Weird temperature curve while heating hot end (423C)

Hello,
We have made our own hot-end and we where testing it, how hot we can get it. But when it reached the 423 degrees celsius something weird happend.The temperature drops but the heaters where still on. When we turned de heaters off the temperature dropt further till a certain point and then the temperature started rising again while the heater was off. We are using the newest marlin software. And a thermocoupler with a AD597. We thought because the arduino is 5v/1024 we could reach max 500 degrees. Does somebody know how to fix this problem?

Here is a link how the graph looked, shame I did'nt make a picture from the actual graph so we have drawn one to give you an idea. graph

Kind regards,
Tim

Hello,
Did today another test and made a screen shot of the Graph. We also looked at the code in marlin but we don't really understands were the problem lies. return ((raw * ((5.0 * 100.0) / 1024.0) / OVERSAMPLENR) * TEMP_SENSOR_AD595_GAIN) + TEMP_SENSOR_AD595_OFFSET; we thaught that the problems lies in the oversamlenr in this part of the code but we can not find what that number really did. Because we did the math and concluded that the samplenr being <1 till the 423°c and after the 423°c being >1 could give a dropping temperature while it is actually rising.
Hope someone could help us out

Kind regards,

Tim

What temperature is your sensor rated for? How hot can your heater run before it is damaged? It sounds like you are running far hotter than most people do.

Is there a way of printing the raw values? It will likely be a lot easier to tell what's happening from the raw data than the scaled numbers.

Hello,
I tried to get raw values but I can't find a way in marlin to do that. I knew in repetier you can use M105 X0 but this didn't work with marlin. Does somebody know how I can get the raw values? For the thermocouple we use a K-type and we found in the datasheet an maximum temp of 750 C so thats not the problem.
We where going this hot to test the max of our hot-end and than this weird temperature curve occurs so we are interested in what is happening..
Kind regards,
Tim

Hello,

We still looking for a solution? Has anybody an idea?

Kind regards,
Tim

what control board are you using?

We are using a Ramps 1.4 with the newest marlin software.
And voor de thermocouple board a AD597

I wonder if the poly fuse is tripping. It would still look like it was heating.