RedTechNeck
Tech Assistance for Escaping Grid Slaves
- Joined
- Mar 6, 2022
- Messages
- 16
I've been noticing that BMS units currently manufactured and advertised seem to employ large banks of MOSFETS, and brag about being less than .02 ohm resistance. Did any of you know that the present state of the art in silicon MOSFET technology is less than .001 ohm "on resistance" in one transistor! I've seen some, depending on voltage rating at 600 micro-ohms or less. If you bank say 4 of these together you would get 150 micro-ohms. Amazingly the current limit for these modern mosfets individually is usually only limited by the current capacity (melting) of the lead frame and wire bond to the die. BMS units typically need 2 mosfet banks back to back to control charging and discharging.
Using more up to date components a 400 amp BMS is easily obtainable with only four mosfets per bank and only about 150 micro-ohms resistance. This would save a lot of power and extend battery discharge time. Better for cloudy days.
Conclusion is that old generation dirt cheap mosfets are being used in most "current" BMS units. But......... you can buy them real cheap too! I've been designing with mosfets for several decades and just couldn't help noticing this issue. Guess I'll have to eventually build my own BMS units after I buy some cheap ones to get me by for the a little while.
Also, it seems like these BMS units being sold now days might need additional heat sinks and cooling if you run them at max ratings for any length of time.
Paralleling existing BMS units on one battery stack to get more amps is not the best idea either as small imbalances will exist that will cause headackes and trouble.
Using more up to date components a 400 amp BMS is easily obtainable with only four mosfets per bank and only about 150 micro-ohms resistance. This would save a lot of power and extend battery discharge time. Better for cloudy days.
Conclusion is that old generation dirt cheap mosfets are being used in most "current" BMS units. But......... you can buy them real cheap too! I've been designing with mosfets for several decades and just couldn't help noticing this issue. Guess I'll have to eventually build my own BMS units after I buy some cheap ones to get me by for the a little while.
Also, it seems like these BMS units being sold now days might need additional heat sinks and cooling if you run them at max ratings for any length of time.
Paralleling existing BMS units on one battery stack to get more amps is not the best idea either as small imbalances will exist that will cause headackes and trouble.