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Thread: Problem with battery charger for Teensy 4.0

  1. #1
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    Problem with battery charger for Teensy 4.0

    I have this charger: https://www.adafruit.com/product/2124
    It works fine if I wait for the battery to get fully charged. But if the battery is low and charging, the voltage on Teensy 3.3V output drops to about 2.5V and poor thing goes into a coma.

    What charger do you use which keeps 3.3V on Teensy even while charging a totally drained battery?
    And I don't want to use any additional switches other than the new on/off button on Teensy 4.0
    Ideally, I want to have an analog output pin on the charger which shows the battery level, so that I can show it on Teensy while the battery charges or not.
    So, my Teensy should work just like my phone: it shows that the battery is low, I connect it to the USB and it keeps working with no interruption, showing that the battery is charging now.

    I don't need a complete board. I'm need a chip and schematics for it, so that I can integrate it onto the new board I'm making.

    Thanks.

  2. #2
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    How did you wire the charger to the Teensy?

    I had similar Problems with ESP32 boards with built-in LiPo charger. The problem was, the ESP32 plus the charger drew so much current that the voltage on the USB port crashed. This did not happen while using a 2A USB charger.

    The Teensy 4 takes around 300mA alone. Depending on code and clock speeds it takes even higher peaks. If you watch the current on a scope, this tells about missing decoupling.

    One solution could be to limit the charging current so not to exceed USB specs, which is 500mA on a 2.0 Port.
    A bit of help could be to add capacitor to stabilize the charger input, because the charger tickles current as well. But here is the problem of che capacitor charging current (by USB specs called "inrush current"), which could, if too high, lead to the USB port being disabled or even a fuse on the motherboard blown, rendering the port useless until repaired. So there is a limit of 10F in total, according specs.
    The best solution would be to monitor Vusb and adjust the charge current accordingly, by a program on the Teensy. So you may use a high-current charger or program the Teensy on a PC, without needing to switch something or using a second charging port.
    Last edited by radias; 11-06-2019 at 09:22 PM. Reason: clarified logical relations

  3. #3
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    Well, it's wired "by the recipe": cut the wire on Teensy, VUSB goes to the charger, the battery to VCC on Teensy.

    I guess I know about the problems you describe, but I'm asking whether someone has a tested schematics and components for all this.
    I'm trying to save time here.

  4. #4
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    So you've done everything right. The only real "problem" is the hard limit of 500mA (or be it a bit more, depending on th capabilities of the port). You could use some (absolutely out-of-specs) Y-cable to add the available current of two ports or to add an additional charger.

  5. #5
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    (I do not understand, why posts get sent unintentionally. So here is the next sentence as a new post.)

    Anyway, have you left the jumper on the underside of the LiPoly Backpack open? If you closed it, it will never work with Teensy 4 on a common USB port without adding additional power.

  6. #6
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    I didn't touch the jumper, so it's on 100mA now.
    I just want to see what other people use. And I want the "Battery level" indicator with a pin on the charger.

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