Heated bed power requirements for new design

Greetings!

I'm investigating the power requirements for my latest printer, a coreXY with a print volume of 24x12x12.

I'm planning on using 2 x 300mm heated beds, the power requirements for 1 of them is ~12v@20amps, but I'm considering going 24v - Would the amperage requirement for 2 of them be 20 amps for 2 of them run at 24v?

Thanks in advance.

If you go to 24V you will connect the two 12V heaters in series and they will require 20A total.

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

The heated beds are capable of being powered with 12 or 24v. Am I correct in my understanding that as voltage goes up, amperage requirements go down within the same circuit?

The goal of this question is to determine power supply requirements for the heated beds.

If they work with 12 or 24 V, each heater is probably two separate resistance circuits that use 12V at 10A each (in other words, two 1.2 Ohm resistors). If you jumper them in parallel, one heater unit will take 12V at 20A. If you jumper them in series you will need 24V at 10A. In either case you're using 240 Watts for one heater unit. Since you're using two heater units, you can jumper each heater unit for 12V and then put the two heater units in series or you can jumper them for 24V and put the two heaters in parallel. Either way they should take a total of 20A from the 24V supply for a total of 480 Watts.

I use a 450W heater on my 1/4" x 12" x 12.5" aluminum bed and it heats to 105C in about 5 minutes. Since you're using a bigger plate and approximately the same power, you can expect it to take a bit longer to heat up, especially if you put a slab of glass on top of it.

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

I think 480W may be marginal for that size bed. However, if you will be using a LED power supply with a voltage adjustment pot, you can turn the voltage up (as long as your electronics can take a bit more than 24V) to get some extra power.

Why not use a silicone bed heater on the back of an aluminium tool plate instead? These people [alirubber.en.alibaba.com] will make a heater to your size, voltage and power specifications at a good price. They made me a 300mm diameter 230V 350W heater for my delta printer. If you choose a heater slightly smaller than the plate, then you can use the edges of the plate to attach fixings, and also bed clips if you intend to print on glass.

Don't even consider using 12V. Use either 24V or AC mains voltage for the bed heater. Most electronics other than RAMPS can handle 24V.

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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].

Sorry to chip in on this without a solution to the problem, but as this is the most current thread mentioning silicone heaters, I thought it would be better here than a new thread. I'm currently looking to finish my bed design, hoping to get it right first time otherwise i'll manage without for a while, choosing the right combo/layering for the job. A while back I had the idea of using a flat silicone sheet(trivet) as a heat barrier, between the bed & under carriage, and also for motor gaskets, then I discovered people where actually making silicone heaters, pity they aren't black but orange will have to do.

So the silicone absorbs a lot of the heat, I assume it helps distribute more evenly, but the core must be rather hot, depends on thickness of silicone as to how much is absorbed.

So you/i could have aluminium & glass(& PrintBite) or just glass above it, aluminium below.
Obviously using fewer items is better, I found some nice 300mmx600mm 6mm glass shelves with a nicely finished edge, I knew they would come in handy one day. but there are no premade mounting holes in it so I need alternate items to hold it all in place.

For my build I was going to go with the Mk3 Black 3mm aluminium(cheap), but then you read people like using 5-6mm alu' plates
I wonder if 2 of these beds could be used together on top of each other, or 4 in your case(yeah I know it does 24v) laminated 3mm might not deform, I've seen people printing on the black side with the printed triangle warning, rather than the aluminium side???

Other thought would be magnetic induction hot plate/hob they are quite cheap but heavy, I wonder if a way can be found to have it heat a flat sheet under the glass, so you dont need a metal pan.

It would be so cool if something like this could be modified, save a lot of hassle, all in one unit.
[www.ebay.co.uk]
even if it meant using a flat sheet of the most suitable metal above.

Edited 2 time(s). Last edit at 10/12/2015 06:38PM by MechaBits.

Glass is a thermal insulator and not an ideal surface for a print bed because of temperature variations across its surface. Temperature variation matters because prints may let go at cool spots on the bed. Tempered glass shelves are frequently not very flat. I started with one of those in my printer and it had a wavy surface- see MegaMax print bed. Glass is commonly used on top of aluminum for two reasons:

1) Cheapness. Printer kit makers supply a heater attached to a thin piece of aluminum as a "heat spreader" and then expect you to put a piece of glass on top of it because the thin aluminum isn't/won't stay flat in the printer, often because of a poorly designed "leveling" system (4 screws) that actually bends the plate instead of leveling it. Using that arrangement allows them to say they have a heated bed without actually providing a flat plate to print on because that would add to cost and no one wants to spend more than $300 for a printer. This is also the reason so many kits come with underpowered heaters that take forever to heat up to print temperature, if they reach it at all.

