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Use a SSR or Power-Expander to externally power Heated bed – Part 1

I’ve had a few inquiries about how exactly to use a Solid State Relay and an extra powersupply or main power, so decided to write about how to make it work, and explain some while at it


  • Solid State Relay :: SSR from now on
  • powersupply :: PSU from now on
  • Mains power :: AC

Silicone Heater

Here’s my 500w silicone heater from Keenovo (opes eBay shop) powered using AC power. It comes with an attached pad of 3M MP386 heat resistant and transferring extremely sticky tape. You can have them made with other types of sensors, like a thermocoupler if you like.

I decided to include the Power-Expander (opens link to as it is a great alternative to a DC-DC SSR, and because you are sure not to get a counterfit SSR.

I have personally only used SSR from RobotDigg (opens their shop), but the brand Fotek is also a good quality. Problem is lots of counterfits (open UL site) & here (instructables) around, so be carefull where you buy your stuff.

Types of relays – usage scenarioes

We allready touched on the subject above, so lets take a look at the different options we have.


The denomination before the – is the input or control type. We are only talking about DC- here.

The listing after the – is the LOAD type. So if it is listed as DC-AC, it means we control it using DC from the output on controller and the LOAD we are using is AC if we have a silicone heater as listed at the top of this page.

  • DC-DC SSR or Power-Expander are interchangeable in most cases, so I’ll list them as such.
    • Notice the input type and range listed at the lower end. In this case 3-32 Volt and the type is DC
      Load type os listed at the upper end, and is 6-220 volt and also DC, so we really have some power here.
      Amperage is listed in the center, and this SSR is rated at 25A. It means the LOAD can be current up to 25amperage
    • Option 1: if your main powersupply is not powerfull enough to power a heated bed in addition to the electronics. It might also be used
    • Option 2: if you just want to use 2 seperate powersupplies for the electronics and heated bed: you might be running electronics at 12v but want 24v on heated bed.
    • You want a DC-AC SSR if you have a heated bed powered using AC. Most common if you have bought an AC silicone heater.
  • Shield
    The SSRs I’ve bought comes equipped with a clear shield/cover.
    It is important to use this to avoid accidents, as the terminals are open and easy to get to.
  • Heatsink
    Read on the specifications and compare to your needs wheter you need a heatsink or cooling. I have not needed this on my build as a 500w AC heater only use 2-2.5amperage at most.

Wiring up

The next big question is how to wire it.

If you use an AC heater, you might want to add a grounding wire. You might also want to do it if you use DC, but in any case, I have added one here, as you can see.

I must admit I can’t see a scenario where it would be needed, but better safe than sorry, and it’s easy to just add an extra wire.

Here’s the wiring braided and sleeved up with the Silicone heater taped to the plate. It takes 24 hours for the glue to fully harden, so put it under pressure a day or so, before putting it upside down – don’t put pressure on the center part where the thermistor lives.

Ground Wire

People have aruged that I should have attached the ground wire to the black print-plate, but I admit I simply only had in mind to ground the entire Z-stage, so bolted it to the z-stage liftplate…

If an AC wire comes loose I guess it would it the plate.. in any case.. I leave it to you, how you want to attach it.


Next parts…

In the next part of this, we will go through the complete wiring of controller, psu, ssr and heated bed.

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BeTrue3D Printer build part 5 – LEDs

You might have read my part 3 where I had a section on installing LEDs.

Here are some thumbnails from the previous post.

This blog-post is all about getting it to work, including installing a front-mounted simple mechanical switch.

  1. Planning
  2. Execution
  3. Mounting
  4. Getting 12v in 24v system?
  5. Testing and wiring
  6. LED Installation
  7. LED Testing
  8. Video testing LEDs

I’ve tried taking some more photos due to popular demand 🙂


I had a hope the small on/off switch could be placed as you see on the photo. I removed the bracket, measured up, and drew some lines. I made 0,5mm extra space between the switch and extrusions – giving me some margin of error to work with.


