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Max heated bed wattage

Discussion in 'RUMBA' started by woodencase01, Feb 10, 2013.

  1. woodencase01

    woodencase01 New Member

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    Feb 10, 2013
    I'm currently working on a delta printer. I've calculated that I would need about 135W for the heated bed to heat at 110°C in 180 sec.

    I've looked at the PCB layout and it seems to have a 11A mosfet PWM, but I'm not sure at all if this is related to the heated bed.

    What is the maximum wattage we can get from a 12V system? If the RUMBA can't provide enough power, what is the alternative?
     
  2. Jelle

    Jelle New Member

    Joined:
    Feb 10, 2013
    The solution is pretty simple: ditch that 12V power supply. Like you have seen, you need to switch quite a lot of current to reach a measily 120Watt (assuming 10A max limited by the fuse). If you switch to a 24V power supply you can get much more power from the same controller and heater. On top of that, your motors get a top speed almost twice as high, which is good for a bot build for speed like a delta bot. That also allows you to choose a different motor with a little more torque, should you need it.
    The 'meanwell' type of switching power supplies is relatively cheap to get on ebay or elsewhere, either 24 or 36V.
     
  3. woodencase01

    woodencase01 New Member

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    Feb 10, 2013
    Hi Jelle,

    Thank you for your reply. Sadly, I've already bought my power supply and my steppers that would work on 12V. Is there anything else I could do with it?
     
  4. Jelle

    Jelle New Member

    Joined:
    Feb 10, 2013
    You mean you have bought steppers rated for 12V? Those will probably not work well with the microstepping drivers installed on the rumba board. Those drivers limit the current going through the board, meaning you can drive them with much more voltage than what they are rated for. If you don't, the microstepping feature will not work good. In other words; if you use a pololu (-like) stepper driver, you can use a much higher voltage without any harm to your drivers or steppers. You should, of course, not put anything higher on their 5 volt rail.
    So sell the 12V power supply and buy a better 24V one.
    Or just be a little more patient, which is not a bad thing with 3D printers.
     
  5. woodencase01

    woodencase01 New Member

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    Feb 10, 2013
    Hi Jelle,

    I think I've made a mistake. You are saying that the steppers drivers are automatically dropping the output voltage to 5V ? I bought the RUMBA with the included stepper drivers. I thought the drivers wouldn't control the output voltage. I bought steppers rated at 12V to match my power supply voltage. I might still have time to cancel the order.

    Thank you for your help.

    If I understood correctly, event if I get either a 24V or 36V power supply, the rumba and steppers drivers will output the right voltage for my steppers?
     
  6. David Rosendahl

    David Rosendahl New Member

    Joined:
    Jan 30, 2013
    Hi woodencase!

    No, he is not saying that the stepperdriver is automatically dropping the output voltage. He is saying that the steppers and drivers can handle 24V. (I don't know what he meant by 5V rail since there are no 5V rail from the driver to the motor.)
    http://reprap.org/wiki/Stepper_motor#Unscientific_rules_of_thumb_for_motor_purchases

    You probably wan't 24V and not 36V, even though some of the components, including the steppers might handle 36V, it might get you in problem with the some of the rest of the components. If you are comfortable working with high voltage you can buy a cheap power supply from a place like sureelectronics or similar. PLEASE make sure that you know what you are doing if you use a power supply like that, cover every exposed high voltage part before you connect it to the wall.
     
  7. Jelle

    Jelle New Member

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    Feb 10, 2013
    The driver board has no internal regulator, so it needs 5V too to power the logic chips.
    I have no idea what the components might be that are intolerant of 35V. I guess only the drivers and the 12V regulator are exposed to it?
     
  8. David Rosendahl

    David Rosendahl New Member

    Joined:
    Jan 30, 2013
    Ah, you meant the driver. The driver is automatically fed by the internal power regulator on the RUMBA board and you don't need to worry about that at all as long as you place the driver in the right direction. That has nothing to do with the 12V/24V/36V power supply. It's nearly"impossible" to do wrong there.

    Components that are intolerant to 36V (and 24V) might be for example fans. But RUMBA also includes an internal power regulator down to 12V so you can use that to power equipment with SMALL current requirements. Do not use it to power hotend or bed.
     
  9. woodencase01

    woodencase01 New Member

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    Feb 10, 2013
    Thank you for your help, both of you. It is a lot clearer now.

    I'll get a 24V PSU and it should do the trick.
     
  10. Jelle

    Jelle New Member

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    Feb 10, 2013
    On the rumba board is a switching voltage regulator, it can do 3 Amp! At 19V that would be enough to power an ultimaker, at 12V it's still good for one hotend.
    http://www.ti.com/product/lm2596#features
     
  11. David Rosendahl

    David Rosendahl New Member

    Joined:
    Jan 30, 2013
    Since the 12V regulator is already put at 12V, 19V is out of the question (why bring it up?). 12V 3A is just 36W, that one will be close if you use ABS, especially if you want to print fast. And then you have nothing for the fans. No, much much smarter to use the main power for the hotend and limit it by lowering the maximum of the PID output to the hotend in firmware (if needed).

    (Observe that reprapdiscounts 12V heating catridges are 40W so already one of them would be pressing the 12V regulator over its specification limit if you are using maximum 255 in firmware PID)

    If I had a resistor/cartridge for the hotend that was intended for 12V and had a power supply with 24V, I would still use the main power for the hotend (24V) and set the PID maximum to about half (around 128).
     
  12. Jelle

    Jelle New Member

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    Feb 10, 2013
    Sure, it's silly to do. I brought it up to show it's not that small a load, and that is a good thing, actually.
     
  13. woodencase01

    woodencase01 New Member

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    Feb 10, 2013
    I'll be using NiChrome wire for both the heated bed and the hot end, is there a need to use the RUMBA 12V regulator? Keep in mind that I'll be using a 24V PSU.
     
  14. BubbleRep

    BubbleRep Administrator Staff Member

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    Nov 11, 2012
    well the 12V regulators are for hardware that only is able to handle 12V for example FANs...
     
  15. woodencase01

    woodencase01 New Member

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    Feb 10, 2013
    I guess 36W is plenty for a hot end then.
     
  16. Jelle

    Jelle New Member

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    Feb 10, 2013
    That is one thing that seems a bit overlooked to me: most regulation in the reprap world is done with voltage regulation. But selfmade heaters might be better regulated with current control. But on the other hand, constant current devices are not really expensive as they are made en masse for leds.
    But to get back to the question: run your heaters from raw voltage and make sure the resistance is matched to them.
     
  17. BubbleRep

    BubbleRep Administrator Staff Member

    Joined:
    Nov 11, 2012
    the 12V regulator is only for small current, so hotend will be way too much
     

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