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Thermal sensor -thermistor 12V or 24V  

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ludodg
(@ludodg)
Estimable Member
Thermal sensor -thermistor 12V or 24V

hello,

I have some older material in my spare box.
Is there a way to find out if a thermal sensor is 12v or 24V?

I know there is a way to recognise the 24V Heatsink by measuring the resistance.
Can the same be done with the thermistor? thx!

Posted : 09/10/2020 4:32 pm
RedDawg
(@reddawg)
Reputable Member
RE: Thermal sensor -thermistor 12V or 24V

It may not make a lot of difference. From what I read, most thermistors are manufactured with at least a 100% safety factor, meaning one "rated" for 12 volts would probably still be functional at 24 volts. The calibration would be different for sure, but that's a different part of the circuit. There is probably a trim capacitor or variable resistor that makes that calibration, or there may be a routine in the firmware that handles it. I've never had to replace one (although I thought I might have to, so ordered a spare.) There should be a topic in the Knowledge Base that gives the procedure, although it probably assumes an apple-for-apple exchange.

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Posted : 09/10/2020 4:56 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Thermal sensor -thermistor 12V or 24V
Posted by: @ludodegreef

hello,

I have some older material in my spare box.
Is there a way to find out if a thermal sensor is 12v or 24V?

I know there is a way to recognise the 24V Heatsink by measuring the resistance.
Can the same be done with the thermistor? thx!

Important is the internal resistance, which for Prusa thermistors is about 100kohms at 25 degrees C. The thermistor table in the firmware is adapted to this type. If you use a different type you have to use a different table and recompile the firmware.

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Posted : 09/10/2020 8:36 pm
Milos V.
(@milos-v)
Prominent Member
RE: Thermal sensor -thermistor 12V or 24V

Based on the knowledge base, the thermistors are supposed to have resistance 100kOhm at 25°C. They do not mention any differences for 12V and 24V printers.

Also Prusa eshop sells the same part for all printers. So I belive it is really usable for both voltages.

https://help.prusa3d.com/cs/article/multimeter-usage_5299

https://shop.prusa3d.com/en/mk3mk3s/205-hotend-thermistor-e3d.html

 

Posted : 09/10/2020 8:41 pm
--
 --
(@)
Illustrious Member
RE: Thermal sensor -thermistor 12V or 24V

A thermistor is a resistive device, voltage doesn't matter. 

What does matter: and this is critical : is the temperature vs resistance curve, or profile. Exact matches are needed, or if you are an engineer wanna-be and can edit and compile new code, you can use another part number with a different profile. But again, the thermistor and the profile in software must match. 

This post was modified 3 years ago by --
Posted : 09/10/2020 8:47 pm
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