Ultimaker heated bed MosFET relay hack - V2

youmagine

New Version Released! Check it Out! I'm really disappointed when I hear about people buying SSRs or even mechanical relays instead of just using a MosFET. So, I decided to create a DIY solution that would make this problem disappear. Here's the thing: Mechanical Relays Are Not Great for DC (especially 24V, 200W), and Solid-State Relays are way over-engineered because they're made for industrial control applications where safety certificates and electrical isolation matter. I came up with a hack that uses a MosFET (rated for 120A actual rms current!) to switch the heated bed's power from an Ultimaker 1 electronics board without using any current from the UM1's original power supply. Of course, you'll need a second power supply dedicated for the heated bed - I've included recommendations in the BOM. Remember that these power supplies come without wiring, so don't forget to add that! I strongly recommend using a 24V power supply over 12V because it means less current, which means less stress on your wiring and connectors. Less current also means less electromagnetic interference. This hack includes a printable circuit board - you print the circuit board with your 3D printer, put in the components, and solder them using their own legs (full instructions in the files). All you need is a soldering station (preferably with temperature control) and some standard electronics solder. The design also features an LED indicator that lights up when the heatbed is activated. It's fully ESD protected and enclosed, so don't be afraid of the long instructions - it's really easy to solder the components together! Note that you need to use the case if you want the thing to be protected against ESD effectively. The current design uses self-tapping screws for thermoplastics (aka "plastite screws"). If you really need a design that uses standard M3 screws, let me know - I can adapt it. You could also just use a drill and drill through the small holes. Then, you can put screws through and add nuts on the bottom. Important: Make sure you don't put the MosFET relay on something that gets hot (such as the power supply unit)! It will not get warm by itself, but you don't want it to melt down and short-circuit... The BOM includes supplier information for www.mouser.com. I recommend getting the parts from there - they ship worldwide, and if you take one of the power supplies listed in the BOM, you should also get free shipping. Note that Youmagine decided to rotate the picture and crop it. I tried it three times, but it keeps rotating it. See the assembly instructions for more pictures! Update: Added the SketchUp source file! I completely forgot about it earlier - sorry! Update 2 (2015-06-02): Added Wiring.pdf as a better display of how to hook this thing up. IMPORTANT NOTE: This hack is intended to be used with the Ultimaker Original power supply and electronics platform. Don't use it with anything else than that - this hack is not an universal design but really just a "hack" to get the UMO working with a heatbed. Update: Other platforms may work as well, as long as there are no differences in how the heater outputs are switched (compared to the UMO electronics). ANOTHER IMPORTANT NOTE: Due to the way the heatbed output works and the fact that this MosFET relay hack does NOT feature an electrical insulation between input and output, you MUST use the second (heatbed) power supply EXCLUSIVELY for the heated bed and nothing else. The MosFET relay only works when it can break the GND connection between the controller (UMO electronics) and the heated bed. If you create any other GND connection between the controller and the heatbed power supply, then you bypass the relay, keeping it always in "ON" state. As long as there is no other GND connection, the hack is completely safe to use as long as you solder all the joints correctly!