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Battery Fuel Gauge Recommendations for Rechargeable + Non-Rechargeable Mil Spec Batteries

OscarZ
Prodigy 80 points
Other Parts Discussed in Thread: BQ35100, BQ34Z100-R2

Hello, 

I was hoping if TI could help me recommend a battery fuel gauge or an IC that would protect our batteries at cut off when they are depleted. We are using Mil-Spec batteries, particularly the rechargeable BB-2590 and BA-5390. We have a hysteresis circuit that cuts of the supply from the battery at 10V and won't turn back on until it sees 10.5V. Our customer gave us a heads up that during testing with the batteries mentioned above, they saw their units continuously turning on and off at the cut off voltage on another application. They did not give us a measurement as to how high the deplete battery voltage level went up other than saying that it turned on and turned back off. For safety reasons, we would like to make sure that if a battery has been deplete that it does not go thru this cycle.

My questions for the TI team is: 

- Are there any fuel gauges that would be recommended to monitor the batteries mentioned?

- Should the hysteresis circuit account for a much higher voltage level for it to turn on? Since we don't have values, we are not sure that the depleted batteries will jump, say, from 10V at depleted state to 12 V with no load and then back to 10 V with load. 

Any help would be appreciated. Thanks in advance. 

  • 0
    TI__Genius 17085 points

    Hi,

    Can you provide the datasheets for the batteries you are using and the cell count (ex: 2s2p) to help me better recommend a battery gauge?

    I am confused on what exactly you are asking for the second question can you further explain the circuit and the concern?

    Regards,

    Evan

  • 0 in reply to Diego
    Prodigy 80 points

    Hey Evan, sure thing. Here is the link to one of the batteries that the customer plans to use. https://www.ultralifecorporation.com/ECommerce/product/ub0023/type-ba-5390a-u-15v-111ax2 

    As for my second question: We set the cutoff voltage from the battery to about 10V and set the system to accept battery power again if it sees 10.5V or over. However, we are unsure about the battery's voltage when it gets disconnected from a load. My assumption is that the battery's voltage will rise when it becomes disconnected from the system, however, how much it would increase is unknown. If that voltage on the battery exceeds 10.5 V when disconnected from a load, then the system could potentially turn back on and then back off (due to the battery being depleted already). This could lead to unwanted power oscillations on the battery since it is already been depleted, which could pose a  safety risk. Since this poses a safety risk, I want to make sure that unwanted power oscillations on the battery are prevented at cutoff.

  • 0 in reply to OscarZ
    TI__Genius 17085 points

    Hi,

    For the Non-Rechargeable Battery mentioned in the title, I recommend the BQ35100, this gauge is for primary batteries.

    For the Rechargeable applications, BQ34z100-R2 would probably be the best option, because it is a top of stack gauge and has a wide voltage and current tolerance. 

    I encourage you to look at the full portfolio. Battery fuel gauges product selection | TI.com

    For your second question, thank you for explaining. This will be chemistry dependent. My recommendation is to fully discharge the battery record the voltage then let the battery relax for 2 hours and record the voltage. This should tell you where your threshold will need to be to avoid the unwanted power oscillation.

    Regards,

    Evan