Yo's-

And/or you can take the existing fried resistor to Al Lasher's Electronics on University Ave in Berkeley and they'll find a replacement, either exact-same or very close (the tolerances on resistors used as heaters are pretty wide). If it's a 3 to 5 watt resistor it shouldn't cost more than a couple bucks.

Al Lasher's is an oldschool electronics shop that everyone in SR ought to know about: their stock of raw component parts is fantastic, and the folks who work there have been around forever & know their stuff. You'll probably find stuff there that suggests new projects to do.

Chances are if you bring in the heat sink with the resistor glued on, they'll also be able to tell you what kind of glue is needed, and they probably have it in stock along with the resistor.

Re. putting an LED on the heating element:

Good idea and will need a dropping resistor ahead of the LED, otherwise the LED will probably fry the first time it's turned on. If the voltage used to run the heater resistor is AC, then wire two LEDs together, one in reverse polarity with respect to the other, and they'll both light up.

To estimate the value for the dropping resistor, measure the voltage input to the heater resistor and the current it draws (after you replace it with one that works), and compare with the specs for the LEDs you're using. If the dropping resistor or the LEDs get warm when in use (aside from ambient heat from the heater resistor), or the LEDs are excessively bright, substitute a higher value dropping resistor.

If I was doing this, I'd just go empirical and use a large variable resistor in series with the LEDs, and turn it down slowly while in operation, until the LEDs light up to a sufficient degree (not dim but not too bright), then measure the value of the setting on the variable resistor and find a fixed resistor of similar or slightly higher value.

Useful tools for these types of purposes:

A resistance decade box, and a capacitance decade box. These let you do empirical tests by switching-in progressively different values of resistors and capacitors into circuits until you get the desired result. Lasher's probably has at least a resistance decade box in stock. The reason these are called "decade boxes" is because the traditional version has selectors with ten positions each, and the values of each selector increase by factors of 10 relative to the next lower selector on the box.

The exception to the use of decade boxes is where a component handles a large power level, such as a heater resistor, or an electrolytic capacitor in a power supply. I'm guessing that your heater resistor handles from 3 - 5 watts, but it may be more. The resistors in decade boxes are typically rated at 1/4 watt to 1/2 watt and are designed for testing signal/control/audio circuits rather than circuits that carry higher power levels.

-G

=====

On 13-11-01-Fri 5:20 PM, Jake wrote:

I retract my assertion that you hadn't put any text in your email.

as for the printer, it seems clear that you and steve are right that the resistor is burned out. I wonder what caused this - i haven't heard of it happening a lot but miloh would know.

perhaps our machine has a bad solder joint on the transistor that turns the heating element on and off, and it got left on somehow? I remember a while ago (before the element was replaced i think) that the temperature was not very well controlled. surely there's an explanation somewhere.

There are PID values programmed into the heater controller, sent as G-code to the machine, which may be having an effect on the way the heater is controlled. That would be a software explanation. We should try to get more info about what the correct PID init string should be for our machine.

that init string lives in the config for the slicer, as it is inserted at the beginning of any gcode generated.

I expect miloh will help us replace the heating element, which is made of aluminum, a resistor, and some sort of heat-conducting glue i believe. The design is open-hardware so we should be able to find out the part number of the resistor and the type of glue if we want to replace it.

We should add an LED to the heater connector so we can see if it gets left on somehow. Actually that is one possible explanation - since the machine has no timeout function for the heating element, anytime a print is aborted before the G-code is completely executed the heater will be left on. It's supposed to be thermostatically controlled so it shouldn't overheat, but it will still cook the PLA inside the head into a hard resin that clogs everything up, if not burn out the resistor eventually.

-jake

P.S. Hol I read the discuss list on the web rather than letting it into my inbox, so i click on messages to read them. Yours looks like this:

http://lists.sudoroom.org/pipermail/sudo-discuss/2013-October/004279.html

there is no content there, although there is an HTML attachment which I didn't click on because usually there is nothing in it, and if there is the formatting is so bad it's pretty hard to read.

On Sat, 2 Nov 2013, Hol Gaskill wrote:

jake you forgot to read at all - this is what showed up in my inbox:

"Hi Folks,

The 3D printer needs a new heating element. Steve and I got everything fired up and ready to start singing dubstep, and then had to do a little probing to reveal the cause. Whoever knows what
kind to get, can you PM me a link to the specific model required? I'll go ahead and order a new one, or a few if they're cheap.

Thanks,
Hol
"

steve covered it - it's the heating element

cheers,
hol

on Nov 01, 2013, Jake <jake@spaz.org> wrote:
      Hol,

      you forgot to put any text in your post at all! please be clear of how
      you came to this conclusion.

      The heating element is a resistor glued into a block of metal on the end
      of the extruder. It has two wires which go to a connector a couple inches
      from it, and they go back to the machine.

      To test the heating element, one can unplug this connector and use a
      multimeter to measure its resistance. It should be something like 8 ohms,
      i don't know the exact value but 100 is too much and indicates it's bad.

      it was replaced a little while ago by a technician from the corporation
      that made it.

      If the machine is acting up about heating, we need to know whether the
      problem is with the heating or the temperature sensing. If the
      temperature sensor is reporting ambient temperature, it's probably
      working.

      if the temp sensor is working but the heating element isn't making it heat
      up, it could be the heating element (see test above) or it could be the
      connector near it, or the wires from there back to the main board, or
      where those wires connect to the brain.

      can you give more information about what you tried and what you observed?

      -jake
_______________________________________________
sudo-discuss mailing list
sudo-discuss@lists.sudoroom.org
http://lists.sudoroom.org/listinfo/sudo-discuss