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  1. #1

    Difficulty with using external Mosfet

    Dear Members,

    I have a 3D printer where I use a Ramps 1.4 and a 200x300 [mm] PCB Heatbed. I wanted to upgrade it with an external Mosfet but it haven't succeded so far. I followed the wiring which I attached. After turning on the heatbed in Simplify3D the bed started to heat up from room temperature to 40 degrees celsius, but the external mosfet and the heatsink of it also heated up so much within a few seconds that I wasn't able to touch it. I guess it is not supposed to work like this. It looked like an easy and few minutes upgrade but I failed. Could someone please help me what to change to make it work? I attached the parts I use, the wiring I followed and the wiring which was done by me.

    Thanking you in advance for your help.
    Attached Images Attached Images
    Last edited by vikovarga; 12-06-2018 at 02:51 PM.

  2. #2
    Engineer-in-Training Roberts_Clif's Avatar
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    Sorry

    I can not tell how you have wired the External mosfet with the pictures supplied.
    Could you supply pictures of both sides of the external Mosfet and the controller for a better look see.

  3. #3
    Yes of course. I attached 2 additional pictures of the wiring. Sorry if it is not visible perfectly but there is a little chaos between the wires.
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  4. #4
    Engineer-in-Training Roberts_Clif's Avatar
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    Thank you

    I am confused the 1st picture mosfet driver is different style form the 2nd picture mosfet driver.

    Need to see the external Mosfet Pin-labels ,
    It appears you have the supply Power wired correctly.
    Would like to see the controller bed driver pins to the External mosfet driver.

    Tried to look up your External mosfet but could not find one that look like your to check the wiring by.

  5. #5
    Super Moderator Roxy's Avatar
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    Most people use a SSR (Solid State Relay) to do this kind of thing.

  6. #6
    Yes, you are right in the opening of the thread I provided a picture about another style of mosfet than mine, just because of showing the wiring I followed. But the plugs are the exact same like mine. I don't know if it helps but I found a pin label kind of picture which I attach. I think everything is wired correctly but the mosfet heated up rapidly within a few seconds as I mentioned earlier.
    Attached Images Attached Images

  7. #7
    Thank you for your answer. If I don't manage to make the mosfet work, I'll probably try using SSR.

  8. #8
    Engineer-in-Training Roberts_Clif's Avatar
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    Your wiring is perfect, I can not find anything that you have done incorrectly.

    The External Mosfet must be either defect or not capable of handling the power requirements needed.

  9. #9
    Super Moderator curious aardvark's Avatar
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    200x300 is a pretty big bed. you could try fitting a fan on the mosfet heatsink.

  10. #10
    It is big but the original mosfet which is on the Ramps 1.4 without a heatsink and with a higher RDS(on) resistance doesn't get hot after hours of working... So there must be something wrong which a fan wouldn't solve. But thank you for your suggestion.

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