Temperature drop from 208 to 195

Hi guys, i have some problems with my hotend.
Already replaced the resistor, but still it doesn't want to heat up properly.

Sometimes I am pre-heating it for a print and when it almost hits 210 celsius, it suddenly drops fro 208 degrees celsius to 195.4 degrees celsius.

This happens a LOT.

I am running:
- Sanguino 1.3a
- Marlin v.1

Also did the M303 check and input the Kp Ki and Kd codes into the firmware. (I took the second run of M303 results).

Anyone know where I can check for more heating problems?
I'm still a pretty new user.

- Marinus

Is your thermistor seated correctly?

Hi yes, it worked before, but my hotend gives very inconsistent results. I have replaced the resistor and fitted it with aluminum foil also.

The thermistor is in the right spot.

Worked like a charm yesterday, only to get filament jams again today..

I pulled the plug, too much setbacks for more than a month. I'm done with this machine not working properly.



lazzymonk Wrote:
-------------------------------------------------------
> Is your thermistor seated correctly?

Edited 2 time(s). Last edit at 04/03/2013 02:18PM by Ohmarinus.

dont give up.

can you take some photos of your hotend? might help.

also, which type of filament are you using? if pla, do you have a fan blowing on the hotend body?

Hi, I'm using this variant:

[www.printedparts.nl]

It has a 6.8 Ohm resistor and a 100k Thermistor.
I have wrapped the resistor with alufoil, removed the metal ring and added a wooden plate between the aluminum block and the PTFE.

Also removed some of the black isolation gunk.

Heatbed doesn't reach 110 degrees celsius also by the way.
The heatbed is connected by using a relay that comes in between the heatbed on/off switch on the Sanguinololu and the 12v PSU and should be heating fine, but doesn't. Maxes out at around 87 degrees celsius.

Why the hotend takes so long to heat up and then drops a lot in temperature... no idea. I have also added a insulated wall on the left side and backside of the printer, and I have insulating foam underneath the heatbed and underneath and on the sides of the printer area to prevent some draft and cold radiation.

Also did run the M303 setting again with S = 210 and input the Kp Ki Kd values in the firmware and reuploaded again.


I measured the current and voltage:
10.5 V * 1.6 A = 16,8 W


Update
FInally after half an hour the hotend got to 210.
Started printing, but about 15 minutes into printing the temperature of the hotend drops to a staggering 192 degrees celsius.
I paused the printing. hoping I can continue, this always happens. I got the 7805 fixed a week ago and now this. I have NEVER been able to print normally with this machine

The temperature just drops constantly.

Can it help to to M303 PID autotune multiple times?

Edited 4 time(s). Last edit at 04/03/2013 04:05PM by Ohmarinus.

While power off, measure the resistance between the V+ of the psu, and the point where the extruder resistor connects to the mosfet. This is to say measure the resistor resistance but at some point far away from it. So it should measure 6,8R but not less. Wiggle resistor a bit while doing this. This is to check for shorts across resistor for example current flowing through the alu foil or block instead of going through resistor. Try doing same for heated bed resistance.

If there is a short like that across extruder resistor, then ofcourse mosfet heats up and at some point enters thermal protection, and cuts off the heater current flow, so the heater temp falls off also. This is also consistent with the voltage drop: an atx psu shouldnt fall in voltage to 10,5v with 2-3-4-5 amps load. Perhaps if you draw a hole lot more current, like a short, it then can go as low as 10.5v but otherwise wont get so low. Bottom line, i think you probably have a short somewhere, more probably rather across extruder than bed. Should be fairly easy to check either way.

Or a borderline condition to the above, where the bed just has too low resistance, draws too much more current than the psu is willing/able to supply (got bleeder resistor for 5v line?), and by this way voltage drops to 10.5v (or temporarily even less?) and then extruder resistor isnt able to keep temperature up enough coz voltage is too low. Try not using the heated bed at all, see if it works fine with bed disconnected. Sort of if the extruder is fine and the bed alone causes this. But this feels bit less probable, like a strech. Also could try changing the psu to check if thats the root of the problem.

