I found one more thing that i cannot understand.
I have a ceramic heater. Presumably it is based on PTC.
As we know, PTC increases resistance when temperature rises. I have read many datasheet on PTC, app notes and some theoretical and experimental articles.
They do not state anything special about PTC. Just that that R does drop rise right away. It actually goes down up to Curie temperature and the rise very rapidly.
The drop in R from datasheet is about 3-5 times from 25C to 130C
Alright. Thta's clear.
Now, i disassemble a simple PTC heater. It is a 500W heater. It have two ceramic modules in paralle.
In cold state R is about 360 Ohm.
Then i heat it and watch power consumption on wattmeter. It goes up to almost 700W and then drops below 100W.
Good, looks like PTC behavior.
Then i measure the resistance and i see 40 Ohm!
Here is video (it is in russian, but there is no point in listening to me rating, just watch the numbers on instruments)
https://www.youtube.com/watch?v=...
So, temperature is crazy high, but resistance dropped almost 10 times.
But i am lost here. If resistance is 40 ohm per section, then current should be around 5A per section, 10A total, 2 KW total.
But wattmeter shows less than 100 W. HOW?????
Then i did an experiment. I used another heater fan to heat the heating element and measured resistance while heating it.
The resistance dropped to 60 Ohm. Well, maybe i cannot reach the breaking point, but when it was selfheating it should have reached it.
I am totally lost.
Some people report and interesting finding about NTC resistors. If they a heated at the edge the resistance actually goes up, instead of going down.
Maybe the same effect is present here. Maybe power gradient is important.
But i did not find anything about this in anything i have read about PTC and NTC.
Any idea?
turn it on without fan and protection cicuit an