Heated bed Specs.



  • I have a mini Kossel with a (old) duet 0.8.5 which I'm happy with.
    I'm now getting intermittent heater bed errors, where I have to switch off then back on to clear. I'm pretty sure the bed heater is playing up and it has got some brown scorch marks on. Can you tell me if I can use NTC 100K 3950 (0.72 ohm) and a 12v 200 watt heater. I think the fuse rating for the bed heater is 15A so I think the heater should be ok but not sure about the sensor as the one I have is i think 4700 ohm.



  • @Dave-Parry said in Heated bed Specs.:

    Can you tell me if I can use NTC 100K 3950 (0.72 ohm)

    a 100k thermistors hould be about 100,000 ohm at room temp - the 200w bed should be 0.72 ohm for 12v operation. which is a good fit for 15A fuse, got the wires mixed?



  • Thanks for confirming the heater rating is ok, but my other question was at present my bed sensor is a 4700 ohm one. all the new bed heaters seem to have ntc 100k. I wanted to know if I can use that into my duet. The wires are ok, I havent taken them out yet.



  • you post is a little confusing to me, how about you post the configuration for the bed sensor before the intermittent issues started?

    i think you have a 100k ntc sensor which is super common and can be used with any duet. and the 4700 ohm you refer to is the series resistance on the duet?



  • Ok, here is the config file. This has not been changed since the duet was installed, probably 4 or 5 years ago. But you have confirmed that the duet will accept 100k sensors .Panel Due config file 2.txt



  • relvant section

    ; Heater and thermistor section
    
    ;*** If you have a Duet V0.6 board NOT stickered "4.7K" change R4700 to R1000 to the following M305 commands. Leave at R4700 for all Duet V0.8.5 boards
    M305 P0 T100000 B3950 R4700 H14 L0	; Put your own H and/or L values here to set the bed thermistor ADC correction
    M305 P1 T100000 B4388 R4700 H-8 L0	; Put your own H and/or L values here to set the first nozzle thermistor ADC correction. DC42 recommends 4388 for E3D V6 with Semitec 104-GT2 thermistor
    M305 P2 T100000 B4388 R4700 H0 L0	; Put your own H and/or L values here to set the second nozzle thermistor ADC correction.
    M570 S180				; Hot end may be a little slow to heat up so allow it 180 seconds
    

    jupp (already configured for) 100k ntc sensor with 4k7 series resistance on the duet.



  • Ok, Thanks. I thought that the R4700 referred to the sensor rating. Thanks for the info.


  • administrators

    @Dave-Parry said in Heated bed Specs.:

    I have a mini Kossel with a (old) duet 0.8.5 which I'm happy with.
    I'm now getting intermittent heater bed errors, where I have to switch off then back on to clear. I'm pretty sure the bed heater is playing up and it has got some brown scorch marks on. Can you tell me if I can use NTC 100K 3950 (0.72 ohm) and a 12v 200 watt heater. I think the fuse rating for the bed heater is 15A so I think the heater should be ok but not sure about the sensor as the one I have is i think 4700 ohm.

    A 12V 200W heater should in theory draw (200/12) = 16.7A so a little above the rating of a 15A fuse. However, the Duet 0.8.5 doesn't have a fuse.

    The other consideration is the current rating of the traces on the Duet. 16.7A is OK for the mosfet but higher than the traces of a Duet 0.8.5 can probably handle. AFAIR the weakest trace is the one between VIN+ and bed heater +. You can add a wire link on the back of the board to bypass that, or connect the bed heater + wire directly to V+ on your PSU instead of to bed heater + on the Duet.

    Caution, at high currents there is a risk that the VIN and bed heater terminal blocks on the Duet will overheat if the screws do not remain tight.


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