I soldered two wires on female USB type A pins,one wire to ground and the other to the VCC pin.
I was trying to check the battery voltage of the li-ion battery in my flashlight,
I connected the a voltmeter to the VCC and the ground wires of the female usb-A connector. The female USB-A connector I connected to the the flashlight cable: one side has a male USB-A connector and other side has a male USB-C connector which is connected to the flashlight.
I haven't gotten any result (0000.)
Why?
I tried it on a cellular phone and I got only 0.4V,Vwhile on the phone it says 80%, so the 0.4V is probably a result for something else.
Is there any simple way to improve the connector to be able to read the voltage of the battery?
Best Answer
The battery of a device goes through a protection circuit, then usually a boost converter, then powers the device. For charging, the input connection connects to a charging circuit, which is not directly connected to the battery, as this raises safety issues if a metal object is inserted into the charging port, or if there is a fault with the charger.
The reason you detect 0.4V on your phone is because your phone is likely trying to negociate under the USB Power Delivery protocol, so your voltmeter is able to see that there is ocassionally some activity on the power pins to turn on any connected device for a time long enough for it to send power delivery data if any. However this explaination only works if you see short blips of voltage, without an osciliscope it hard to tell.
You could probably unscrew your torch and measure the voltage of the Li-ion battery that way.