Thermistor question

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tom10122
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Thermistor question

Postby tom10122 » Tue Jun 05, 2012 7:16 pm

When you install the thermistor, do you put some silicone, then the thermistor, then more silicone or is it just the thermistor then silicone. I am thinking the first way would affect the thermistor accuracy.

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Re: Thermistor question

Postby Polygonhell » Tue Jun 05, 2012 7:42 pm

It might make a difference, but your not really measuring the actual temperature anyway. The temperature that matters is the one inside the meting zone in the hot end. What you really care about is repeatability and I don't think it would affect that.
You end up having to print and adjust temperatures just because of the variation in plastic anyway.

All I can say is get plenty of silicone in there to hold it in there, the way I lost my first hotend was the thermister creeping out of the hole, rather than suddenly showing a low temperature which I would have spotted, the temperature creeped up to the point the PEEK in the hotend melted.
My second hotend has a LOT more silicone on it.

tom10122
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Re: Thermistor question

Postby tom10122 » Tue Jun 05, 2012 8:22 pm

Thanks, i've heard of quite a few hot ends melting down, i dont want that to happen on my first print

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michaellatif
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Re: Thermistor question

Postby michaellatif » Tue Jun 05, 2012 10:35 pm

First put the thermistor in then 'glue' it in place. Second, I used Kapton tape around the outside to ensure that the thermistor would stay in place. Third, make sure that connections to the thermistor are solid, this is how I lost a hot end.
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Re: Thermistor question

Postby mhackney » Tue Jun 05, 2012 10:53 pm

+1 on the Kapton tape wrap. I used crimp connectors to attach the thermistor leads to the wires to eliminate the possibility of a broken connection.

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Re: Thermistor question

Postby DaGroundZero » Fri Apr 05, 2013 7:54 am

I melted my hotend yesterday. I think the thermistor backed out, so this time I put lots of silicone on it to help hold it in place. I also put there thermistor in before the silicone. I don't know if that had something to do with it melting or not. Try 2 today.

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Re: Thermistor question

Postby thosj » Sat Apr 20, 2013 12:06 pm

How do you guys "melt" the hot end? I cannot get mine above 200C or so no matter if I leave it full on all the time. Two 6.8 OHM supplied resistors, crimped AND soldered to both the series connection and connectors from the PS, supplied 12 volts from the 450 watt PS shipped with the H.1. I have a newer hot end, not the original H1 hotend, from Seemecnc. I have the resistors firmly in the hotend and I added setscrews to actually snug them some more. I have thermal transfer paste on them. I'm using a Vellman with the resistor changed for the extruder higher temp. I turn the pot all the way up. It heats to 200c and the Vellman never clicks off and the temp doesn't go higher. I turn the Vellman down and it'll click off at some point maybe 20% down from the top, but the hot end never gets above 200. This would seem to indicate my Vellman is built right and the R5 resistor is correct. I'm using a Klein mm200 and supplied thermocouple embedded 3/16" into the hot end aluminum to read the temp. The Klein seems accurate checking against anything else. It'll melt PLA OK, haven't tried ABS because I can't get anywhere near 230C recommended for that. I understand that the temp at the thermocouple embedded in the periphery of the aluminum body MIGHT be different from the temp inside the extruder tip, but don't understand why I can't get hotter.

So........what do I need to do to get it hotter? Not currently worried about "melting" my hotend, more worried how I can get it hotter. It seems there isn't enough "power" to get the hotend up to temp, to me, but I don't know. I don't remember for sure, but I think I hooked the hotend rersistors directly to 12VDC from the PS and it still never got to 230C.

Also, what about the cartridge heater elements now sold on Seemecnc?

http://shop.seemecnc.com/12V-40W-Heater ... -26601.htm

How would those work? Anyone tried those units? I guess for $5.50 each, I'll try a couple, machine up a new aluminum hotend piece for the 6mm diameter and see.

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Re: Thermistor question

Postby Polygonhell » Sat Apr 20, 2013 3:26 pm

If you can't get up to temperature there is something wrong.
Measure the resistance of the hot end when disconnected from the board, it should be in the 3Ohm range, if that's the case you probably have a PSU issue, test the voltage from the PSU when the Hotend is turned on. If that looks good test the voltage from the veleman board to the resistors when the Hotend is on.

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Re: Thermistor question

Postby thosj » Sun Apr 21, 2013 7:52 am

OK, something is wrong, I guess, 'cuz I can't get over 200C.

But........if two 6.8 Ohm resistors add up to 30 Ohms then that's what's wrong. Mine add up to 13.6 Ohms, which I think is right. Don't resistors in series equal the sum of all? How/why would/should I get 30 Ohms?

So......I have to check voltages again, but I think they're all 12 volts, plus/minus a little. What voltages SHOULD I have at all these places? Twelve, it seems, and I do, but I'll check again today. I have the hot end out and laying on an insulating brick all wired up and exposed, so I can check voltages. I'll be back, and in the mean time I ordered two of those 40 watt heater cartridges and I'll be designing up and making a new aluminum head to fit them.

Thanks

Edit 4/21 8:35 CDT

Resistance IS 13.6 Ohms

Voltage is 12.89 free, out of PS and out of the Velleman
Voltage is 12.24 running the resistors, right at the resistors
Hottest the resistors get, out of the hot end and free, tested with Klein MM200 thermocouple is 390F/200C, they never get hotter than that.

So why can't I get it hot enough?

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dbarrans
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Re: Thermistor question

Postby dbarrans » Sun Apr 21, 2013 11:27 am

That's not 30 Ohms, it's 3 Ohms. Actually closer to 3.4 Ohms. The heating resistors should be in parallel, not in series.

- dan

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Re: Thermistor question

Postby Polygonhell » Sun Apr 21, 2013 12:04 pm

Yes it sounds like you have the resistors in series they should be in parallel.


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