home made pcb heated bed?

so ive made my own pcb bed, a 12" but I was wondering if it is possible to make one that can run directly from mains, and be controlled by an ssr. I need to make an 18" bed, and if it gives out the same wattage as the standard 8" pcb heated beds its about 600 watts, it seems pretty wasteful to use a power supply to heat it because it will not be very efficient, afterall the heat element will work the same if its on 12v dc or 120v ac. can a regular 1oz double sided pcb hold up to 120v ac current?

I think safety would be the big problem doing that. There are many mains voltage heaters available which can then be controlled by an ssr. I would start there.

I might be wrong but If you are using a switching supply I am sure the power wastage is negligable compared to the watts you are using for the head bed and I am thankfull not to use mains as it is so easy to make a mistake!

I think It can hold up to the current if you increase the resistance of the tracks (thinner & longer tracks) and prehaps use a diode to half wave recitfy the voltage down (basically im saying decrease the current as 110vac through 1.5ohms is a lot! ) remember you also need to put a very inulating unscratchable material on the surface. Not to discorage but I personally think its too much fuss and danger unless you use a pre-made mains heater like those sillicone heatbeds.

If using mains I would also make sure the entire metal frame is connected to earth.

Edited 6 time(s). Last edit at 01/09/2014 07:00AM by clack.

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clack
I might be wrong but If you are using a switching supply I am sure the power wastage is negligable compared to the watts you are using for the head bed and I am thankfull not to use mains as it is so easy to make a mistake!

Ok just looked it up, ATX PSU suppliers mostly quote around 20% wastage! thats about 120W right?

[en.wikipedia.org]

well i can produce the pcb traces at whatever width I want, and I also understand that the insulation on top of the pcb would need to be something thats hard to scratch away, perhaps some high temperature paint. also I could add a fuse inline with it.

ok well if the mains is too volatile for a home made pcb, has anyone used a higher voltage supply like 48v to power a heated bed, you could use thinner wires, right now with my 12" bed im running 2 pairs of 14ga copper wire to the bed and they get barely warm, with one pair of 14ga wires they get quite hot. if i run the bed on 48v then I could get away with 1/4 the thickness, compared to 12v.

I strongly advise against creating your own mains-connected PCB if you don't know exactly what you're doing. However, if you want to have a mains-connected heating solution, you might want to look into silicone heaters. Mains-connected heating has the advantage of being able to achieve much higher heating power without the hassle of getting a suitably powerful low-voltage power supply. This enables faster warm-up times and higher bed temperatures, but you also need to be especially careful when it comes to the wiring. As long as you don't need the power, I wouldn't recommend a mains-powered heated bed. If you do, then at least get a professionally-made and properly insulated product.

any idea of where i can get an 18" silicon bed with 600+ watts that will run off mains?

I don't want to give direct recommendations as I'm currently still in the process of building my printer. Preliminary tests seem to indicate that my normal-sized mains-powered silicone heater works just fine, but they're only preliminary. I got it from a Chinese company selling custom silicone heaters via Aliexpress. It was more expensive than a standard PCB heated bed, but I wanted to have custom dimensions and a higher-powered heater, so price was not of great concern. Silicone heaters are really flexible, so you need to attach it to something stable like a sheet of aluminium, which will also even out uneven heating. Unfortunately, I couldn't really test it yet, as my printer is not finished. It heats up sufficiently uniformly and reaches its target temperature when controlled by a SSR, though. If I were to order one again, I'd probably get a small cutout in the middle for placing the temperature sensor directly against the print bed. For finding out a suitable heater power, try to look around the web for similar-sized silicone heaters and their target temperatures.

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aduy
well i can produce the pcb traces at whatever width I want, and I also understand that the insulation on top of the pcb would need to be something thats hard to scratch away, perhaps some high temperature paint. also I could add a fuse inline with it.

ok well if the mains is too volatile for a home made pcb, has anyone used a higher voltage supply like 48v to power a heated bed, you could use thinner wires, right now with my 12" bed im running 2 pairs of 14ga copper wire to the bed and they get barely warm, with one pair of 14ga wires they get quite hot. if i run the bed on 48v then I could get away with 1/4 the thickness, compared to 12v.

It's not really that the PCB wouldn't be able to handle it, that part is fairly trivial as it's a simple to design a track on a 12" square board with the appropriate resistance for 110v. The problem is you're giving up all the safety features that are intrinsic to even a basic power supply. If you find yourself needing more power but don't want terribly thick cables, 24v PSUs are fairly easy to come by and there's plenty of people here that have used them successfully. I'd suggest starting there, since you're far less likely to have things go horribly wrong, and it'll be much less costly than a 48v PSU.

Edit: I just tried to use "catas" plus "troph" plus "ically" and the filter prevented me from posting. What the crap is wrong with that word?

Edited 2 time(s). Last edit at 01/09/2014 08:43PM by Rezer.