Edited 1 time(s). Last edit at 04/03/2013 04:30PM by NoobMan.

Oh, do you really mean you have a hotend like this one? Looks like 2 washers sandwich with resistor in between and the empty space filled with silicone. Or is it an actual metal block there? I am not quite sure what is under that. Nvm i spoke too soon, i figured from the smaller picture of the hotend that is actually a block there. So its just looking for a short somewhere then.

Edited 2 time(s). Last edit at 04/03/2013 04:49PM by NoobMan.

I have been trying autotune PID three more times:

P - 76.38
I - 3.50
D - 416.74

P - 55.12
I - 2.26
D - 335.92

P - 224.02
I - 29.47
D - 425.75

Very inconsistent values. Is this normal?

Set with: M303 S215

Last time printing, the hotend temp dropped from 210 to below 180.

Here is a picture of the hotend, I hope you can see this:
[forums.reprap.org]

I have taken out the metal washer and put a piece of circular wood board to keep the heat from travelling up in a straight line.

Edited 2 time(s). Last edit at 04/03/2013 04:59PM by Ohmarinus.

Usually if the derrivative part is too big, it crashes the system. That is what i know from dynamic systems control. Derivative part is what gives it the responsiveness, makes the system react faster, but too much of that isnt good coz it can easily crash. All your derivative coefficients look kinda too big to me. Just as a note, i personally I dont use pid for extruder in reprap, coz i think its overrated on the account of PID name which is usually a very neat thing. But our pid is not actually pid, coz is implemented via pwm which is brutal and kinda defeats the main objectives of using pid, which is smoothness and stability. Using a DAC and a system to go with it like that is more complicated, but better in terms of smoothness, and i guess thats why the name is appreciated, but again thats not our case.

Change config.h of whichever firmware you use to use bang-bang instead of pid. Also in config if there is a PWM setting, make sure its 255 (not 170 or such). If you use bang-bang and problems are gone, then you can confirm that it is not about shorts and it is just about pid values. Imo should still check for shorts, aint that hard, and may be well worth the time doing it.

If it all is ok and it is only about pid values alone, could easily change the starting pid values in config.h. There are many approaches for this. Tweaking pid values is more of an art than a logic procedure, and you have to test a lot. My suggestion is to start with a PI only controller, that is to have derivative part = 0. Put like 2/3'rds in proportional coefficient and 1/3rd in integral and check if that is stable, e.g. no fluctuations or temp swings (if swings, decrease integral in favor of proportional). A PI regulator is capable to hit the target, but its slow, thats where derivative part comes in: derivative part increases the responsiveness of the system, makes it faster. Take some from the integral and put it in derivative, keep doing that and test the system untill the system is responsive enough, e.g. heats up in ~3-4 mins, but still does not overshoots too much e.g. not more than 4-6-8 degrees (at first target hit), and on top of all that, is responsive enough to deal with plastic flow.

Okay, I will test Bang-bang first, I have commented the line that creates PID settings, so I guess it's bang-bang from here on up.

The temperature seems to go up quicker on the hotend, with about 1.2 degrees celsius each time the monitoring checks it.

The heatbed is now set for 80 degrees still, that one still takes long to heat up, and heats up much slower too, but it's a bigger thing, but I had expected it to heat up faster anyway.

I have checked and so far I haven't found any short.
Maybe I will re-do the wiring for the beatbed, I have now normal connecting wires, should be enough, but maybe thicker wires will help? I don't know for sure.

Thanks for your tips so far, the hotend went from 45 to 145 in just 3 minutes, so I guess that is quick, but now from 145 and up it slows down a LOT.


Short test:
Temp was at 186, i pressed 'extrude 5mm' a few times and after five extrudes the temperature of the hotend dropped to 182.

This was while the hotend was heating towards 212, so it wasn't that the hotend was not being powered or anything.
Weird huh, I thought melting filament shouldn't cost so much heat in a hotend.


Great, because the filament jams all the fricking time the hobbed wheel is now filled with filament scraping and slips up all the time so I have to take apart the entire extruder and clean it all out.

