Question on thermister mounting

Hi, my first prusa is almost ready to start printing (need a cap, MOSFET, and endstops). I have my hot end essentially done, I am using wildseyed simple hot end. I have the power resister mounted to the aluminum via heatsink compound. But I am unsure of how to mount the thermister. Where and how should it be mounted?

Thank you

A kungfu mastah

Hi AKM!

I'm glad to hear you are using the Wildseyed (it's my design). Did you have a look at my build instructions on the wiki?

The thermistor glass bead need only touch the block AND copper MIG tip where they meet on the bottom. What I usually do is spread the wires about a half inch apart, and wrap then in kapton tape, right up to and including just a bit of the glass bead, to avoid any shorts. Three or four layers of kapton should be enough.

In my instructions, it shows me using Rescue Tape to secure everything to the aluminum block, but I don't do this any more, as it does not hold up when printing ABS (250C). Now I use kapton to wrap everything. About 6 layers is good, You want to totally insulate the block, resitor, and thermistor, but NOT the brass. that needs to be open to the air so it can bleed off excess heat.

I will be updating the instructions and pictures later this weekend when I build another tip.

Let me know if you have any specific questions beyond this.

-Wildseyed-

Thanks, so the thermister controls the current to the power reisister, which is what generates the heat correct?

Also what adhesive should be used between the aluminum block, and the brass coupling?

A kungfu mastah

Temperature is measured by the arduino, using the thermistor. When the temperature is lower than the desired setting, the arduino turns on a digital line that engages a MOSFET that drives voltage to the power resistor. Whe the temperature reaches the desired setting, the arduino turns the digital line off.

The aluminum is held to the brass using a set screw. If you want to maximize the heat transfer, you can apply thermal compound like what is used on PC heat sinks.

jcabrer Wrote:
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> If you want to maximize the heat transfer,
> you can apply thermal compound like what is used
> on PC heat sinks.

Arctic silver becomes quite conductive when heated so it probably a bad choice. Other cheaper heat sink compounds work well.

I work on the side as a PC hardware reviewer / tech writer and I have quite a few different high end thermal paste and hatve contacts at all the major manufacturers. I will have to run some test and figure out what works the best for our application here. Once I get my machine up and running I will get started on it.

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Charles Gantt.
Build blog [themakersworkbench.com] <---- my personal site
Build worklong [www.thebestcasescenario.com]

The last of the artic silver was used to mount the power resistor. I purchased some of the alumina for heatsinking the pololu drivers. Will this be sufficient for the aluminum block to brass coupling?

I would have picked up some Arctic Silver Thermal Epoxy for the heatsinks. That's what we use when adding heat sinks to the RAM on video cards when we water cool them.

---

Charles Gantt.
Build blog [themakersworkbench.com] <---- my personal site
Build worklong [www.thebestcasescenario.com]

I had some but the second part was dried out. Lucky I got enough for the power resistor. I got alumina because I'm on a budget ^^