heated bedOne of the great wonders of 3D printing, is being able to print with a great number of materials with different attributes. Every material has its own technique and properties that require different factors or temperatures. For example, PLA material requires the hot-end temperature to be between 205-220ºC, but it also needs a cooling fan to cool down the material very quickly, this way we can produce a piece with high definition. Others need the print bed to be hot so when the material is placed on top, the base needs to be around 70ºC. This can be achieved by installing a heated bed on the printer.

The heated bed consists of a printed circuit that contains a resistor that heats up when tension is applied (and consequently releases heat). When the bed has a higher temperature than the surrounding environment, the material won´t react as much to the difference in temperature when extruded through the hot-end,  which improves the adhesion.

We need to bear in mind that to get the heated bed to reach a temperature of around 70ºC, we need to supply it with a high current, which will make the printer consume a very high amount of energy. So before we can install the heated bed, first make sure that it’s totally necessary. The heated bed can consume around 10 amps, which is a very high and dangerous level of consumption. If the installation is not done correctly, it could result in a short circuit,  which could be very dangerous. As result, we have to stress that the installation of the heated bed carried out entirely at your own risk. At the end of this article, we will explain how to create a protective circuit. Before we begin with the instructions on how to install the bed, I will show you an overview of the connections, so you can have a rough idea of what we are going to do.

Diagram of connections

Diagram of connections

Installing the bed

To install a heated bed, the first thing we need to do is to connect the relevant cables. The bed I’m using is the bed available from our store as a kit (link), and it includes all screws, springs, cables and a thermistor. The first thing we need to install is the thermistor on the bed. You will need to solder the fine black-red cable to both thermistor cables. These thermistor cables are exposed and you will need to cover them with Kapton tape or a retractable tube to create a safer connection. Please take care with these cables are they very thin. Next, place the thermistor in the centre of the bed on the side  without stripes so that it pokes out from the top. Bend the cables in a straight angle and stick it to the base; you can use Kapton tape due to its high heat resistance. Next you will need to solder the thicker cables to the pins on the print bed. It’s important that the cables come out through the lower part of the base, so that way they are not in the way when printing. You will need to solder the cables to the metallic part so they make contact.

Pins on the lower part of the base

Pins on the lower part of the base

Don’t worry about the colour of the cables, as the heated bed has no polarity. If you place Kapton tape on top of the soldering, it would be even better. You will see 6 pinholes at the bottom of the bed, where two LEDs and a resistor can be installed to work as a signal, so that we know when it is on. The installation can be done with two normal LEDs or SMDs. Two LEDs are used so that you can place each one in the opposite direction, so that only one of them will turn on. Place the resistor on the other side. These components are optional, as they simply serve to indicate that the heated bed is on.

Once these cables are in place, the bed will be ready. If you have already installed another bed,  remove it. You will need to position the bed on the printer and screw it into place correctly. Keep in mind that you also need to place the springs between the bed and the base of the platform, with the screws passing through them, so that when you tighten the screws, the force of the springs will prevent the base from moving.

Springs in detail

Springs in detail

Now that the base is in place, all you need to do is connect it to the electronics. We have used a RAMPS 1.4. You will need to plug in the thermistor directly, on the same side as the extruder connector. The heated bed needs to be connected to the D8 output. This would be the direct connection, but in this article we have added some extra safety measures, which are explained at the end. I would advise you to revise the final step before placing the heated bed. Lastly, you will need to connect the power supply correctly. You need a power supply that generates 350 W. If you have a Prusa i3 Hephestos, you will to need to change the power supply, as it does not provide sufficient power to heat the bed. Going to the electronic input pins, the two pins on the right are designated for the extruder, which is where you connect the positive and negative, the next two are for the heated bed, which is also connected in the same order, positive and negative.

Installing the Firmware

To install the Marlin firmware, you first need to download version 1.4.2.

Once you’ve downloaded the ZIP, you need to decompress all of the files, as you’ll have to make some changes before carrying out the compilation.

  • Access the folder \Marlin\config\ModeloDeSuImpresora\ and cut all of the files contained in the folder. “Configuration.h”, “Configuration_adv.h”, “language.h” and “Makefile”.
  • Paste the files into the folder \Marlin\.
  • Next, access the folder \Marlin\libraries\SdFat\ and as you did before, cut all of the files contained in the folder.
  • Go back to the folder \Marlin\ and paste the files.

