Lipo Cutoff Voltage

The GWS ICS100Li ESC has Lithium cutoff, but at 5.5V/8.3V it may be too low for modern Lipos. Fortunately the cutoff voltage can be raised to 6V/9V by changing the value of one resistor. The part which is marked 05C (=11k Ohms) needs to be removed and replaced with a 10k resistor, preferably one with 1% tolerence. Alternatively, a 100k resistor can be soldered on top of it (11k in parallel with 100k equals 10k).

Circuit Description

The 'brains' of the ICS100Li is a PIC 12F675 microcontroller. To detect the battery voltage it uses a comparator with one input connected to pin 7, and the other input connnected to an internal voltage refence. The reference is set to 1.04V for 2S and 1.56V for 3S. The two external resistors connected to pin 7 form a voltage divider which reduces the battery voltage by a factor of 5.3, so 5.5V at the battery becomes 1.04V at the microcontroller. By increasing the voltage divider ratio we are able to raise the cutoff threshold to a more approriate level.


Faults and Repair

The ESC uses an LM2940 5V 1A voltage regulator to provide the BEC (Battery Eliminator Circuit) function, as well as supplying power to the microcontroller. Unfortunately this regulator has a tendency to short out when overloaded, which usually destroys the microcontroller. The regulator can be replaced with an L4941BDT. Although it is a little larger than the original chip, it still fits on the PCB. The L4941BDT is used in many commercial ESC's and has proven to be very reliable.

I have developed compatible firmware for burning into a replacement 12F675.

ICS100Li source code
ICS100Li hex file


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