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How to build a Cheap 350 watt ebike

Updated: Feb 24, 2023

Have you ever thought about making a cheap electric bike yourself?

How my journey began to build a cheap ebike while walking around my neighborhood. I discovered a lot of bikes that were put out for the trash and no one really wanted them. I said to myself what a shame because eventually they would be picked up by the scrapers that comb the streets looking for anything metal to fill up there pickup trucks. Unfortunately the bikes will be broken down striped of there aluminum and there steal frames cut up and scraped. I know this is recycling and they make a little money from taking these bikes to the scrap yards, but some of the bikes with a little TLC could be used again and maybe given to people that might need them.

I own a nice bicycle and don't need anymore but I don't have an ebike. After some pondering over this I came up with an idea, maybe I could build an ebike out of these unwanted bikes. A couple of weeks later I was walking home from the store and I saw a bike out at the trash, the tires were flat the seat pole was missing, it was covered in dirt, and the chain was gone, this continued for awhile. I found random adult bikes but mostly kids bikes out at the curb, some have signs on them saying free or please take, most of the bikes were missing parts. The missing parts didn't bother me so I wheeled them along with me and eventually took them north to the cottage where I do all my builds. I knew I could combine all the parts from all the free finds and put together some working bicycles first.

More blog ahead this is the build video below if you want more info.

Now the work begins to try and build a working ebike, I wanted to build something somewhat decent so I decided not to go with an old school approach of using a starter motor and toggle switches. I was willing to invest some money into the project but wanted the price to be reasonable. First thing I need a decent motor, I searched online and found a DC motor on Amazon it was a 24v 350 watt brushed DC motor, it was on sale for 35$, hurray. I figured it was a good start and to build around this motor, but a problem arose.

After doing some research online about what is a good wattage for an ebike, I discovered that a 350 watts wasn't enough power for an adult size bike and would only work as assist. With all that info in mind I ended up choosing a kids bike as my experiment, by having the smaller wheels the motor wouldn't need so much gearing to work with ease. I continued to do research on other parts the controller, throttle, freewheel bearing sprockets and the chain size I would need for this 24v DC motor, I've never worked with these H25 chains before, only bicycle chains.

Next the materials I would need is a 24v DC brushed controller to be able to smoothly control the speed of the motor, I found one on Amz for about $20 with the throttle, now I already had some free find SLA sealed lead acid 12v batteries so that saved some money for now. I would also need a freewheel bearing and a decent size H25 sprocket and H25 chain that matches the motor pinion, I ended up ordering all the parts off Amz and had them couple weeks later. With more knowledge on the mounting of the motor I found most people mount there drive sprocket onto the same side as the pedals, the only problem is you have to remove the cassette with your gears and add an adapter for your motor drive sprocket. You end up losing all of your rear gears on the hub and only have one speed on the hub, I didn't want to lose any gears that's why I ended up welding a freewheel sprocket onto the left side hub of the wheel.

Once I had my freewheel installed, I installed the sprocket with 4 nuts and bolts and the wheel was now ready. I started to design the mounting of the motor, I never use plans I just figure it out in my head as I go and for me building the project just seems to manifest itself most of the time so with some fiddling around with the chunks of metal and aligning them things start coming together. I just cut up some pieces of scrap angle iron and some peaces scrap 1/8'' steal plate, than I welded it all together.

I understand some people cant have access to welding, you could get someone to weld the freewheel onto your hub and you can mount the motor with u-bolts, metal, wood whatever laying around or you can find on the curb, it can be done. I did rush on this build and it could have turned out a lot better of quality, I do admit it, but I'm not a perfectionist its function over ascetics 👍

I think most unique part of this build is I turned this kids bike into a comfortable adult size, I used the frame and seat pole from an old adult frame and welded it over the kids bike seat pole, I think this modification is a must. After mounting the motor to my homemade brackets I now need to attach the chain and do some testing. The motor and chain worked perfectly, so I ended up attaching the controller wiring and batteries, In the video below theirs more info about the motor wiring and batteries. Please check it out if you want more info.

My conclusions of this build and the honest performance: The bikes top speed with my weight of about 150lbs is around 32kmh 20mph maybe a little more on flat ground. Now It's not super fast or powerful but I have done many trips of about 40mins straight battery life, with only pedaling on two step hills, I could easily ride this bike for hours and use the motor on hills when needed, that's what this lower power ebike is all about. Now it does need some help up very step hills and it's defiantly not for motor cross, but It works well, super quiet and a grate little run about that's light weight.

As of now I only have SLA batteries on the bike but I would love to upgrade to a 24v 10-20 Ah lithium battery pack that would extend the range and shed some weight from the bike. This is my first ebike but I have made four other ebikes so far and will be posting them here soon. I feel these cheap DIY ebike builds are useful information, defiantly in times of rising prices, that's why I think it's important to share info and inspire others. Please check out my YT channel for lots of other DIY

How-tos Homemade tech. Thanks for reading! hope you found this useful.

I'm new to Blogging but I'll try and post a new one every couple weeks.

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