The firmware will now be ready to be opened with Arduino IDE. It’s important to use version 1.0.6 of Arduino IDE, as later versions have presented some compilation errors. You can download version 1.0.6 here.

Now open the file “Marlin.ino”, contained in the \Marlin\ folder, to continue configuring Arduino IDE.

  • Go to Tools>Card and select “Arduino Mega 2560 or Mega ADK”.
  • Go to Tools>Serial Port and select the COM port which the computer has assigned to your printer (which must be connected to the computer).

Now that Arduino IDE has been configured and the printer is connected to your computer, you just need to make a few changes to ensure the firmware is ready to work with a heated bed. To do so, go to the “Configuration.h” tab and make these changes:

  • Search for the line “#define TEMP_SENSOR_BED 0″ and change the value 0 to 1.
  • Search for the line “//#define HEATED_BED_SUPPORT” and delete the slashes (//) which appear at the beginning of the line to uncomment the code and activate it.

Everything is now ready. Just click the compilation button and wait for the bar to load completely. If everything has gone correctly, you’ll now see two temperatures on your LCD. The one on the left is for the thermistor and the one on the right is for the heated bed. If the temperature of the base is 0ºC, either the surrounding area is too cold, or the thermistor is not positioned correctly.

Firmware modifications

Firmware modifications

There’s little left to do. We’ve got everything ready for our printer, but when we generate the Gcode we need to state that we have a heated bed. I use Cura, so I need to go to “Machine > Machine settings…” and tick the Heated bed box. Now to the left, you will see a box where you can type in the desired temperature. Around 70ºC is usually ok, but it depends on the materials that you’re using and their attributes.

Cura settings

Cura settings

Now you have everything ready. The heated bed should heat up correctly and you can now print with it. Be careful not to put your hand on top, as you could get burnt.

Extra safety measures

You have everything installed, but any extra safety features are always welcome. The heated bed is a component that consumes a lot of power, so we need to prevent any incidents. Personally, I don’t like so much current to be flowing through the electronic board, I prefer it to come directly from the power supply, if possible. To do this, we can add an extra component as a relay. A relay is an electromechanical device that acts as a switch. One part is the input, which contains a coil. When activated, it creates an electromagnetic field that activates the second part. The second part is the output, which consists of a switch that closes when the input is activated. In our case, we are going to connect the input to the D8 output. This way, when we want to activate the bed, the D8 output will be activated and the relay output will be closed, enabling the heated bed to work directly from the power supply. We will serially connect the heated bed to the output, directly using the power supply, so that the relay output will serve as a switch. The circuit will look like this:

Relay diagram

Relay diagram

This way, we can prevent all of the current from the heated bed from flowing the electronics, by going instead from the power supply and passing through the relay to the heated bed. You need to keep in mind that the relay input is a coil and when it is activated, it generates an electromagnetic field due to the intensity circulating through it. When we stop applying this current, the coil returns to its previous idle state but a small residual charge remains, which could damage our electronics. As a result, and since we´re talking about safety, the best option would be to connect the input of the relay to a diode in antiparallel. When there is an unwanted current, it will pass through it rather than the electronics. A diode has two pins, an anode and a cathode.  The current must pass from the anode to the cathode in order to circulate. So the said diode needs to be placed in antiparallel to the D8 output or the relay input. Once the bed is working, we will set the diode as an open circuit (it will not work), so when it is used the other way around, it will receive the current generated by the coil.

Once you have made these improvements, you will have installed your heated bed correctly. If you do a case study on this, you would need to weigh up the pros and cons. On the plus side, the heated bed can offer the possibility to print with different materials, such as ABS, and it also improves the adhesion of other materials. On the downside, there´s the high  consumption of electricity, the issue of modifying the printer (which could invalidate the product warranty), the risk of high current  circulating through the electronics, etc. But what is clear is that the heated bed is an extra that can be added, which gives our printer possibilities that we wouldn’t otherwise have. Now it’s up to you to decide if it’s worth it in your particular circumstances.

Ruben Sierra (@sgruben in Twitter) is an industrial engineer technician, specialising in Industrial Electronics. He is a maker and is passionate about programing, robotics, and 3D printing. He currently works in 3D tech support at BQ.