PTC Thermistor

Can you elaborate more about the mounting and pressure applied to the contacts? Is one side connected to a heavy chassis which might sink heat? Or is there parts that vibrate or deform with heat?

What application is it being used for? Part number? Power/current it is handling or dissipating? Duty cycle? Ambient temperature?

Hello!

Sure I can.

So, it is mounted like it is shown on the picture in attachment. On the first picture, you can see the PTC pill mounted, and other is without so you can see the springs.

So both sides are equally conected (with four pins), but the damage is only on the one side. (previous pictures)

"Is one side connected to a heavy chassis which might sink heat?"

-Answer: I would say no.

"Or is there parts that vibrate or deform with heat?"

-Answer: There is one frequency because the PTC is assemblyed on the compesor in the refrigerator. 

"Power/current it is handling or dissipating?"

-Answer: 100-115 V, 50-60 Hz, and the current is AC average was 2,9 and the highest measure was 3.4 A. 

"Duty cycle?"

-Answer: Max "switching" per hour is 6-7 and in 24/7. 

 "Ambient temperature?"

-Answer: 20-30⁰C

Thank you very much for your support!
If you have any further questions I will do my best to provide an answer to you!

Best regards.

Hello!

Sure I can.

So, it is mounted like it is shown on the picture in attachment. On the first picture, you can see the PTC pill mounted, and other is without so you can see the springs.

So both sides are equally conected (with four pins), but the damage is only on the one side. (previous pictures)

"Is one side connected to a heavy chassis which might sink heat?"

-Answer: I would say no.

"Or is there parts that vibrate or deform with heat?"

-Answer: There is one frequency because the PTC is assemblyed on the compesor in the refrigerator. 

"Power/current it is handling or dissipating?"

-Answer: 100-115 V, 50-60 Hz, and the current is AC average was 2,9 and the highest measure was 3.4 A. 

"Duty cycle?"

-Answer: Max "switching" per hour is 6-7 and in 24/7. 

 "Ambient temperature?"

-Answer: 20-30⁰C

Thank you very much for your support!
If you have any further questions I will do my best to provide an answer to you!

Best regards.

Judging from your later photos - my best guess is that the PTC is somehow overstressed or aged and is dissipating more power than expected.

The heat seems to be affecting the plastic, causing it to melt slightly, bowing outwards to the point that the springs no longer supply enough pressure to make good contact with the PTC or changing the metal spring properties to become less springy (hence applying less pressure)

One side always will end up with better/worse contact than the other, and the weaker mechanical contact is probably leading to small arcs, generating even more heat and burning away more metal material in the process, which is why the damage is only on one side. Ordinarily you might expect because of AC currents, damage from AC effects on the PTC would show up evenly throughout the pellet (i.e. from both sides).

That's just my best guess at this stage.

- Gough

EDIT: Compressor vibrations may also affect the contact especially when its weak ... that may make it even more likely for arcing to occur because a weak spring would cause rapid "bouncing" of the metal on the surface similar to a noisy switch.