DIY heat bed
September 10, 2015 05:33PM
I need to build a heat bed as I am building a large printer, I found the use of resistor to build a 400mm x 400mm heat bed from Mega i3 instructions, the question is, I want to build a 800mm x 800mm heat bed, going by the instructions, I will need to use 16 of them resistors for the size I hope to build, anybody have any idea which resistor I need for this setup, I can work out I need 16ohm resistors, 16 of them comes to 1ohm in parallel, but how does the voltage and wattage works?

thanks

Edited 1 time(s). Last edit at 09/10/2015 05:33PM by deaconfrost.
Re: DIY heat bed
September 11, 2015 03:00AM
@12V you draw 12A giving 144W
@ 24V you draw 24A giving 576W.
Re: DIY heat bed
September 11, 2015 03:18AM
Hi,

Large heatbeds are usualy powered by AC current,
because it's cheaper than a huge PSU and it works better.
You just have to use a relay to control it.

++JM
Re: DIY heat bed
September 11, 2015 04:50AM
These people [www.aliexpress.com] will make a silicone bed heater to your size, voltage and power specifications, with adhesive sheet on top, with or without thermistor. For a printer of that size, I suggest you use an AC mains powered heater with 700W to 800W power output. You can control it via a SSR-25DA solid state relay. You can attach the heater to the underside of an aluminium bed plate.

Be sure to take proper safety precautions with AC mains, in particular protective grounding of the bed and other metal parts, and strain relief at the ends of the heater cable run if the bed will be moving.



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].
Re: DIY heat bed
September 11, 2015 04:53AM
I can wire up a 12v relay to D8 to drive the bed that's not a problem. But what components should I get to build it that way? I don't really mind running a single high power 12v psu either. They have come down in price a lot these days, I remember the days I use to pay 150+ for the pc's psu to run 4 hdds, sli and what not on a 1kw plus psu. I don't think I would need that kind of power to run the large printer. Only thing is I have only 1 way to run 8 hotends at the minute is run it like 4 printers in one, 2 color print at a time with 4 ramps setup. Plug in different board to use different hotends with different sizes nozzle, from 0.3mm to 1.2mm volcano

Edited 1 time(s). Last edit at 09/11/2015 04:55AM by deaconfrost.
Re: DIY heat bed
September 11, 2015 05:07AM
Thanks for that info, exactly what I need, now I'm looking forward to get this monster built
Re: DIY heat bed
September 11, 2015 05:55PM
Quote
deaconfrost
I can wire up a 12v relay to D8 to drive the bed that's not a problem. But what components should I get to build it that way? I don't really mind running a single high power 12v psu either. They have come down in price a lot these days, I remember the days I use to pay 150+ for the pc's psu to run 4 hdds, sli and what not on a 1kw plus psu. I don't think I would need that kind of power to run the large printer. Only thing is I have only 1 way to run 8 hotends at the minute is run it like 4 printers in one, 2 color print at a time with 4 ramps setup. Plug in different board to use different hotends with different sizes nozzle, from 0.3mm to 1.2mm volcano

please remember that to generate heat, you need watts. At 12VDC your Amps to produce 'x' watts will be a LOT higher than the amps from 220VAC ( or whatever your mains supply is ) to generate the same watts.

Also, if you're using a Ramps board, they do have a limit of the amount of current that you can pass thru the board - I think there is an on-board fuse.

Maybe you should look at using the Ramps to control an SSR ( solid state relay ) which uses low 12VDC current for control, and control AC supply to a stripped down clothes iron element ( or 2 if it's a large bed ).

Irons run around 900W or more, and will heat up very quick, and are dirt cheap and easy to replace.
Re: DIY heat bed
September 11, 2015 09:41PM
I could stripe down the iron and use it to heat the bed if I can spread the inside around a bit
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