Why would PTC heater performance degrade?

[davidd31415]

I am investigating what would cause the performance of PTC heaters to degrade.

The heating elements are a PTC carbon paste. After being powered at 14V for anywhere from 200 - 3000 hrs at various temperatures the current draw of the heaters drop from 2A to 1A. The resistance of the heaters increases as well but I do not have data for this.

What might cause a resistor to increase in resistance?

I am beginning to experiment with the heaters but if anyone has insight into what might cause the heater resistance/performance to change, I would appreciate hearing it.

 

[itsmoked]

Sure. Oxidation of the actual heater material or oxidation of the connections to the paste matrix. Remember every 10 degrees doubles any chemical reaction rates.

Try encapsulating the entire heater connections and element to see if this radically changes the result. You might also try a test with the entire heater in an inert atmosphere. Cheaper would be nitrogen.

You might run this thread by the chemical engineering forum. In this case it wouldn't be considered cross-posting.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[IRstuff]

If it's a paste, how do you know that you're not boiling or burning off the binder? If the binder goes, the resistivity would presumably go up, even with no oxidation.

I'm a bit surprised that one would try to get consistent behavior from a paste material.

TTFN

FAQ731-376