Thermal Cut-off Problem Identification

Hi,

I just opened a Panasonic Cordless Phone Adapter which was used for just 14 months then, it stopped working.

There was this small black component in series with the Primary Winding of the transformer. When i searched it of the net i came to know that it is a Thermal Cut-off

The picture is given below:


The component that i have is same as in the picture (like the temp. ratings and current ratings).

The link for the Datasheet is given below:
http://aupo.com.hk/egproduct/1af.htm

Now, the question is:

1. How can i check if the Thermal Cut-off is working or not using an Digital Multimeter?

2. The Adapter is a 110V to 6V. But, I was using a 220V to 110V converter transformer. So, the Thermal Cut-off was sand-witched between the adapter's transformer and the external converter transformer. So, suddenly how it stop working?

Bye,
PRAVARDHAN

It looks like a resetting thermal trip so if you measure across it's wires at room temperature it should appear to be a short circuit. If it is open circuit, either it is faulty or it wasn't temperature but excess current that tripped it and you will have to replace it.

Using it in the way you did shouldn't cause any problems.

Brian.

Hi,

Thanks for the reply.

I Checked it using the Multimeter is Resistance Range upto 2 Mega Ohms, but the multimeter showed infinite resistance.

I have got another Thermal Cut-off, which is in a different shape, like a 1W resistor with Silver colour. This shows 1 Ohm resistance.

But, the print on the Panasonic Adapter says that the input current it draws is 72mA with 120V. So, how can the thermal cut-off stopped working suddenly?

Bye,
PRAVARDHAN

Hi,
Maybe you must check what is your current in these adapter; possibly you will measure some over100 mA (ev. a short/dead electrolythic...), if not_ thja, than we tell "it was some effect of transient/HV spike"...
Such "Poly fuses/poly switches" are build from Bourns & Raychem..
But possibly, its only a simple "bimetall/thermopill" fuse_maybe you find equivalent types from Farnel/ Newark or Mouser.
K.

Some times they just go faulty but more likely it overheated at some time. In a normal fuse it's the current through the wire that heats it and melts it, on these devices it's outside temperature that melts it. Usually you find them very close to, or even inside the windings of transformers so anything that caused an overheat could have blown it, even lack of ventilation.

Brian.

Hi,

Thanks for the help. I will buy a new Thermal Cut-off and then try.

Betwixt was right, the Thermal Cut-off was Tapped on to the primary side of the transformer and there was no ventilation either.

Bye,
PRAVARDHAN