Heatbed did not get to 100°C



  • Hi Guys,

    yesterday i get my new 24V / 20A / 480 Watt PSU and wired it up with my SSR 40DD direct to the Heatbed.
    (This one: http://www.reprap.me/pcb300.html))
    (This is the Thermistor i use: https://www.amazon.de/gp/product/B01FFFA98M/))

    It needs about 10min to get to 70°C….
    Is there something that i should tweek in the Software or did i need more Power?

    This is my gcode for the Heatbed: M305 P0 T100000 B3990 C0 R4700



  • Try running

    M303 H0 P100


  • administrators

    Your mistake is in using a SSR40DD. It's probably getting hotter than the bed. See https://duet3d.com/wiki/Connecting_a_bed_heater#Low_voltage_.2812V_or_24V.29_DC_bed_heater.



  • @dc42:

    Your mistake is in using a SSR40DD. It's probably getting hotter than the bed. See https://duet3d.com/wiki/Connecting_a_bed_heater#Low_voltage_.2812V_or_24V.29_DC_bed_heater.

    That's not true.
    I also thought that it could be getting hot or about 30°C but the SSR is still at room Temperature.



  • @number40fan:

    Try running

    M303 H0 P100

    P = Power and 100% = P1 😉

    I used: M303 H0 P1 S100
    And get:

    Auto tuning heater 0 using target temperature 100.0C and PWM 1.00 - do not leave printer unattended
    Auto tune phase 1, heater on

    Auto tune cancelled because target temperature was not reached

    Max Temp was about 77.2°C

    By the way on https://configurator.reprapfirmware.org/ in the Heater Section i checked in the past for the Heatbed the Banbang Methode i belive.
    Any Ideas?


  • administrators

    @AS-3D:

    @dc42:

    Your mistake is in using a SSR40DD. It's probably getting hotter than the bed. See https://duet3d.com/wiki/Connecting_a_bed_heater#Low_voltage_.2812V_or_24V.29_DC_bed_heater.

    That's not true.
    I also thought that it could be getting hot or about 30°C but the SSR is still at room Temperature.

    Have you measured the voltage drop across it when the bed heater is running at full power?



  • The Problem with that SSR is that it will drop in the order of 1.6-2 volts across it which means your heater may be getting 22 Volts rather than the 24 and I guess the only reason it feels cool is cos you have it on a large heatsink and are checking the temp on the plastic surface try checking the heatsink of it.

    This is why most of us are now using AC Heaters with ssr's which are run so far inside there capacity you don't get the heat build up.

    You are also on the limit of your PSU suggest you look for one at least 25Amp to cater for that heatbed according to rerap.me it draws 20 amps on it own. also tweak the voltage up a bit if it is only used for the bed then up it to 26 volts or so but keep very careful check on that SSR they are know to fail short (ie switched ON)

    just my 2 cents worth of advise.

    Doug


  • administrators

    There are good DC-DC SSRs that have a very low voltage drop - see the link I posted earlier. However, even if the use of a better SSR results in 24V at the bed heater terminals instead of 22V, the increase in heating power will only be 19%.

    The web page gives the heating power as 115 - 128 Watts, which is too little for a 200x300mm bed. A bed of that size needs at least 180W and preferably about 240W.



  • Ok. my Voltage is exactly 24V on the Heatbed and as i sad i got a PSU with 24V / 20A / 480 Watt.
    So it should work.



  • Is it still 24 Volts at the Heatbed when on Full load? If it is then I would suggest that the heatbed is not living up to what you need.

    Can you measure the actual Open Circuit resistance of the bed (is it the 300mm sq one or the 300x200 one)?


  • administrators

    Your bed heater is woefully under powered. It doesn't matter that you have a 480W PSU, the bed heater itself is, according to the power specification, inadequate for printing ABS and other filaments that require a bed temperature greater than about 60C. It should be OK for printing PLA. See my response 4 posts up.


  • administrators

    To add to the above post, it's extremely common for PCB bed heaters to be under-powered. With a 200x200mm 12V bed heater you can usually resolve the problem by turning up the PSU voltage to 14V (if you are using a Duet or other good electronics - don't try this with Arduino/RAMPS). For anything larger, I suggest a silicone heater instead, either 24V or AC mains voltage, with a power density of about 0.4W per square cm. That said, E3D has a 24V 200x300mm PCB bed heater in the works, which should be adequate when it is available.



  • Are you running the bed in 12 volt mode or 24 volt mode. It looks like you could run it in 12 volt mode while supplying 24 volts, but then your PSU might not keep up since the specs say it could use up to 576 watts!


  • administrators

    @number40fan:

    Are you running the bed in 12 volt mode or 24 volt mode. It looks like you could run it in 12 volt mode while supplying 24 volts, but then your PSU might not keep up since the specs say it could use up to 576 watts!

    Turning the power supply voltage down to the minimum it provides (probably 19 to 20V) will offer some mitigation. But be careful not to exceed the current rating of the Duet bed heater output (18A for the series 2 Duets).



  • I figured he'd still be using the SSR with 24v PSU and the bed set to 12v.

    I am guessing that is why he has the SSR. Separate PSU for just the bed.



  • @number40fan:

    I figured he'd still be using the SSR with 24v PSU and the bed set to 12v.

    I am guessing that is why he has the SSR. Separate PSU for just the bed.

    Yep, the Heatbed runs in 24V Mode and the contact is there but maybe i should realy buy a other Flat Heatbed instead of this.
    But it is still strange that the Heatbed don't do what reprap.me says…

    Maybe i should ask those Guys why there Products are not like they describe.



  • It sounds like it is doing what it is supposed to be doing. It is just under powered for the size.



  • Is it possible (test this in a few hours) that the PSU give my Heatbed more Power if i'am connect all - and + Ports?
    For Example: If i got 3 + and 3 - Ports on the PSU i Connect from Port 1 - to port 2 - and from 2 - to 3 - and so on…
    do i get more Power?


  • administrators

    No, however if the cables from the PSU to the Duet are long or too thin then you could be getting excessive voltage drop on them. Similarly for the cable from the Duet to the bed heater. To check this, use a multimeter to measure the voltage at the PSU output terminals, the Duet VIN terminals, and at the bed heater.

    If you are getting excessive voltage drop between the PSU and the Duet, you can use 2 sets of wires between the PSU and the Duet. At the Duet end of the cables, use 2-into-1 ferrules. At the PSU end, use 2 sets of output terminals.


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