2 Nov
2013
2 Nov
'13
6:55 a.m.
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(a)att.net wrote:
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:
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:
"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 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
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I retract my assertion that you hadn't put any text
in
your email.
jake you forgot to read at all - this is
what showed up in my inbox: