Bike left

Bike right

After I moved to Venice FL I discovered it is an infinitely more bicycle friendly place than my previous VA location.  I also live very near the start of a 20 mile bike path that occupies the old train track path that brought the circus here to winter.  I ride almost daily for exercise and have seen almost every bicycle type available.  The electric bikes caught my eye and planted the seed.  A Sarasota retailer was very negative about do-it-yourself E-bikes, so that also inspired me to prove him wrong.  Granted, this is not a project for you if you have little mechanical and electrical aptitude.

 There are tons of electric bicycle sites you can research.  I think I read in Forbes that E-bikes are a $10 billion business in China, $2 billion in Europe, and only $1/2 billion in the US.  No doubt due to the American car culture and lack of safe riding roads.

Real E-bikes can be bought for $1800 to $3000 which is more than I can spend so I decided to build my own. This is what I put together.  My objective was a reasonably reliable, quality, and comfortable bike, for as little as money possible.  I think I got just what I wanted for about $800.

 Let’s get the frequent questions out of the way. 

 How fast will it go? – Faster than I need.  I’m not a daredevil and I think 15 MPH is plenty.  I have had it up to 20 MPH and it seems to have a lot left.  Bicycles like this are not designed to go very fast and I believe they can become unstable at very high speeds.

 How far will it go? – This depends on many factors like weight of rider, hills, wind, speed, and how heavy you are on the throttle.  My first couple of rides have taken it to 28 miles on a charge and I believe there is probably at least 10 miles remaining.  I am cautious to not unload the battery hard and deep until I install a watthour meter so I know exactly what’s going on.  More detail later.


The Frame

 The criteria for the frame included pedal forward design, 7 speed, hand brakes with rigid mounting (not the kind that mount with a single center bolt), reasonable quality, 26”, and possibility of mounting a good rack for the battery.

 I wanted a cruiser style frame for comfort.  Something with a pedal forward design like the Electra Townie.  These are hard to find at a good price, so after looking for a few months, I just bought a Walmart $99 bike to start with.  After I pedaled it 2 miles, I loaded it up and returned it.  It wasn’t very comfortable and just lower quality than I wanted to start with.

 An ad for an electric bike on Craig’s list caught my eye, just because of the shape of the frame and the price.  The seller (kid) could not tell me the make.  It had a bizarre motor hung below the bottom bracket with a freewheeling sprocket that the chain was routed through.  The crank shaft had been extended out on the sprocket side by over an inch.  There was no battery.  The rear wheel was badly bent beyond repair, the gear shifter was broken, and it was pretty ugly.  A wreck. So – I bought it for $75 because I liked the shape of the frame.

 It turns out the bike is a 7 year old Sun Drifter, designed in Miami, and retails for about $450.  It has an aluminum frame that is good and stiff, with steel front fork.  After I cleaned it up, put a new cartridge bearing in the bottom bracket, replaced the cranks, derailleur, chain, and installed the rear wheel & brake leavers that came with the motor kit, it turned out to be just what I wanted.  I learned a lot about bicycles I never knew. 



 The Motor

 I decided to use a direct drive rear hub motor.  My neighbor (more on him later) recommended a 48 volt system.  I wanted some sort of digital display and a system with throttle pedal assist.

 I settled on this 750 Watt system found on eBay for right at $200.  It was as described and everything fit together nicely, except the pouch meant for the controller was too small.  I wanted a more waterproof controller box that would also have room for all the wire connections so I didn’t really care about the pouch.

 The tube and tire are not mounted when it arrives.  I installed them both without thinking and experienced my first flat at about 35 miles. This is a nice double wall rim so the spoke nuts are not touching the inner tube and there was no rubber protector band like you normally see on a wheel.  However there are holes in the outer wall for access to the spoke nuts. These holes had slight burrs and one made a small hole in the very thin tube that came with the kit.  I de-burred the holes and used the punctured tube to make a protective band.  Then I installed a new heavy duty inner tube and included a few ounces of Slime.  If you are 10 miles from home, a flat is no fun. Luckily I was only 2 blocks away. From now on I will carry a small pump on the bike.


The controller is actually rated for a 1000 Watt motor and has 12 MOSFET’s for power switching which I was happy to see.

 After getting everything running, working with the Chinglish instructions and additional instructions found on the web for the LCD panel, I still can’t get the pedal assist mode tuned in. It adds way too much assist when it starts up so I will likely disable that mode.  Others have complained about the same problem on forums.  It has an interesting “walk” mode that is like cruise control at 6 mph.  That is too fast for walking but works nice for riding really slow.  However, you can only start that mode from a dead stop. It also has a Watt meter so you can see the load.  Not sure how accurate it is since it appears to jump in increments of what would be 1 amp current draw. Like 52 – 104 – 156.  I also can’t get the speed limiting function to work.