I'm going to take a break for a week, buy another hotend from Ebay and see if I can find something better. I see a few nice hotends there, at least they LOOK good. Don't know if they actually work good..

Edited 2 time(s). Last edit at 04/03/2013 06:16PM by Ohmarinus.

Check these to have 256, not lower:
#define BANG_MAX 256 // limits current to nozzle while in bang-bang mode; 256=full current
#define PID_MAX 256 // limits current to nozzle while PID is active (see PID_FUNCTIONAL_RANGE below); 256=full current

Also, double check for mintemp and maxtemps stuff.

For further testing put instead 170, try like #define EXTRUDE_MINTEMP 195
so if it plastic gets too cold at least wont extrude anything, to not force extrusion, at least wont turn into other problems.

Does the extruder heats up properly with the bed disconnected?
Check for futher shorts between the extruder metal block and the thermistor wires, maybe it touches at some point and gets incorrect readings.

Hi, I have these values in there:

// PID settings:
// Comment the following line to disable PID and enable bang-bang.
// #define PIDTEMP
#define BANG_MAX 256 // limits current to nozzle while in bang-bang mode; 256=full current
#define PID_MAX 256 // limits current to nozzle while PID is active (see PID_FUNCTIONAL_RANGE below); 256=full current
#ifdef PIDTEMP
  //#define PID_DEBUG // Sends debug data to the serial port. 
  //#define PID_OPENLOOP 1 // Puts PID in open loop. M104/M140 sets the output power from 0 to PID_MAX
  #define PID_FUNCTIONAL_RANGE 10 // If the temperature difference between the target temperature and the actual temperature
                                  // is more then PID_FUNCTIONAL_RANGE then the PID will be shut off and the heater will be set to min/max.
  #define PID_INTEGRAL_DRIVE_MAX 255  //limit for the integral term
  #define K1 0.95 //smoothing factor withing the PID
  #define PID_dT ((16.0 * 8.0)/(F_CPU / 64.0 / 256.0)) //sampling period of the temperature routine

// If you are using a preconfigured hotend then you can use one of the value sets by uncommenting it
// Ultimaker
    #define  DEFAULT_Kp 76.38
    #define  DEFAULT_Ki 3.50  
    #define  DEFAULT_Kd 416.74

Will measure the resistance of the heatbed in a sec, also re-measure the resistance of the hotend at various point on the way between sanguino and hotend.
Furthermore I will today redo the wiring on the heatbed with thicker wire.

The wires running to the hotend should me more than sufficient.



Update:
Measured the resistance, it;s 7.5 ohms, same as just the resistor, so thats measured from the PSU V+ to the far end of the resistor.

The bed itself from + to - has 1.2 ohms resistance.

I am not so good with measuring, so some guidance is adviced



Also, see pic, printing started out good, but this time Filament Jam.....


NoobMan Wrote:
-------------------------------------------------------
> Check these to have 256, not lower:
> #define BANG_MAX 256 // limits current to nozzle
> while in bang-bang mode; 256=full current
> #define PID_MAX 256 // limits current to nozzle
> while PID is active (see PID_FUNCTIONAL_RANGE
> below); 256=full current
>
> Also, double check for mintemp and maxtemps
> stuff.
>
> For further testing put instead 170, try like
> #define EXTRUDE_MINTEMP 195
> so if it plastic gets too cold at least wont
> extrude anything, to not force extrusion, at least
> wont turn into other problems.
>
> Does the extruder heats up properly with the bed
> disconnected?
> Check for futher shorts between the extruder metal
> block and the thermistor wires, maybe it touches
> at some point and gets incorrect readings.

Edited 2 time(s). Last edit at 04/04/2013 01:17PM by Ohmarinus.

The resistance increases a little at high temperatures, but seems there are no shorts and measurements feel reasonable.

So i understand the extruder heater properly stays at high temperature now?

What caused this jam, did hotend temperature drop again? or what else?

When I took that picture, I had turned down the heatbed to 80 degrees celsius, but I want it to be 110 degrees!

No temp drops indeed, but when I put the bed temp to 85 the hotend starts having problems staying hot. I don't know why... The PSU delivers enough amps for both easily.

