13 January, 2017

Improving the Ebike with Arduino to monitorize battery and add anti-theft alarm 2/2

As discussed in the previous post, my goals to put a microcontroller programmed with Arduino on electric bike they were:
  • With an RGB LED display the charge / status of the battery monitoring one of the (weaker if possible) cells, to avoid surprises of not having enough charge for the trip the next day, showing orange when needed recharging (between 20 and 40%).
  • With an accelerometer and a powerful piezoelectric speaker  (and a mosfet to activate) we can add an anti-theft alarm, easy disabled with a button hidden from view, which is very handy against foreign's friends.
  • And even (this slope time), add light automatic brake  using the accelerometer (which changes from low intensity to high intensity when the accelerometer receives a deceleration in the axis of the fly), to keep usage statistics (number of refills, airtime, or adding small OLED display to show instant consumption in Ah with  a Hall sensor  (such as Allegro ACS75x, etc), battery charging, etc.
So this Christmas I could get down to work, and start to test in a breadboard to get something functional:

12 January, 2017

Extending the range and power of the bike by adding two cells in the luggage carrier

Before this project, the battery of my bike consisted of 8 cells in series of 6 batteries LiFePo4 A123 in parallel each, and I realized that I could have some more top speed and range by adding two cells with the previously left over LiFePO4 A123 batteries, and changing the BMS for the one I found of 10S and 60A (much better than the previous 15Ah only):

BMS / Control LiFePo4 charging battery cells 10 and 60A  maximum.
I will not cease repeating that if ye ride yourselves a Lithium Ion battery, you must put always a BMS, as this is essential prottection for the battery, cutting the flow of current in both overload and over - discharge in any of the cells.
One important note: This only works if you use the SAME type and state of cells for the additional cells (or you will get an unballanced battery fast, or worse, damaged cells that can't cope with the current).

On the other hand, increasing only 6V maximum load, I can still use the configuration of the motor control for 24V (having automatic cut if they drop too low voltage with the BAC-281P ebike controller, we cut prematurely the current if we use 33V battery with a 36V configuration). 

Features of BMS 10S LifePo4 60A load balancing ref. BMS-10SQZ6060LF375 :

Important data:
  • 10 Cells LiFe 3.6V, 36V full.
  • Maximum peak current: 90A
  • Constant current approx. without sink: 30A
  • Standby power consumption: 0.1 mAh (100 microamperes / hour).
  • For the rolling is effective with only 70mAh per cell balancing, the load should be as slow as possible (depending on the difference of load cells), recommended < 500 mAh.
As  I noted, the 12 could fit on a damaged old hard drive enclosure aluminum made.