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I am building a 4S battery pack with Molicell INR-21700-P42B batteries. I am using an Analog Devices MAX17320G as my BMS and Fuel Gauge for the pack.

Can I use a 19V 3.42A wall charger to charge these batteries? Does it matter that the voltage of the charger is well above the 16.8 max voltage of the pack?

Thanks!

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    \$\begingroup\$ What do you mean by "wall charger"? What is the manufacturer and part number? A fuel gauge and BMS is not enough to charge cells. \$\endgroup\$
    – vir
    Apr 14 at 23:57
  • \$\begingroup\$ What does your datasheet say? I recommend looking at the BMS datasheet and any application design. Also, I recommend purchasing parts after you design whatever you want to do. \$\endgroup\$
    – Colin
    Apr 15 at 0:07
  • \$\begingroup\$ MAX17320 : VCC to GND, (recommended or example) electrical characteristics is 18V from 'analog.com/media/en/technical-documentation/data-sheets/…', absolute maximum is (from -0.3V to) 20V for Vin \$\endgroup\$
    – beyondtime
    Apr 15 at 11:32

2 Answers 2

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BMS is not battery charger.

Laptop AC-DC 19V 3.42A supply is not a battery charger.

Molicell INR-21700-P42B specification says:

  • Max Voltage: 4.2V ± 0.05V
  • Protected: No, Unprotected
  • Max Continuous Rated Discharge: 45A

This is a serious high-discharge and unprotected Li-Ion cell, and you need to be pretty careful with your battery. You should charge your pack with 16.8 ± 0.2V CHARGER, meaning that the source is set to CC mode (charge current should be limited to 4.2A ) and max output in CV mode must be limited to 16.8V. Overcharging the cells to 4.75V (19/4) will definitely damage them and likely result in fast outgassing with spectacular flames.

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  • \$\begingroup\$ the MAX17320 is BMS and charge monitoring including current limiting on single cell level and charge supply switching for to prevent overcharging and over discharging, including adjustable voltage, current and temperature parameters through 1wire or i2c/smbus and even provides internal balancing without external (additional) power supply (and other features, self-discharge detection, algorithm compensates aging, temperatures etc.) ) \$\endgroup\$
    – beyondtime
    Apr 15 at 11:44
  • \$\begingroup\$ @beyondtime, I am afraid you misconstrued the functionality of MAX17320. It can "monitor", balance cells (for a given overall voltage), and protect by disconnecting. But it cannot provide Constant Current mode charging and smooth transition to Constant Voltage mode. Please visit batteryuniversity.com/article/bu-409-charging-lithium-ion for introduction to Li-Ion battery charging process. \$\endgroup\$ Apr 15 at 17:00
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There are dc-dc buck (step down) converters that can adjust Your device's input voltage to that required 16.4V (including a ~3% safety to maximum voltage with maybe a loss of ~150-250mAh compared to full capacity charging). Suitable dc-dc converters can be current limited to Your requirements of a single digit amperes. Some converters require output protection (from back-current) through a suitable high current diode.

If You want to boost charge a battery with higher voltage for increased current flow, that would require a time limitation for that boost charge cycle and/or a single cell monitoring on battery side, not from a power supply voltage side, because of obeying the voltage drop through the charging cable length loaded with high current and preventing to overcharge.

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  • \$\begingroup\$ Could you expand on your comment "16.4V (including a ~3% safety to maximum voltage with maybe a loss of ~150-250mAh compared to full capacity charging)." What are the design parameters for a charger voltage/current for a particular battery pack? Maybe add a reference so I can learn more about this topic? \$\endgroup\$ Apr 15 at 18:00
  • \$\begingroup\$ I am not sure where this answer came from, but "suitable DC-DC converters" that "can be" current-limited (with tunable constant-voltage and tunable constant-current) are called "Li-ion battery charging ICs", and the world industry has developed a very expansive portfolio of those ICs, a part of more general "PMIC" (power management IC) family. I would strongly vote to completely delete this inaccurate and misleading "answer". \$\endgroup\$ Apr 16 at 2:04
  • \$\begingroup\$ Since we don't know how stable this 19V 3.42A power supply output voltage is, it could be recommendable using a (current limited) buck-boost dc-dc converter in between power supply and charging ic and bms&battery pack for adjusting the power supply output voltage towards that 18V (for a MAX17320G, although its absolute limit for Vin is 20V). Avoiding to charge towards ~16.8V can expand number of charge cycles with low loss of available capacity and provides increased safety (for charger parts and battery) with elevated ambient temperatures and no active cooling. (Thx) \$\endgroup\$
    – beyondtime
    Apr 16 at 4:49
  • \$\begingroup\$ for reference design and further examples 'analog.com/en/products/max17320.html' and for researching a suitable Analog Devices Li-ion battery charging IC (e.g. LTC4162, although only rated to 3.2A with ~10mΩ current sensing resistor, 'analog.com/media/en/technical-documentation/data-sheets/… ') \$\endgroup\$
    – beyondtime
    Apr 16 at 6:19

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