I started out using a small quality drill from proxxon with a pointy tip to get an accurate starting point (I don’t know one of those fancy tools to make a small indentations)

After I had it going I switched to a more sturdy drill and worked on it. Using plenty of cutting oil and cleaning away aluminium parts all the time.

I used a tray as a drill-platform as I do not own a proper workbench (I have a small portable one, but it was packed away). I’ve put it over the sink in the kitchen. Worked great as the metal parts just ended up in the sink, and the drill didn’t go down into a tabletop or similar.


After finishing the pilot hole I measured the diameter I needed for the switch and used the right sized drill for the job.



The on/off switch is within the bracket, so that’s as planned. I had previously used the switch, so allready had in and output wires on it. I use the male plug (2 exposed pins) as input and the female connector as output. Doing it like this, so any wires/plugs with active current is not in the form of bared metal pins.


I soldered on male connectors to the wires coming from the LED strips. Using a portable gas weller solderpen I had from my time as network techie 🙂

I took a photo of the small hand tool, as that is enough of a tool to crimp on most connectors. A proper crimping tool is prefereble, but if you only need it for 1 project it is fine to skip buying it.


Getting 12v in 24v system?

So, the next step is to get 12v in my 24v system, as the LEDs are running on 12v. The Duex5 can be configured to output 12v, so I might go that route eventually, but I’d like to initially have power available to the LEDs as soon as the PSU is on, regardless of setup.

I’m using a small “hardwired” 24v DC to 12v DC step down. It can even output at 3amp, which is a lot for such a small thing! I like these things compared to the one you adjust manually, as they never put out that annoying high pitch coil whine you sometimes get from “normal” DC-DC step down modules.

Photo shows front and rear of the board.


I’m going to solder on small pins, as I’m not sure what I want in the longer run regarding these. Alternative is to just solder on the wires.

Using the foam pads to keep the pins in place while soldering them on.


Ready, get, set go, and finished. The fan is homemade with a carbon filter.. it’s really super nice.


Testing and wiring

I’m using standard female dupont connectors and just using standard  tools.

I have a super nice Lambda Vega-Lite 550 powersupply I found at a bargain price. Going to convert it into a proper “lab psu” at some point with banana plugs etc.

I’m making sure the output is in fact 12v and not something else.

Putting the wires in place using duct-tape (untill I can print some other cable-management things) and mounting the small Step Down below the Duex5. I’ve just used double-sided tape for now, and have not wired it up any further.. propably going to be directly hooked up to the PSU though.

LED installation

This should had been in the previous post, but since I didn’t take any photos of it, I do it now. You can see how the power input comes up through the floor paneling through a small indentation, and each section of the LEDs are conneted using a small piece of wire.

I’ve put white heatshrink over the exposed solderpads.

LED testing

It might be hard to see, but here are 2 photos showing the BeTrue3D Printer with LEDs on and off.

Video showing a test of the LEDs

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BeTrue3D Printer build part 4 – Printbed

This post is about my brand new super nice PEI-Coated black oxidized 5mm aluminium plate with lasered logo/url and about a lot of wiring I’ve spent time doing.

I also put in the last paneling. I ran out of the white 5mm card board material and am using some whiteish acrylic I had untill I can get some more of the white plates.


First up is the printbed. This is the single most expensive item in my printer at around €85 including shipping! Especially when combined with the 500w AC heater at around €35. You can get the plate much cheaper if you get it in natural color instead of black though.

Here’s the finished result, which I’ll go through in steps, to show how I did it.

I’m very pleased with the result, if I might say so 🙂

Keenovo heater used

I’m using a 500w AC heater from Keenovo. You can get it in custom sizes at no extra prize, and they really deliver high quality. Included is 1 big pad of preapplied heat resistant and -conducting 3M MP486 tape, which is the best for the job.

It comes with premounted 2 wires for AC power and 2 wires for the build in thermistor. It generally reads 10c above actual surface temp of the printbed.. guess its due to heat dissipation. You can get other sensor types as well

The CE is “China Export”, so it doesn’t mean it is CE certified

Ground and sleeving

I wanted to ground/earth my Z-gantry directly, in case of a mishap, so needed an extra wire. I also enlarged one of my 3mm holes to 4mm to make it fit perfectly.

