GPy & FiPy report different voltages when being charged

  • I've got an application that needs to know when it's being charged. The hardware was developed using a GPy in a Pysense and experiments showed that if the battery voltage as returned by pyCoproc.read_battery_voltage was over 4.45v then we could safely say we were being charged. This was consistent and worked correctly across a number of GPy modules.

    Due to a momentary lapse of reason on my part, one of the GPy modules was destroyed and to get the unit working quickly I substituted a FiPy module, however, the unit could no longer detect a charging condition. Further testing revealed that while a GPy always shows above 4.45v when charging, a FiPy only shows around 4.01v. Does anyone have any idea why the difference?

    This is a long life battery based application, so at the point the battery voltage is checked all radios should be turned off. I can't simply set the limit to 4.0v as a freshly charged GPy in a pySense shows around 4.2v - which seems too high.

    If I get time today I'll do some more work on it, but I was wondering if anyone else had figured this out. Is there a difference between the way the modules detect battery voltage? (I'd check the schematics, but wait...).


    pySense running v0.0.8
    GPy and FiPy running 1.20.0rc4

  • @john-baird please do update this is the results are different and ill have the team look into it.

  • @jcaron Yes, it's exactly the same physical hardware, I just swap the GPy for a FiPy. They are both running exactly the same code. I have another FiPy on its way to me. I'll try that in case it's a one-off hardware issue and update this thread.

  • @john-baird the voltage is measured by the Pysense, not the module, so it should work the same. Are you testing using the same Pysense module, and the same (type of) battery?

    The voltage will probably depend on the actual load, but that seems like a big difference, and I’m surprised that the charge voltage is lower than the max discharge voltage.

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