Charging LiFePO4 Batteries in Series

Discussion in 'General Electronics Chat' started by jpanhalt, Mar 6, 2015.

  1. jpanhalt

    Thread Starter AAC Fanatic!

    Jan 18, 2008
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    Microchip makes this chip (MCP73223) that includes a claim for charging a 2S pack. FMA makes a charger that is sold on eBay for the same claimed purpose (http://www.ebay.com/itm/320855658568?_trksid=p2060778.m1438.l2649&ssPageName=STRK:MEBIDX:IT). There are also bare bones boards for series charging on eBay.

    Does anyone have experience charging two-cell packs in series without using additional connections to the pack for balancing? In particular, has anyone used the MCP73223 chip, FMA charger, or bare-bones boards?

    John
     
  2. Roderick Young

    Member

    Feb 22, 2015
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    Sorry, I haven't. Seems to me that if you had two cells that were reasonably identical, you could charge them without balancing, and it would sort of work. I note that there are NiMH chargers that put two cells in series without a second thought, but have yet to find one that puts 3 or more cells in series. Again, I'm no authority, but have heard that LiFePO4 is more rugged and less fussy than other types of Li-Ion. Maybe they're just tolerant enough of overcharge that you can put two in series without getting into serious trouble?

    All the big battery packs do seem to have some sort of equalization scheme.

    If you learn more on this subject, I'd certainly like to hear about it.
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I have 2 cells in series, about 2500 mA hr & are now about 4 years old. When not in use I check V about every 6 mo & top off about every year.
    Discharge 5.6 V
    Operate 6- 6.6V
    Charge to 7.2 V @ about 200 mA from 12 V supply with 20 ohms in series.
    All measurements by eyeball.
     
  4. jpanhalt

    Thread Starter AAC Fanatic!

    Jan 18, 2008
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    I have read enough comments about the robustness of FePO4 cells, including one from a battery manufacturer that indicated balancing was not necessary, that I went ahead and ordered the Microchip evaluation board (MCP73X23EV-LFP). Also, it seems the biggest killer of these cells is trying to get near 100% charge capacity, which I don't need. Since my two cells will be regulated by a 5V LDO (TI LP2989) charging to only 7.2V or even a little lower will not be a problem.

    From the evaluation board datasheet:
    upload_2015-3-7_13-12-14.png

    I wonder if the pre-condition current has anything to do with creating balance without balancing? I will be able to test that out before I put the batteries in my device.

    John
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    looks like will do two cells at 7.2v total, should work..
    also linear technology do a chip LTM8062a
     
    Last edited: Mar 7, 2015
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