Duet3d WiFi - MOSFET usage
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I am about to upgrade my Wanhao Duplicator 3i v2.1 with a Duet3D Wifi board. I was all set to do this when I saw another article where the user showed a diagram where he had used several MOSFET units to protect the board. I don't know enough about the MOSFET usage to decide whether I should include one (or more) of these in my new build and would appreciate some guidance from someone who is a little more knowledgeable.
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if your hotbed exceeds 15A you should consider using an external mosfet.
you can also use a mosfet to use a different power supply for the bed and the rest.
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would help if you provided a link to illustrate your concern. the duet boards seems to me to be about the most robust board available.
and if you know that voltage and currents the bed and heaters of the Wanhao Duplicator 3i v2.1 need then it'll be much easier to confirm or deny. none of the product pages i briefly looked at had that information readily available.
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From what I can find out;
Source: https://3dprinterwiki.info/printer-board-melzi-info/
Source: https://3dprinterwiki.info/wanhao/part-specifications/The board is powered from 12VDC which is then regulated down to 5V by a 7805 linear regulator.
The stepper drivers are A4988 chips. Newer v4.3 Melzi board usually are accompanied by different stepper motor with 950ma max current but have been reported to be set for the 1.3amp motors.
I am assuming that my v2.1 i3 is the “Newer”.
12V MK3 Aluminum heated bed. Voltage:12V/24V. Resistance between 1.4 and 1.6 ohm for the 12V
Resistance between 5.0 and 5.4 ohm for the 24V.Mine appears to be running 12v.
Not sure if this helps, but based on the comments I understand that the requirement for a MOSFET is something I could add if I want additional protection. Historically it was fitted to the Wanhao i3 to address reports of melted wiring.
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@b0m0a0k You should be fine but to be sure, measure the resistance of the bed heater if you can. Assuming it's a 12V bed heater and you are going to use a 12V PSU, and assuming the bed is worse case as quoted above at 1.4 Ohm, then from Ohms law, I=V/R so the current draw will be 12/1.4 = 8.57 Amps. The Duet bed heater outputs (Mosfets) are rated safe at up to 18A (used to be 15A) https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater.
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As @deckingman says, there is on need to use an externaL MOSFET because your bed heater current requirement is much less than the Duet rated output.
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@b0m0a0k said in Duet3d WiFi - MOSFET usage:
Not sure if this helps, but based on the comments I understand that the requirement for a MOSFET is something I could add if I want additional protection. Historically it was fitted to the Wanhao i3 to address reports of melted wiring.
Ad the others have pointed out, you'll be fine for the built in mosfets with those numbers, but you could always add an external as it would be easier to replace if it should get damaged due to a fault.
as far as melted wiring goes the only cure for that is thicker wires, or higher voltage and lower currents. (i.e ~100w bed at 12v pulls ~8A needs thicker wires than 100w bed at 24 which only pulls ~4A)