Hot End problems

Hi can any please help,

I have built a REPRAP Mendel pro for use in a school. Everything works great apart from the hot end extruder. The original build was shorting out and the wire melting on the cable so I reordered all the components and started again.

Problems encountered this time.

The 2R7 heating resistor brought the temp up at first but then started glowing and then stopped heating up after several attempts to increase the temp further. Is it normal for the heating resistor to glow or is that a bad.sign?

Please any advice would be grateful.

Yes, glowing is a bad sign!
Either the temperature is too high or it is not fit snugly into the hot end so that the heat is not being transferred.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

2R7 ..... err thats leaning towards overkill for a heating resistor
@12v that resistor is trying to dissipate 53watts and if you are running a 24v powersupply then it'll be trying to dissipate 213 watts,

i would suggest a 4R7 resistor or better yet a heater cartridge

Thankyou for the replys.

The 2R7 resistor was supplied from a RepRap supplier and is on the WIKIpage on how to build a Mendal pro. Is this a mistake from the supplier as I have followed all instructions 3 times to make sure there was no mistake made. Does anyone have any idea how to get this hot end working from this situation? Is there an already built Hotend off the shelf that could help as I am trying to get this machine up and running so students can use it as soon as possible.

At the very least you need a new resistor as I'm pretty sure you fried the one you have when it was glowing...

But you also need to figure out WHY it was glowing...

a) (on a J head style hot end at lest) If you have the resistor inserted correctly, and it's insulated properly, I don't know how you could even see the resistor...

b) It should never get hot enough to glow! If your hot end was not heating up, there's definitely an issue conducting the heat from your resistor to the heat block... You should use a thermal paste or cement to take up any gap between the resistor and heat block.

I would personally swap out the resistor for a 4R7, the 2R7 is most likely roasting and dying