Li+ battery, losing power shortly after startup

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  • I think my Li+ battery regulator circuit is cutting off power after about 30s of operation. This is the battery. I assume the Espruino Wifi (along with the other slave devices on a PCB) are drawing too much current. How do I select an appropriate battery? This battery is sufficient for just the slave devices on the PCB alone.

  • That's strange - I use a similar kind of battery quite a lot, and it seems fine. Those should supply well over an amp, and realistically Espruino WiFi isn't going to draw any more than 0.5A - even for fractions of a second.

    How do you have it connected, and do you have USB connected as well? That can be difficult on Espruino WiFi

  • Black battery wire to GND, red battery wire to VUSB. The wires soldered into the back side of the JST connector where the battery plugs into the PCB. There's a fuel gauge in the circuit, but I think that's just for charging. I used a modified USB cable so that the ground and V+ from the computer is not connected, only the data lines are connected. My PCB was designed with a USB connector on it for charging the battery, so I provide the USB power there, until I get the board redesigned.

  • Great! That all sounds fine to me - and you're sure that the battery voltage really is dropping out - like the protection circuitry is disconnecting it?

    Could it just be that there's some issue with the control board which means that the battery hasn't charged fully? The auto-disconnect in those batteries can trigger because of overcurrent or low voltage

  • It has to be happening in the battery circuit, because there's no other circuit between the Espruino and the battery cells, except for that built-in circuit. The PCB's power LED goes out, and the Espruino disconnects from my computer and disappears from available devices.

    I changed the wiring so that the Espruino isn't powered by the battery, but via USB only, and the battery is lasting and functioning properly. What it's powering is the PCB which has the fuel gauge and a couple I2C devices.

    It's an ugly hack, but I'm on a deadline and this arrangement allows me to power the Espruino off an external USB battery pack.

  • I could make it work by adding a 2nd of the same battery, one for the PCB and one for the MCU, but I don't have a 2nd charging circuit.

  • What about connecting the two batteries together in parallel? Just make sure they'.e both fully charged when you do it - there shouldn't be a big problem sticking cells in parallel as it's basically just like having a bigger battery.

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Li+ battery, losing power shortly after startup

Posted by Avatar for CriscoCrusader @CriscoCrusader