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Modular Li ion Pack

PCMR

Aug 9, 2017
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I am planing to build my self a massive powerbank. It would be nice, if i can disconect a section, and later connect agen. I have read, li ion cells musst be at the same volltage to connect them (paralell). So, i came to this Solution.Unbenannt.PNG
The idea is, that there are to positive rails. one for load and the other for charger. If the left 3 cells have a lower Voltage, and i am using power, it will take power from the right cells, until bouth sections have the same voltage.

Are there any big problems in this plan?

PS: Sorry for bad english.
 

Harald Kapp

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Nov 17, 2011
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Are there any big problems in this plan?
Not big but... You'l have a voltage drop of 0.3 V (for Schottky) to 0.7 V (for silicon) across the diodes. This will lessen the efficiency quite a bit.

Why would you disconnect a section and reconnect it later? As per your scheme the batteries will all discharge to the same voltage level, so when the output voltage of your circuit becomes too low, every single cell stack will have the same voltage - too low. Therefore you need to recharge all stacks.

It might by more efficient to have two sets of batteries. You'll need only one controller board for each stack, not many as in your circuit and you will not need the diodes. When one stack becomes drained, swap it for a fully charged stack.
If you need hot plug capability (no interruption of power during swapping of the batteries, look for "ideal diode controller" using your favorite search engine. These use controled MOSFETs instead of diodes to minimize voltage drop and therefore losses.
 
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