robby
Photon Vampire
- Joined
- May 1, 2021
- Messages
- 4,178
I have three Fortress Power eFlex Batteries and one EG4 LL Battery all in parallel using equal length wires going to Busbars and then to a Sol-Ark 12K Inverter.
My eFlex batteries (Grade A) will charge by 11am in the morning. My EG4 LL Battery (Grade B) will take until 1pm to Charge. This was something that was obvious on day one. What I have learned since then is that the Eg4 Battery wastes a bunch of PV power trying to balance the cells.
Where as the eFlex batteries will balance in 15 minutes and do so with minimal power draw. The EG4LL is continually drawing 14 Amps then discharging 10 Amps alternating between the two every 2-3 minutes and spends a good two hours doing this balancing.
The first problem is the fact that the EG4 battery has several cells that will reach up to 3.65V very quickly and several that will be at 3.35V and trying to catch up while the eFlex cells all charge up nice and evenly to 3.43V and just need a slight tweak to a random cell, maybe one is at 3.40V.
The difference in the way the balancing happens on a cheap BMS versus an expensive one is kind of interesting. The expensive one will take power from the higher charged cells and reroute it to cells that have lower voltages until the pack is balanced, this is the way I would expect it to be. It may pull a bit of power from the Inverter to complete the process but not much.
The Cheap BMS with B cells is basically charging the pack until a single cell hits 3.65V and then it stops charging. At this point several cells in the pack may still be at 3.35V and what the BMS does is bleed off some of the power 10Amps at a time to the Inverter until the 3.65V cell drops to 3.60V then it will charge the pack again for a few minutes with 14 Amps of power until the 3.60V cell once again reaches 3.65V and repeats the cycle.
The Idea seems to be that during this charging period the 3.35V cell will get up to 3.40V and the cycle will repeat until all the cells are at around 3.43V. The reality is that when the 10 Amp discharge happens the 3.35V cell of course loses energy so it ends up at 3.32V. So that 14Amp charge might bring it up to 3.37V and not 3.40V. So this cycle will rinse and repeat in a two step forward one step backward motion with each cycle using 4 Amps of extra power for nearly 2 hours.
If you switch off the Breaker on the EG4LL and are thinking that it will balance itself you can forget it. The moment the breaker goes off and the battery cannot discharge the 10 Amps the whole process stops and the cells remain at whatever voltage they were at even though the BMS is on.
The eFlex on the other hand will continue to balance the battery even when turned off.
My eFlex batteries (Grade A) will charge by 11am in the morning. My EG4 LL Battery (Grade B) will take until 1pm to Charge. This was something that was obvious on day one. What I have learned since then is that the Eg4 Battery wastes a bunch of PV power trying to balance the cells.
Where as the eFlex batteries will balance in 15 minutes and do so with minimal power draw. The EG4LL is continually drawing 14 Amps then discharging 10 Amps alternating between the two every 2-3 minutes and spends a good two hours doing this balancing.
The first problem is the fact that the EG4 battery has several cells that will reach up to 3.65V very quickly and several that will be at 3.35V and trying to catch up while the eFlex cells all charge up nice and evenly to 3.43V and just need a slight tweak to a random cell, maybe one is at 3.40V.
The difference in the way the balancing happens on a cheap BMS versus an expensive one is kind of interesting. The expensive one will take power from the higher charged cells and reroute it to cells that have lower voltages until the pack is balanced, this is the way I would expect it to be. It may pull a bit of power from the Inverter to complete the process but not much.
The Cheap BMS with B cells is basically charging the pack until a single cell hits 3.65V and then it stops charging. At this point several cells in the pack may still be at 3.35V and what the BMS does is bleed off some of the power 10Amps at a time to the Inverter until the 3.65V cell drops to 3.60V then it will charge the pack again for a few minutes with 14 Amps of power until the 3.60V cell once again reaches 3.65V and repeats the cycle.
The Idea seems to be that during this charging period the 3.35V cell will get up to 3.40V and the cycle will repeat until all the cells are at around 3.43V. The reality is that when the 10 Amp discharge happens the 3.35V cell of course loses energy so it ends up at 3.32V. So that 14Amp charge might bring it up to 3.37V and not 3.40V. So this cycle will rinse and repeat in a two step forward one step backward motion with each cycle using 4 Amps of extra power for nearly 2 hours.
If you switch off the Breaker on the EG4LL and are thinking that it will balance itself you can forget it. The moment the breaker goes off and the battery cannot discharge the 10 Amps the whole process stops and the cells remain at whatever voltage they were at even though the BMS is on.
The eFlex on the other hand will continue to balance the battery even when turned off.
Last edited: