Thermal Runaway with 3.0.6?  

Re: Thermal Runaway with 3.0.6?

A drop of 0.05 Volts at the connector is not a lot, but it really should not happen. However, that drop could be in the meter leads or in the meter itself and is probably insignificant.

When you measured the resistance of the heater cartridge, did you also check that the meter leads were not adding a resistance? Check the resistance of the leads by touching the probes together.

11.9V is about right; the rail is probably at about 12.1V. A 24 Watt heater cartridge is a bit on the low side - I think mine is running at about 27W. If you increase the PSU output by about 0.5V, that should be enough to compensate for the lower output of the heater.

Good call, Peter. I have an inexpensive auto-ranging meter (yeah, auto ranging was a mistake) and it appears that there is 0.2-0.3 Ohms resistance in the the leads, giving some variability in the heater power from 23 to 25W.

Is it better to replace the heater or increase the PSU output?

I've adjusted the POT to output 12.5V, up from 11.99V. When I run my fan torture test included upthread, the heater still can't quite maintain temp. During the test, the heater is at 215, gcode sets it to 220 and turns on the fan 100%. The nozzle temp falls very slowly now, instead of plummeting. I think that if this torture test is a worst-case scenario, this MIGHT be ok.

I'm still very interested in what the root cause is.

Re: Thermal Runaway with 3.0.6?

Curtis

OK, so you now have almost exactly 27W heating (5.6Ohm @ 12.3V that's 12.5V - 0.2V drop in the MOSFET).

You could push the voltage by another 0.2V which will push to 28W. Everything should still be very safe according to the RAMBo specs.

The bed heater is the only part pushing things @ 12.5V, but that is still well within the fuse rating, assuming the bed is 1 Ohm or greater (should be 1 to 1.2 Ohm).

Peter

Re: Thermal Runaway with 3.0.6?

I just started my first print sliced using the prusa flavor of slic3r downloaded today and at about layer 5 I got a thermal runaway error. I had some fiberglass insulation from a previous printer so I put some of that on the side of the heater block exposed to the layer fan and am trying the print again. On the knowledge base it is mentioned that E3D is coming out with a silicone insulator. Anyone know when this will become available?

Update

Quick update, insulating the hotend seems to have done the trick. I am now 5 hours into the print that failed earlier and the temperature is holding steady. I plan on buying the official E3D cover as soon as it is released but for now my makeshift insulation is working!

Re: Thermal Runaway with 3.0.6?

I am having this exact same issue.

I am printing the Batman symbol from the SDcard, when the front fan kicks on the temp drops until it hits thermal runaway and stops.

So it looks liek my options are use Tape or sock to reduce the cooling effect of the fan, figure out how to up the power of my PSU, or get a 40w heater?

Is this the right heater? 12v40w? http://e3d-online.com/Electrical/Heater-Cartridge-12v-40w

I really hope PRUSA will do something for me here I just bought this and now I have to come up with my own solution it seems. 🙁

Re: Thermal Runaway with 3.0.6?

Christopher

Firstly send an email to PR; they should be able to help. In the short-term, you can wrap with kapton tape or use a sock if you have either, or if you are feeling sufficiently competent, you can push the voltage by 0.5V - take the plastic cover off the PSU where the leads are and there is a small trimmer pot close to the terminals.

The other option is simply to slice your own models with fan speed set to a maximum of 60% until such time as PR get back to you with a solution.

Peter

Re: Thermal Runaway with 3.0.6?

Peter,

thanks

Just a little frustrated
Sent email to PR
going to try some Kapton tape tonight.

I have no issue with upping the voltage, but I may leave that as a last resort. Even though a small increase in voltage shouldn't cause an issue I rather not risk it if I do not have to.
I might just order the 40w heater if the Kapton tape doesn't work

thanks
Chris

Re: Thermal Runaway with 3.0.6?

Chris

There is a reason I didn't include the 40W heater as an option. E3D quote:

40w heater cartridges' also need a lot more supervision compared to 25w or 30w cartridges.

And although installing a 40W heater you will be approaching the limit of the 5 Amp fuse protecting the heater and other parts.

If anything, you would be better off getting a true 30W heater cartridge.

Peter

Re: Thermal Runaway with 3.0.6?

Peter,

What do you mean by"getting a true 30W heater cartridge"? What did I get with my printer, I thought the MK2 came with a 30w catridge.

Prusa support told me to lower the fan speed, which I did, but it didn't help with PETG, I had to remove the Fan Nozzle to get prints to work and now I am getting curling sometimes. I am trying to redesign the Fan Nozzle part to blow more air at the print and less at the heatblock, but so far nothing has worked.

I guess next step is to try and increase voltage. I understand that 3D printers require fiddling, but I feel as if that hotend should be able to hold temp even with the fan at 100%, this one struggles to hold 240 degrees even with the fan at 50%. Something must be wrong but I am not sure what.

Is it worth taking the heater cartridge out and reseating it? maybe it is not making good contact? maybe I need some better
Thermal paste?

