Anet A8 prusa-i3 mosfet-supportframe

by Sjouke, published

Anet A8 prusa-i3 mosfet-supportframe by Sjouke Oct 28, 2016
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This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/9L4bGM2yMXo

more information about schematics and how (and why) to setup your printer with a mosfet you can find in the WIKI pages https://3dprint.wiki/reprap/electronics/heatbed_mosfet

How I Designed This

The topbit screws onto your frame as usual the bottom bit for the mosfet has on its back room to insert some M3 nuts for the screws to fasten into so no holes drilling in your acryllic frame required just add the wiring and fire safety is 90% better.

I used an easy way to wire this using the stock 12 volts wire. Without cutting it , just removing about 1 cm of the insulation (to connect the mosfet), ran it from psu to mosfet to controlboard.


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Hello, I have no idea how to use Tinkercad, do you have Fusion360 Files? Or could you maybe add a (seperately printed) Pi Zero W Mount at the top? Thanks so much

since it screws to the frame with only the 4 mainboard thingies, the bottom bit "hangs" underneath that (no problem weight keeps it in place). By adding a similar bit to the top it would under the force of gravity start to bend forwards after a while (or one would have to drill holes in the frame to secure it) If you still want to change the design to what you would like, .....Just give tinkercad a try, it is not that hard to figure out how it works.

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I ordered my MOSFET and it is a different style with the heatsink in the middle. Thanks to tinkercad and sjouke, I've remixed it here: https://www.thingiverse.com/thing:2485366

Thanks sjouke!!

Anet A8 prusa-i3 MOSFET Support Frame For Heatsink-Split MOSFET
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To print of 100% filling and 0.08mm layers ... SUPER COOL THING.... really important to print ... USEFULLY for every Anet A8 owners

I had a issue printing this was getting spaghetti i slowed the top and bottom layers to 7mm's and its printing fine now! :)

Sorry to ask a probably dumb question, but I have a MOSFET that looks identical to yours, but after wiring it up, my bed caps out at about 33 degrees, and the heat sink on the MOSFET gets very hot. It seems like it's seeing a huge resistance somewhere. Do you think it's a bad solder connection somewhere on the board, or is there something I need to do?

if the bed does not heat up but the mosfet dos get hot, a high current is flowing, it looks like the hotbed is somehow bypassed (shortcircuited). Check your wires and connections are all good. Not a huge resistance, but a super low resistance in the hotbed circuit bypassing the heater.

the polarity on the mosfet is not marked for the hotbed connections and the control in do i just need to figure this out with a voltmeter? same with were you connect the wires to the main board its not marked

hotbed heating element is just a large resistor not polarity sensitive

Hi, Thanks for the upload. It printed out fine. I hope to upload when its wired-up and running. Mine came without a cable / connector for the 'Control In'. I am a bit scared about back-wiring it! Also, Not sure how heavy the cables on the control in line need to be? From your pic, it looks like you have the terminal marked '+' on the the control in on the module wired to the -ve terminal on the Anet board hotbed connector but it may just be the angle of the photo? I saw another picture on Amazon where it was wired + to + and - to - so well confused now! Any help greatly appreciated. All the best. Oops, deleted multiple posts - pc froze up! Sorry!

the control in line (signal line) that is the little white connector needs a simple little bit of wire that connects to the controlboard where the hotbed WAS connected, there is just a little signal going through there with a lot higher resistance and virtually no current anymore. the bed with its low resistance is no longer connected to it.
The 12 volts connection: Always follow the connections marked on the boards for + and -. There are different versions of controllboards, where the INPUT for 12 volts have been reversed with the introduction of the newer type connectors.+ goes on + always, and - on to the -

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HI on your picture above , could you please tell me where the HOT END wires conncet to please and just to comfirm the 2 hot bed wires replace the red and black wires out of the 4 thats on the hot bed . Cheers Andy

Hi Andy,

The HOTEND wires stay connected through the original setup from the controlboard. They carry a lot less current than the HOTBED and don't pose that big of a risk. (* as long as you have it all connected properly) Hotend thermistor connects to controlboard to white plug marked ET

The HOTBED should have 4 wires, the 2 for heating (thick red./black ?) these are the ones where the other end connects to the green plug on your controlboard. and 2 thin (white most of time) for the thermistor they connect to the controlboard with the little white connector marked BT

For connecting the HOTBED to the mosfetswitch you need to put the wires that go to the green plug marked BED to the MOSFET connector marked HOTBED, the little white connector (signal line) from the mosfet needs to be connected to the hotbed output from the controlboard (where your hotbed originally was connected) . And finally you need to connect the 12 volts INPUT to the DC IN on the mosfet.. I did it the easy way by looping my original 12 volts wire from PSU to mosfet dc in to 12 volts controlboard in. (as you can see in de photo of my wiring around the 2 pcb's)

I thought their is supposed to be a separate wire supplying power to the board and to the module, but youre method seems more elegant . this method saves me a lot of wire running all the way back to the ps, have u had any issues this way??? thanks , imprinting this thing now.

Hi, i've had this methode of wiring for around 6 weeks now and no problem. The wire itself is thick enough to carry the total current of the printer. the melting problems always happens where there is a connection (bad connection in this case with the green connectors) with a transitional resistence, and the heat developement in the bit where the resistence is. Make sure you don't cut the wire (where it is connected to the mosfet), just carefully make a cut around the plastic insulation and remove about 1 cm, leave the coppercore intact, loop the wire from psu to mosfet to controlboard. The bulk of the current will be diverted away from the controlboard and the mosfet will do what its there for.

Is it recommended to do it this way or can I run separate wires from the psu to the mosfet?

most people probably want to use separate 12volt wires for the mosfet and controlboard. I did not have a suitable piece of wire lying around and did not want to have to go to a shop, that's why i used the lazy way ;-) since the stockwire is thick enough to carry all the current

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Hi, can you post a link to the module you used?

hi i used the one below and ordered a couple of extra FANs of which i cut of the plug + 10 cm wire to use for connection.



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