Heated Bed Possibility: Hot Plate Heating Element

If the heating element from a hot plate can be removed from its housing, it might be a good option for a heated bed. Multiple heat settings, low cost, no need to create a separate setup just for the hot bed, just plug it in and you're good.

If this is a possible alternative to the current heated bed solutions, it could make heated beds become very inexpensive: [www.walmart.com] $18
[www.mcmaster.com] $12

That's a heated bed setup for only $30. Has anyone tried something akin to this? How were the results? Is this a feasible option for a heated bed?

The biggest problem this would have, I think, is getting to the required temperature for an ABS bed (120-220C, Reviews say that the hot plate in question can boil water, so it can reach 100C, but 120C is another question). The inability to display exact temperature poses another problem with this idea (although this could easily be fixed with a thermometer).

Edited 3 time(s). Last edit at 11/24/2010 11:59PM by An Original Name.

I actually tried this with one I got from a local walmart several months ago. It had two heaters, but it looked very much like the one you are showing. What I found was that the heating element was encased in cement, which was attached to a very heavy iron plate. Much too heavy for sensible use on the reprap.

I did find some really thin, fairly light heaters on ebay though. Apparently they were pulled from some old military equipment or something. I don't know what, but it seems to be working really well. It is a 240W, 120V heater. I really lucked out when I found them. They were the perfect size (about 6" OD) and It was very easy to attach. I just used a couple of machine screws to clamp it onto the under side of my build plate with an aluminum strap. There are two bolts that serve as wiring terminals.

If you go this route, I suggest using a solid state relay to control it. Mechanical relays are cheaper, but they will wear out faster. Also beware of putting AC voltage near communication wires - especially if you use PWM to run your heater. I have not had any coms interference issues, but I don't run a separate extruder board either. Normal Gen3 electronics might be more sensitive. Using a relay with zero-cross switching might help keep interference lower, but it will also affect your temperature control and it seems to cause a lot of PID instability. I'm using one with zero-cross switching, but I have PID disabled on my bed heater.

Edited 1 time(s). Last edit at 11/27/2010 05:27PM by dazed.dnc.

Thanks for the feedback. You saved me 12 dollars.

Do you know how much weight the bed can handle?

I can't really put a number to it, but if you use stepper motors that have a higher torque (IE nema 23 size motors instead of nema 17) you could increase the limit.

Reprap firmware normally uses accelerated movements, which will help overcome the problem by slowly changing direction instead of jerking things back and forth. Theoretically, you could also adjust your printer's speed to suit the characteristics of your printer, but it will take longer to make your parts.

The problem isn't so much that the build plate can't hold the weight, it is that the motor will skip steps when you try to make it change direction if the build plate and printed part have too much inertia. Obviously there is a limit to how much the plate will hold before something breaks, but you are unlikely to find something that fits on the printer and has that much mass.

I plan to make a few more mendels, so I hate to part with these heaters. But, I do have three more. For $4 plus shipping, I could send you one. If you wait, I will even have a solid state relay I could throw in for another $5. The relays may not be here for another month or so. I might even have an old CPU heatsink, terminal block, thermistor, and wire to send with it. If I can find these parts, I'll throw them in at no charge. If you want to buy parts from me, PM me and we can discuss the details.

I'm not sure I want to go thought all the complicated wiring of setting up those, and I probably won't be ready to set up a heated bed for at least a few more months. I may contact you later to see if you still have them, but in the mean time I've been brain storming.

What if instead of using the iron and concrete heating element of the hot plate, we just replace that with a length of nichrome wire attached to the bottom of the bed? The resistance would need to be compatible, but that wouldn't be too hard to measure with a multimeter. There are a few vendors on ebay selling raw nichrome wire (no insulation) for very cheap. Of course, special care would be needed to ensure it doesn't short on anything (more kapton anyone? ).

What do you guys think? Could this be done?

Edited 2 time(s). Last edit at 01/17/2011 06:11PM by An Original Name.

If you do that, by all means put a thermal fuse on there too. Nichrome taped to the bed was actually the first thing I tried. I abandoned it because it felt so unsafe. When I heated it, the tape wanted to peel loose and the nichrome began shifting. If you do get a short circuit, you could end up with a runaway heater. A thermal fuse will give you some assurance that it will shut down rather than set fire. You might want to get a range of fuses so that if the first one you select is too weak and it blows due to vibration then you have a stronger one to try. Maybe try one rated for 130C first?

I'm not sure those bi-metallic thermistors are reliable enough for being the sole temperature control mechanism. Especially one out cheap import kitchenware. A variance of +/-5C can have an impact on the print quality, so you might get better results out of using the arduino to actively control the temperature. That means either using 12V (I think most people who try this decide 12v bed heaters are not practical) or using mains voltage and an extra relay.

If you are still set on trying nichrome, the best way to do it is to get the pre-insulated stuff. It will cost more, but it will be a little safer since your tape is not going to peel apart or burn away and allow a short circuit. You might also get better heat transfer since you won't have to deal with kinks or air pockets in the tape keeping it from making good contact. Ultimachine sells pre-cut sections of insulated nichrome. If you want longer pieces I think they just cut it off a roll, so you might try asking for whatever length you want. If you want to try buying a bulk roll and selling off whatever you don't use yourself, Pelican wire might be another source worth looking at.

There was some talk about a nicrome heater pre-insulated with kapton from mcMaster carr. I think it cost something like $60 though, and you still need 120V to run it. If it fits well enough, it will probably give you more even heating than the ones I have. There was also another one from somewhere outside of the U.S. that was coated in silicone. I don't remember what that one cost.

What could one use to regulate the temperature of the insulated kapton from mcmaster? Seems like the specs would be too much for any electronics out there right now. Unless I am misinformed about current electronics.

Here is a link to what I am looking at here

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- Andy
digifabindustries.blogspot.com

An Iron works fine, they usually have a basic cast Aluminium plate, and not much else, so are very light.

Just watch out for the mains voltage, it's not for everyone, but it will work if you are happy to hack one apart, my one was brand new for under £4 from Tesco here in the UK. - Hacked Iron

Good Luck.

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[richrap.blogspot.com]

Have you had a chance to test it with ABS, richrap? What were the results? Thanks.