 Despite the above issues, it seems to work great as a throttle controlled motor.  I like the odometer and trip meter.  It has plenty of power with my 14S battery.


The Battery

Now for the most expensive part of the bike.  The battery. 

 No question my battery was going to be a Lithium battery.  A neighbor is an E-bike enthusiast (like 9500 mile E-bike ride around the country enthusiasm level) and designed a modular system for assembling 18650 batteries. He has applied for a patent on his design.  He manufactures the plastic components with a 3D printer.  I like the idea that the battery pack can be assembled using hand tools and there is no need for welding battery straps to the ends of the cells. This makes the pack repairable in the event a single cell goes bad.  The assembled battery fits into a piece of 4” PVC fence post cover and makes a nice assembly. You can read about and buy his system here:  http://www.batteryblocs.com/

 The 18650 cells are the same ones used in a Tesla battery.  They use over 7000 of them in one car!  There are so many low quality 18650 cells being sold, I was skeptical about buying a completed battery pack and not knowing what it was made with.  A strong reason to build your own.  Once I bought some NiMH batteries on eBay.  Upon receiving them I picked one up and just laughed. It weighed about ¼ what it should have weighed.  I charged it on a hobby charger and it could only take about 20% of the stated capacity. When I complained to the seller, they refunded my money immediately.  No doubt they knew all about the reality of their batteries.

 At my neighbors recommendation I opted for a 14S/5P configuration.  That’s groups of 5 cells in parallel connected in a series of 14 groups. That’s 70 cells for 17 Amp Hours at 52.2V nominal, or 887 Watt Hours.

 This is probably the most difficult pack of his design to assemble because each block of 10 cells is split by a diagonally cut top strap.  You have to pay very close attention when arranging the components or you will short a cell.  It only takes a few seconds for a shorted cell to become too hot to handle, and is dangerous.  Also the red and black of the plastic pieces means nothing, since the bottom (red here) pieces serve to connect the positive to negative of two groups.


Battery Bolc components arranged in the assembly pattern.  Notice the 2 center cells are opposite ends up.

Blocs arranged

Extreme caution must be taken when working on a battery pack like this.  The cells deliver very high amperage.  There is a lot of exposed conductor and if you drop a nut or washer across a junction with potential it will instantly weld to the conductors causing a short.  Also it is very important to insulate the ends of cut wires to avoid those touching conductors.  They will also weld and short.  I speak from experience.

 My battery includes a BMS (battery management system) that is supposed to balance charge the cells so they all have the same voltage, protect the cells from over and under voltage, and shut off power if any cell goes below its minimum voltage, or if the pack goes over or under voltage.  I have heard a lot of bad stories about these cheap Chinese BMS’s but there seems to be no very affordable option.  Commercial battery packs use this same type BMS. 

This is a photo of a BMS with the cover removed.  You can see the high density.  The resistors that bleed off charge to level the pack are so small.


Don’t be fooled.  It is a lot of work to assemble a battery pack.

 I left about 3” of space in my battery pack because I plan to install some voltage monitors that will display the individual cell voltages, visible through a window on the side of the box.  That way I will know if the BMS is balancing the charge.  I also installed an extra set of leads to the cells for the cell monitors.  I think BMS’s will only get better and ultimately I predict one that will transmit the cell voltages over Bluetooth to my cell phone.  (Actually I have seen one that is not quite ready for the market yet).

 I also plan to install a separate Watthour meter on the bike so I can tell how much energy has been used from the battery pack.  This is the best way to know the fuel level.

 My end caps are machined out of PVC plate.  I use a keyed automotive battery cut off switch for isolation and security.  My charger connects through a panel mount XLR connector since that is what my charger came with. 

Assembled battery getting its first charge outside on the patio – being cautious

Naked Bat

The cased up battery ready for the bike.

Boxed Bat

I got the charger from my neighbor (Available on his web site).  It is one he has made with a dual voltage selector.  The idea being that if you do not fully charge the battery it will last much longer.  I plan to always use the reduced charge method and not cycle the battery too deep, to make it last longer.

 The rack is another story. When I was looking for a rack on eBay, I found the one you see and noticed it was from a seller also located in Venice, FL.  I contacted him to see if I could save $20 shipping on a $20 item by picking it up. It turns out he lives in my neighborhood and runs an electric bike factory/business.  He designed the rack to fit 4 different E-bike battery types; mine included.  Mine was $20 because it was used.  He has a lot of E-bike knowledge, having lived in China and visited a lot of the manufacturers.  When he returned to the States, he had his own very efficient motor, which he uses on his bikes, designed and manufactured in the US.  Unfortunately his motor kits are 4 times the cost of the one I used. No doubt they are better quality and more efficient.  Efficiency can be a big factor when the battery is so expensive.  You want the energy turning the wheel, not generating heat. His bikes are here:


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