Thermocouple Question

[Lisa M]

Hi folks,

It would seem I've damaged the thermocouples on my school's Makerbot Replicator 1 Dual.  It seems really easy to damage and really expensive.

One of my students go really excited and said we could just make them easily because it is just two pieces of wire made of different material.  While the theory sounds right I told him I think it matters what the material is and the diameter of the cable in order to work with the makerbot board.  I don't really know because I am not an electronics person and have never been strong with general electricity knowledge.  However I wasn't too keen to try it with our own in house electronics stuff and risk damaging the printer further.  That idea is on hold pending further research :)

I looked for other thermocouples and found some as cheap as $1.00 on ebay but I don't know if they'd actually work with Makerbot or what the risks are. We are curious as to why a replacement thermocouple from Makerbot costs $55.00 since it is just made of two different types of wire.  Is it the extra insulation and connecters?  Could they really amount to such a hefty price tag? ...or is it something else? 

It seems I'm a bit "all thumbs" with this stuff and I'm worried I'll cause the same issue again.  I would love to have a cheap solution so I could have a few on hand but I'm not sure it is wise.

If you have nothing better to do after reading this post (maybe trying to avoid real work or maybe feeling especially generous with your time) I'd love to hear more information about the ins and outs of thermocouples.

 

[Nick Wimpney]

Ugh.. I just did some googling, and it looks like they've made their thermocouple junctions just by twisting the wires together. and crimping them in the brass lug.  I'm amazed that problems aren't more common if this is actually the case.

I would probably remove them from the lug, and weld them together, but unfortunately, that's probably beyond the average tinkerer's abilities. :/

I don't know if that $55 one is better in that regard.  If it's the thor one, it looks like the one referred to here: http://bilbycnc.freshdesk.com/support/solutions/articles/128882-makerbot-replicator-2-thermocoupler-upgrade-replacement

I'm not sure how they've done the junction, either, but _maybe_ they did it properly?

Personally, I would probably buy a cheap bare-ended (welded!) k-type thermocouple (I'm assuming K-type... Anyone know for sure?), and see if you can squeeze the crimped part of the stud back open to get the wire out, and then crimp the cheap one in.

It's probably a bit daunting though if you're not really DIY. :/

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[Julian Rendell]

I found this thread that has links to a couple of suppliers:

https://groups.google.com/forum/#!topic/makerbot-users/nuGXSFDOFJI

Although your student is thinking along the right physical construction, thermocouples have different characteristics dependant on which conductors are employed.  Take a look at https://en.wikipedia.org/wiki/Thermocouple - scroll down to the different types (‘E’, ‘K’, etc) - you’ll see a graph of voltage change per temperature change which differs based on the conductors used. You could use any thermocouple with the right temperature range but you’d have to adjust the lookup tables/formula used in the makerbot firmware to convert the voltage to the correct temperature.

It seems the rep 1 uses a ‘K’ type thermocouple (https://en.wikipedia.org/wiki/Thermocouple#Type_K).

You could try taking the machine to Lee’s electronics and see if they have something usable in stock.

Personally I’d also go for one that is electrically isolated; if your heater power were to short to the extruder block I suspect it’d destroy your controller electronics.

Good luck!

Julian

[Derek P]

Not sure why a thermocouple would need to be expensive. Here's one on Robotdigg for $1. Digikey has them for about $12.

http://www.robotdigg.com/product/58/K-type-Thermocouple

-Derek

[Nick Wimpney]

I'd agree in general, but in a lot of cases electrically isolated will also be more thermally insulated, which isn't ideal.

Something like a thin layer of kapton, or thermal epoxy would be good, though.

To view this discussion on the web visit https://groups.google.com/d/msgid/3d604/B406E32E-5A2C-4134-B416-7ABE53082943%40gmail.com.

[Lisa M]

Thanks for all the feedback folks.  Info is appreciated.

I know so little about electronics that I get easily lost out there on the internet trying to find answers.

I did breakdown and buy the expensive thermocouples because they are supposed to be a sure thing ...however my troubles still continue.

May be time to send my replicator to the graveyard.

On Tuesday, 16 June 2015 17:19:58 UTC-7, Lisa M wrote: