I have two of these spotwash machines. They are portable systems that use a 12V power tool battery consisting of three 18650 cells. One of the batteries recently failed. 12V appears at the terminals but there appears to be a fault condition - machine flashes LEDs when you attempt to power up. When you plug in the battery directly (the machine charges through a USB-C port, but there is a second USB-C port on the battery itself for some reason that can also be used for charging), the green LED lights and a dim red LED lights next to it solid. By comparison, a working battery will flash green only.
On physical examination there are no visible signs of damage, each cell obviously tests OK too. Within the device there is what appears to be some kind of I2C interface with pads exposed (GND, CLK, DAT, VDD). On the battery's main connector there are 6 pads (+12V VCC, RX, TX, KJ, CH+, GND). Everything is slathered in conformal coating so I have no idea what any of the ICs are.
On measurement, my first observation is that there is 70 ohms between VDD and GND. +3.3V appears at VDD when you plug the battery in and the two LEDs light up. If you inject +3.3V across VDD and GND the same thing happens, the board pulls 49mA and nothing gets warm. By comparison, the working battery measures 50kOhm between VDD and GND.
Q30, Q31 and Q32 (transistors for the balancing by the looks of it) all test OK. The low ohms measurement appears at C31, C32 and various other places around the board. The thermistor is OK, 1kOhm from NTC to GND on the board but measures the expected 89kOhm when removed and tested in isolation. By comparison the working battery measures 89kOhm both on and off the board.
Pic attached. Any ideas where to start looking?
On physical examination there are no visible signs of damage, each cell obviously tests OK too. Within the device there is what appears to be some kind of I2C interface with pads exposed (GND, CLK, DAT, VDD). On the battery's main connector there are 6 pads (+12V VCC, RX, TX, KJ, CH+, GND). Everything is slathered in conformal coating so I have no idea what any of the ICs are.
On measurement, my first observation is that there is 70 ohms between VDD and GND. +3.3V appears at VDD when you plug the battery in and the two LEDs light up. If you inject +3.3V across VDD and GND the same thing happens, the board pulls 49mA and nothing gets warm. By comparison, the working battery measures 50kOhm between VDD and GND.
Q30, Q31 and Q32 (transistors for the balancing by the looks of it) all test OK. The low ohms measurement appears at C31, C32 and various other places around the board. The thermistor is OK, 1kOhm from NTC to GND on the board but measures the expected 89kOhm when removed and tested in isolation. By comparison the working battery measures 89kOhm both on and off the board.
Pic attached. Any ideas where to start looking?
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