can PID work with PTC chamber heaters?

r123

Wondering if chamber temperature can be PID tuned if heating delivered through SSR / PTC heater? Reason being, since the resistance of the heater changes with temperature, that might be confusing to the PID algo who then finds it's ON cycles have less / more impact than expected? A second thought would be that it will surely have experienced just that during the tuning, so no surprise. But then a third realisation is that the "temperature" it receives from the sensor has nothing to do with the "temperature" of the heater element (and thence it's resistance) because, whereas in a hotend block the two are the same, chamber air can be at a very different temperature to heater element. Thoughts? Experience?

o_lampe

@r123
there is a thermal coefficient for thermistor definition which could probably deal with the PTC-curve.
But the resistance is still low and won't work like a common 100k thermistor.
And you must not aim for a higher temp the PTC is made for, this would switch off the PTC and would be seen as thermistor/heater fault.

fcwilt

@r123

The whole point of tuning is to try and determine the behavior of the system.

Why would the temperature of the heater be of any interest? It's the effect of the heater on the chamber that is of interest.

Have you experienced problems tuning your chamber?

Frederick

r123

@fcwilt Have noted that there is now a fashion for PTC heaters for safety reason. What I would like to know is, if I order a PTC heater will I then be able to PID tune the chamber or not? Or whether it is necessary to implement some other kind of control mechanism?

o_lampe

@r123 said in can PID work with PTC chamber heaters?:

Or whether it is necessary to implement some other kind of control mechanism?

What about fan control? I've read about chamber temp controlled by a separate 'exhaust' fan.

fcwilt

@r123 said in can PID work with PTC chamber heaters?:

@fcwilt Have noted that there is now a fashion for PTC heaters for safety reason. What I would like to know is, if I order a PTC heater will I then be able to PID tune the chamber or not? Or whether it is necessary to implement some other kind of control mechanism?

Thanks for the feedback.

I think @dc42 would be the one with the definitive answer but PID is used in all sorts of control systems.

Are these heaters expensive? Too expensive to buy and try?

Frederick

r123

@o_lampe Yes, I've heard of people controlling the fan intead. But don't like the idea of that because intend to blow the air at print level so want it to arrive close to correct temperature, not have a dribble (for example) of very hot air.

@fcwilt the heaters are dead cheap but will take some time to arrive - and if it doesn't work, then will take more time to order something else and wait for that to arrive. UR right, should have ordered to try a long time ago.

o_lampe

@r123 said in can PID work with PTC chamber heaters?:

because intend to blow the air at print level so want it to arrive close to correct temperature

I only have limitted experience with ABS printing in a heated chamber, but in my book you must not blow air accross a fresh print.
Even if it's hot air, it's definitely a temp-shock for the part.
The means of a chamber heater is to keep environment above a certain temp but let the part cool down slowly to that temp.

Other filaments may be different
Just my 2 cent

r123

@o_lampe paragraph 0050 (and a few leading up to it) may interest you (in conjunction with associated drawings).

https://patents.google.com/patent/US20190240969A1/en?oq=++++++++++US20190240969

fcwilt

@r123 said in can PID work with PTC chamber heaters?:

@fcwilt the heaters are dead cheap but will take some time to arrive - and if it doesn't work, then will take more time to order something else and wait for that to arrive. UR right, should have ordered to try a long time ago.

Well if this kind and the "other" kind are both cheap order one of each.

Frederick

dc42

@r123 as you say, PTC heaters can be challenging to use with PID. The issue is that if you tune them at one temperature, the PID may be unstable or respond very sluggishly at other temperatures.

We have some work planned to better support PTC heaters in RRF 3.4.

moth4017

@dc42 Hi, did any work get done on the PTC heater ?