Change of Bicycle and Completion of the Hardware

A project log for The 200W+ AA Battery Electric Bicycle

A 200W+ electric bicycle powered by a bank of regulated super capacitors that are charged by 10 AA batteries.

David ScholtenDavid Scholten 05/14/2017 at 04:230 Comments

There has been a change in bicycle due to mounting issues, which led me to use my old childhood bike from my parents house:

Working on the change over last night:

The motor has been successfully mounted/welded on. This was an extremely tedious process that I would care NOT to repeat.

Coupled through a separate chain, the motor can easily change its gear ratio by swapping out its cog connected to the chain. Practically though, this is not going to happen any time soon.

The throttle control is working great and there are no problems whatsoever.

The DC-DC converter is mounted directly under the seating. Water proof for the most part, it fits in snugly. However, I did confirm that it is NOT a true DC-DC converter. It has no inductive output filter and no output capacitor. It essentially applies a variable duty cycle (throttle control) square waveform voltage directly across the DC motor. Although this still supplies the correct "average" voltage to the motor (e.g. 50%), the back emf does not follow the square wave. The difference in voltage is dumped across the winding resistance when the motor is pulsed.

Effectively, this DC-DC converter acts as a linear regulator, but dumps the dissipated heat into the motor. This was confirmed through a harsh test ride with a battery (the DC-DC converter was cold and the motor was burning to the touch.

Next we can see the super capacitor in the fabulous basket:

Unfortunately, there is a harsh truth to the use of super capacitors in this project:

There just isn't enough energy storage.

Below is a video of just how fast the 24V stall current of the DC motor chews through the stored energy in the super capacitors.

I'll consider adding an inductor and flyback diode to the DC-DC converter of the bicycle to increase the efficiency, but it's not looking good.

Regardless, next up is a test drive with the super caps to the local store.