Heated bed, Relays and power suplies

Hi everyone,

We have just about finished building a printer that will have a build area of 600mm x 300mm but I am struggling to get my head around heating the bed.

From an old printer I have a HKS BASE V1.1 board and a 12v 360W power supply.

I am thinking that my best and most practical option would be to purchase 2 x 300mm x 300mm silicone heated mats like below.

http://www.ebay.co.uk/itm/300x300mm-Square-Silicone-Rubber-Heater-Pad-w-thermistor-220V-500W-/162405685931?var=&hash=item25d0221aab:m:mjTu-4wBABfLQjcKiz3SJIw

My question is how do I wire them? Do I need some sort of relay?
- Would I be better off buying a 24v PSU and if so what Wattage should I be looking at?

Thanks

220V heatbeds are easily controlled using a solid state relais. It works just like a normal relais, but without the moving parts.
Something like this would be pretty much perfect
[www.ebay.de]

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

Make sure you earth the frame, any metal heat spreader that is part of the bed, and the solid state relay and use an Rcd or ground fault interrupter. A thermal fuse is also a very sensible precaution in case the solid state relay fails with current flowing which would heat the bed up to quite a scary temperature, mine is 700w RRF reckons it would reach 500 deg C if left on!

But in all fairness compared to DC beds even 24v ones mains powered is awesome. 330mm 6mm tooling plate bed 20-120 deg C in 3 mins.

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Simon Khoury

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

For that size bed I suggest about 720W heating power, based on 0.4W per sq cm. If the bed will be very thick aluminium, you may want to go a little higher e.g. 900W. You could use those heaters you linked to, but an alternative is to have a silicone heater made to your own size, voltage and power specifications here [www.aliexpress.com].

Choose a heater a little smaller than your bed plate (e.g. 15mm smaller all round) to leave room at the edges for fixings.

Controlling a mains-voltage bed heater using a zero-crossing DC-AC SSR such as SSR-25DA is easy, but of course you take appropriate safety precautions.

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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].

Thanks the responses guys!

Quote
dc42
For that size bed I suggest about 720W heating power, based on 0.4W per sq cm. If the bed will be very thick aluminium, you may want to go a little higher e.g. 900W. You could use those heaters you linked to, but an alternative is to have a silicone heater made to your own size, voltage and power specifications here [www.aliexpress.com].

Choose a heater a little smaller than your bed plate (e.g. 15mm smaller all round) to leave room at the edges for fixings.

Controlling a mains-voltage bed heater using a zero-crossing DC-AC SSR such as SSR-25DA is easy, but of course you take appropriate safety precautions.

So I can keep my 12v 360w PSU, Ask the supplier in that link for a 220v 600mm x 300mm 800w-900w silicone heater. And buy that SSR-25DA and everything should work?

I was expecting to have to spend much more on more PSU's etc so this is great news!

I have just about got my head around the wiring and how relays work now aswell.

There is a summary of precautions to take when using a mains powered bed heater at [duet3d.com].

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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].