It's this PSU:
[www.ebay.co.uk]

Would the thin wires I use for the heatbed be too thin maybe?

Also, part of my frame broke when I was stress-testing it today, so I have glued it together now and I hope it will stay together properly...
I hope the PU-glue I have here is enough to keep it together, but I think it is good for now.

Furthermore, I am currently printing on a mirror, it seems the mirror is just too slippery for the ABS to stick to, so I will cover it completely with translucent tape I have here, lets hope the ABS sticks to it a bit better.

So the main problem is still here from the beginning:
Can't have the heated bed and the hotend on the desired temperature at the same time.

Hotend can be 210 when heatbed is 80.

When heatbed goes above 80, hotend temperature crashes.



NoobMan Wrote:
-------------------------------------------------------
> The resistance increases a little at high
> temperatures, but seems there are no shorts and
> measurements feel reasonable.
>
> So i understand the extruder heater properly stays
> at high temperature now?
>
> What caused this jam, did hotend temperature drop
> again? or what else?

Silly q: What thermistors are you using on the hot end & the bed (aka what did you choose in the marlin config)?

I doubt this is the issue, but could some of this be caused by the granularity of the thermistor tables?

Basically, if the thermistor can't provide a fairly close bunch of readings around the target temps, then PID control can't be very responsive, which could lead to wild swings in temp.

Knowing what thermistors you've selected will help in determining if it could be something like that.

Ok, they are 100k thermistors, I have chosen the correct ones in the firmware, don't worry

The swings aren't wild/quick btw, it's just constant, and then suddenly it drops without stopping the drop it very slow and very constant.

Here a video of that one magical moment when the machine worked for once:
[youtu.be]

Update:
Re-set the original Marlin PID settings, re-wired the heatbed, and the PSU wires, added a nice 'panic button' to the front of the machine, put a layer of tape on top of the printbed and am now heating up the hotend. It seems promising, but I am not testing it with the hotbed on yet, for now it has gone from 20 to 115 degrees in a minute. Hope it keeps going up that quick after 165 degrees.

Update 2:
Ok, I am now 27.64% into printing a isocahedron, bed temp 80º and hotend temp 205.8º
Didn't test if I could get the bed temp higher, the hotend temp tends to go between 203º and 206º which is an ok temp swing for me atm.

The only problem is that the first layer didn't adhere that well (adding a tape surface didn't work so well after all I guess...) so it will probably let go of the surface during printing. And I really set the heatbed well! Four times I checked all corners with a thin piece of paper inbetween. At school we have a Replicator x2 and I calibrate it a lot for the guys over there, the machine is overrated though. Better have a self-built machine where you understand what the machine does instead of having a machine being brought to you that doesn't do it's job flawlessly.

Oh, and I also taped the heatbed thermistor onto the bottom of the heatbed instead of having is in the gap in the middle, so it has less wear & tear when I level the heatbed up and down for print hight calibration.

Hotend hasn't jammed yet, and I'm at 40.02% of printing now.
Temperature seems stable.

Oh! And also cleaned out the hobbed wheel with aceton, the ribs in the pin were completely gunked with ABS scrapings because the hotend kept on jamming before.

Fingers crossed!

Update 3:
Worked! BUT, now it seems the hotend is getting hotter than before. It says: 205º, but is looks more like 230º, bridging a gap in my isocahedron worked before, but now the ABS was too hot to do it so it formed a dent on top because the ABS was too warm.

Will try again to print tomorrow with lower temperature settings. Maybe 200º for ABS printing. Also the shape seemed much harder to remove from the printbed, which gives me hope.


Final update #4:
Video!
[www.youtube.com]



Cefiar Wrote:
-------------------------------------------------------
> Silly q: What thermistors are you using on the hot
> end & the bed (aka what did you choose in the
> marlin config)?
>
> I doubt this is the issue, but could some of this
> be caused by the granularity of the thermistor
> tables?
>
> Basically, if the thermistor can't provide a
> fairly close bunch of readings around the target
> temps, then PID control can't be very responsive,
> which could lead to wild swings in temp.
>
> Knowing what thermistors you've selected will help
> in determining if it could be something like that.

