Thread: Low cost BMS
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Old 11-18-2013, 07:20 AM   #108 (permalink)
Astro
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Just had a thought that i would like to run past you all.
When top balancing a battery pack, if i understand it correctly. The charger puts out full charge current until the first cell reaches a set voltage. Then the charger goes to low current mode and the BMS modules switch a load across each cell as they reach the top balancing set voltage. This load effectively keeps them in a holding pattern until all the other cells catch up.
My thought was, why not have the BMS module switch a load across the cell with the highest voltage right at the start of the charging process. That way the charger could stay in high current mode. The cell with the highest voltage effectively gets charging current minus whatever the BMS module load absorbs.
As the other cells catch up another cell may become the highest voltage and so its BMS load is activated. So you are constantly reducing the charge rate of the cells with the highest state of charge.

Basically the cells are all in a race and you want them all to reach the finish line at the same time. So instead of letting the fast cells get to the finish line and then have to wait for the others. Simply reduce the fastest cells charge current allowing the slower cells to catch up mid race.
This way the charger stays in high current mode the whole time and you avoid the long wait at the end of the race as the slowest cells are slowly brought to the finish line with the reduced charger current.

I am new to this BMS stuff but i am slowly learning so please be gentle if this question is a total noob question.
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