Budget watch/tools demagnetiser modified by incorporating thermal protection.
Credit to TheHWcave for the research, test and trial on the YouTube link below.
Thermal protection based on a PTC (Positive Thermistor Coefficient), the power lead is moved to the opposite side to ensure that nothing is near the PTC as it generates heat (+130 C) when current flows through by increasing its resistance, and I also perforated the back cover to improve cooling.
The maximum current of the demagnetiser is around 200mA.
The following thermistors were considered and I opted for B755, mainly due to its availability.
Note, during operation, the thermistor's surface temperature can be very high. Ensure that adjacent components are placed at a sufficient distance from the thermistor to allow for proper cooling.
B755 EPCOS/TDK
DC/AC 550V
230R - 500R
Tref 130C
Ir 28mA
Is 55mA
Is max 1.4A
Dimensions mm
width 13, hight 18, thickness 7.5, leg 35
Datasheet
https://www.tdk-electronics.tdk.com/inf/55/db/PTC/PTC_ICL_OC_Leaded_260V_1000V.pdf
PTCCL05H390HBE VISHAY
PTCCL05H390HTE
DC/AC 265V
260R
Tref 120C
Ir 39mA
Is 59mA
Is max 300mA
Dimensions mm
width 5, hight 10.5, leg 15.5
Datasheet
https://www.vishay.com/docs/29087/ptccl265vseries.pdf
The video instruction is available here
The demagnetiser is bought on Aliexpress, costed less than €10
PTC B755 5pcs €10
https://www.ebay.ie/itm/35581758210...h2gJ7fPRBW&var=&widget_ver=artemis&media=COPY
Credit to TheHWcave for the research, test and trial on the YouTube link below.
Thermal protection based on a PTC (Positive Thermistor Coefficient), the power lead is moved to the opposite side to ensure that nothing is near the PTC as it generates heat (+130 C) when current flows through by increasing its resistance, and I also perforated the back cover to improve cooling.
The maximum current of the demagnetiser is around 200mA.
The following thermistors were considered and I opted for B755, mainly due to its availability.
Note, during operation, the thermistor's surface temperature can be very high. Ensure that adjacent components are placed at a sufficient distance from the thermistor to allow for proper cooling.
B755 EPCOS/TDK
DC/AC 550V
230R - 500R
Tref 130C
Ir 28mA
Is 55mA
Is max 1.4A
Dimensions mm
width 13, hight 18, thickness 7.5, leg 35
Datasheet
https://www.tdk-electronics.tdk.com/inf/55/db/PTC/PTC_ICL_OC_Leaded_260V_1000V.pdf
PTCCL05H390HBE VISHAY
PTCCL05H390HTE
DC/AC 265V
260R
Tref 120C
Ir 39mA
Is 59mA
Is max 300mA
Dimensions mm
width 5, hight 10.5, leg 15.5
Datasheet
https://www.vishay.com/docs/29087/ptccl265vseries.pdf
The video instruction is available here
The demagnetiser is bought on Aliexpress, costed less than €10
PTC B755 5pcs €10
https://www.ebay.ie/itm/35581758210...h2gJ7fPRBW&var=&widget_ver=artemis&media=COPY
