Dual Thermistors on Ramps/marlin?
November 18, 2013 02:19AM
So a little while ago I had my first huge printer failure. Low quality thermistor died and melted a hot end. After it happened I remember reading somewhere that it is possible to hook up 2 Thermistors to your hot end and if they dont agree (within 2-3 degrees of each other) the printer will shut down. For the life of me I cannot find where I read this now. I just replaced my hot end and wired up an extra thermistor (inb4 yes they are the same) and was wondering if anyone has done this or knows where the hell I read it? I refuse to melt another hot end because a sensor decides it would be funny.
Re: Dual Thermistors on Ramps/marlin?
November 18, 2013 03:08AM
hello,

does this help? I found it in the discussion bit on Github [github.com]

I *think* the second pin is called TEMP_2 in the pins.h file of your firmware folder... it will probably be -1 at the moment (disabled). smileys with beer
Re: Dual Thermistors on Ramps/marlin?
November 18, 2013 05:13AM
Another enhancement to Marlin would be to determine if turning the power on to the hot end actually changed the temperature.
i.e put some error checking in the PID control system

But perhaps the additional code to do this would load the Arduino too much.
Re: Dual Thermistors on Ramps/marlin?
November 18, 2013 12:28PM
Some discussion here:
[jheadnozzle.blogspot.com]


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Re: Dual Thermistors on Ramps/marlin?
November 18, 2013 01:31PM
If MinTemp and Maxtemp were set
shouldn't this have protected your extruder?
It should have turned the heater OFF if the thermistor failed
unless the thermistor failed indicating a bogus high temperature.
A thermal fuse in the power line to hotend it may protect it.

confused smiley
Re: Dual Thermistors on Ramps/marlin?
November 18, 2013 01:37PM
Quote
NewPerfection
Some discussion here:
[jheadnozzle.blogspot.com]

This is what I read. So basicly its a waiting game til marlin implements it? I'm not much of a programmer.

@cozmicray My thermistor did not completly fail at once so much as change values as it burnt out. indicating a lower tempurature than was actually present for long enough to melt the hotend.
Re: Dual Thermistors on Ramps/marlin?
November 18, 2013 03:34PM
I agree, this is a good idea. I had a thermistor come detached from the heater block which was then giving false temp readings (slightly higher than room temp). This caused the heater coil to continue to heat until it was red hot. Luckily I caught it before it caused any damage but it was a close one.
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