Best DIY Bike Trainer Generator




About: Interested in green energy with a keen interest in human power.

>> Also see my Spin Bike Pedal Generator plans <<

Why would anyone want to build a pedal generator? There are many reasons.

  • To be prepared for the next hurricane that takes power out for days, weeks or longer
  • To supplement your off-grid system
  • To have one of the coolest interactive science fair projects
  • To be more environmentally friendly and create a smaller carbon footprint
  • To have a backup plan should terrorists or nation states take out our power grid
  • To be prepared in the event of a zombie apocalypse (ok, a bike generator probably won’t help in this case – but add a set of the key electronics in your Faraday box will help should we see a Starfish Prime type attack)
  • Or like me, a fair weather mountain biker, you want turn your efforts on an exercise trainer in the off season into tangible outcome (in addition to better health). For me, that outcome is a charged cell phone, tablets and other mobile devices, and a satisfaction that I contributed, if only in a small way, to preserving the earth we live on.

Whatever the reason, you’ve come to the right place for an easy to build, efficient bike trainer generator. In this post, I will provide step by step instructions and all the information you’ll need to source the parts for this project. I’ve always had an interest and fascination with alternate energy and human powered energy in particular. As a fair weather mountain biker, I find pedaling on a trainer or spin bike in the off season uninspiring, and often think “what if I could harness some of this energy”, or “I wonder if I could power the TV I’m watching” while I pedal. I wonder no more.

I’ve checked out many pedal generator products on the market as well as in the DIY world and found the commercial products for sale were too expensive, and the DIY projects were often really complicated and/or required you to take your bike apart to hook it to the generator. My first attempt at a pedal generator was expensive to build, although not extremely complicated. So I set out to design a low cost and easy to build bike generator that you just drop in your bike when you want to generate electricity, allowing you to easily take your bike for a ride when you are not.

I built this bike generator so I could charge my iPhone and other mobile devices while I get a workout. If I want an easy workout, I’ll just charge my phone and a battery pack or two. If I want a more challenging workout, I add more stuff to charge, or power a fan or TV!

Some things I’ve charged or powered with my bike generator, and the typical watts they require:

Some people have a need or desire to charge a 12 volt batteries, and this bike generator will do that if desired, but I would suggest that direct charging/powering is more efficient due to losses in charging lead acid batteries (15%), so putting 100 watts in gives you only 85 watts out. Read more about this in my blog post:

Step 1: Parts List

Optional parts:


Step 2: Remove Magnetic Resistance Parts From Trainer

First we need to remove the guts of the trainer's resistance unit. Unscrew the three Philips head screws holding the outer shroud and remove the shroud. Pry out the metal ring with magnets from the outer shroud.

Use Allen wrench to remove the Allen bolt holding the other magnetic resistance parts. Pull out inner metal housing. Take care not to get your fingers pinched when placing near the other magnet ring.

Turn the cable tension adjuster so the cable is loose, and with fingers or a pair of pliers work the cable end out and remove.

Step 3: Add the Shaft Coupler

The motor I am using has an 8mm shaft, and the trainer has a 10mm shaft. This shaft coupler connects the two shafts together quite nicely. I tried a grub screw style shaft coupler, but it created a bad vibration, this one worked great! If you use a different trainer or RC motor, be sure to measure what you have before ordering the shaft coupler - they make many different sizes and you should find one that will work.

Put on the coupler, tap with a mallet if needed to get it seated all the way in - being careful to not tap the shaft out (brace the flywheel side when tapping). Tighten the Allen screw on the trainer shaft side.

Step 4: Attach RC Motor to Outer Shroud

A bit about the RC motor selection process - math alert!

In selecting an RC motor, we need to determine which motor will give us between 9-15 volts at normal pedaling speeds:

