RCinFLA
Solar Wizard
- Joined
- Jun 21, 2020
- Messages
- 3,564
I did a thermodynamic simulation some time back on the 16S/24S JK active balancer BMS. I was not confident in my thermal resistance calculations on the irregular MOSFET epoxy plastic topside surfaces. Then I saw Andy's (Off-Grid Garage) video where he smoked the new 4S/8S JK BMS, drawing about 210 amps to charge his Tesla so I decided to update the original 16S BMS simulation to the new but similar 4S/8S BMS.
Using Andy's data point where he smoked the BMS with 210 amps I checked my simulation, and it was pretty close to showing the same 'smoke' point.
As with most of the Chinese BMS's, the main issue is poor heat transfer from MOSFET's due to using the epoxy plastic case side of MOSFET's to dissipate heat. It creates a big temp difference between MOSFET temp and heat sink temp due to the thermal resistance going through MOSFET epoxy plastic case. Even if you replace the flat aluminum case plates with heat sink fins cover plates it will not help much on reducing maximum MOSFET temperature.
These simulations (both models) are for continuous load current with 25 deg C ambient air temp. Short period peak load current temp rise is a lot tougher to simulate.
Using Andy's data point where he smoked the BMS with 210 amps I checked my simulation, and it was pretty close to showing the same 'smoke' point.
As with most of the Chinese BMS's, the main issue is poor heat transfer from MOSFET's due to using the epoxy plastic case side of MOSFET's to dissipate heat. It creates a big temp difference between MOSFET temp and heat sink temp due to the thermal resistance going through MOSFET epoxy plastic case. Even if you replace the flat aluminum case plates with heat sink fins cover plates it will not help much on reducing maximum MOSFET temperature.
These simulations (both models) are for continuous load current with 25 deg C ambient air temp. Short period peak load current temp rise is a lot tougher to simulate.