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Extruder Heat Profile

Posted by ankurb 
Extruder Heat Profile
March 12, 2008 07:24AM

We are calibrating the machine to run on HDPE, and during the extruder heat profile test, I got the following:

CAPA extruder vRefFactor set to 15
Heater output 31 is 102.0C after 699784ms
Heater output 47 is 127.0C after 273546ms
Heater output 63 is 145.0C after 151965ms
Heater output 79 is 169.0C after 151970ms
Heater output 95 is 169.0C after 60783ms
Heater output 111 is 169.0C after 70905ms
Heater output 127 is 169.0C after 60772ms
Heater output 143 is 169.0C after 60271ms
Heater output 159 is 169.0C after 60280ms
Heater output 175 is 169.0C after 61780ms
Heater output 191 is 169.0C after 60272ms
Heater output 207 is 169.0C after 60272ms
Heater output 223 is 169.0C after 60271ms
Heater output 239 is 169.0C after 60267ms
Heater output 255 is 169.0C after 62788ms

The max temprature was set at 250C. As you can see, the temprature did not go above 169C. The extruder exerciser also failed to heat it up to 200C. Have read similar posts here, and I have the following thermistor from RS

Glass-Encapsulated Temperature Sensor
RS Stock No. 484-0149 (10k ohm, upto 300C)

Cannot seem to figure out what the problem is. Have i got the wrong thermistor? My Cap is 100nF.

Re: Extruder Heat Profile
March 12, 2008 07:42AM
You don't say which electronics platform you are using. The PIC electronics cannot measure high enough temperatures for HDPE with the 10K thermistor. The problem is that the resistance becomes so low that the PIC cannot drive enough current. The solution is to use a 100K thermistor.

Re: Extruder Heat Profile
March 12, 2008 09:45AM
Well Nophead beat me to the answer.

I have also found that I was only able to get 220 Deg. C. with the 100k thermistor.

Re: Extruder Heat Profile
March 12, 2008 10:16AM
I ran into a similar problem. If you watch the heater LED, you'll notice that it'll flicker normally for most of the heat profile, then it'll start turning off for short periods and the temperature will level off. As far as I can tell, it's some sort of interaction between the over-temperature protection and a lack of resolution at high temperatures. To get reliable high temperatures, you pretty much need to switch out the thermistor and C3.

Have a look at these:
Re: Extruder Heat Profile
March 13, 2008 11:27PM
Yeah, I only made it to about 239. I then began fiddling around with the C3 value logged into the preferences page. I got it to register a cool 279--not actually that hot--and I got melted plastic. Unfortunately the plastic still wasn't hot enough to adhere correctly. I'm swamped with Dead Week and Finals right now so I haven't been working on it. I should really, actually, truly be doing my DiffEQ homework right now but I'm farting around on the forums. Who wants to do method of undetermined coefficients when they could be reading about world changing technologies that they are actually working on! :-)

Anonymous User
Re: Extruder Heat Profile
March 14, 2008 10:06PM

You do indeed need the 100K thermistor. This is because the Pic is not able to supply the amount of current that the cap requires when the 10k thermistor's resistance gets low . A 1 mfd cap works fine for me. read the discussion here for details and graphs.



Re: Extruder Heat Profile
March 15, 2008 12:01AM

Yeah, I wasn't clear. I have the 100k thermistor and have calculated the appropriate C3 for my beta and Rz. Thing is, it still isn't working properly. I'll try updating my firmware next to see if that does anything. Has been awhile. (shrug) Also followed that thread when it originated. Was a little unclear at that time what the issue was. I'm very clear now.

A frustrated
Demented Chihuahua
Anonymous User
Re: Extruder Heat Profile
March 15, 2008 12:10AM

Are you running the latest firmware?
I needed Andreas's firmware fixes as well as the thermistor fix.
It has been a while, but I seem to remember that not all capacitor values worked as advertised.


Re: Extruder Heat Profile
March 15, 2008 12:16AM

No, I don't have the latest firmware. I need to go get it. Pain, but necessary. I've been pretty swamped with Dead Week and Finals crawling down my throat. Not to mention having took on construction of *another* repstrap for my college. I'm getting pretty familiar with both electronics setups. Not familiar enough, as it happens, to make mine print properly. Still, it's fun.

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