  • A typical 26 inch mountain bike tire is 2068mm in circumference Ref:
  • The drive wheel diameter on the bike trainer is 30mm, circumference is 94.25mm.
  • For every rotation of the tire, the drive wheel will rotate 2068/94.25 = about 22 times
  • A comfortable riding pace is about 15 MPH. At 15 MPH, a mountain bike tire is spinning at around 194 RPM Ref:
  • At 15 MPH, the bike trainer drive wheel is rotating at 194 x 22 = 4268 RPM
  • RC motors are sold in xKV, meaning to get x RPM(K) it will need (or generate) (V) volts, so a 1000KV motor will generate 1 volt at 1000 RPM, 2 volts at 2000 RPM, etc
  • To get to around 12 charging volts at 15 MPH (4268 RPM / 12v), we need a motor with around 355KV rating. I wasn't able to find any RC motors at that exact rating, I went with a motor with slightly lower (320KV) RPM because I'm lazy and don’t want to pedal as hard to get to 12v.
  • Vary your RC motor selection based on your expected riding MPH and wheel size using the reference links above. If you’re a faster road rider, you may want to use a higher KV motor than I am, if you’re looking for a more casual pace or will be using this trainer with a 24 inch wheel bike for instance, then a lower KV motor might be a better choice.

Drill the center hole of the shroud a little bigger so the RC motor shaft won't rub. From here, there are options on how to attach the RC motor to the shroud, here are two ways:

1st way: Screw on the + bracket to the RC motor. Place over the shroud hole as close to center as possible. Align holes in bracket with solid part of shroud, mark holes, drill and bolt the + bracket to the shroud. You may also want to do some Dremel work to remove some of the plastic in the shroud in order to secure with a nut and washer, but I've found that it wasn't necessary, the only purpose of the bolts is to keep the motor frame from turning.

2nd way: Attach the motor without the + bracket, drilling and bolting directly through the housing. I found I needed to add a couple washers for spacing so the shaft lock washer and bearing didn't rub. This way is more challenging to measure where the holes go, using the 1st way you can just use the + bracket as a guide to center, mark and drill.

Once the motor is mounted to the shroud, we need to slide the motor shaft onto the shaft coupler, while lining up the 3 screw points. Once pressed on all the way - tighten the Allen/hex bolts onto the motor shaft. I found drilling a 1/2 inch hole in the bottom of the shroud made it easier to access the hex bolts. Put the 3 screws back into the shroud that were originally used to hold it in place.

Step 5: Turn AC Electricity Into DC

The 3 phase bridge rectifier sounds fancy but serves a simple purpose, it will convert Alternating Current (AC) coming from the 3 wires of the RC motor into Direct Current(DC) which is useful for charging. A small amount of voltage is lost in this conversion process (about 0.7 volts), and some heat is generated, but this unit has substantial cooling fins so heat should not be a problem at the amperages we will be working with. Okay, let’s make three (3) wire connectors between RC motor and 3 phase bridge rectifier - we'll need bullet connectors on one end and female spade connectors on the other. Solder 3 x 4mm bullet connectors (if you use a different motor, check motor bullet connector size with caliper before ordering) to 3 equal lengths of wire, then cover with heat shrink tubing to insulate from shorting with the other bullet connectors. I’m using 12 AWG wire, you could go as low as 18 AWG wire. Crimp and/or solder 3 female ⅜” spade connectors to the other ends of the wires. Finish with heat shrink tubing if desired. Connect the bullet connectors to the RC motor wires, connect the 3 other ends to the 3 Alternating Current (AC) male spade connections on the bridge rectifier. The AC posts are marked with a ‘~’. The order of the connections to between the bridge rectifier and the motor make no difference.

Alternate: If soldering is not something you are comfortable with, this project can be completed with a pair of wire crimps and suitable connectors. You would need to cut off the bullet connectors on the motor, strip wire ends and crimp on 3/8" connectors. Where I have used XT60 connectors, just use spade connectors or Anderson Powerpoles.

Step 6: Make a DC Connector Assembly

Add ⅜” spade connectors to a black(-) and red(+) XT60 wire assembly and connect to the 2 Direct Current (DC) male spade connections on the bridge rectifier, ensuring to put the red(+) on the + connector and black (-) on the - connector.

Step 7: Add a Meter

Adding a meter is optional, but strongly recommended to ensure you don’t go over on voltage, and to help measure how many watts you are actually producing! For our build we used an RC power analyzer connected using XT60 connectors. This meter will show Watts, Volts, Amps and scroll through Watt Hours (Wh), Amp Hours (Ah) and other measures. The XT60 connectors make solid circuit contact and prevent plugging things in the wrong way. Wire so the “source” is the bike generator, soldering each connection and sealing with heat shrink tubing.