Edited 6 time(s). Last edit at 04/04/2013 09:42PM by Ohmarinus.

There are a lot of 100k thermistors out there, and they all have different temperature graphs. That could of course explain the temp difference. Too much metal/ceramic glue/kapton around the thermistor can also create a temp offset like that of course.

The thermistors are "interchangeable" only in 0-150C interval. After that point, each thermistor has its own mind, even from same lot. If you really want accuracy you have to calibrate the thermistor with a thermocouple attached to the hotend, and change the values in firmware table in the temperature column. You issue a command to heat up to a temperature in the table row, that heats up untill the adc comes to that value, then read the thermocouple value and next update use the real value for that place in that table row for that adc value. No way around this: you either calibrate your own thermistor table and you can say your 230C= real 230C, or you have to settle to "some" reading that represent "some" level that starts and stops the heating, and read values can very well be +/-20C or even more error from real temperatures.

Congrats for your print

Can we assume that its all working ok -or there are any other problems left?

Alright I will look into the thermistor part, thought I dont know if a thermocouple cost a lot of money, considering I'd rather spend money on other parts.

I am still having difficulties with the heatbed though. It heats up slowly even though I have now placed very thick wire on the whole route from PSU to the relay to the heatbed.
It's what the seller told me to do, but still, thicker wire is not the solution.

Also I am now soldering everything but I would really like to convert to start using sockets of maybe model airplanes. I know in the model aircraft world they use a lot of nice sockets to connect the wires and make it easy to replace/alter configurations. And now that most parts are soldered and crimped together it's much harder to repair and perform maintenance.

I was refering to multimeters which can measure temperature and for this purpose they come with a thermocouple probe.

If you dont calibrate with something like that, then at least keep in mind that what shows 200C isnt the real thing, it could be 240C. There is no absolute reference anywhere. If you put in table a value like 1million degrees, that is what pronterface will report you: your hotend will have around one million degrees. Its very important to be aware of that. Fortunatelly in your case it shows less than it is. For example you seem to use like 200C for ABS printing, while the real temperature most likely is around 240C. If it would of been the other way, say it would of shown 240C when real temperature would of been 200C, then you would of tried extrude abs at real 200C, which means you would of tried to force extrude a cold plastic and could get something broken.

So you dont have an absolute reference and cant trust what your readings are like (not calibrated), then if you get a plastic and you dont know where the extruding temperature should be, try finding best temperature like the following, "by hand". Take away the bearing that pressures the filament onto the hobbed part, so you can push the filament by hand. Heat up the hotend at different temperatures, slowly increasing the temp setting, and try push the filament by hand - gently. As the temp increases, you will find a first point where the filament starts to be pushed fairly easier. Following that point, it becomes easier and easier, untill the effect levels down. Meaning regardless if you increase the temp, the plastic doesnt seem to be any different in pushing through. Basically it stops being related to temperature, and it is fairly easy to push through, and it doesnt become any easier after. This or the first part of this is a good setting, see what temp says it is and use that. Extruder will need least amount of force to do its job, so extruder will be happiest with that setting. Its pretty weird to try explain this, but i am confident that you will better feel it at hand and will understand when you try it.

If you dont try to find at least a good setting like that, then you just "guess" a setting, which you did. If such setting is before that "easy pushing" interval, then you dont realize it. You cant see that extruder has a hard job to do. But you are rather forcing the extruder coz it needs more force than it should. So that explains the chips of filament on your hobbed bolt area. Once you find its good setting, the hobbed area should be clear of abs chips and shouldnt require cleaning at all, not even once per year.

I am now conducting some printbed material research. I have made a printbed design and lasercutted it this afternoon.

2 different translucent acrylic ones, a white one (PetG) and a red acrylic one.

Trying the first one now I think the mirror loses it's heat quicker so I wonder what happend to the acrylic printbed, the heatbed seems to heat up quicker with the acrylic one.

All are 3mm thick, I will monitor warping, heat dissipation and other qualities, while printing with ABS.

