Modification for heater block


#1

I was trying to use PVA on a duql head K8400, but were always struggling with extrusion problems of th PVA. Additionally a sparling was noticeable when the extruder was in “standby”.

I realised that this effect was related to a too hot nozzle, as it was reported already earlier (viewtopic.php?f=62&t=15032&p=76296#p76296)

For my understanding the poor thermal connection to the thermistor is the major problem of the deviation. Furthermore I was annoyed from the damage of the isolator at the bottom of the heat block which will be introduced by subsequent cleaning steps due to smeared material.

I replaced the NTC by a PT1000 in ceramic housing, which is assembled from the side of the heat block.


In this configuration I could measure a temperature drop in the nozzle tip of 10°C with respect to the nominal temperature (210°C -> 200°C nozzle temp). With fans working this drop becomes 2 - 3°C larger.


A drawback of this configuration is a noticeable noise in the temperature reading. But an uncertainty of ±1 °C is more acceptable than an unpredictable error of 50°C.

This may be an idea for an improved redesign.


#2

[quote=“hoh61”]I was trying to use PVA on a duql head K8400, but were always struggling with extrusion problems of th PVA. Additionally a sparling was noticeable when the extruder was in “standby”.

I realised that this effect was related to a too hot nozzle, as it was reported already earlier (viewtopic.php?f=62&t=15032&p=76296#p76296)

For my understanding the poor thermal connection to the thermistor is the major problem of the deviation. Furthermore I was annoyed from the damage of the isolator at the bottom of the heat block which will be introduced by subsequent cleaning steps due to smeared material.

I replaced the NTC by a PT1000 in ceramic housing, which is assembled from the side of the heat block.


In this configuration I could measure a temperature drop in the nozzle tip of 10°C with respect to the nominal temperature (210°C -> 200°C nozzle temp). With fans working this drop becomes 2 - 3°C larger.


A drawback of this configuration is a noticeable noise in the temperature reading. But an uncertainty of ±1 °C is more acceptable than an unpredictable error of 50°C. heating repair portland

This may be an idea for an improved redesign.[/quote]

In my opinion you have to use thick wire to connect the thermostat because thick wire have less resistance as compare to thin. IN these way the the connection are not getting heat up.


#3

Thank you for the feedback. My redesign is actually driving in another direction, but a short comment to the wiring:

thin wiring: relative high electrical resistance (in this case approx. 0,1 Ohm
thick wires: low electrical resistance: < 0,01 Ohm, cannot be measured directly

there is a physical principle, that good electric conductors are good thermal conductors. This is at least applicable of all metals.

So having a temperature difference of about 200°C between the hotend and the connectors at the PCB I get a low thermal flow between these two points.
Having thick wires is resulting in a good heat flow between these points, heating up the PCB and cooling down the temperature sensor. Depending on the configuration this can introduce a significant error in temperature reading.

On the other side: Using PT1000 the resistance is 1800 Ohms at approx. 215 °C, an additional 0,2 or 0,01 Ohm is irrelevant for the temperature reading and cannot be resolved with the hard- and software.


#4

The final design is here: http://forum.velleman.eu/viewtopic.php?f=64&t=18082