Steve
On Saturday, November 2, 2013, Hol Gaskill wrote:
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.
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.
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!
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
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.
cheers,
hol
Nov 1, 2013 05:45:36 PM, g2g-public01@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
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.
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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.
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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,
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.
>
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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.
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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.
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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
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.
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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.
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-G
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=====
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On 13-11-01-Fri 5:20 PM, Jake wrote:
>
>I retract my assertion that you hadn't put any text in
your email.
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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 bu on Nov 01, 2013, Jake wrote:
>
Hol,
>
>
you forgot to put any text in your post at all! please be
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
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.
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it was replaced a little while ago by a technician from
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
whether the
>
problem is with the heating or the temperature sensing. If
the
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temperature sensor is reporting ambient temperature, it's
probably
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working.
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if the temp sensor is working but the heating element
isn't making it heat
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up, it could be the heating element (see test above) or it
could be the
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connector near it, or the wires from there back to the
main board, or
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where those wires connect to the brain.
>
>
can you give more information about what you tried and
what you observed?
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-jake
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