Step 8: Add a Socket Adapter

Add a car socket adapter – in the parts list we link to a 3 port socket connector that should be suitable for 80% of users. The 18 AWG wires limit the total wattage to about 150 watts, which is fine for most people and has been plenty for me, but strong riders may want to build something with 12 AWG wire using separate sockets and a project box. To hook up the 3 port socket adapter, just solder on the XT60 connector to the matching wire colors, add some heat shrink tubing (put the tubing on before soldering, far up the wire so it doesn’t get hot) and plug in!

Step 9: Done!

Get charging! If you just plug in car charger adapters, most will start charging at around 9v input, and the good quality chargers (like the Anker models referenced in optional parts) will handle up to 24v input without a problem. If you only charge with these type chargers, you can pretty much pedal to your heart’s content if you followed the design as I've outlined, and not worry about limiting voltage. Need an easy ride, just plug in a cell phone or two. To add more resistance, add more car adapters and devices. I’ve tested this generating up to almost 400 watts. It can go higher, but that’s nearing the limit of the 50 year old pushing the pedals (me!). The motor itself is capable of up to 1820 watts. Can you push 300 watts? Anybody up for 1000 watts? Want a challenge? Brew some coffee!

If you want to power something that plugs into a wall outlet using an inverter, or have a desire to charge a 12v battery, then you’ll need to be mindful of the voltage you are generating, and keep it to under 14.7 volts or so.

Let me know if you build this, I'd love to hear your feedback!

Step 10: Detailed Build Video

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15 Discussions


Question 2 months ago on Step 10

Hello Gene.
I like your project. I want to make one but I would prefer a regulated output for the safety of what I am plugging into it. I am thinking about spinning a custom PCB with connectors, bridge, 12v and 5v buck regulators all included that will all fit inside the housing. If I made this board would you like to include it in your design? I will probably make it for myself either way but figured if you or others might like it too I would give you the option. I could sell the bare PCB’s through Amazon for your audience. But if I sold the fully functional design with parts on it I would have to FCC certify which is sort of expensive. Tell me what you think?

I am also thinking it would be good to swap out that motor for one with a lower k rating to ensure over a wider range of wheel speed that the voltage stays up above 12. Not required but probably a mod I will make.

thanks for your consideration.

1 answer

Answer 2 months ago

Hi uWave - what you are proposing makes a lot of sense. When I initially set out on this journey of building pedal generators, my intent was to make a product or products I could sell. Those dreams were squashed by the accounting department (wife) and the scheduling department (also wife) so with limited time and funds I decided to just give away my designs - and here we are. I make a few dollars a month by people following my links to Amazon, so I guess that's something for my time. In my first design, I did add a charge controller which works perfectly for powering anything 12v (up to the limit of you and/or the charge controller). Creating a purpose build PCB with a controller that gives both 12v and USB 5v output, along with a meter in a nice box that can be mounted on handlebars was actually part of my "grand plan" design. Meter should show amps, watts, volts, total watt hours and total time (along with a reset button). Also adding in bluetooth LE output for watts generated for the Zwift users out there was another feature that I'd include. You'd probably sell the heck out of that. Happy to collaborate with you on the design if you'd like my guidance.


Question 2 months ago

Hey great work man
I have the same motor and rectifier connect bicycle 26 inch wheel, my voltage is 12-20v
I have no problem to get 100-150 watt, butt when I try 200 watt and upwards with my inverter, my voltage drops to 9v when current kicks in then my inverter kicks to safe mode.I don't understand how you get above 150 watt in your video.When I tried with super capacitor between I reached 300-400 with out issue.
my question is what do I do wrong here any solution

2 answers

Answer 2 months ago

So thrilled to hear you built it - please share a picture of your build! The challenge when you get up in watts drawn is we humans aren't creating steady power - it's very difficult to keep the pedals cranking at exactly the same speed/power. You've also hit on the solution by adding the super capacitor. The other option is to drop in a 12v lead acid battery to the circuit, which is the approach I have personally taken. Adding the battery works as a buffer of our varying input (likewise with the ultra-capacitor), smoothing out the voltage input to the inverter.


