Aluminium i3 extruder element issue (?)

[Msoucek@volny.cz]

Hello everyone,
I am a new owner of Aluminium i3. After assembling I have discovered weird issue: the heating of the extruder is on even if there is no command. It heats until overheating error is displayed. I have measured the heating element and it seems to be with one end shorted to ground. So if the MOSFET is switching to the ground then of course the extruder heating must be permanently on. I have ordered another heating element, but if I measure it, it is also one end connected to element case, therefore shorted to ground. My question is: is it normal, that these heatng elements are with one wire connected to case/ground or do I just have bad luck to two faulty pieces? Does anybody have the same experience?
Michal

[_kaktus_]

Hi Michal.


In my opinion, this situation is not correct.
I propose to check all connections. Additionally, pay attention if there is a short circuit somewhere.
On the forum you will find the schematic diagram of the controller board, may be helpful.

[Msoucek@volny.cz]

It also seems to me incorrect. In fact I have on my desk a brand new extruder heating element (not installed yet) which shows zero resistance on one of the leads and approx. 4 ohms on the second one (both measured in reference to the extruder body), just like on the old extruder. So I was wondering why and I tought it is perhaps normal construction property of the heating element. But in this case it would work only if the extruder is completely isolated from the printer body, which is not the case. That is why I am so confused...

[_kaktus_]

It's hard and hard to say anything more about your case.
I don't know your printer model.
But I checked if in my printer the heater have a common potential with the housing. They do not have an electrical connection.

I was surprised when you said that you have the GND potential connected to the printer body.

[Msoucek@volny.cz]

My printer model is i3 prusa aluminium. Since it has the frame completely made from aluminium, all the parts fixed to it are on the same potential. The control board is fixed to the frame using four screws through holes in PCB which, as I think, are copper plated and on GND potential. Unfortunately I cannot find the schematic, so any tip where to find it would be appreciated.

[_kaktus_]

Hello.


When you specify the model and version of the controller board I will help you find the circuit diagram.


I propose to use PCB distance.

21894.jpg (13.45 KiB) Viewed 12569 times

No potential should be connected to the printer housing.

[Msoucek@volny.cz]

Hello. Thanks a lot. Meanwhile I have found the schematic on reprap.org. My control board says "Sanguinololu Rev.1.3a" and it is published here: https://reprap.org/wiki/File:Sanguinololu_1.3a.png.

With the plastic distance it is a good idea, anyway in case that it is normal that the heating element has one pole connected to the cartridge case, it would be more important to electrically isolate the hotend, the heater itself, or the whole extruder. This will require some ceramic isolator I think. Because if not isolated, then according to the schematic, it will always send +12V to the case (either directly or through the heating element resistance.

Anyway I still think that the heating element case/cartridge should be isolated from the power leads. Can you possibly measure in your system the resistance between hotend/heating cartridge case and the power leads? I would expect that these should have no connection to the outer case, but as I have mentioned, I have on my desk already second piece, which shows 0 ohm between one lead and case and about 4 ohms between the second lead and case.

[_kaktus_]

Hi.


I have the same opinion and I will emphasize it again.
No potential should be connected to the body of the printer or any of its components.
Because it is simply dangerous.

If we connect any cables to the casing, it is only a protective ground (earth).
And this is the only exception. In addition, reasonable.

I have to talk about this topic with the Geeetech team when the Chinese holiday is over.

I have already answered your request earlier.

...
But I checked if in my printer the heater have a common potential with the housing. They do not have an electrical connection.
...

In other words, the resistance at the points of interest to you is infinite. Lack of conductivity.
Cables of the heater do not have electrical contact with metal parts of the head.

Do you make measurements when the cables are disconnected from the socket.?

[Msoucek@volny.cz]

Hello, Thanks a lot for your effort. That means I have bad luck and have second new heating element shorted . And yes, I was measuring it completely isolated. The first one after removing from the hotend and disconnecting from control board and the second one (brand new) just after unpacking from plastic bag. I have already ordered another one as it is not so expensive part. Anyway I think maybe making the hole in the hotend 1-2 mm bigger and inserting the element in isolated e.g. using a piece of kapton tape or film may also help. Kapton should withstand up to 400 degC, so 250 degC would not be problem.

[_kaktus_]

Hi

The problem is that we don't know what our friends from the Far East have made up for. And I expect that the next heater you buy will have similar features.
The fact that we have a similar opinion in this respect is not an exponent.
Tonight I will remove the heater from the new hot end which I own and show you a photo. You will have to compare.

Kapton tape should be a good electrical insulator. I would reconsider enlarging the hole. Maybe it can be avoided?

Have you already bought distance pins made of plastic