|My Boosted Board shortly after purchase.|
|My Boosted Board after the battery upgrade :]|
|These LEDs are bright!|
Batteries, Batteries, Batteries
The Boosted Board uses Lithium Iron Phosphate (LiFePO4) batteries. In a nutshell, this battery chemistry trades capacity for higher power and longer shelf life. Boosted has a blog detailing the design process behind the selection of battery chemistry and size. The battery inside the board is a 99Wh, 12 cell LiFePO4 pack.
You may have been shocked to read that I selected Lithium-Ion cells to extend the range. I built two 92.5Wh 10 cell Li-Ion battery packs. This should immediately register as cause for concern. Li-Fe cells have a nominal voltage of 3.2V and Li-Ion cells have a nominal voltage of 3.7V. There are 12 LiFe cells in the board which gives a nominal voltage of 38.4V. My 10 cell pack has a nominal voltage of 37V. This is very close.
|Verifying the internal voltage|
To ensure that this could be done safely, I measured the voltage of a fully charged Boosted Board to be 40.7V. My external pack, when fully charged is also 40.7V. What this means is that I can connect the batteries in parallel. The load of the motors will be distributed across the battery packs.
In addition to adding more capacity to the board, the efficiency of the internal battery will be increased. A battery that is discharged slowly is more efficient than a battery that is discharged quickly. Win win!
|Two cells and a balance cable extension|
The pack was assembled with all cells next to one another to keep the profile low. I researched different options for my batteries and found that many were too tall. There are several 10S packs available from RC hobby shops such as Hobby King but they are too tall. Clearance under the board is at a premium so it is important that any additional components are as short as possible.
|Tabbed cells with the balance lead attached|
These cells need to have a minimal layer of protection. I used 185mm shrink tube to protect the cells and provide rigidity to the pack. I added electrical tape to the ends of the cells as well. This made it difficult to slide the shrink tube on, so only one of the packs have this feature. It would be great if these batteries had a housing, they will take a beating so close to the ground. This will have to do for now.
I settled on HXT connectors to connect the batteries to the board. They are rugged connectors with high current handling. In retrospect, I wish I had gone with something that is easier to terminate and provides better keying. Overall, they have been durable and able to withstand over 20 miles of riding so far.
|Finished pack :]|
|First Charge Test at 100mA, making sure the magic smoke stays inside the batteries ;]|
|Charging at 2.5A|
I had to modify the Boosted Board to externalize the supply rails from the internal battery pack. I picked up a multimeter and started probing around inside the Boosted Board. The ESC (Electronic Speed Controller) designed for the Boosted Board is impressive to say the least. It supports regenerative braking which allows energy used to brake the motors to be stored in the batteries.
|The Boosted Board ESC|
|Exposed supply rail from the internal battery|
|12AWG external battery cable|
I routed these wires through the loom at the back of the board and out the side. I should note that the use of an external battery is completely optional after this modification.
|External Battery Cabling|
|Velcro mounting on the battery and board|
The batteries are mounted next to one another. I am currently using electrical tape to hold excess wire and balance connectors to the bottom of the board. I will come up with a more permanent solution soon, but this works for now.
|Mounted battery packs|
You may have noticed the LED lights that appeared in the pictures above. This system is designed by Third Kind. I was not impressed with many aspects of their design, namely the fact that the LED strip must be disconnected from the battery in order to recharge. I designed a lighting system based on WS2812 LEDs and an Arduino.
The lighting system runs from an internal LiPo battery that was salvaged from the Third Kind system. It was a 3S pack that I reduced to 2S. Two LM7805 linear regulators provide 5V for the LEDs and Arduino. The LEDs are split across two 5V rails to avoid exceeding the current of one of the regulators when running at max brightness.
In order to ensure that the battery does not reach an overly discharged state, the ADC is used to measure the battery voltage through a resistive divider. When it reaches a pre-determined cutoff voltage, the LEDs will switch to a low duty-cycle flashing mode to indicate that the main power should be switched off and the lights recharged. Currently charging is performed using the same 1010B+ charger used for the external battery packs.
|Lighting system with the box open|
The construction is very simple with point-to-point used for all components. The Arduino is wrapped in shrink tube with the programming headers exposed. I decided to stick with the Arduino bootloader for the simplicity of updates. I am not a fan of the boot delay and may consider loading code using my AVR-ISP directly.
The mode button allows switching between various animations. So far I have only wrote one, but have plans for a few more. I may also consider adding an IMU (Inertial Measurement Unit) to detect motion of the board. For example, when slowing down the LEDs could automatically fade to red and glow with a brightness that is a function of deceleration (after some signal processing and filtering, of course).
The lighting system looks great and is extremely bright. I was able to come up with a color of orange that matches the Boosted Board reasonably well. I call it "Boosted Orange" which in the color gamut of the WS2812 LEDs is encoded as #ff1900. I used the light_ws2812 driver from cpldcpu on GitHub. It works very well for the purpose and makes no assumptions about usage of the Arduino framework (which I don't use).
|Front-facing and downward facing LEDs|
|Now this is a loaded deck ;]|
|Lighting system cover and screws|
The LED lighting system is currently charged by removing the door. I expect approximately 2 hours of runtime which means a recharge will be necessary after every couple of night rides. I should probably add a durable external connector to make recharging easier.
|FTDI Programming Interface|
Using any of the information contained in this article to modify your Boosted Board will void the warranty. You risk damaging the board and injuring yourself. This article is provided for informational purposes only. If you decide to perform the same modification you accept any liability associated with doing so.
Proceed with caution and always wear a helmet.
I hope you enjoyed reading this article as much as I enjoyed working on this project.
Your comments are always welcome. Thanks for reading!