completelycharged
Active member
- Joined
- Mar 7, 2018
- Messages
- 1,083
And now for something completely different.... queue monty python music.....
This is a bit of a thought in progress and very open to all kinds of feedback, feedback including monty python quotes will be more highly rated...
Diagram is missing a current sensor...
Been thinking about BMS units for 2 years now and have been delaying adding a BMS (yep been running the battery back with no BMS for 2 years) but a solution is maybe now getting much clearer for me.
I was originally planning to go down an ESP route with an ESP per battery pack but it still had issues to deal with and was not going to be able to active balance, plus lacking some of the critical measurement functionality.
So, after browsing at parts for 2 years and forgeting and remembering things over that timeframe I think I have a solution, but it's a little more different.
Basically just a relay switched charger with a difference (or not so much aof a difference).
The idea is that the top right unit (RS485 ADC unit) measures 2 cell voltages in parallel and the key measurement is the voltage differential between the cells own voltages. i.e. if one cell is 3.10V and the other is 3.21V then the criticla measurement of interest is 0.11V. The absolute cell values are not too critical at this point and a relative reference.
The battery pack discharge or charge rate is then taken into account to corrrect some of the bias that a high charge or discharge may be introducing to the cell voltage differential.
Process would be to switch between all cells in the pack and measure all of the differences. This would then provide a full pack picture as to which cell is the lowest or which ones have the greatest imbalance.
Then the charger would be switched to those cells and charged (power supply buck in the bottom left corner is fuly isolated 36-72V buck) and the exact energy charge could then be measured and monitored. The CC CV buck (bottom right) would be set to 5A and 8.4V (to allow for both cells in parallel to be charged if needed) and that way the full picture as to what is going on with the pack can be catured.
My oiwn pack is 22s (LTO) so my cell voltages are a little different and would need 3 x 16 channel 3 x 8 channel relays to allow for cell switching.
Any thoughts as to why this could not work ?
This is a bit of a thought in progress and very open to all kinds of feedback, feedback including monty python quotes will be more highly rated...
Diagram is missing a current sensor...
Been thinking about BMS units for 2 years now and have been delaying adding a BMS (yep been running the battery back with no BMS for 2 years) but a solution is maybe now getting much clearer for me.
I was originally planning to go down an ESP route with an ESP per battery pack but it still had issues to deal with and was not going to be able to active balance, plus lacking some of the critical measurement functionality.
So, after browsing at parts for 2 years and forgeting and remembering things over that timeframe I think I have a solution, but it's a little more different.
Basically just a relay switched charger with a difference (or not so much aof a difference).
The idea is that the top right unit (RS485 ADC unit) measures 2 cell voltages in parallel and the key measurement is the voltage differential between the cells own voltages. i.e. if one cell is 3.10V and the other is 3.21V then the criticla measurement of interest is 0.11V. The absolute cell values are not too critical at this point and a relative reference.
The battery pack discharge or charge rate is then taken into account to corrrect some of the bias that a high charge or discharge may be introducing to the cell voltage differential.
Process would be to switch between all cells in the pack and measure all of the differences. This would then provide a full pack picture as to which cell is the lowest or which ones have the greatest imbalance.
Then the charger would be switched to those cells and charged (power supply buck in the bottom left corner is fuly isolated 36-72V buck) and the exact energy charge could then be measured and monitored. The CC CV buck (bottom right) would be set to 5A and 8.4V (to allow for both cells in parallel to be charged if needed) and that way the full picture as to what is going on with the pack can be catured.
My oiwn pack is 22s (LTO) so my cell voltages are a little different and would need 3 x 16 channel 3 x 8 channel relays to allow for cell switching.
Any thoughts as to why this could not work ?