Thermal Performance Tests

[pasrom]

Introduction:

Our aim was to conduct a thermal investigation of the BMS to determine how hot it gets at a current of 100 A or more.

Test Setup:

The picture below illustrates the BMS setup during the testing phase (with heatsink). The tests were performed without actual battery, as described here.

Used Devices:

• Power source: E/A Power Supply PSB 10750-120
• Sink: Deutronic xxx
• Temperature measurements: "TIM QVGA/HD" thermal imaging camera
• Linux & Windows Computer

Boundary Conditions:

• Ambient Temperature: ~24°C

Test Scenarios:

Three different scenarios were tested:

1. Without Heatsink:

   • Current: 100 A
   • Measured Temperature: ~91°C after 35 minutes
   • BMS Position: horizontally on the table
   • The thermal camera image below displays the temperature distribution upon concluding the test, highlighting the MOSFETs as the area of highest temperature.
   

2. With Heatsink (1):

   • Current: 100 A
   • Measured Temperature: ~49°C after 25 minutes
   • BMS Position: 5 cm above the table (floating, cooling fins facing down to the table)
   • The thermal camera image below displays the temperature distribution upon concluding the test, with the PCB layer of the shunt being the hottest area.
   

3. With Heatsink (2):

   • Current: 122 A
   • Measured Temperature: ~66°C after 4 hours
   • BMS Position: identical to Measurement 2
   • The thermal camera image below displays the temperature distribution upon concluding the test, with the PCB layer of the shunt being the hottest area.
   
   • Below graph shows the current profile, temperature rise of the internal sensors and thermal camera temperature areas over time (area 2: small rectangle, area 3: big rectangle).
   

Conclusion

The BMS can comfortably manage over 100 A while maintaining a temperature within an acceptable range.
If feasible, the PCB layer should have a thickness greater than 70 µm to minimize the heating around the shunt.
Further work could involve identifying the maximum current that results in a temperature of around 80°C.

[pasrom]

@martinjaeger I performed an 80 A test without the heatsink using the latest hardware.

Test Setup:

Libre Solar BMS C1 v0.4.1 (03/2024)
bms firmware: commit hash ad92b6acd5a589f23704c59ea708b19479d0f4ea

Boundary Conditions:

Ambient Temperature: ~21°C

Test Scenario 80 A without heatsink

• Current: 80 A
  
  Left: 80 A power source. Right: 80 A sink.
• Measured Temperature: ~58°C after 60 minutes
• BMS Position: horizontally on the table
• The thermal camera image below displays the temperature distribution upon concluding the test, highlighting the MOSFETs as the area of highest temperature.

Below graph shows the current profile, temperature rise of the internal sensors and thermal camera temperature areas over time.

Test Scenario 100 A without heatsink

• Current: 100 A
  
  Left: 100 A power source. Right: 100 A sink.
• Measured Temperature: ~87°C after 60 minutes
• BMS Position: horizontally on the table
• The thermal camera image below displays the temperature distribution upon concluding the test, highlighting the MOSFETs as the area of highest temperature.

Below graph shows the current profile, temperature rise of the internal sensors and thermal camera temperature areas over time.

[martinjaeger]

Nice, thanks for posting the test results!

[pasrom]

I added the 100 A test without a heatsink to the post. I believe 80 A without a heatsink is acceptable at temperatures below 60 °C, but 100 A without one is not recommended because it reaches nearly 90 °C.

[martinjaeger]

I added the 100 A test without a heatsink to the post. I believe 80 A without a heatsink is acceptable at temperatures below 60 °C, but 100 A without one is not recommended because it reaches nearly 90 °C.

Thanks. Even more interesting, as it can be compared to the same test with previous hardware. It looks like the new 80V-rated MOSFETs didn't make a huge difference compared to the previous 100V-rated ones. Only 4 K colder, but the ambient temperature was also 3 K lower.