Reply 2 months ago

Hey thanks for answer:)I had a build with e-bike 350 motor before I saw your build, but that motor was outside bike spinner, that was not practical like your solution,Then I buyed a out runner 270kv motor and copyed your motor setup, that small motor was pumping same amount of current even better, problem with the hub motor was to high voltage and take more space.Now I don't think about fry electronics:)Because 12-24v its standard on most electronic.Yeah I will go for 12v battery thank you,i will share a picture when cable work is finish


3 months ago

You could get or make a Permanent Magnet Alternator from sure it's expensive...but at the 2000 rpm you are's generating 20v at about 120A...
Then I believe only a single phase rectifier would be long as the voltage is above the 14.8vdc of lead will absorb the current and keep the output voltage at a regulated voltage...even with the less than perfect charge will produce MUCH more power that than hobby motor.

1 reply

Reply 3 months ago

As cool as it might, be - I’m never going to be able to produce 2400 watts with these legs (show me a human that can). By the way, the motor I use has more capability than I’ll ever push - it’s max rating is 1820 watts, so the limiting factor on watts produced will be the person spinning the cranks on the bike. I’ve personally generated almost 400 watts with this setup (and I’m an old, out of shape, fair weather mountain biker), I’m sure others can do much better.


Question 5 months ago on Step 10

Awesome guide! Question, why did you go with an AC motor and convert to DC? Why not use a DC motor instead?

1 answer

Answer 5 months ago

Good question! There are a couple reasons:
1. DC motors typically use brushes, which are both noisy, and can wear out
2. AC RC motors come is a wide range of Kv ratings, so I was easily able to find one that matched the RPM of the trainer drive shaft to get us to the ideal 10-15 charging volts.


10 months ago

This is very cool. one question, how difficult would it be to put in some sort of warning system (either a blinking LED or a beeping device of some sort ... or both) for when you are approaching the upper end of your safe output, so you don't pedal too fast and melt your devices? this way you don't have to monitor the read out while watching the TV run on pedal power :)

1 reply

Reply 10 months ago

Very good point, Lorddrake! One of the very reasons I like this Drok meter as you can set it up to blink the screen when you reach an upper limit on voltage. I used this meter for the box you see in the video mounted on the bike. Another nice feature of this meter is it 'remembers' the total watt hours generated even if you stop pedaling.


1 year ago

I'm still in the mist of what motor I need to use considering that I'm able to flow 300W at once into a lipo battery using the above stated battery balancer. My problem is the two intervals we'll be facing: pedalling speed and voltage input (cr. Attachment).

Following your definition of Kv, it makes sense to spend my own human energy as economical as possible. A motor with the lowest Kv value (63Kv), serves this goal: I can pedal at a slow pace while generating the highest voltage output (28v). However, I know I can pedal much faster and release more human energy. As I don't want anything to blow up, I should limit the generated power with a motor with a higher Kv. In this case, I would choose the 220Kv motor. This is because I am at hitting 28v as the preferable output instead of a lower 10v.

While writing this process, one question comes to my mind: what voltage output SHOULD I be aiming at? You did not mention anything about current and amps. I reckon if we know this, we could determine what motor is the most appropriate choice for use in combination with the 300W battery balancer?

1 reply

Reply 1 year ago

I see your quandary - let me try to clarify. To your last statement - the current (amps) will be defined by the load, so when I’m charging my 5500mAh 11.1v Lipo battery, the proper settings to charge it are 5.5 Amps and the volts are managed by the balance charger, starting out at whatever the battery is at, usually around 11.2v. Watts = volts * amps, so we get 61.6 watts of resistance while pedaling. Not exactly - the charger isn’t 100% efficient, so that load is more like 70 watts. The wattage will actually increase as the battery charges until the battery gets to 12.6v, at which time it will taper off as each cell reaches a fully charged state (which makes for a good cool down). To your question about which motor to choose, what you really need to determine is what RPM range you will be in, from low to high. If you’re using a bike with multiple gears, you can always adjust the RPM by shifting up or down. The load will remain relatively constant, and as long as you are in the voltage range of the charger (10v-28v), the charger will be happy. I think your calculations to go with a 63kv motor are off a bit as this would put your voltage at about 68 volts @ 15MPH (using a mountain bike tire as I have in my calculations). Don’t overthink the motor, I’d go with a 320kv for a mountain bike tire and a 350kv for a road bike tire.


1 year ago

Great first instructable! I'd love to set something up like this for my computer desk.

1 reply

Reply 1 year ago

Thank you! You could easily make this work as a pedal desk, using a DC to AC inverter to power the computer. For better efficiency, get a 12v DC charger for your laptop. Another great trend is USB-C charging on newer laptops - you can directly charge with a USB-C car adapter, like this one: