Hello,
I know the pros and cons of BMS are hotly debated. Please do not do that here.
I am starting this thread in hopes of avoiding WHETHER there should be a BMS and instead wish to discuss WHAT TYPE of BMS would work best, what are necessary features, and what are optional features. (I am assuming Lifepo4 as the current standard).
First, a little background to give a common starting point:
If EV's are to be mainstream, they need ABSOLUTE reliability. I am talking 10-20 years and 200,000-300,000 miles as is common with internal combustion engines.
My grandmother is NOT going to check cell voltages and "bring up" low cells. This is a ridiculous concept. Rickard (EVTV.ME) has proven the need for some type of BMS. After a mere 3,400 miles his pack already varied by ~.6 volts. Way too much to meet the long-term reliability function described above. This is worse than points ignition and carburetors. Unacceptable.
Here are the 3 things I think are absolutely necessary in a BMS:
1. High voltage cutoff (HVC). Right now, shunts seems to be the most popular and effective way to do this. They pass the charging current past a "full" cell to those still in need of charging.
2. Low voltage cutoff (LVC). Could be an alarm or total system shutdown.
3. Capacity balancing. (bleeding energy from the strong cells to the weak). A pack is limited by it's weakest cell. Capacity balancing seems like the only way to utilize the extra energy from the stronger cells and not be limited by the weakest cell. This could be a resistor system or a capacitor system not unlike the failed evassemble junk. This seems especially important as packs age and the capacity difference becomes greater.
I am building an EV using the EVpower bms. It only has #1 and #2. Is there a simple/inexpensive/compatible way to achieve #3? It seems like the key to getting maximum range AND max life from the pack. Any input/experiences on the evpower bms appreciated.
Cheers!
I know the pros and cons of BMS are hotly debated. Please do not do that here.
I am starting this thread in hopes of avoiding WHETHER there should be a BMS and instead wish to discuss WHAT TYPE of BMS would work best, what are necessary features, and what are optional features. (I am assuming Lifepo4 as the current standard).
First, a little background to give a common starting point:
If EV's are to be mainstream, they need ABSOLUTE reliability. I am talking 10-20 years and 200,000-300,000 miles as is common with internal combustion engines.
My grandmother is NOT going to check cell voltages and "bring up" low cells. This is a ridiculous concept. Rickard (EVTV.ME) has proven the need for some type of BMS. After a mere 3,400 miles his pack already varied by ~.6 volts. Way too much to meet the long-term reliability function described above. This is worse than points ignition and carburetors. Unacceptable.
Here are the 3 things I think are absolutely necessary in a BMS:
1. High voltage cutoff (HVC). Right now, shunts seems to be the most popular and effective way to do this. They pass the charging current past a "full" cell to those still in need of charging.
2. Low voltage cutoff (LVC). Could be an alarm or total system shutdown.
3. Capacity balancing. (bleeding energy from the strong cells to the weak). A pack is limited by it's weakest cell. Capacity balancing seems like the only way to utilize the extra energy from the stronger cells and not be limited by the weakest cell. This could be a resistor system or a capacitor system not unlike the failed evassemble junk. This seems especially important as packs age and the capacity difference becomes greater.
I am building an EV using the EVpower bms. It only has #1 and #2. Is there a simple/inexpensive/compatible way to achieve #3? It seems like the key to getting maximum range AND max life from the pack. Any input/experiences on the evpower bms appreciated.
Cheers!