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Original question:

BQ24195: Choice of battery

BQ24195: Consequences of use with sealed lead acid

Ian Cunningham
Prodigy 30 points
Part Number: BQ24195
Other Parts Discussed in Thread: BQ24450, , BQ24650Using with Particle Electron so the part can’t be easily changed.... I need to use sealed lead acid rechargeable batteries (Enersys Cyclon 4V 2.5Ah), what are the consequences from using the charge controller with a sealed lead acid? The charge limits are lower than the battery maximum charge current, and the maximum voltage is lower than the lead acid max. So, is charging possible but not optimal? Or, are there any safety issues or damage to the battery possible? Are the BQ24450 and BQ24195 directly replaceable post-production? Thank you, for your time.
  • 0
    TI__Guru**** 166626 points
    Hi Ian,

    The BQ24450 and BQ24195 are not interchangeable. BQ24195 is not a good solution for charging lead acid batteries. BQ24450 is designed for charging lead acid at lower currents due to the low efficiency of a linear regulator based charger. The higher efficiency BQ24650, and other members of the BQ246xx buck converter based charger family can be modified to optimally charge lead acid batteries as explained in the app note here: www.ti.com/.../slva437a.pdf. The BQ24650 is designed to be power powered from a solar panel but doesn't have to be powered that way.
  • 0 in reply to Jeff F
    Prodigy 30 points

    Thanks for the response.... Accepting that it’s not a good solution, is it also a posing a risk? Are there consequences to its use with SLAs?  The problem is that the part is already populated on the SoM by the 3rd party manufacturer (not our choice), but we need SLA batteries to achieve a -40C temperature rating (absolute requirement).  If we can’t substitute a BQ24650 then we are stuck with the BQ24195 and SLA batteries.   Later we may create a new design but at the moment we want to use the SoM’s BQ24195... it’s fine if it’s ‘not a good solution’ but not fine if there are more severe consequences.  Any further elaboration you can offer?

  • 0 in reply to Ian Cunningham
    TI__Guru**** 166626 points
    The BQ24195 is only designed to charge a single LiIon cell so its max BATREG voltage (slightly higher than 4.2V) is likely not high enough to fully charge your SLA (12V?). Also, for long life, the SLA's charge profile is recommended to include an overvoltage then trickle charge at a lower voltage as explained in the app note. The BQ24195 will not automatically perform that profile but the host could send commands to perform that profile.
  • 0 in reply to Jeff F
    Prodigy 30 points
    Thanks Jeff, Enersys Cyclons have a nominal charge voltage of 4.0V so they are very similar in that respect to our Li-ion cells. The BATREG will limit the charge, though, as you mention in the second part of the response, the over voltage recommended by Enersys does exceed the 4.2V limit by a few tenths of a volt.

    Appreciated the follow up, we’ll use this only as a temporary testing solution until we have a chance to design in a BQ24650 on our own board.

    Ian