Printing with the Mendel 12V 20A power supply.

All,
I have been using the 12V 20A power supply that came with an earlier Mendel - and found that the voltage drop (with both heater and bed on) to be about 0.1 V (So with heater and bed on - I see 12.1V)
With the ATX power supply, I see a voltage drop of about 1.2V (So, with heater and bed on - I see 10.8V)
Wonder why the ATX power supply was used in the first place when a 12V 20A power supply is so much more steady?

Also, did anyone actually measure the current draw at full load with the ATX power supply? (Theoretically, with the heater and bed resistances+stepper motors+Duet, one shd infer 12-15A??)

Yes, the ATX isn't ideal - the 12V output isn't at all well regulated. The bed takes approx. 10A, extruder 4A and the steppers add a couple more Amps typically. The 12V rail will quite happily provide all this current - and plenty more, but the volts will continue to drop. I think the low cost of the ATX is the reason it's bundled with Ormorod which is an exercise in low cost product design. In practical terms it only really affects printing in higher melting point materials. PLA will print just fine.

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RS Components Reprap Ormerod No. 481

I found that the Alpine PSU supplied with the kit was just fine for PLA printing. Although I haven't tried ABS printing yet, I did some tests on higher bed temperatures, and concluded that it would be just about adequate for ABS printing too, although the bed heating time was about 30 minutes. However, in preparation for ABS printing, I replaced it first by a Corsair CX430M that I already had, which holds the 12V rail much better under load, and is a modular supply so all the unused cables are gone. Now I have gone further and I use a PSU similar to the one used in the Mendel kit, but 25A instead of 20A (it was only £1 more). It is adjustable, so I will probably turn it up to 13V for ABS printing. Here are some photos:



Parts:

PSU [www.ebay.co.uk] (300W version)
Mains IEC socket/switch/fuse [www.maplin.co.uk]
20A locking connector [www.maplin.co.uk] + [www.maplin.co.uk]
Neon [www.maplin.co.uk]
12V cable [www.maplin.co.uk]
Printed box files [dl.dropboxusercontent.com] [dl.dropboxusercontent.com]
Sundries: spade terminal receptacles, 20mm fuse (I used 3A quick, but 2A slow might be better), M3 screws, wire, IEC mains lead.

Edited 3 time(s). Last edit at 02/12/2014 04:57AM 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].

Thanks for the URL. I've just got one of those PSUs, and attached are files to print/modify an end piece for the connectors (I'm printing it out now). I plan on using Farnell parts 1856749, 1856747 and 1430808 for connectors, but the OpenScad file is parametised and modular so it should be easy to modify for use with similar shaped PSUs of a different size and different connectors. First time I've used Scad, so the coding is a bit clumsy, but it seems to work OK. The only misgiving is that the part must be printed end-down, which means that the layers are not in the most favourable direction for where the strength is needed most, but I'll see how it goes. It's easy to change all wall thicknesses in the Scad file, or I might try printing it in a different orientation, though there would be some major bridging.

Dave
(#106)