Is there any reason not to use an AC powered heat bed?
-
So I have a pair of Makerbot z18's I bought a long time ago because I needed the 12x12x18 build volume, and I really wanted the heated build chamber too. But incredibly, MB didn't put a heated print bed in these things, which was a real show stopper for me. So a few years ago, I retrofitted both with my own HBP and built an Arduino controller that I mounted to the front, it worked well but was a bit of a kluge.
Fast forward a few years and the Z18 has become an orphan, I decided I want to replace the controller and go with open source firmware. I am trying to plan out the new build which will require a new QC toolhead and I'm revisiting the HBP as well. The Z18 has two 12V chamber heaters and I was planning on using the built in bed driver for that, then using an AC bed heater with an SSR.
Since I've never done anything but low voltage DC heaters I'm just checking to see if there is any reason (other than aversion to mains) that I would not want to do that? It saves me the second power supply so I can tuck everything inside the chassis easily, so desirable just from that standpoint.
-
@frontrange, no reason at all. Go for it!
It is best to ground the build plate to AC ground and I would plan to use a heat fuse of some kind in case the SSR fails for whatever reason. -
@frontrange said in Is there any reason not to use an AC powered heat bed?:
Since I've never done anything but low voltage DC heaters I'm just checking to see if there is any reason (other than aversion to mains) that I would not want to do that?
The only reason not to do it is if you don't have enough knowledge and experience to do it safely. Things to consider:
- The metal parts of the printer (including those on the bed) must be grounded, for safety
- The terminals carrying AC mains power must be safely kept away from prying fingers
- The wires must be sufficiently insulated and prevented from chafing. This is easy if the bed is fixed (e.g. in a delta printer), more difficult if it is moving. A moving bed requires strain relief at both ends of the cable to prevent it breaking where it enters the terminal.
Additionally, you should consider what will happen if the bed heater gets stuck on at full power. With an AC mains bed it is easy to use a high powered heater that will raise the bed temperature to a dangerous value. So you should either choose the bed heater power carefully so that the temperature rise will be limited to a reasonably safe value at full power, or use a thermal cutout mounted on the bed or bed heater.
For a 300mm x300 mm bed I would definitely use an AC mains bed heater.
