1 Topic by josh.aeauto (edited by josh.aeauto 2015-09-16 16:12:57)

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Topic: Discrepancy on bed heater reading

Okay, I posted a little while back about my bed heater (Airwolf) taking forever to heat up. This is somewhat of a continuation on that since I'm still having that problem too and it might be related.

Problem #1:
I have the bed running on 15v (up from the original 13.5). I bumped it up because it wouldn't reach 140C needed for polycarbonate parts. It would top out at 130C, and at that temperature things start to come loose from the build plate. Now it's doing the same thing with 15v - it will top out at 138C and takes FOREVER to go the extra two degrees to start the print (15 minutes +).

Problem #2
Because of the above, I decided to check the actual temperature of the bed. I am using a digital thermometer. The reading on the printer display says 140, but the thermometer reads 110 steady - and it's not raising at all, so that leads me to believe that the heat isn't just "not soaked in" yet. Actually, it's going down, not up! (It's down to 105 now after 10 minutes) That's a THIRTY degree difference!! No wonder I've been having adhesion problems!


At this point the printer I just built for 1/8th the price is working far better than the $4,000 Airwolf.

Has anyone else had a problem like this? Should I just look into upgrading the bed? Or am I doing something wrong? Thanks in advance!


*EDIT: By the way, the heated bed is made up of a rep-rap style aluminum heating plate underneath 4mm glass.

-Prusa i3 MK2s
-Airwolf HD2x w/ E3D v6 + Volcano
-Custom built Solidoodle 3 clone w/ E3D v6+ Volcano    -Solidoodle Press w/ E3D Lite6
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2 Reply by josh.aeauto

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Re: Discrepancy on bed heater reading

Just an update on this.

Here's the results of a tried print. I can't seem to get anything to stick.

In the picture, you see that the thermometer is reading 108C - this is measured from the print side of the glass; meanwhile the printer is measuring 140C.

http://soliforum.com/i/?HHkrtAW.jpg

-Prusa i3 MK2s
-Airwolf HD2x w/ E3D v6 + Volcano
-Custom built Solidoodle 3 clone w/ E3D v6+ Volcano    -Solidoodle Press w/ E3D Lite6
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3 Reply by elmoret

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Re: Discrepancy on bed heater reading

IR thermometers aren't super accurate for this sort of things, especially on reflective things like glass or shiny metals. It is also possible that the thermistor on the Airwolf is located closer to the heater - the top of the glass will always be cooler than the heater itself.

Not surprised that the printed you built is working better than the Airwolf, though.

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4 Reply by josh.aeauto (edited by josh.aeauto 2015-09-16 17:07:54)

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Re: Discrepancy on bed heater reading

elmoret wrote:

IR thermometers aren't super accurate for this sort of things, especially on reflective things like glass or shiny metals. It is also possible that the thermistor on the Airwolf is located closer to the heater - the top of the glass will always be cooler than the heater itself.

Whoops, i forgot to mention I'm using a thermometer with a thermocouple - it's taped to the glass with kapton tape.

I tried the theory of the printer's thermocouple being closer to the heater, so I placed my thermocouple directly on the heater (under the glass) and I'm still only getting 112C, a full 28 degrees less than the printer is measuring

-Prusa i3 MK2s
-Airwolf HD2x w/ E3D v6 + Volcano
-Custom built Solidoodle 3 clone w/ E3D v6+ Volcano    -Solidoodle Press w/ E3D Lite6
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5 Reply by elmoret

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Re: Discrepancy on bed heater reading

It is possible the thermistor is located right next to the coil of the heater. Also possible that the thermistor table is incorrect.

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6 Reply by josh.aeauto

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Re: Discrepancy on bed heater reading

Hmmm. How do I determine if I'm using the wrong table? Could it be that I messed something up when I changed the firmware for the hotends?

Maybe the silicone 110v heater on the other printer is just making me spoiled haha...

#define TEMP_SENSOR_0 -1 
#define TEMP_SENSOR_1 -1
#define TEMP_SENSOR_2 0
#define TEMP_SENSOR_BED 7
-Prusa i3 MK2s
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-Custom built Solidoodle 3 clone w/ E3D v6+ Volcano    -Solidoodle Press w/ E3D Lite6
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7 Reply by elmoret

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Re: Discrepancy on bed heater reading

Impossible to know without knowing what thermistor you have, and they're so small that nothing is printed on them. You could calibrate yourself and build a new table if you want, but it seems easier to just mentally compensate.

Filastruder - the robust, inexpensive filament extruder
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8 Reply by josh.aeauto

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Re: Discrepancy on bed heater reading

I might look into getting the parts to switch it over to 110 anyway, like the other. It can heat up to 140C in about two minutes. It would be about a $100 upgrade but worth it.

I have two or three E3D thermistors laying around, is there any problem with using them?

-Prusa i3 MK2s
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9 Reply by elmoret

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Re: Discrepancy on bed heater reading

No problem, just use the right table (5 in Marlin).

Filastruder - the robust, inexpensive filament extruder
E3Dv6 All Metal Hotend - the premier 3D printing hotend

10 Reply by josh.aeauto (edited by josh.aeauto 2015-09-17 19:49:44)

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Re: Discrepancy on bed heater reading

I ordered the parts to put in a silicone 120V, 360W heater. I replaced the existing rep-rap style 12v heater with an 1/8" sheet of aluminum and used the E3D thermistor included with my E3Dv6 that I used a thermocouple for instead.

I am now seeing temperatures of 140C on the surface of the glass (give or take 5C around the edges of the glass).

Does this, plus the fact that it was taking FOREVER to heat to their suggested temps, mean that the original heater is no good? It measures 1ohm at room temp, so I'm guessing it's a 140W heater? It looks just like this one: http://www.ebay.com/itm/8-4-X-12-6-Heat … 1106200264 The wires going to the thermistor were also severely discolored (a white wire is now brownish-black).

-Prusa i3 MK2s
-Airwolf HD2x w/ E3D v6 + Volcano
-Custom built Solidoodle 3 clone w/ E3D v6+ Volcano    -Solidoodle Press w/ E3D Lite6
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11 Reply by elmoret

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Re: Discrepancy on bed heater reading

I'm not sure its "no good", more likely just that Airwolf specced a weak heater. It looks like the build area is 88 square inches, in my experience you need 3 watts per square inch to hit 150C reliably. The SD2 had a 50w heater and could do 100C just barely, with 36 square inches of bed area. 140w on a 88 sqin area is about 1.59w/sqin, just slightly higher than the SD2's power density.

Printer manufacturers are motivated to spec weaker heaters because it lets them use cheaper electronics and power supplies. It is unfortunate, but common. Odd in this case though since the HD2x has a 320w power supply according to their specs, and the motors/hotend/electronics wouldn't pull much over 50w. Maybe their power supply isn't really capable of 320w.

Filastruder - the robust, inexpensive filament extruder
E3Dv6 All Metal Hotend - the premier 3D printing hotend

12 Reply by josh.aeauto (edited by josh.aeauto 2015-09-17 20:10:43)

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Re: Discrepancy on bed heater reading

Hmm, odd indeed.

One more thing to add to the list of under-specced parts on the Airwolf.

At least now I have a spare hotend AND heated bed! Haha..

On the note of the power supply, it can supply 23.8A at 13.5 volts according to the label, so that at least is correct

-Prusa i3 MK2s
-Airwolf HD2x w/ E3D v6 + Volcano
-Custom built Solidoodle 3 clone w/ E3D v6+ Volcano    -Solidoodle Press w/ E3D Lite6
Filastruder #1577