Need some serious help with an external mosfet.

I am having an issue as my previous external mosfet never got warm (even at 110c) until it burnt up (burned me bad) and was the smaller version but now the new one is supposed to handle 5A more YET this thing gets too hot to touch at 55c. 1.3-1.4 ohm MK3 12v from a Melzi running Repetier firmware with a 24v power supply to the MK3 through the MKS Mosfet. Something is terribly wrong but I don't know what. I tested it with my limited abilities with probes that were far too small but even with them it was about 16A when it first started to heat up which is close since these long probes are only 18ga wire (internal resistance and all of that). Anyone have any ideas? I went from working perfectly to suddenly POP on the old smaller mosfet board to this HUGE one being the same. There is no way I can print like this but if the ohms and amps didn't change then what in the world could it be?

Oh, I did try and lower the MAX from 255 but it wouldn't even heat up this 330x330 heated bed until around 220 and even at that it went very slowly up (.1mm every second or two) but still burns you.

[www.aliexpress.com]

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I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.

... check the RDSON resistance and threshold value uf the new type.

MOSFETs stay cool even with high currents, if 100% switched ON/OFF (as used in bang-bang controlling) ... but heat up with much lower currents, if "hold" at a level (switching gate voltage too low) or used for analogue controlling with PID ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Quote
VDX
... check the RDSON resistance and threshold value uf the new type.

MOSFETs stay cool even with high currents, if 100% switched ON/OFF (as used in bang-bang controlling) ... but heat up with much lower currents, if "hold" at a level (switching gate voltage too low) or used for analogue controlling with PID ...

With bang-bang 255 it still got hot enough to burn flesh.

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I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.

... look into the datasheet of the MOSFET which activation/switching voltage it needs -- if same or more than your driving voltage, then it will heat ...

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Quote
VDX
... look into the datasheet of the MOSFET which activation/switching voltage it needs -- if same or more than your driving voltage, then it will heat ...

Being from China no references given but someone clued me in. The diagram shown from the seller's site (every seller shows the same diagram) has the wiring hooked up wrong. Do NOT use the BED out from the controller to the BED in on the external fet use the SIG side. He suggested that and I tried it and the over heating is gone. With so little documentation on these things even the diagram on how to use it is wrong. I am not sure what the BED side is for but I do know it isn't for our controllers to it. Our suspicion is that it is maybe for an analog voltage of some type and possibly of 5v maximum.

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_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.