Hi,
I would be interested in building a balance simulator for a Bosch gen1 ebike (model year 2011-2013). The purpose of this would be to allow using a no-name 36V battery on a Bosch ebike. The problem is that the Bosch BMS inside the battery communicates with the motor through CAN. Therefore it is not immediately possible to use a non-Bosch battery on these closed systems.
However, it should be possible to use the BMS from an old Bosch battery and connect it to a no-name battery (having its own BMS) and just make the Bosch BMS think it is connected to a well balanced pack. The Bosch BMS would thus simply be used to allow the CAN communication with the motor but not to monitor cells in the battery pack. This would allow using larger battery packs than the stock 11Ah pack.
The idea is to connect to Bosch BMS to GND and +36V of the new battery and then use a voltage divider to simulate 10 well balanced groups of parallel cells with voltages increasing by 3.6V steps. The outputs of the voltage divider would be connected to the Bosch BMS through a FFC cable with 21 pins (as balance wires on the Bosch BMS use this type of connection).
I came up with the following circuit:
Some questions:
- Do you think that such circuit would work? I guess it should work as long as the balance wires on the Bosch BMS do not draw any current and only monitor voltage. Note that the Bosch BMS would NOT be used for charging and that it would never actually balance the cells of the pack. The pack must have its own BMS for that. I prefer not using the Bosch BMS to actually monitor the cells of the new pack because it needs to be modified (shunt modification) to allow getting more Ah from a battery (it is designed for 11Ah packs and will cut the power too soon if a larger pack is used because the Bosch BMS does not only monitor voltages, it also monitor how many Ah flow out of the battery to send a shut down signal to the motor apparently.
- How should I choose the value of the resistors in the voltage divider? Currently I chose 10 kOhm resistors but any serial connection of 10 resistors with the same value should work to get 3.6V increments. Should I just use the largest possible value in order to minimize current draw in the voltage divider?
thanks!
I would be interested in building a balance simulator for a Bosch gen1 ebike (model year 2011-2013). The purpose of this would be to allow using a no-name 36V battery on a Bosch ebike. The problem is that the Bosch BMS inside the battery communicates with the motor through CAN. Therefore it is not immediately possible to use a non-Bosch battery on these closed systems.
However, it should be possible to use the BMS from an old Bosch battery and connect it to a no-name battery (having its own BMS) and just make the Bosch BMS think it is connected to a well balanced pack. The Bosch BMS would thus simply be used to allow the CAN communication with the motor but not to monitor cells in the battery pack. This would allow using larger battery packs than the stock 11Ah pack.
The idea is to connect to Bosch BMS to GND and +36V of the new battery and then use a voltage divider to simulate 10 well balanced groups of parallel cells with voltages increasing by 3.6V steps. The outputs of the voltage divider would be connected to the Bosch BMS through a FFC cable with 21 pins (as balance wires on the Bosch BMS use this type of connection).
I came up with the following circuit:
Some questions:
- Do you think that such circuit would work? I guess it should work as long as the balance wires on the Bosch BMS do not draw any current and only monitor voltage. Note that the Bosch BMS would NOT be used for charging and that it would never actually balance the cells of the pack. The pack must have its own BMS for that. I prefer not using the Bosch BMS to actually monitor the cells of the new pack because it needs to be modified (shunt modification) to allow getting more Ah from a battery (it is designed for 11Ah packs and will cut the power too soon if a larger pack is used because the Bosch BMS does not only monitor voltages, it also monitor how many Ah flow out of the battery to send a shut down signal to the motor apparently.
- How should I choose the value of the resistors in the voltage divider? Currently I chose 10 kOhm resistors but any serial connection of 10 resistors with the same value should work to get 3.6V increments. Should I just use the largest possible value in order to minimize current draw in the voltage divider?
thanks!
