[sudo-discuss] 3D Printer - needs new heating element
Hol Gaskill
hol at gaskill.com
Tue Nov 12 14:35:48 PST 2013
the new heating resistors came in - to anyone who's interested in replacing the heating element, i'll be doing it before next week's meeting unless someone is itching to handle it themselves before then. It does require kapton tape from what i've read - anyone have a few inches of that stuff lying around?
Nov 2, 2013 09:58:15 AM, steveberl at gmail.com wrote:
Is the tape wrapped around the hot end anything special?
>Steve
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>On Saturday, November 2, 2013, Hol Gaskill wrote:
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al lashers is great! they don't stay open late enough for me to go there after work though, so i usually get this kind of stuff online.
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it is 12vdc so the LED warning is easily done. for AC you could still just use one LED at just under 50% duty cycle and it'll block the reverse current.
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i don't know about all that empirical stuff - say you want 3V at the LED at 30mA, that's a 9V drop over the series resistor and R=V/I=9V/.03A = 300 ohm resistor. could also just slap a chunk of 12V led strip down and call it a day - definitely bright!
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i would be curious to know if the problem resulted from simply being left on or what. the fan was not running iirc so that could have had alot to do with it, will have to check that as part of the repair - for now i'm just going to get these http://www.amazon.com/Resistor-Heating-Element-Printer-RepRap/dp/B00C44TBPA
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jake i'd be interested in learning more about how to tune the PID settings. no idea about the temperature sensing status since it stayed at room temperature, didn't think to use body heat or anything to test it but that'll be an easy enough check. i did not check the thermistor (or is it a thermocouple?) for continuity.
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cheers,
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hol
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Nov 1, 2013 05:45:36 PM, g2g-public01 at att.net wrote:
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Yo's-
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And/or you can take the existing fried resistor to Al Lasher's
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Electronics on University Ave in Berkeley and they'll find a
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replacement, either exact-same or very close (the tolerances on
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resistors used as heaters are pretty wide). If it's a 3 to 5 watt
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resistor it shouldn't cost more than a couple bucks.
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Al Lasher's is an oldschool electronics shop that everyone in SR
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ought to know about: their stock of raw component parts is
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fantastic, and the folks who work there have been around forever
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& know their stuff. You'll probably find stuff there that
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suggests new projects to do.
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Chances are if you bring in the heat sink with the resistor glued
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on, they'll also be able to tell you what kind of glue is needed,
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and they probably have it in stock along with the resistor.
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Re. putting an LED on the heating element:
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Good idea and will need a dropping resistor ahead of the LED,
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otherwise the LED will probably fry the first time it's turned on.
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If the voltage used to run the heater resistor is AC, then wire two
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LEDs together, one in reverse polarity with respect to the other,
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and they'll both light up.
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To estimate the value for the dropping resistor, measure the voltage
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input to the heater resistor and the current it draws (after you
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replace it with one that works), and compare with the specs for the
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LEDs you're using. If the dropping resistor or the LEDs get warm
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when in use (aside from ambient heat from the heater resistor), or
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the LEDs are excessively bright, substitute a higher value dropping
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resistor.
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If I was doing this, I'd just go empirical and use a large variable
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resistor in series with the LEDs, and turn it down slowly while in
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operation, until the LEDs light up to a sufficient degree (not dim
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but not too bright), then measure the value of the setting on the
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variable resistor and find a fixed resistor of similar or slightly
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higher value.
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Useful tools for these types of purposes:
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A resistance decade box, and a capacitance decade box. These let
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you do empirical tests by switching-in progressively different
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values of resistors and capacitors into circuits until you get the
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desired result. Lasher's probably has at least a resistance decade
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box in stock. The reason these are called "decade boxes" is because
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the traditional version has selectors with ten positions each, and
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the values of each selector increase by factors of 10 relative to
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the next lower selector on the box.
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The exception to the use of decade boxes is where a component
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handles a large power level, such as a heater resistor, or an
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electrolytic capacitor in a power supply. I'm guessing that your
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heater resistor handles from 3 - 5 watts, but it may be more. The
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resistors in decade boxes are typically rated at 1/4 watt to 1/2
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watt and are designed for testing signal/control/audio circuits
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rather than circuits that carry higher power levels.
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-G
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=====
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On 13-11-01-Fri 5:20 PM, Jake wrote:
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>I retract my assertion that you hadn't put any text in
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your email.
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as for the printer, it seems clear that you and steve are right
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that the resistor is burned out. I wonder what caused this - i
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haven't heard of it happening a lot bu on Nov 01, 2013, Jake wrote:
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Hol,
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you forgot to put any text in your post at all! please be
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clear of how
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you came to this conclusion.
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The heating element is a resistor glued into a block of
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metal on the end
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of the extruder. It has two wires which go to a connector
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a couple inches
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from it, and they go back to the machine.
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To test the heating element, one can unplug this connector
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and use a
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multimeter to measure its resistance. It should be
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something like 8 ohms,
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i don't know the exact value but 100 is too much and
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indicates it's bad.
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it was replaced a little while ago by a technician from
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the corporation
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that made it.
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If the machine is acting up about heating, we need to know
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whether the
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problem is with the heating or the temperature sensing. If
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the
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temperature sensor is reporting ambient temperature, it's
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probably
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working.
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if the temp sensor is working but the heating element
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isn't making it heat
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up, it could be the heating element (see test above) or it
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could be the
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connector near it, or the wires from there back to the
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main board, or
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where those wires connect to the brain.
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can you give more information about what you tried and
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what you observed?
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-jake
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>--
>-steve
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