Demagnetiser adding Thermal Protection

[SAMyMAS]

Budget watch/tools demagnetiser modified by incorporating thermal protection.

There are discussions within watch enthusiasts, whether it’s a safe and/or necessary to use demagnetiser on quartz movement. I leave this question out of this topic, which aims bringing an awareness of lacking tool’s thermal protection and providing solution.

SEIKO memo about magnetic influence

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 Datasheet  PTCCL05H390 Datasheet

Video instruction

The demagnetiser is bought on Aliexpress, costed less than €10

PTC B755 5pcs €10

 

[Paul80]

A good writeup, thanks for that.

The one thing to remember is that when you read reports on the few of these machines that have supposedly over heated, in every case it's the owner doing something wrong that resulted in the over heating, so for those people some form of thermal protection would have helped.

For those who don't do stupid things like place them upside down on the desk or putting books on them so the button is constantly pressed there is no real issue or need to panic.

There are loads of electrical items that don't have toc protection that get too hot when incorrectly used, but are fine when used correctly.

So no need to panic