How to infer thermistor setting?

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WillAdams
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How to infer thermistor setting?

Post by WillAdams » Fri Jul 25, 2014 3:58 am

Remembered I had a hot end on my as-yet-unused Ord Bot Quantum, so pulled it and installed it.

Then I remembered why it wasn't running yet --- I don't know what sort of thermistor it has in it. Tried:

EPCOS100K

(per a suggestion on the RepRap forums) and repetierHost flickers between:

767.40, 841, 936.40, 1102.40, 1523.90

which even I know isn't Celsius for room temperature (should be ~77 degrees Farenheit) --- is there any way to puzzle out what the thermistor might be if those are the readings at room temperature?
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criznach
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Re: How to infer thermistor setting?

Post by criznach » Fri Jul 25, 2014 4:15 am

I'm just getting started in this stuff too, but can you measure the resistance? I see some of them are 100k, some are 10k, etc... That might be a start. And if it's not glued in, you can buy a new thermistor of a known type on ebay or from digikey for a couple of bucks. I just bought the first one on the list of supported ones for my hot bed.

cvoinescu
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Re: How to infer thermistor setting?

Post by cvoinescu » Fri Jul 25, 2014 10:38 am

That, to me, looks like a reading caused by a very low resistance for a hot-end thermistor -- possibly even a short. 10 kΩ is too low for a hot-end thermistor, so it's unlikely; and any 100 kΩ type should read close to the correct value at room temperature (they're different only when hot). What you have there is in the tens of ohms, which is why I suspect a short.
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WillAdams
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Re: How to infer thermistor setting?

Post by WillAdams » Fri Jul 25, 2014 11:59 am

Or, I managed to get the plugs swapped around and had the thermistor running through the heater, and vice-versa.

Swapped.

Used a multimeter to try measuring, I believe I got 9.74 @20K @ ~23 degrees Celsius.

Tried all the possible values:

EPCOS100
RRRF100K
Honeywell100K
Semitec
HT100K

and didn't get anything reasonable.

What measurement would one get w/ a bad connection? (I had to wire in a molex connector and I'm not certain I did it right).

Guess I'll need to make a second connector to test for continuity.
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cvoinescu
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Re: How to infer thermistor setting?

Post by cvoinescu » Fri Jul 25, 2014 12:43 pm

All of those types should measure just under 100 kΩ at that temperature. Your measurement is consistent with a 10 kΩ thermistor, though. Your best bet in that case is type 4, but my recommendation is to replace it with a 100 kΩ one -- the resolution of a 10 kΩ thermistor above 150°C is so bad it's nearly useless (and not enough for PID control).
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WillAdams
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Re: How to infer thermistor setting?

Post by WillAdams » Fri Jul 25, 2014 5:46 pm

Thanks!

I swapped in the Semitec and seem to be printing fine now.

Anyone rebuild Reifsnyder J Heads?
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vexpertise
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Re: How to infer thermistor setting?

Post by vexpertise » Fri Jun 09, 2017 12:10 pm

Tried all the possible values: 3d printing mumbai pune
EPCOS100
RRRF100K
Honeywell100K
Semitec
HT100K

and didn't get anything reasonable.

What measurement would one get w/ a bad connection? (I had to wire in a molex connector and I'm not certain I did it right).

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