Extruder thermistor broke

Hi there, I’m hoping someone can help me out.

My 100k NTC that goes in the small hole in the heater block recently broke and i’m struggling to source a replacement as the velleman spare parts distributors in my country have proven unreliable.

I bought another one off eBay, but the glass bead was too large (2.3mm) and wouldn’t fit in the hole.

I wanted to ask 2 questions:

  1. are there any problems that could occur from using a third party NTC (ie not the one that official comes from velleman) as I understand different thermistors will have different temperature curves, and are there any ways around them?
  2. does anyone know which thermistor comes with the kit so that I can source it elsewhere? or at least the diameter of the glass bead or hole would be very helpful!

Thank you very much in advance!

There should have been packed in the kit
You can check the Velleman website.
This is offered as a spare part.

I accidentally broke one during assembly and none of the distributors have them in stock, i’d have to wait over a month.

and not to be rude, but you haven’t actually answered either of the two questions I asked.

for a 3d printer design that’s based off a reprap, i’d like to think you wouldn’t be constrained to only purchasing Velleman parts.

I did answer one of the questions
If you go to it’s webpage you can get the specs and match it that way to find another one.
However I would this it would be best to use the correct part for the machine.

As for the other question I’m in the USA I have no idea of where you are so I have no idea of what is around you.

I apologize I was just trying to help

none of its specs are offered by velleman on their website or by any distributors. the only information given is that its a 100kohm thermistor for the k8200, unless i’m missing something here
there are various thermistors with different properties such as their beta value and the size of the glass bead etc.
this is where i’ve been getting most of my info on them: reprap.org/wiki/Thermistor

What i really wanted to know is either the manufacturer/model-number for the ones supplied with the kit or the diameter of its glass bead and whether or not using an alternative that can fit into the hole is a viable option?

Thank you for taking the time to reply Wrong Way, sorry i’m a little frustrated with trying to find this part - spending £700 on a kit and being unable to source a part that only costs a pound or two to get it working again is annoying to say the least!

I understand you being frustrated.

Lets try this a different way.
Velleman’s Part number is NTCMJB2/SP.
Just looking at the part number tells me it’s a NTC Part Number.
the /SP I think stand for Spare Part.
Searching for just NTCMJB2 bring you back to Velleman.

How ever I did a search looking for NTC MJB2.
I first list gave me the specs and what the numbers were all about (info below)
The next few listings were pages on Ebay.

MJB2 series NTC thermistor is one where the thermistor chip is welded with leads by alloy soldering process, then partially treated by glass sealing. The element has a bead form with good stability, small size and rapid response.

The suffix number of MJB (0, 1, 2, 3,…) represents the dimension of glass head. The characteristics for a series of products with different suffix are expressed same. So, no difference is made in the introduction to this type.

Like I said I have no idea of where you are but maybe you can find on in your area.

Hi bashraf,

you’re going about this the wrong way (no pun intendend!). You already found your way to the RepRap wiki, now it’s just one step further.

In the Marlin firmware, the thermistor is specified by a type number, which is 5 in this case. The type no. is used to select a calibration curve. There’s also a lot of documentation in the code, which gives “ATC Semitec 104GT-2” as one possible part number for this type. Others are e.g. #1 for Epcos 100k thermistors and #7 for some type from Honeywell, so if you mount a “wrong” thermistor, you can easily correct this in the firmware.

In many RepRap stores, you’ll find thermistors with this type number specified, so you don’t have to dig through the tables to find the right one.

As for the size: did you throw away the old one? Should be easy to measure it with a calliper, or alternatively measure the hole.


kuraasu, thank you so much!
I googled the ATC Semitec 104GT-2 and it seems to be just right - it’s got a 1.35mm diameter (the hole seems to be 1.6-7mm) and operates in the right temperature range

PLUS I can order it from mouser who have loads in stock

Thanks again to everyone who offered advice, it’s really appreciated!

Also, it is possible to use the larger thermistor with the stock K8200 hot end.

I happened upon the same situation as you, i.e. buying one from eBay with a huge diameter (noticed first after receiving it). My solution was to align the big one over the opening of the hole and then wrap the hot end tightly with Kapton tape; in my case the 5 mm narrow one (also bought on eBay). This has the added benefit of protecting and fixating the thermistor, as well as providing thermal insulation. Worked like a charm. (Now I have swapped the stock hot end for an E3D v5 using kuraasu’s adapter, and couldn’t be happier …)

This specific part (and just about any part for the 8200) is available from CPC see https://cpcireland.farnell.com/velleman-kit/ntcmjb2-sp/spare-thermistor-ntc-extruder/dp/HK01405
(edit… sorry I only just realised this is NOT from march 2019!!!)