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I am designing a solar 7.4V Li battery charger, and want to include gas gauging, and cell balancing. If I use passive cell balancing, I waste power and cause my coulomb counter to lose count. Is there a way to balance the cells without affecting my gas gauge? I'm trying to stay away from the complicated $10+ active balancing ICs. Is there a discrete solution?

Specs: Max charge/discharge: 2.1A

Max Vin: 8.4V

Battery: 2Series, ~2000-3000mAh

Two ICs I am considering:

DS2745 <-Gas Gauge

BQ29209 <-Cell Balancer

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  • \$\begingroup\$ Any resistive method is lossy, active or passive. Patented Methods with bridge, storage inductor and PWM are needed to conserve charge current. But this should not occur during 80% of the time or so during CC mode from say 50% SoC and only significant cell imbalance is more than 1%. Long Life is with good balance from the start and trade-offs always are your choice. \$\endgroup\$ – Sunnyskyguy EE75 Feb 17 '17 at 19:04
  • \$\begingroup\$ @TonyStewart.EEsince'75 "But this should not occur": What is "this"? "during 80% of the time or so during CC mode from say 50% SoC and only significant cell imbalance is more than 1%": I know what CC & SoC are, but it's unclear what you mean. Thanks for the reply \$\endgroup\$ – Boone Angel Feb 17 '17 at 19:30
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    \$\begingroup\$ If your batteries are already matched <1% V at full charge then during CC mode when coulomb rate is max constant, it should not be need any balance current wasted, rather only during the final stages of charging when current is reducing in CV mode to meet your expectations of efficient balancing. \$\endgroup\$ – Sunnyskyguy EE75 Feb 17 '17 at 20:28

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