MK3 heatbed 12v or 24v, relays?

Wrapping up my P3Steel build (1st 3D printer), I will be printing ABS.
I have decided to run a separate PS for the MK3 heatbed.
.
Is there any advantage to going 24v over 12v ?

What is the min power requirements at each voltage? (I checked around and can not find it)

Solid state or mech relay ?

Many thanks,
Slack

Found the power requirements, 115-144w
thinking 24v 150w power supply ?

While by the numbers 150W would be enough, experience tells that a cheap PSU should be oversized. In this case i would get 200-250W.
I switched from 12V to 24V and i am very happy with it. Lower currents make it easier to use small connectors, thinner cables etc. Also the stepper motors have a bit more snap to them @24V.
Never use a mechanical relay, use either a MOSFET, like it is already integrated in most printer electronics, or a SSR.

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[www.bonkers.de]
[merlin-hotend.de]
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Srek,
The 24v PS would be only used to power the Heated Bed,
I would retain the PS that came with my P3steel kit, and add a solid state relay and 24v PS just for the Heated Bed, or that was my plan ?

Slack

Not a bad idea, but dependent on the board you use you don't need the SSR. The RUMBA for example allows you to drive the heated bed with 24V while the rest runs on 12V.

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[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

How big is the print bed? I run a 450W heater on my 317 x 305 bed and it takes about 5 minutes to heat up to 105C for printing ABS. Look for about 0.5 W/cm^2 to get similar performance. With lower power density you'll be waiting longer or maybe not even getting up to 105C.

Is your printer enclosed? If not you won't be printing ABS. You need to enclose it and get the temperature inside up to about 45-50C to keep ABS from delaminating. Your bed heater may be sufficient to get the temperature inside the enclosure up, but it may require additional heat.

Use PID control of the bed temperature to ensure best print quality. That means you also want to use a MOSFET or a SSR to switch power to the heater because a mechanical relay will drive you nuts with the clicking and won't last long under PID operation.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

@Srek - Why not use a mechanical relay? With Bang bang control these function really well. The control of the bed temperature is very stable. Simple and effective, plus you can get a version with a built in automotive fuse.

@Digital Dentist - PID control for the bed might help with a large bed such as the one you are referring to. A 20cm x 20cm bed which I run on the smartrapcore alu, off a mechanical relay with bang bang control, heats up in 3-5 minutes and maintains a very stable temperature. The relay is quite quiet compared to everything else that's running and its reassuring to hear it working.

@Slackdaddy - Going to dual PSU and moving the bed to 24v with some sort of relay makes a lot of sense, as mentioned smaller wires/connectors and faster heating, but the really big one it removes the high current part of the printer from the ramps board which means a really big reduction in fire risk/overheating and leaves you lots of overhead on your 12v power supply. Assuming you have a chinese LED/brick power supply you can "downgrade" to a laptop style PSU which are practically lying around everywhere and use the brick for something else.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

+1 for relay control -- it works well, it's available in any automotive parts shop, the internal resistance is very low (unlike many SSRs) and in both my printers that have a relay it's proved 100% reliable.
I don't really see the need for PID control of a heat bed, mine doesn't overshoot with just bang-bang control. Maybe if your sensor is a long way away from the heater part it might be useful, but for most heated beds just plain old bang bang works fine.