Cast aluminum tooling plate is flat and thermally conductive. It costs a little more than glass but doesn't suffer from the temperature variations that glass does.

2) Swapping glass plates so you can start printing again very quickly. This is a marketing dept driven concept that sounds good but for most people probably doesn't mean anything because who is on such a tight printing schedule that they need to keep printing so fast they can't wait for the printer to cool down before they start the next print? Some people who subscribe to the glass plate swapping idea will say that glass is better than aluminum for this because aluminum is fragile and scratches easily.

The problem with that argument is that scratches don't matter and dropped aluminum plates don't break into razor sharp shards.

My printer has a 12" x 12.5" x 1/4" cast tooling plate bed covered with kapton tape. I can print nearly edge to edge on it without any messy stuff applied to the bed to get prints to stick. It has a 450W heater and a three point leveling system that actually levels it instead of bending it.

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

Yes I read the guide, and will probably read it a few more times, I believe alu is one of the best materials to print on, I wonder if a cheap MK3 under your plate would be enough, but the plate's more expensive than the heatbed, you still put some tape on it, the local fablab seems to be coping quite well on the ultimaker with a little hairspray or prit stick. Float glass would be flat though, I wonder if silicone insulates more than glass?

Edited 1 time(s). Last edit at 10/13/2015 12:49AM by MechaBits.

Quote
MechaBits
I wonder if a cheap MK3 under your plate would be enough,

Today i bought a 250mm x 260mm 8mm thick aluminum from a local supplier. It was cheap but on my way to home i got terrified with the possiblity the heater will be unable to heat up this mass. I intend to take to to the mill and do it from 8mm->6mm but i concern about the heater. It is a mk3b heater with both 24/12v supply.

If you guys have any experience please let me know.

@ dentist - what kind of heater is the 450w one ?

Edited 1 time(s). Last edit at 01/14/2016 11:53AM by Gaou.

I think you will struggle to reach ABS printing temperatures using a standard 120W PCB bed heater on a bed of that size. Also the thermal mass of the thick aluminium will increase the heating time. My suggestion:

1. Check that the aluminium is flat enough. If it isn't tooling plate, it may not be.

2. Buy a silicone bed heater a little smaller than the aluminium, to allow space around the edge for fixings, and also bed clips if you intend to use a glass sheet on top. Stick it on the underside of the aluminium plate. These people [www.aliexpress.com] will make a custom heater to your size, voltage and power specifications. I suggest about 200W and either 24V or mains voltage. They list a 225x225mm 24V 192W heater which should be a good match.

3. Use cork sheet or corrugated cardboard insulation under the bed to reduce waste heat.

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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].

I use a Kapton heater that I got from Trinity Labs before they went under. You can probably find something similar via Aliexpress or ebay. The 450W heater gets the bed up to 105C in about 5 minutes with no insulation on the underside (I already have more than enough moving mass in my printer's Y axis). If you go much over 200W, I'd suggest using a line voltage heater instead of a low voltage unit, but you'll have to be extra careful about wiring it, especially if it moves in the Y axis. My bed's heater is a 24V unit that takes about 20A and I power it with a very heavy transformer. The advantage of the transformer over a DC supply is that the SSR that switches power to the heater doesn't have to be heatsinked. If you switch DC you need a rather pricey SSR or a cheap one with a big heatsink.

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

thanks guys for ur feedbacks but somethig more.

i ve read the duet is capable of supplying 24v is that right or i missunderstood ? if it can how amps can it handle ?

i ll test the heater to see if it can reach 80c and in what period of time and if i saw it cant at all i ll leave it to but a bigger one as you have already suggested . But for now i am out of budget and i ll have to wait.

The Duet can handle up to 30V. The bed heater circuit is OK up to at least 12A, and probably more on the version 0.8.5 board.

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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].

Today i got my heater . So i 've run a test. The aluminum is 5.7mm and pluging the heater to an old pc psu i saw that it was able to heat up the aluminum. The psu is weak enough with the 12v rail supplying only 10v and dont know how many amps ( i imagine less than 7).

The intention was to test the cables soldered on the heater and i saw that it worked pretty well for about 10-15min. I 'll change my psu and i ll test again . I didn't had a temp sensor so i used my hand and it seems it could reach 60-70celcious.

So i am glad and hopefully it will work .

Why not a 220V AC heater with a SSR, low current not a lot of heating of the SSR. Also available on aliexpress.

plugging 220v ac to a printer ( or anywhere ) require some skills ( which i dont have ) to avoid accidents .