I drilled an extra small hole where I can zip-tie the cables onto the lift-plate for stress-relief for the wires/headpad. It is places so the wires does not grind on the edge of the plate.

I originally wanted to use a cable drag-chain, so hadn’t planned on using zip ties.

I braided the cables and sleeved the part that’ll be visible ind the print chamber.

I do not insulate the bottom of the plate, as I want the increased heat output to act as a sort of “passive” heater element for the heat-chamber effect I’ll get by doing this.



I’ve planned to use the Ultimaker 2 fingerscrew system. I really like it, as it is discreet and runs very nicely, while at the same time can be tightened down really tight so the bed doesn’t wobble.

It means I’ve had 3 holes at 6.5mm made in the lift-plate for the fingerscrews, which lines up with corrosponding countersunk holes on the print bed.

The fingerscrew assemblies are made up of the fingerscrews, spacers, springs and m3 scews.

For best result I have put on lithiumgrease between the fingerscrews and spacer, and again on top of the spacer.

Note: I’ve used some other types of grease on other printers with great result as well, so no need for special grease. Just use something.


After fixing the cables at the back edge of the bed, as shown in photo a bit above, I placed the springs at the right spots, and placed the bed on top of them (took a bit of balancing in order not to knocking around the springs with the plate).

The springs are 20mm long and has an inner diameter of 7mm.

I used a caliber I can lock into place and put it at 10mm. This means I can do a rough calibration of the bed. It’s not precise, but close enough to start calibrating using printer software.

Note: The distance I used might not fit on other printers, due to thickness of plates and length of m3 screws and springs. So tighten down the springs untill you can depress the corners with your fingers, but not so easily that the bed can wobble. The springs must be tightened down good, but not all the way.

The give in the sprigns is an insurance if you accidentailly have the hotend smash down onto the plate. If the plate can’t move, something else is likely to break.

Clean it up using Acetone or Isopropyl alcohol when done. Can see my sticky fingers on the photo above 🙂


I originally wanted to use a dragchain… but I’m just not that big a fan of them, and found it looked bulky in there.. even a thin one. I know this is a subjective view, but there it is. I liked the sleeved version I made, so stuck with it.

I drilled an 8mm hole for the wires to get out to the back compartment, along with 2x 3mm holes for a ziptie to hold the cable in place.

The cable can flex up behind the z-stage.. even if it wanted to get under the bed, there is plenty of space for it in there, so it can’t cause any troubles.

Cables out back

I couldn’t get good photos of cables out back, but one of the AC wires went to the Load side of the SSR module at the connector labeled 1. The other AC cable went to my PSU at the AC N connector.

The Ground/Earth cable went to the AC earth connector, while the 2 thermistor wires went to the bed thermistor.

Cabling – Wire harness.

So much wiring when custom building printer!

As I created a connector plate for the 5 extruder motors, I did the same for my wire harness going to the carriage/hotend. It’s a LOT of wires for sure, but they are needed.

The 6-pin plug to the left is for BLTouch. 2 of those pins are for z-min and 3 for servo. 1 is unused.

The big 9 pin plug is for heater (2), heatsink fan (2), printobject fan (2), thermistor/thermocoupler (2-3 – some thermocouplers has 3 or even 4 wires)

The handdrawn “labels” are meant for my reference untill I get it working. I plan on printing some nice versions at some point.


Internal view

So many wires! I had a lot of cable clips from my old Um2 extrusion clone project, but recently threw them away… need to print some new to get rid of the duct tape when I find the time 🙂

Rear connectors

Here we can see how the new connectors looks; with and without the matching wire-harnesses hooked in.

I havn’t put connectors on the far end (at hotend) which’ll wait till I get the last parts I need to make the Y axis and carriage in order to make the correct length.

That’s it for now.

Hope you liked it, and thank you for following my proejct. 🙂