Extruder constantly heats

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Joined: Tue Feb 28, 2017 9:19 am

Extruder constantly heats

Post by Jaran » Tue Mar 07, 2017 3:30 am

Hello there! After a few days of building I have finally gotten my priter somewhat close to the first print.

- I have a Geeetech I3 Prusa Aluminium printer

The issue: The extruder does not stop heating. As soon as I power on the printer it starts heating.

What I have done so far:

First off the problem was that the extruder did not heat at all. I did some wire checks and refit the wires. After this the extruder started heating(Can't runderstand how as I am 100% certain it was not due to a bad connection. Oh well, it heats.

After this I have done some meassurements to see if it all works as intended(see pictures below). The port where I should connect the extruder has about 6V +- constantly now, which it did not have before I refit the wires :?

Here is the port I connected the extruder to:

Thermostat connection(to the right):

What the display says:

The volt meassured at the extruder port(5-6V+-):

The resistance of the extruder at 27celsius:

Looks like I had some resizing issues... Here are all the pictures: http://imgur.com/a/ubtTu

The thermostat should be fine too as it does track the temperature as intended. Any ideas what might be wrong? Appreciate any help!


With some more fiddling around I got it back to how it was. The extruder does not heat at all now. Everything has been wired the same way the whole time, but disconnecting and connecting the wires seems to make a diffrence somehow. I swapped the ports so the bed was on the extruder port. While doing this the bed did not heat up like the extruder did, I could control it myself. The extruder though the bedport did not work. The voltage is as 12V on both ports aswell. The extruder port seems to not power the extruder even with 12V output, but it does automaticly heat up with 4-6V.

I can't really wrap my head around how it would heat the extruder to above its max limit with 4-6V, while it gives no sign of anything with 12V.

From some searching around I found out that it COULD be the MOSFET. Does this sound likely?

And yet another update...

Been following this guide: viewtopic.php?f=13&t=17117

While meassuring the resistance of the extruder I end up with OL no matter what range im aiming for mega oh, kilo ohm and so on). While I meassure the bed I get about 2 ohm.

While meassuring the voltage the bed got 0V as intended while it should be off, but the extruder has anywhere between 2-40V(this did not happen earlier, was around 4-7V last attempt). Is it safe to say its the MOSFET thats faulty? If so, could someone help me out with finding the right one?

Some quick searching for local stores that has mosfets I found pretty much only one: https://cdn-shop.adafruit.com/datasheet ... asheet.pdf
Is it useable?

Update: Got my hands on a new heating catridge wire and that solved the problem. New wire meassured to 4.2ohm, and there are no signs of wrong currents from the heating ports now. Yay :D
Last edited by Jaran on Tue Mar 07, 2017 8:31 am, edited 1 time in total.

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