24"x24" Prusa I3 Bed Power

I'm planning on building a 24"x24" prusa i3, and i wanted to know how to control the four 12"x12" beds all at once.

Any suggestions?

Edited 1 time(s). Last edit at 02/02/2015 10:55PM by ed328.

provided you do not exceed the current limit for power supply and switching mosfet you could put all the heaters in parallel. you should only connect one of the thermistors.

Multiply external PSU and use relays. 13A/heatbed under 12v or 9A/heatbed under 24v. To me, the prusa i3 architecture is not scalable that much. You can increase a bit Y and Z but I would keep X dimensions as close possible as the original. Scaling a machine is not as simple as increasing dimensions. You should increase exponentialy structure profiles, guides and transmission. Price will increase exponentialy too. At last if you want to reach the same print quality as its parent.

Edited 1 time(s). Last edit at 02/03/2015 04:25AM by Zavashier.

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

If you do this, you should probably use a sheet of aluminum or something with good thermal conductivity as a bed. The reason being that the gaps between the actual heated spots on the heatbeds is large enough to cause discrepancies in how the bed reacts.

For the thermistors, I would use 4, which can be connected using a series/parallel configuration which will average out the results into something that the firmware can understand:

+---/\/\---+
|          |
+---/\/\---+
|          |
|          +---/\/\---+
|          |          |
|          +---/\/\---+
|                     |
|                     |

If each of these is a standard 100k thermistor, the result with these 4 will look like a single 100k thermistor to the firmware, which will result in them reporting the average temperature over all 4 locations.

Quote
Zavashier
Multiply external PSU and use relays. 13A/heatbed under 12v or 9A/heatbed under 24v. To me, the prusa i3 architecture is not scalable that much. You can increase a bit Y and Z but I would keep X dimensions as close possible as the original. Scaling a machine is not as simple as increasing dimensions. You should increase exponentialy structure profiles, guides and transmission. Price will increase exponentialy too. At last if you want to reach the same print quality as its parent.

Thanks for the input. I see what you mean. However, I was only using the Prusa i3 as a guide. I've taken into account how much the size will change everything, and I have made changes to account for it. I've already bought everything , so I just hope that I compensated enough for the change in size.

Quote
SupraGuy
If you do this, you should probably use a sheet of aluminum or something with good thermal conductivity as a bed. The reason being that the gaps between the actual heated spots on the heatbeds is large enough to cause discrepancies in how the bed reacts.

For the thermistors, I would use 4, which can be connected using a series/parallel configuration which will average out the results into something that the firmware can understand:

+---/\/\---+
|          |
+---/\/\---+
|          |
|          +---/\/\---+
|          |          |
|          +---/\/\---+
|                     |
|                     |

If each of these is a standard 100k thermistor, the result with these 4 will look like a single 100k thermistor to the firmware, which will result in them reporting the average temperature over all 4 locations.

You should probably know thermistors can not be averaged because their transfer function is not linear.

Yeah, I know... However from a practical standpoint if all 4 are measuring similar temperatures due to similar circumstances (each is at the center of a powered heatbed running the same duty cycle) then it works out okay. I'm familiar with the rating curves. Due to tolerances, you'll probably have variations, where each heat bed is at its own temperature, some hotter, some cooler, but the overall temperature will come out close to correct, probably more so than any other solution, certainly more so than a single thermistor placed in just one heat bed. Also, there will be variations in the surface temperature where the heat bed edges are, it's something that's just going to happen. That's the reason I advocated a plate with high thermal conductivity.

If you want to use four standard PCB heatbeds, then I suggest you use an aluminium heat spreader as has already been suggested, and put a single thermistor at the centre. If they are 12V heated beds, connect them in series/parallel configuration as has been suggested for the thermistor, and run them from 24V. Then you can use either a single mosfet or a pair of paralleled mosfets to switch them.

Personally, if I were building such a large heated bed, I would use AC mains power for the heater and switch it using a zero-crossing SSR. But of course, you then have to take additional precautions because of working with mains voltage.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Just as a point of reference, I have a bed that is 12.5" x 12" x 1/4" aluminum plate and it takes about 6 minutes to heat up to 105C.

hi, did you complete the 3d printer 24" x24" -- (600mm x 600mm)

i starting on get input and material to build one. I find it on ebay a Chinese company who makes custom silicone bed 24x24" that i can attach to a sheet of aluminum, not sure what voltage/watt to get it yet.
i am thinking to get a 24vdc, about wattage not sure
thx for any input.

I've been busy, so I haven't been able to work on it. I ordered a 600x600 silicon bed from alibaba about a week ago. I think that's the way to go. If I find any problems I'll tell you.

thx for the reply , one more question did you find out which control board is better to control this big heated bed beside use a solid relay switch "ssd".

Hi, can you share some info on what kind 3d printer frame did you use to build it a 12" plate, what main board use it and hot bed specs.
Thank you.

Edited 2 time(s). Last edit at 03/15/2015 11:34PM by magnetos.