SSR controlled heater setup query

droftarts

@900turbo said in SSR controlled heater setup query:

I took the readings at 200ohms

I don't know what you mean by that? Do you mean you get 200 x 30 = 6000 ohms? I'm used to modern digital multimeters!

Check you are measuring the resistance of the temperature sensor, by measuring ohms across the two wires that come from the bed. Looking at your picture of the bed, these are the red wires. The second pair of wires, the thicker white ones, are for the heater. Usually, these will be low resistance. Check you're measuring the correct wires, they will be the thinner ones.

For a 100k thermistor, you should get something like:
25 degrees = ~100k ohms
50 degrees = ~33K ohms
70 degrees = ~15k ohms

Ian

900turbo

@droftarts I mean this as in 200 set on the multi meter , there are 5 pins on the heater bed loom of which only 2 produce a reading so I assumed it’s temp sensors wires

Thank you

droftarts

@900turbo can you show a picture of the 5 pins? Try setting the meter to 20k or 200k.

Ian

900turbo

@droftarts at 20 and 200k I don’t get a reading just 0.00

900turbo

@900turbo

deckingman

@900turbo 30 Ohms sounds more like the heater resistance than a temperature sensor. Is it 110V mains or 240V? If it's 240V then using ohms law, 30 Ohms would mean it draws 8 Amps which is about 2,000 watts. If its 110V then 30 Ohms would mean about 3.7 Amps giving about 400 Watts. Do either of those wattage figures sound like the spec for your heater? If so, that confirms that you are measuring the heater resistance, not the temperature sensor. If that's the case, try again with your meter set to read 200K.

900turbo

@deckingman
The heater draws power straight from the PSU at 100-240V so I'm not sure what it draws. However I tried what you said using 200K and got the following results
25 degrees = 128.9
50 degrees = 38.0
70 degrees = 19.0

Thanks for the help!

droftarts

@900turbo With those results, I'd say it was a 100k NTC thermistor, which uses a beta value of 3950. So use:

M308 S0 P"temp0" Y"thermistor" T100000 B3950

For more information on thermistor parameters, see https://docs.duet3d.com/User_manual/Connecting_hardware/Temperature_connecting_thermistors_PT1000#typical-parameter-values

Ian

deckingman

@900turbo said in SSR controlled heater setup query:

@deckingman
The heater draws power straight from the PSU at 100-240V so I'm not sure what it draws. ........................

What I meant was, do you happen to know the wattage of the heater? From Ohms law, if we know the voltage and the resistance, we can calculate the current draw and then voltage x current = wattage. But anyway, it sounds like you've now found the correct pair of wires for the temperature sensor........

900turbo

@droftarts When I use the calculator i get a beta value of 3018 should I use this or 3950 ?

jay_s_uk

@900turbo use 3950

900turbo

@jay_s_uk Thank You.

droftarts

@900turbo Use 3950 to start with. If it proves to be inaccurate, you can recalibrate it later.

If I put your data into the thermistor calculator here https://www.thinksrs.com/downloads/programs/therm calc/ntccalibrator/ntccalculator.html and then set the Beta model coefficients for 100k NTC with Beta 3950, your 50C and 70C results match the curve well, but the 25C result is out. I'd guess that this result is inaccurate; either your meter is reading erroneously, or the temperature is closer to 20C rather than 25C. Most thermistors are 100k at 25C.

Ian

900turbo

@droftarts I agree with this due to the significant bed size 700x700mm using a 10mm thick sheet of Aluminium with a 5mm glass sheet on top I believe there is some lag in terms of the heating/temp reading , Am I correct in saying for R25 I just need to enter 128900?
Thanks for the help !

droftarts

@900turbo In the configuration tool, use the "QWG-104F-3950 (QU-BD silicone bed)" option. That gives the correct values.

Ian