedal generator require a battery to function?
How noisy will this bike charger be to operate?
What is the upper limit of watts this bike generator can generate?
Before I came up with my pedal generator designs, I looked at many of the plans you will find on the internet. Some plans are better than others, but I would argue the plans you’ll find here at Gene’s Green Machine are superior for the following reasons:
Can be built for $130 US Dollars or less
No welding required, can be built with tools you probably already have
Possible to build without even soldering
Is simple to build with clear instructions
All components are readily available, no custom components or 3D printing required
Built with highly efficient and durable permanent magnet RC motors
Eliminates the need for a charge controller or voltage regulator by choosing a motor that will generate power in a very usable voltage range (10-15 volts), making this design even more efficient
No need to modify your bicycle, so you can still ride it when not being used as a pedal generator
Small footprint and easily stored
No battery required to generate power
This pedal charger is quieter than most designs – the brushless motor used in this design is the reason. No brushes to make noise or wear out.
The RC motors used have an upper limit of over 1000 watts, and I have personally generated almost 400 watts using the bike trainer generator
You can find other bike generator plans (or even products for 100’s of dollars) on the internet, but look closely at all the details and I think you’ll find the faults with those designs and why the plans you’ll find here are well thought out and among the best options. Ready to get started? Go to the Bike Generator Plans!
Following the theme of my bicycle trainer pedal generator, I wanted to build something with a more substantial flywheel in order to take advantage of momentum the added weight will provide. An exercise spin bike is a perfect candidate for making a pedal generator with just a few parts and fairly simple electronics. Like my other design, we will use an RC motor and a 3 phase bridge rectifier for the core of the design. This design should be adaptable to most other spin bikes with little or no modification.
– U bolt – to attach project box to handle bar – measure your spin bike handle bar to get the right size – 12v car sockets, 2, 3 or more depending on the size of your project box and how many things you want to charge at once. You can also consider getting a splitter/extender as well.
Let’s figure out how to choose the right RC motor for this project. Our goal is to have a motor spin at a rate that will generate between about 12 and 15 volts when we are spinning on the exercise bike. RC motors are rated by how many volts they produce per RPM. A 1000Kv motor would need to spin at 1000 RPM to produce 1 volt. To get to our 12-15 volt range in this case, we’d need to spin the motor at 12,000 to 15,000 RPM. Let’s get some basic measurements from the spin bike.
– The circumference of the flywheel on my spin bike is 57 inches
– Pedaling the spin bike at a comfortable pace rotates the flywheel between 250-350 RPM, which I confirmed using a digital tachometer
The BaneBot wheel we chose is 2 7/8 inches diameter = 2.875″. You’ll recall that circumference is Pi times diameter. The circumference of this wheel is about 9″.
If we take the low end and use 250 RPM and multiply that by the 57 inch circumference of the flywheel, we get 14,250 inches per minute. Dividing the 9″ BaneBot wheel circumference, we get 1583 RPM. We want our motor to produce 11-12 volts at this RPM, so divide by 11 and 12 and get 131.9 and 143.9. So our target motor should be around 140Kv. We found this Balancing Scooter RC motor that fits the bill.
If you have a significantly different circumference flywheel, or choose to use a different drive wheel than what I have, you can use the above steps to determine an appropriate motor to use. Otherwise, just use the 140Kv motor as I have.
The Motor Mount
There are many ways you could mount the motor, but in this project we choose to use 2 flat punched steel braces along with some nuts and bolts/all thread and washers. First you’ll need 2 equal lengths of flat punched steel.
7 or 8 inches each is fine – use your hack saw to cut, then file the rough ends so no one gets cut on the burrs.
Now the trickiest part – measuring and drilling the holes to screw onto the motor. – measure the distance across the face of the motor from one threaded hole to the other hole on the opposite side of the motor shaft. Do this with calipers preferably. Check and double check your measurement. Mine was 38mm center to center. Now, measure and mark where you should drill two holes on each side of a punch hole in the flat steel in about the middle of the bar.
The motor shaft will go through the punch hole. The bolts for my motor were 2mm, so I drilled holes slightly bigger so the bolts would fit in. Drill the holes and mount the motor with the Allen head bolts that came with the motor.
