Thermocouple Faults to 2000

[Billsrf]

Thermocouple Faults to 2000 when I plug in my heater for nozzle. Unplug it and it works fine. What am I missing? I am using braided and shielded thermocouple wire all the way to the daughter board. I did not have this problem on my last machine and I am using all the same equipment and set up.

[dc42]

It sounds to me that you may have one of both of the following problems:

1. The thermocouple junction needs to be electrically isolated from the heater block. The thermocouples sold by E3D are isolated (unless faulty); many other types of thermocouple are not.

2. You may have leakage or a short between the heater cartridge and its metal case, or between the heater wires and the heater block.

[Billsrf]

@dc42 thank you, I will check both places and update you.

[Billsrf]

checked all wiring and then rewired machine making sure nothing crosses or was twisted. Still have the same issue. touch the thermocouple to the hot end, it faults. Used shielded wire and isolated the thermocouple. I am using an ssr with a 110v heat band for a heat source.

[dc42]

@billsrf, have you checked the thermocouple with a multimeter, for a short between the thermocouple wires and its casing? Ditto for the heater cartridge.

[Billsrf]

@dc42 I have tried 3 different TC's and it does it now as soon as I touch the TC to the extuder, even if the heater is unplugged, it shows 2000 and it faults. I have also swapped the sister board and have completely rewired the machine to insure no crossed wires. I am stummped!!!!

[dc42]

Do the TCs have the junctions electrically isolated from the casing? The ones sold by E3D do, but many others do not.

[Billsrf]

Here is what I'm using.They have worked flawlessly on my last 3 machines. Same batch, same set up. I'm missing something some where. Could it be a grounding issue?

[Billsrf]

[dc42]

These possibilities occur to me:

1. You have a short between the braiding of the thermistor and one of the two thermocouple wires, but you don't have that on your other machines.

2. The braiding is grounded on your other machines, but not on this one.

3. The hot end metalwork is grounded on your other machines, but not on this one.

[Billsrf]

@dc42 I have swapped all components 3 times. Still same result. I am using an aluminum enclosure to house everything including the power supply. Could it be a grounding problem with the power supply being grounded to the machine?

[dc42]

@billsrf said in Thermocouple Faults to 2000:

@dc42 I have swapped all components 3 times. Still same result. I am using an aluminum enclosure to house everything including the power supply. Could it be a grounding problem with the power supply being grounded to the machine?

If the PSU case is connected to mains ground and to the machine frame but the negative side of the PSU output isn't also connected to mains ground, that could be part of the problem. But if you use a USB connection to the Duet, see the wiki page on USB ground loops.

[Billsrf]

I unbolted the PSU and remounted it with non metallic fasteners, isolating it from the case. Now it works fine! Now, my question is, should I take the ground on the 24 volt side(-) to chassis ground to avoid this in the future???

[dc42]

The chassis of the machine and the PSU mounting plate should be connected to mains ground for safety. the PSU mounting plate is probably connected internally to the mains ground input terminal. So it would be better to leave the PSU bolted to the chassis, check that the chassis is connected to mains ground, and also link mains ground to the negative output of the PSU. This is what I do on my delta.

[Billsrf]

Is this what you are describing?

[dc42]

Not really, I am suggesting that you connect chassis directly to mains ground, and mains ground to the negative output terminal of the PSU. In this image you can see how I have done this on my delta.

[Billsrf]

@dc42 ok thank you. I will try that also. I did put a piece of captan tape on my thermocouple to isolate it. It works, but I’m afraid it will not read properly. I ordered a coupe of Cartridge TC’s from E3D to try out.

[wilriker]

@dc42 said in Thermocouple Faults to 2000:

[...] and also link mains ground to the negative output of the PSU.

What is the rationale behind this specific connection?

[Billsrf]

There isn't a rational thought behind it. I have tried everything I can think of. I wired it as per your delta picture and it is still faulting when i home the machine, and when the Zero sensor activates it goes in to a 2000c fault mode. I put a piece of captan tape on the TC's ring terminal to isolate it and I no longer get a fault. But, I am sure it will not read accurately.

[dc42]

@wilriker said in Thermocouple Faults to 2000:

@dc42 said in Thermocouple Faults to 2000:

[...] and also link mains ground to the negative output of the PSU.

What is the rationale behind this specific connection?

Safety, in case a fault develops inside the PSU. ATX PC PSUs always have this connection internally.