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)
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.
turn it on without fan and protection cicuit an