I have made them the same size as the heatbed, the mirror I was using before, was slightly smaller so I missed out on some all-around printing area of around 15mm's.
Also the Y-endstop is very badly designed, it is keeping me from making use of the entire printbed so that will be one of the first things now I am going to re-do.

I will ask my friends is they have this thermocouple to see if I can somehow calibrate this thermistor. Otherwise, are there thermistors for sale that are already known for their properties of measuring above 150º celsius?

Thanks for your very complete reply!
- Marinus


Update 1:
Printing on Acrylic is a total disaster, the ABS adheres to it like there is no tomorrow.

Edited 1 time(s). Last edit at 04/05/2013 01:36PM by Ohmarinus.

Ofc there are better things for ~250C, like using matched pairs of hermetically sealed thermistors, and there are other sensors like RTC (Pt thin film), thermocouples, etc. But we reprapers are fatally attracted to cheapest things possible, and that seems incurable. However dont get me wrong, thermistors are ok for use in reprap, evidently just need to note that operating range is bigger than interchangeability range, and overall its not a bad solution. One just needs to understand the implications and how to deal with them, other than that thermistors are perfectly fine.

One of the implications is that when we exchange the extruder thermistor tables we assume our thermistors are "interchangeable" at 250C. They are interchangeable for bed temperatures, with a fair margin up to 150C maybe, but higher than that they stop being interchangeable, so our tables shouldnt be either. However absolute values dont really matter in the absolute sense, its all relative, even celsius scale itsels is relative. And just dont think if some1 on forum says "extrude this as xxx temp" and if you set on your printer "xxx temp" you will get that same temp, coz you wont. Beside that your temps should be consistent, meaning your xxxx temp today will be exactly same tomorrow, and thats what is important.

About print surface, i use some pcb blank (copper cald or what the name is), double sided. Its 1,5mm and very easy to cut into shape. I put kapton on one side, and i clamp them on top of the bed with paper clamps. After print i take it off to cool down and flex a little and the parts easily snap off. Tried metal plates like 1mm thick, but arent so good coz when it accidentally bends, it remains bent. The pcb is ideal coz it can flex alot and always recovers to the proper shape.

The glass/mirror is only good for pla so you can print pla directly on it, without kapton tape, that is sort of economy.

OKay I will keep it in mind, I am looking for another hotend anyway, this one sucks and I have seen reasonably priced ones on Ebay, are there any not so crazily expensive ones you can advise me?

I live in the Netherlands so shipping cost also play a role, I have found these few to look very affordable to me:

Good looks:
[www.ebay.nl]

Very cheap and mainland for me:
[www.ebay.nl]

This one looks very well developed:
[www.ebay.nl]


Ohhh and special mention:
[www.ebay.nl]
Dutch seller, free shipping, and it looks vert trustworthy!

Edited 1 time(s). Last edit at 04/05/2013 04:49PM by Ohmarinus.

I dunno what to tell you, i cant take decision for you. Imo, at least your hotend doesnt leak, and seems to insulate well to the upper part. Which is more than we can say about others. Regarding temperature and stuff, its just a resistor in a hole. If the resistor fits fairly snugly in the hole, its all good. If the hole is too big then nothing good comes from a hole thats just too big.

So, about temperature, the key part is where the resistor meets the aluminium block it sits in. What can go bad is the way resistor is mounted in its hole. If there is too much space between resistor and block, the thermal contact is poor, then resistor needs to heat extremely high and much more than the heater block temperature. Ofc in the context resistor with poor thermal contact wont be able to heat up the high enough nor fast enough. What i also found to happen is that this way resistor gets worn out fast, its cold resistance change, usually increases: i had 6R8 resistors i replaced measuring like up to 8-9+R on a rcl bridge. This is perhaps why your resistor measures 7,5 instead of 6,8, but its not clear: perhaps the 5% margin plus some 0,4 multimeter error could give that 7,5 too.

