Heated bed getting temp

My Mk3 heated bed hasn't been getting hotter than 60°c and it still takes about 5 mins to get too that temp. Any help or advice would be amazing.

VS450 Corsair PSU
Ramps 1.4
14 gauge wire to the bed

There are several possible causes. If you have a multimeter, measure the voltage across the terminals of the bed heater, and the bed heater output and the 11A input of the RAMPS. That will help diagnose what the problem is.

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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].

You are using a PC power supply. Check the voltage and make sure its at least 12v
I have a "LED" power supply from Amazon that I adjusted to 12.3v and I have no issues getting to even ABS temps.
60c is maybe 2-3 minutes for me.

Exactly 12v on the ramps input without load.
11.7v on the ramps input with load (heating bed).
11.2v on heated bed output with load.
11.2v on the bed terminals.
1.7ohms resistance on the bed.
When the mk3 arrived it had one of the negative terminals broken off. This could be the problem but I was also facing this issue with the red heated bed (MK2? Mk1?). The PSU is rated for 30A on the 12v rail, this should be plenty shouldn't it?

1.7 ohms is much too high, that is the problem. If it it a dual voltage 12/24V bed heater and you are only powering one of the two elements because of a broken terminal, that explains the problem.

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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].

What would be a respectable resistance for a mk3 bed?

For a 200x200mm bed, between 1.0 and 1.2 ohms for 12V, and between 4.0 and 4.8 ohms for 24V. But they vary a lot. I suspect that some manufacturers don't control the copper thickness very well. I prefer to use silicone heaters attached to the underside of aluminum plates instead.

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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].

Where would the cheapest place to get a silicone heater mat be? What thickness of aluminium would you recommend? Do the silicone mats heat up faster than mk3 beds and what is the max temp? Thanks

You can find silicone bed heaters on eBay and Amazon. A good power density to aim for is 0.4W/sq.cm. For a 200mm square bed this works out as 160W. Bear in mind that your power supply and electronics need to be able to handle this amount of power. For example, most versions of RAMPS are limited to 11A output, which at 12V is only 132W.

There are two approaches to bed plate thickness. The cheap way is to use a thin plate e.g 1.5mm and clamp it to a 4mm thick float glass plate. The glass provides the stiffness. This is ok for small beds. The better approach is to use aluminium tooling plate, perhaps 6mm thick or greater depending on bed size. Either way, I suggest choosing the heater to be slightly smaller than the bed plate and the glass if any, to allow room for fixings around the edge.

Depending on your goals, you may be better off just buying a new PCB bed heater. They are usually about 120W and can usually reach 100C. To reach higher temperatures you can turn the supply voltage up to e.g. 14V, but don't try this if you are using Arduino/RAMPS electronics.

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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].

Would I use a solid state relay to achieve more than 11amps?

Here are 3 options:

1. Use a solid state relay. See [duet3d.com] for recommended part numbers and what to avoid.

2. Use a 24V bed heater, then the current requirement for a given bed power is halved. You can either convert the whole printer to 24V, or use a separate power supply for the bed.

3. Use a better controller board. Many boards can switch 15A or more.

Edited 2 time(s). Last edit at 03/20/2017 03:08AM by dc42.

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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].