New Electric Bicycle. MKIII


Finally I found the time to write about my new electric bicycle!

This is my latest build and my best build so far.

As you can see from the photo, the bike has a small back wheel (20 inches), front suspensions, disk brakes and a central battery box that contains the battery (obviously), the controller and all the other connections (e-bike computer for example).

Here below I describe the process and all the modifications:

I started by buying a bicycle a few months back. I wanted something light and with front forks and disk brakes.


I bought the above bike for 250$, used and in excellent condition.

In the meantime I also got an used motor, a 9C9807. Originally the motor was laced in a 26-inches rim and had the hall sensors burnt.


I decided to use a sensorless controller, so I decided not to replace the hall sensors, but I replaced the original phase wires with 14AWG copper stranded wire as shown below.

Original wires (thin) vs new ones:




I decided to use a cheap sensorless controller, KU123 from BMSbattery. I upgraded the controller with 100V capacitors and IRFB4110 high quality mosfets to support battery voltages up to 100v. I also “beefed-up” the main power traces on the controller board to improve current flow on the traces.

Original controller:


High quality IRFB4110 mosfets:


Controller modified with new capacitors and mosfets. Please note that the capacitor legs do not touch and they are quite apart, it’s just a camera angle “optical illusion”.


Original board traces:


Traces “beefed-up”:


Then I got to work on the battery box. I wanted something better and larger than my previous bike, so I used a 11.5cm wide wooden board  and built it. Photos are pretty much self explanatory.






Side covers:


I attached the battery box to the frame using zip ties. It holds really well.

Lastly I decided to lace the motor into a 20 inches rim,spokes in a radial pattern, which turned out to be a pretty good choice. The bike has very good torque and can handle steep hills without overheating the motor.



I also added an e-bike computer based on arduino to complete the job, so I have real time data on battery usage, speed, range left and so on:



DIY “Home Made” Balancer for Li-ion / Li-Mn /Li-po Cells


Hi there,

Long time since the last post. I have been working on a lot of projects but I haven’t posted much on the blog.

Here is the project I am working on at the moment. It’s cell balancer for Li-ion / Li-Mn /Li-po cells. Basically it detects if a cell goes above a pre-set voltage during charging and “activates” the mosfet and power resistors in the circuit, draining/bleeding the charging current allowing the cell to stay at or below the pre-set voltage. Depending on the resistor (and mosfet) used it’s possible to set the maximum bleeding/draining current. In the video above the maximum draining currents turned out to be 1.3-1.5 A.

It’s very important for all the lithium chemistries that the single cell don’t go above a certain voltage to avoid damage. In case of Li-ion / Li-Mn /Li-po cells it is recommended not to go over 4.2v per cell. I set my balancer to activate at 4.15v per cell.

Some of you would say: “why don’t you just use a BMS?”. Well, BMS, especially for bicycles and motorbikes have limitations. In particular the charging and discharging current, and most importantly the balancing current, which is normally set to 0.3 A or less. Therefore using a standard BMS can take several hours or days to balance an unbalanced battery pack. The circuit above is designed to speed up the process when bulk charging.

I will have new pcb ready in a few weeks as the one I am currently using has a design error. The current boards are 5s.

Please comment if you have any question or contact me if you are interested in having one of the boards to test it on your setup.


E-Bike improvements


It’s finally warm here in Canada and I have started to use my e-bike to go to work. I introduced some improvements to keep things tidy and easy to use.

Starting with my e-bike computer I used an old printer cable (with many cores) to re-wire the connection between the LCD screen and the main board. I also added a toggle switch that powers off the unit while I am at work or when the bike is not in use, avoiding battery draining.



Everything looks so much tidier now!

I also re-wired the main board with 10AWG cables.



The bike now uses the Hybrid battery (see previous post), 54V nominal and about 9.5Ah (with 7.5Ah of usable capacity to preserve cycle life). I was able to shrink wrap the battery in black PVC tubing, making it safer and more professional looking.The battery is secured to the frame with “backpack” straps.



I am still working to improve the bike.

Next things to do:

  • Use the main battery to power up the e-bike computer (now is powered with an external battery)
  • Introduce a plug for recharging outside the wooden battery frame, weather insulated, and protected ( with a fuse).
  • Reduce the amount of wires.


I am also working on a “cell balancer”, I have done a few tests and I should be able to have a pcb ready for more testing next month..I will keep you posted!