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BQ20Z95: Output voltage does not match cell voltage

Part Number: BQ20Z95

Hi all, I am new to the forums and to gas gauging.  I have a laptop battery pack (For an MSI 2PC Dominator), the model number of the pack is BTY-M6D.  A while ago, my battery pack died, and I thought it would be a good learning experience to try to rebuild it with new cells.  (I bought a new pack for cheap, this is more of an experiment than anything else).  Since then, I've installed the new cells and setup all of the hardware the way that it was previously set up.  Using an EV2400, I have access to the bq20z95.  According to the bqEVSW, the chip is working fine (although in the course of my trouble shooting I completely reset it, and had to use bqEASY to set it back up).  I also have full access due to the manufacturer not changing the Unseal key. 

The problem is, I only get about 10% of the output voltage I expect.  The cells are fully charged and are producing 11.9V, but I only get about 1.2V on the Pack+ and Pack- pins.  This is a problem, as the laptop cannot boot with that small of a voltage.

I suspect the issue is a hardware problem, possibly a blown FET.  I'm hoping someone can help me to either confirm or deny this and to explore next steps in getting this device back up and running.  

Thanks for your help in advance!

  • Hi Gadgethm,

    Without a schematic and known measurements at a set state, it's difficult to even speculate. Please perform an electrical test if you believe it is a blown FET - check the voltage at the gate drain and source to determine if a FET is blown. Also check the chemical fuse.

    Sincerely,
    Bryan Kahler
  • Checking the fets seems to be okay, although one of them has voltage drop of 0.32 V which might be low.  There appear to be two chemical fuses in parallel, neither of which looks blown.  Hmmmm.  I'll look into replacing the fet and see where that gets me. Thanks!