300x300mm Heated Bed Power Issue

Short story, Im upgrading my Prusa i2 to a Prusa i3 and expanding the design to accomdate a cubic foot of printing volume or 2.7 million mm^3. I realized the power issue while trying to expand the base of the Prusa i3 in Autodesk Inventor. How am I going to power a 300x300mm bed? I do have a spare 12V 18A power supply hanging around that can serve as a dedicated power unit for the heated bed. My Prusa i2 currently uses 12V 30A power supply.

You´d need a relais or solid state relais (SSR) to power a bigger heatbed.
This has been discussed and answered many times before.

Use the searching machine
-Olaf

I estimate that you will need at least 250W heating power for a bed of that size, and preferably 500W to reach ABS printing temperatures quickly. So 18A @ 12V isn't quite enough. You could use your 12V 30A PSU for the bed, and the 18A one for everything else. However, handling 25 to 30A isn't easy, so it's better to use a higher voltage for the heated bed. There are two main alternatives to using 12V:

1. Use 24V. Many heated bed PCBs are dual voltage 12V or 24V, and there are inexpensive 24V PSUs. If the bed takes only 10A, then most standard printer electronics will drive it (e.g. RAMPS provides a separate power input for the bed, so you can feed 24V to that even though the rest of the RAMPS is only good for 12V). If it takes up ton 15A, you can use a SevenSwitch. If it takes more than that, you need a DC-DC SSR. Don't use the cheap ones on eBay, they drop about 2V and need massive heatsinks. Crydom sells low-drop DC-DC SSRs, but they are expensive.

2. Use a silicone bed heater powered by AC mains via an inexpensive zero-crossing DC-AC SSR. This creates a number of safety issues, especially on a machine with a moving bed. So only do it if you really know what you are doing or you have advice from a professional electrician.

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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].

Quote
dc42
RAMPS provides a separate power input for the bed, so you can feed 24V to that even though the rest of the RAMPS is only good for 12V

Check the 11A fuse, first. Most china Ramps-clones use 16V fuses only
-Olaf

Quote
o_lampe

Quote
dc42
RAMPS provides a separate power input for the bed, so you can feed 24V to that even though the rest of the RAMPS is only good for 12V

Check the 11A fuse, first. Most china Ramps-clones use 16V fuses only
-Olaf

That's an excellent point. If you supply 24V to the heated bed input, and you get a short in the heated bed circuit, the 11A polyfuse is liable to catch fire. So best replace it with a conventional fuse, e.g. an automotive type.

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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].

This is what I did:



The 24V transformer is big and heavy.

This is the heater:



It came from Trinity Labs, now out of business. Check Ali Express or ebay for similar heaters.

Edited 2 time(s). Last edit at 06/27/2015 07:51AM by the_digital_dentist.