Spurious heater faults and how to avoid them

dc42 · 1 Oct 2016, 18:29

Hi Maurice, those auto tune results look reasonable to me. It's up to you whether you use S=0.8 or 1.0. If you think you will need the full power to extrude at maximum rate, use S1.0.

Here are a couple of tests you might like to do:

1. Heat the nozzle to operating temperature, place it close to the bed, then turn the print cooling fan full on and check how much the temperature drops before recovering. Then turn the fan off and see how much the temperature overshoots before recovering.

2. Heat the nozzle to operating temperature, then extrude plastic continuously at the maximum rate possible, and see how much the temperature drops before recovering. Then stop extruding and see how much the temperature overshoots before recovering.

You are looking for the temperature drop and overshoot to be well under 10C in both cases. I am working on a new firmware release in which this figure of 10C is configurable.

elmoret · 1 Oct 2016, 18:49

What's the resistance of your heater?

Merlin · 2 Oct 2016, 15:33

David,
I will try the tests you suggest.
But in any case I have insulated the hot end with heat resistant material so that it should not be affected by the print cooling fan.
Elmoret,
Resistance is 15.7 Ohm, which I calculate at 24V is 36.7W
Heat up is pretty fast.
Maurice

dc42 · 2 Oct 2016, 16:37

I guess the higher than usual gain is due to your insulation then.

Merlin · 2 Oct 2016, 17:25

Test Results @ S0.8

Fan Test
220 C down to 214.4C then up to 225.8C
i.e. -5.6 + 5.8C
PLA Extrusion Test
22C down to 216.3C then up to 223.5
i.e. -3.7 + 3.5C
Results look pretty good to me.

N.B tried with S1.0 but hot end could not reach 220C in acceptable time, slower enough to 216.1C ?

dc42 · 2 Oct 2016, 18:02

Looking good!

dcaron · 3 Oct 2016, 01:22

@dc42:

dcaron, have you looked in the Console page of DuetWebControl or PanelDue to see the cause of the heater fault?

If you still get heater faults with the heater off, then it must be registering a disconnected thermistor. A possible workaround is to connect a resistor of several hundred Kohms in parallel with the thermistor. This will increase the reading at low temperatures.

After you select a higher setpoint temperature, there is no check on heating rate until twice the heater dead time has expired. So this should get you to 60C without faulting.

Another possibility is to use a thermocouple or PT100 instead of the thermistor. These devices cover a wide temperature range without sacrificing resolution at the ends.

HTH David

Thanks for all your answers.

I did install a parallel resistance and now it's registering a temperature which is obviously off. I don't mind at the moment and I should get the right setting by trial and error.
I do agree it will be better with a pt100 or thermocouple. I now realize I should have gotten the pt100 daughter board with my preorder along with a mini IR probe. Unfortunately, the themocouple connection on a Dyzend is threaded (which is good) but is not compatible with other standard pt100. They do have an adapter for an Ultimaker style pt100. I don't know where I could get a compatible rtd at a decent cost.

Now to get printing…

Merlin · 7 Oct 2016, 07:19

In the Web inrterface 'Paused' the printer and set Heater 1 to 0 deg C. while i was out.
On 'Resume' rest Heater 1 temp but forgot to turn down printer Fan so caused a heater 'error'
"heater temp rising to slowly"!
So tried to reset heater with M562 H1 as per the notes - no apparent result.
So checked RepRap Wiki on g-codes which gave syntax as Pn not Hn
So tried M562 P1 - still no apparent result.
but then noticed in Web interface that Heater 1 was 'inactive'
So tried T0 and then all was well.
Whatever the M562 correct syntax is it looks like Hot End then has to be re-selected!?

dc42 · 7 Oct 2016, 07:41

Yes the heater is turned off when a heater fault occurs so you will need to send a command that turns it on again after resetting it with M562 P1.

I plan to do the hot end heater tuning with the fan both off and on at some point.

iDevelo · 18 Oct 2016, 14:51

This stuff will help a lot:

https://www.fasttech.com/products/1040/10023411/5061400-heating-block-nozzle-insulation-cotton-for-3d

Costs next to nothing but will save you all the headaches especially when layer fans turn on.

I'd advise it on a volcano style block.

curieos · 27 Oct 2016, 22:58

I've been having faults during prints. Its all sporadic, but the time I saw the error it was an excursion error that said the temp changed by more than 10C. I just changed my config.g file to allow up to 20c change and I wrapped my heater block in kapton (I have no other forms of insulation).

I was using an E3D hotend in my Kraken for a while and I recently switched to one of my volcanoes. I'm still not sure why, but I had 0 issues with the E3D. Some differences I noticed are the silicone sock I made for the E3D block, and theres a recent issue with my water cooling setup leaking, but I changed the tubes this morning and it still had the problem. I'm hoping its just an issue with when the AC in my apartment kicks on and that this kapton will fix it (I also added 1/3 of a chamber on the side of my printer to try to eliminate some drafts). I'll post whether this appears to fix my issues or not.

curieos · 29 Oct 2016, 15:29

Turns out it was just a wiring issue, one of the crimps wasn't properly done.

Merlin · 15 Nov 2016, 11:51

For multiple extrusion with a duel Chimera type hot end, the biggest overhead is that,
on every layer, hot end 1 has to cool down to standby temp, while hot end 2 heats up from standby temp to working temp.
So the objective is
a) Have minimum difference between standby and working temp.
b) Take minimum time for cool down and heat up process.
Can this be achieved when PID tuning is enabled or would i be better off going back to the 'old' way of working?
I'm using 24V, 37W heaters
Thanks

dc42 · 15 Nov 2016, 12:48

@Merlin:

For multiple extrusion with a duel Chimera type hot end, the biggest overhead is that,
on every layer, hot end 1 has to cool down to standby temp, while hot end 2 heats up from standby temp to working temp.

You should not be waiting for the active hot end to cool down to standby temperature, just for the new active nozzle to heat up (which takes less time on most systems). The M116 command has optional parameters specifically so that you can achieve this.

T3P3Tony · 15 Nov 2016, 12:49

The PID tuning aims to prevent significant overshoot at the expense of approaching the target temperature more slowly than is possible with more aggressive parameters, that said you can modify the parameters to meet your needs. If you are ok starting printing without the temperature stable then you can be more aggressive.

When I was experimenting with chimera I found it was the cool down time that limited the tool change speed rather than the warm up but that was ages ago before PID tuning in the Duet. I ended up making holes in the M90 fan duct to blow on both heater blocks so that they cooled down quicker, even though that meant they heated up slower.

Cheers

Tony

Edit, David got there first

Qdeathstar · 12 Oct 2016, 18:53

When I issue a M562 H1 I am able to clear the fault, but it doesn't seem like the web interface turns on the heater once I set the temp back up.

It will show it being set to 230, but the temps act like the heater is off

Using v1.16

dc42 · 10 Dec 2016, 20:05

You need to re-select the tool, e.g. send T0.

Qdeathstar · 20 Feb 2017, 23:12

Hi. This is should be a simple question and i think i already know the answer. I am printing a very small part and need my fans running at max and when they first come on they knock about 20c off the hot end temp, so i think just for this small part i want to increase the fault delay so i can get the part printed….

elmoret · 21 Feb 2017, 00:13

Best bet is to ramp up the fan speed, do it before the print starts if you absolutely need 100% even on the first layer.

deckingman · 21 Feb 2017, 08:33

Tuning the heater with the fan fully on may also help.