On short, what i would do, i would replace a brand new resistor there. When putting the new one in, i would fill the hole with some heat transfer compound (just not graphite or silver or ones that conduct electricity). Also i'd put some kapton on the leads of the resistor, so they wont have oxigen to oxidize. Also i'd put *one single* cylindrical rotation of kapton around the resistor. Not more, just a single turn, for best thermal contact. And then if the hole size fits to resistor, it should work nicely.

For now I have discovered that the thermistor is seriously giving out too low readings, this can also be due to the construction of the hotend, so I blame that, not just because it's easy to blame the hotend, but also just because the designer of the hotend has no sense of detail.

When I print ABS at 195 *in pronterface* the real temperature is higher because I can print just fine from 185 to 200 degrees celsius.

Also, when I am printing on a lower hotend temperature, I can even manage to get the heatbed to 90 degrees. After the current print I will try to even up the temp on the heatbed.

Currently printing this thing and the print is at 22.11% now and still going well, except the corners broke free from the print bed because I didn't turn on the heatbed.. I forgot. So now I turned it on during printing and goes to 90 degrees with no problem without having the hotend temp drop.
[www.thingiverse.com]

I have found an old tube of 'Curil' and will try to improve my hotend with that stuff later today. It is a liquid seal for engine blocks, I used to work a lot with four-stroke honda engines and tune, repair and revision them. Curil can hold a seal tight until 180º celsius, but it withstands temperatures well over that. Since I am not using it to seal my engine I will see if it has other usable properties and smear it on the aluminium block of my hotend. I have ordered two new hotends which will arrive somewhere next week so I have time to experiment and mess up my current hotend

And again...

echo: cold extrusion prevented

I'm going to be really anxious when my new hotend arrives!

Update:
Ordered this one, and will be here around thursday:
[www.ebay.nl]

Also ordered two new thermistors that are pre-checked and I have their heating tables, so I can at least rule some problems out if they also occur with the new hotend and thermistors.

Edited 1 time(s). Last edit at 04/09/2013 08:58AM by Ohmarinus.

I'm having a very similar problem, where my hotend won't stay heated up as filament is flowing through it. It takes a very long time to get up to temperature (though less time now in bang-bang mode). I'm gonna try a different resistor tomorrow but I wanted to know, how would one get the temperature tables for a given resistor, and how can that be used to update the firmware? How are PID values calculated? How can I test these—or, what would be an acceptable time for the hotend to heat up? I only have the little on in my RepRap Huxley to compare to, which heats up in a few seconds. The j-head hotend on my Prusa i3 is taking more than a few minutes to get up to 185°C.

If the heating of your hotend is very weak and needs all the power just to climb to 185C, it is normal that it will cool down when printing and is fed with new (cold) filament. Check if the connections of the heater are ok and measure the resistance R of the heater, then compute with the voltage U of your power supply compute the wattage P=U*U/R, which should probably be at least 25W, but better more. The hotend MOSFET should stay cool, if it ges hot while heating, the problem might also be a bad MOSFET. You can measure the voltage drop over the MOSFET between the Minus of the hotend output and the GND of the PS input, it should just be a few mV while the hotend is heating at full duty.

Haven't had a chance to check it yet but I will in a few hours once I'm done with work for the day. I'm guessing this is a MOSFET I can check with an infrared thermometer? I can use that to check the temperature of the hotend and the MOSFET. The heater resistor claims to be 40W, which should be more than sufficient, but I'm definitely not seeing 40 watts worth of heating happening here. If it's the MOSFET that's busted, does that mean a whole new RAMPS board?

Like I said I'll take a voltmeter to the sucker in a couple hours when I've got a moment to mess with it.

Okay! Just got a chance to measure everything. The heater resistor is a little below 15Ω, and the power supply is supplying 12 volts, so I have a pretty good feeling that this resistor is meant for 24-volt systems as with just 12 it is a little under 10 watts of power. That is almost certainly not enough.

The power supply I have has two outputs, so if I were to tie them together theoretically I could get 24V into the printer. As long as the RAMPS board won't freak out if I do that, that may be the best option since that would put me at 36 watts. I'm not sure if it's okay to just hook up the power supply like that though. Should I just get a new heater cartridge that's a lower resistance?