Kossel Heated Bed
One of my printers is an Anycubic Kossel A6 Delta. It is definitely a D-I-Y (do it yourself) project and a great value for the price. It is available only in kit form. Performance has been very good once I got every detail sorted. It produces very good prints and is fast.
One desirable feature it lacks is a heated bed. The controller (Arduino) has the necessary connections for controlling the heated bed. I ordered the hot plate when I purchased the printer kit. The delivery of the plate is another whole story of its own. I ended up with two of them, paying for one. I will send one back if manufacturer will pay or the shipping. I doubt they will see the value in that…
The hot plate is not plug-and-play. It is the main component of several that are required. It has the power wiring soldered on but does not include the thermistor for temperature sensing. I knew that going in, so no surprise. I ordered 5 thermistors with the proper end plug. They are low cost but now I have 4 spares. Ha!
I decided that high temp (red) silicon RTV seal would be an excellent method for mounting and holding the thermistor in place on the hotbed. There is a hole in the center of the plate to locate the thermistor bead. I built a blob of the silicon on the underside of the plate and allowed it to cure.
To use the heated bed the 12 volt low (75) watage original power supply must be replaced by at least a 200 watt unit. Mine is a 250 watt (20 amp). Again an expected extra. The new power supply is a bare bones unit so some extra components are needed there too. I ordered a power cord and some flexible wiring for use between the power supply and the controller. I also added some quick disconnect plugs for the 12 volt wiring.
I thought I could figure out the wiring as it is very basic. The original controller uses a plug-in brick power supply. There are extra wiring terminals on the controller that look like they are certainly connection points for the larger power supply. I thought, "Just disconnect the plug-in supply and wire up the larger power supply."
The problem is there are two (2) of these on board connections. I searched the Internet for information and finally discovered this PDF instruction page. (Click Here) This found information is critical for a proper installation.
Ahhh… OK, both terminals need to be connected. I would not have figured that without some trial and error. I took voltage measurements on both terminals while the controller is powered by the original supply but there is no voltage present on either of these terminals. It appears the terminals are the inputs to on-board voltage regulators. So no back-feed.
The heat from the hot plate is transferred almost entirely by conduction to the glass plate above. It does not get hot enough for much radiation. (It would need to be near glowing!) The manufacturer does not indicate any need to insulate the bottom of the plate which is directly over the controller and the wiring. Any convection will be upwards (warm air rises). I anticipate no problems and I will be monitoring the situation for awhile just in case.
I have stuck my fingers under the hot bed of my Cartesian printer hundreds of times. Very little heat sensed unless I actually touch the bed. The touch is conduction and I will say ouch very loudly…
Of course, Z height needs to be adjusted in the software and the software needs to have a flag set to indicate there is a heated bed available. The flag is described in the instruction PDF. Another point I did not know and would have had to discover with probably much frustration of, “Why isn’t this dang thing getting hot!?”
Both the original and the new power supplies do NOT have built in on/off power switches. Neither does my Cartesian printer. It seems to be a standard for some reason to not have a power switch. My solution is to purchase a low cost plug power strip (The kind with several outlets) that has a built in switch. I plug in both the printer power supply and my work light. This way I know the printer is powered up because the work light is also on. I good indicator that reminds me to shut down the printer “system” when finished. If I ever need just the light, I can just unplug the printer… Simple (KISS) solution.
Follow the photographs and download the PDF file linked above and there will be enough information for adding a heated bed to this printer.
The power supply settng open as shown is not a U/L approved type of installation. High voltage is slightly exposed at the bottom of the terminal strip as shown here. The transparent orange cover (shown open) is normally down and covering screw terminals I don't expect any problems here in my personal experimental hobby workspace but it certainly IS NOT acceptable for a customer or professional workplace Do as I say, not what I do...