1 Nov
2013
1 Nov
'13
5:45 p.m.
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(a)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
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