Mount the T81 hub on the motor shaft using the right size Allen wrench.
Mount the wheel and install the locking snap ring that comes with the hub. This task is much easier if you have snap ring pliers, but can be done with other pliers, a screwdriver and determination.
Motor Mount Bracing Install
Next step for the motor mount is to use all thread or a 5 to 6 inch bolt to connect to the second bar/brace. Tighten the bolt, nut and lock washers on the non-motor side flat punched steel bar. Put on 2 nuts and lock washers on the other side with the motor mounted bar sandwiched in the middle, but leave them loose. Place the non-motor bar against the right inside brace of the spin bike just above the flywheel. Adjust the bolts left or right to get the BaneBot wheel in the center of the flywheel, then tighten the bolts.
On the spin bike, carefully measure and drill 2 holes, just above the flywheel, you want to be just high enough to not touch the flywheel with the all thread or bolt. Use a stack of fender washers, along with lock washers and nuts to mount the motor assembly to the spin bike. Use enough washers to center the BaneBot wheel with the spin bike wheel. Once all lined up, tighten all the nuts. Some thread locker can also be helpful as vibrations from spinning may loosen the nuts.
Final step in the mounting is to add a bungee cord (I used 3 little ones) to add some tension from the motor wheel onto the spin bike fly wheel. The ends of the bungee’s hooked onto the transport wheel brackets of my spin bike, hopefully yours is similar. Only hook up the bungee when using the generator, otherwise you may get a flat spot on the rubber wheel.
We have the motor mounted, now we need to make some electrical connections. We need to take the 3 phase alternating current of the RC motor and convert it to DC using the 3 phase bridge rectifier. The motor I have comes with a female MT60 3 wire bullet connector so I just made a 3 wire whip with one end having a male MT60 bullet connector and 3 female spade connectors on the other ends of the wires.
These 3 female spade connectors plug into the alternating current spade contacts (marked with a squiggly that looks like an “S”) on the 3 phase bridge rectifier.
Order of connecting these wires doesn’t matter. Next we need to come off of the DC plus and minus posts and go into the DC meter (optional, but highly recommended). The Drok meter I used has some wires with alligator clips that seemed to connect securely enough to the rectifier. Maybe I’ll add some spade connectors later. On the output side of the meter, we’ll connect to a 12v socket or two. One socket is easy (use the alligator clips), two or more will need a splitter of some sort. I used some 5 wire connectors I had, but you can splice wires together, use a distribution block, some wire nuts or whatever.
Once you have it all hooked up, give the bike a spin and see how many volts the meter reads. The goal is to have 11-15 volts, which is ideal for using car socket chargers and inverters. If the voltage is too low, pedal a little faster. If that isn’t working, you may need to use a smaller wheel on the motor to get the RPMs up. If the voltage is too high, pedal slower or use a larger wheel on the motor. With the combination I have, the 140Kv motorwith a 2 7/8” BaneBots wheel puts me right in the sweet spot for voltage.
Box It Up!
Lets tidy things up a bit by putting the electronics in a project box. I like the ones from Radio Shack that have an aluminum bottom plate on them because we can use it as a heat sink for the bridge rectifier, which is especially important if you are pushing 50 or more watts for any period of time. The size of the project box really depends on how many 12 volt sockets you want to use, along with the size of the DC meter. In the project box shown, I put in two 12 volt sockets, a Drok DC meter and the 3 phase bridge rectifier. I could have easily put 2 more sockets in this box. Cutting the hole for the meter was the most challenging, but here’s the approach I took. Measure the dimensions of the multi-meter. Place masking tape over the area you plan to cut out for the meter. Measure and mark on the tape where to cut, then use a sharp utility knife cut out the hole. Start gently to be sure to stay on the lines. Keep tracing the lines with the blade, pressing firmer and firmer until you cut through the plastic. I’m sure there is a better way to do this, but with patience this approach works. For socket holes, a 1 3/16″ hole saw does the job very nicely. Drill a hole in the metal backing for the bridge rectifier, and use a nut and bolt to secure. I also used a U bolt to mount the box to the handlebar (measure your handlebar and get the right size U-bolt). A couple more holes in the metal plate will be needed to mount the U bolt. You can either drill another hole in the metal plate for the wires to go through, or you can cut/drill in the side of the plastic box. You can get fancy with a wire clamp if desired. I didn’t this time, I just notched the plastic with some wire cutters for the wires to go through.
Okay, the moment we’ve been waiting for – let’s start charging and powering things with our human powered generator! Drop in some 12v car phone chargers, plug in some devices and see how easy it is to put power into them. You may want a splitter to allow connecting more devices. A basic 12v to USB socket charger will only put about 5 watts to your mobile devices, which is why I suggest using some better quality chargers that can put 10 or more watts into your phones, tablets, e-readers, portable battery banks and other devices. You’ll also find having a fan a welcome addition once you start pedaling.
The more devices you plug in, the more resistance you’ll feel as you pedal. For me, anything under 50 watts doesn’t feel like much resistance at all. 75-100 watts begins to feel like a good workout. Around 150 watts is about my limit for a 30-60 minute workout.
Here’s some typical devices and the watts to power them:
To Add a Battery, or Not to Add a Battery, That Is the Question
For generating and powering mobile devices like cell phones and USB battery banks you won’t really need to add in a 12v battery as buffer. If, however, you are going to power a TV or other devices through a DC to AC inverter, you’ll want to consider adding a battery. One of the nice things about this design is adding a battery to the circuit is quite simple and requires no additional electronics because the 3 phase bridge rectifier acts as a blocking diode (it’s actually a circuit made with a handful of diodes), preventing the battery from putting power into and spinning your RC motor! The easiest way to add a 12v battery is with a car power bank or ‘jump starter’ along with a socket to socket adapter. Plugging in the battery will power the DC meter and provide a voltage reading on the battery. Anytime you are producing more volts that that reading, you’re putting amps into the battery and powering your devices. Be careful, however, to not spin so fast that the voltage goes over 15 volts as this could damage the battery.
Adding the battery will act as a buffer for powering devices that are “spiky”, in other words, that need a bunch of power to start or during various phases of operation, then settle into a more manageable power draw. I found trying to power a 55″ LED TV was difficult without having the battery as a buffer. It wasn’t that I couldn’t generate enough power, it seemed that my pedaling wasn’t “smooth” enough current. Adding the as battery as a buffer solved this problem.
What is the best use of your pedaling time on a pedal generator? There are 3 typical avenues you could direct your watts:
Direct charge: Directly use the watts coming out of your pedal generator, once converted to useful 12 volt current, and charge your devices using car chargers.
Grid Tie: Use a grid tie inverter to send all your pedaling effort into the nearest wall outlet.
Battery bank: Charge a bank of lead acid batteries.
There are advantages and disadvantages to each of these.
Efficient – 90%+ charging efficiency.
You will need to round up enough gadgets to create the appropriate resistance for a good workout.
Directly offsets your utility bill with watts generated.
Grid tie inverters are about 80% efficient in practice. Put in 100Wh from pedaling, only about 80Wh will be put back into the grid.
For those living off grid, augmenting their battery bank may be a necessity.
Lead acid battery charge efficiency is only about 85% – so if you put in 100Wh, you only get out 85Wh. Couple this with the efficiency losses of a charge controller and an inverter to get it back out as AC, and you might get 50% of what you put in.
I advocate for direct charging, and I’ll explain why. Going out on a limb here, but I’ll assume everyone uses a mobile device or two, and maybe a tablet. Assuming you charge these things regularly, let’s look at the scenario of charging these using the methods above.
Pedal generator -> Charge controller (90% efficient) -> Battery bank (85% efficient) -> DC to AC inverter (90% efficient) -> 110VAC wall charger -> Devices(s)
As I discovered in the previous blog post, wall chargers have losses up to 30%+, whereas 2 out of the 3 car chargers tested had losses of just over 1%. Using either grid tie or a battery bank may result in 50% or more of your efforts wasted on conversion losses. I do want to point out that the charge controller used in my pedal charger design is 90%+ efficient, so you will lose up to 10% in that conversion, resulting in a max of about 12% loss if you include the car charger losses – but far better than the other two alternatives!