Noiz Waves

Eagle is powered by several lead acid batteries connected together. Lead acid batteries are the most basic type of battery you can use to power an electric bike, as they are cheap. The are cheap because they are relatively simple, stable, bulky, and have a relatively low energy density (compared to Lithium ion). Given the experimental & sandbox nature of Eagle, I chose to use lead acid batteries to save on cost. They should also provide enough range for me to get to and from work; any more range would really be wasted and bloat the overall cost. Read on for some more details specs on the batteries…

Eagle’s kit included three 12V 10AH sealed lead acid (SLA) batteries. These batteries are wired in series to produce a 36V 10AH power source, which is fed directly into the motor controller. The batteries are placed in a bag sitting at the rear of the bike. To improve the rigidity of the battery pack, I taped the batteries together using a material tape (tape containing material threads in it). This tap securely holds the batteries together and prevents the batteries from hitting into each other on a journey.

In total, the three batteries weigh in at 13.1 kg, meaning an individual battery weight of 4.37 kg. The battery pack by far contributes the most amount of weight in the electric bike conversion process. Due to the location of the battery pack above the rear wheel, the bike does feel a lot heavier to steer and turn. A friend of Dad’s was telling me that the ideal place to locate additional mass on a bike is below a line made between the handlebars and the bottom of the rear wheel. This means Eagle’s battery pack is the least ideal position.

Charging
The kit included a very basic 36V battery charger. It’s so cheap, it doesn’t turn off when the battery is fully charged. This meant a little investigation into lead acid battery specs was in order (to work out when the battery is completely charged). Eventually I stumbled across a very useful website called Battery University.

It describes an ideal voltage that SLA batteries should be charged to. This is somewhere between 2.3V and 2.45V. The higher you go, the greater your risk of overcharging the battery and starting electrolysis of the water inside the battery, which releases gasses. So I’ve decided to use an ideal voltage of 2.3V, which equates to 13.8V per battery, or 41.4V for the whole pack. This is measured across the further most battery terminals with the charger still connected and running.

Once the battery has reached 41.4V, the charger is then disconnected, and the battery left to rest. This is important, as the voltage will slowly decrease to its actual representative value. Battery University recommends 4 to 8 hours for complete resting. Now the state of charge can be estimated based on the battery voltage.