Chris

Re: Thermal Runaway with 3.0.6?

What do you mean by"getting a true 30W heater cartridge"?

Chris

There are loads of comments in this regard on the forum, both old (Mk1) and recent (Mk2).

The specification of the heater cartridge supplied by E3D is 12Volt 30Watt. That specification calculates the cartridge resistance to be 4.8Ohms.

However, many cartridges have been supplied with a higher resistance and therefore lower power output. Couple that with the voltage drop across the heater output MOSFET, the heater can end up generating less than 24Watts. And that is not sufficient for the heater to compensate for fan cooling at higher temperatures.

If you can get a 30W (4.8Ohm) heater, you will not have the problem. You can increase the PSU voltage which will also increase the output power of the heater.

Peter

Re: Thermal Runaway with 3.0.6?

So peter, You allege that some E3D heater cartridges are not up to specification? So it is ok to increase the voltage to the heater cartridge if out of specification. E3D is the defacto hotend of choice and a high spec. amongst many 3D printer manufacturers. Any response from E3D ?

If the heater cartridge is out of specification, I suggest , contact E3D and get a replacement heater cartridge.

Re: Thermal Runaway with 3.0.6?

Chris

There are loads of comments in this regard on the forum, both old (Mk1) and recent (Mk2).

The specification of the heater cartridge supplied by E3D is 12Volt 30Watt. That specification calculates the cartridge resistance to be 4.8Ohms.

However, many cartridges have been supplied with a higher resistance and therefore lower power output. Couple that with the voltage drop across the heater output MOSFET, the heater can end up generating less than 24Watts. And that is not sufficient for the heater to compensate for fan cooling at higher temperatures.

If you can get a 30W (4.8Ohm) heater, you will not have the problem. You can increase the PSU voltage which will also increase the output power of the heater.

Peter

Peter

My Heater Cartridge does read 4.8Ohms, I measure the voltage at the connector coming out of the rambo and it reads 11.8v

Re: Thermal Runaway with 3.0.6?

I have found that the part cooling fan is cooling the thermistor side of the heating block. a temporary fix for this is either to turn off part cooling, or remove the small deflector duct from the front of the head. I have tested the mk2 with both configurations and it print successfully. the pla layer quality suffers a bit, but it will not shut off from runaway.

Re: Thermal Runaway with 3.0.6?

I increased the voltage so that it reads 12.5v at the output to the heater. So far in limited testing this seems to have solved my issue.

The problem with turning off part cooling is overhangs can turn to crap..

Re: Thermal Runaway with 3.0.6?

Chris

Generally with a full 30W heater cartridge, this problem does not exist. My heater is generating about 27W and there are no temperature drops when printing PLA with the fan turning on at 0.6mm.

For information, the RAMBo is rated up to about 28 Volts; the heated bed is protected by a 15 Amp fuse and usually draws on 12 Amps. All stepper motors are current limited. There is absolutely no problem running at 12.5V.

Peter

Re: Thermal Runaway with 3.0.6?

Peter,

it works better now and for PLA I am sure it will be fine, but with PETG at 245 degrees the fan must be left off or at the lowest possible settings

While it was preheating for a print with a target of 245 degrees I told the fan to run at 60 ( I don't know what percentage of max that is because the fan setting in the LCD goes over 200) it was unable to get above 235, it would go to 236 for a second or two and drop back down to 235.

I measured the heater cartridge resistance and it comes to 4.8ohms, I turned up the voltage. I even tried to adjust the PID, but nothing is a clear fix for this issue.

I ordered another 30w and a 40w Heater cartridge from E3D, if you know of somewhere I can get a better Heater cartridge let me know and I will buy it,
I also ordered a Sock from E3D and another type of heat wrap I found on ebay.

I am open to all ideas, I just want to get this fixed. It can be near impossible to get some of the more difficult prints to work with the PETG if I can not use the fan properly.

Re: Thermal Runaway with 3.0.6?

Chris

The fan is powered via PWM with values of 0 to 255, so 60 is just less than 25%.

The E3D sock will certainly help; E3D do sell quality stuff so it really is the best place to buy.

Peter

Re: Thermal Runaway with 3.0.6?

I have finished building my Prusa I3 Mk2 just a few days back and this is my first relatively large print attempt. After 10 hours of printing I got thermal runaway error. This doesn't make sense to me, the printer was able to maintain the temperature continuously for 10 hours, the shape of the part it was printing at the time of failure is the round pillar on the left of the picture, I feel that part would have reflected very little air back up into the nozzle. It is very frustrating to waste this much filament and end up with a failed print.

I will check all my cables for loose connections today and maybe use a hot glue gun to secure the connections in place so that they don't pop out of place.

Re: Thermal Runaway with 3.0.6?

I have got the same issue after 3 weeks of printing. Problem was bad termistor ( )
Prusa has sent me the new one free of charge. Great support.

Re: Thermal Runaway with 3.0.6?

So how did you confirm it was was a bad thermistor? I want to gather as much information as possible before I contact support.

Thanks