Cell sim

Cell Simulator

This cell-sim is designed to mimic a LiPo battery pack for develpoment of the surrounding electronics, like a BMS.

• 16 channels
• Open-Source hardware design, you can embed onto your own HIL setup
• ⚡️ 0-4.5V and 0-500mA per channel
• DMM muxed to each channel for arbitarily precise measurment
• Open-circuit simulation on each channel
• 📏 16bit ADC feedback for voltage and current
• 🔌 USB w/ Python software interface (+ 100MBit Ethernet + WiFi waiting for firmware support)

Design overview

Getting Started

1. Install python if you don't have it already
2. Install the requirements pip install -r requirements.txt
3. Connect the board via USB
4. Power the board with the 12V input (supply: 1A minimum, 3A recommended)
5. Run the example python script python example_set_voltages.py
6. Voltages should be set to 3.5V, then rainbow from 1V to 4V across the 16 channels and current should be close to 0A.

You should see something like this:

Notes

1. To get best low noise performance, use a quality power supply for the input supply.

Manufacturing

Board is intended to be manufactured with JLC, files are in the main directory of the repository. Note, the highlighted isolated regulator needs to be depopulated:

Firmware

Update Firmware

We use PlatformIO to build and upload the firmware via USB.

1. Install PlatformIO: https://platformio.org/install
2. Connect the board via USB (might need to accept connection popup on Mac)
3. Run pio run -t upload or install the PlatformIO VSCode extension and use the upload button.

API Docs

Connecting to cellsim

from lib.cellsim import CellSim
cellsim = CellSim(port)

Enable outputs

Each cell has a relay in series between the cell output and the connector, this can be used to simulate open-wire faults for example.

# Global enable/disable
cellsim.enableOutputAll()
time.sleep(1)
cellsim.disableOutputAll()
time.sleep(1)

# Enable/disable one at a time
# Turn relays on in a wave
for i in range(1, 17):
    cellsim.enableOutput(i)
    time.sleep(0.1)

time.sleep(1)

# Turn relays off in a wave
for i in range(1, 17):
    cellsim.disableOutput(i)
    time.sleep(0.1)

Setting voltages

Each output voltage can be specified between 0.5V and 4.4V

# Set all at once
cellsim.setAllVoltages(3.5)
time.sleep(1)

# Set one at a time
print("\nSetting rainbow voltage pattern...")
for i in range(16):
    voltage = 1.0 + (3.0 * i / 15)  # Spread 1V to 4V across 16 channels
    cellsim.setVoltage(i + 1, voltage)

Measuring voltages (onboard)

Each channel has an onboard 16bit ADC that measures the cell output. Note this is not a kelvin connection to your DUT, the measurement will only be accurate when minimal current is being drawn by the DUT.

voltages = cellsim.getAllVoltages()
print(f"Voltages: {[f'{v:.3f}' for v in voltages]}")

Measuring voltages externally

To take a precision measurement, each channel has a multiplexed output that connects to the DMM connector via a relay.

channel_to_measure = 3
# Enable DMM
cellsim.enableDMM(channel_to_measure)

# take measurment using external DMM
# that is connected to the DMM banana outputs
time.sleep(1)

cellsim.disableDMM()

Load switch

Each channel has a resistor + mosfet across its output, this can be used to speed up the discharge of the output capacitors. For example when transitioning from a high output voltage to a low output voltage, there will be an RC decay time before the voltage settles, typically in the ~100ms range. Turning on the load switch will make this much faster.

cellsim.enableLoadSwitchAll()
time.sleep(1)

cellsim.disableLoadSwitchAll()
time.sleep(1)

Disconnecting session

Once your test is finished, you can use the following to close the serial session:

  cellsim.close()