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Posted by TheBearF8 
January 10, 2014 07:09AM
Hi All,
new to the rewrap community

I was wondering exactly what the hotbed it typically made of ?

I find online most hotbeds are 200mm x 200mm or 8" x 8" and most 3D printers are this size also.

I'm interested in building a bigger printer 16" x 28" so I'm guessing I'll need to build my own hotbed.

Thanks in advance
Re: Hotbed
January 10, 2014 07:53AM
A heated bed that size would require massive amounts of power to reach a usable temperature. Also printing parts that sort of size would take forever and have a good chance of failing.
Re: Hotbed
January 10, 2014 08:00AM
I have a friend with a printer that can do 12" x 12"
He kept boasting he could print a basketball.

Till he tried that is ;-)

He said it took about 2 days to print it !

Put it this way, I've never actually seen it.
Re: Hotbed
January 10, 2014 08:02AM
Thanks for the input (lazzymonk & DaveS)

What then are the realistic large sizes that can be printed

Would 10" x 5" x 3" be reasonable ?

Thanks again
Re: Hotbed
January 10, 2014 08:36AM
Mine can do 200x200x300mm which is about 8x8x12 not that I use all that possibility often at all.

A 5x10 heat bed would have a smaller surface area than a 8x8 so yeah it would be fine. But it is also close enough to 8x8. Do you really need the extra 2? Is the worth the hassle just to get it?
Re: Hotbed
January 10, 2014 08:38AM
The extra 2" on my first project would be real helpful yes
What if you had two beds side by side 8x8 + 8x8 effectively giving 16x8
Is that possible ?

again as I said in my first post I'm new to reprap and this will be my first 3D printer

Thanks again
Re: Hotbed
January 10, 2014 08:45AM
How about something like this [store.qu-bd.com]
Re: Hotbed
January 10, 2014 09:04AM
I have a Mendel max 2 which can do 310x230x220 mm3 or so which might fit the bill. I am super happy with it so far!
Re: Hotbed
January 10, 2014 09:21AM
lazzymonk Thank you for the link
That will work great
Re: Hotbed
January 10, 2014 09:30AM
I have a 12" by 12" bed and it heats within 60s and I routinely fill it with parts with no issues.
Re: Hotbed
January 10, 2014 04:02PM
I'm actually setting up mine right now with two mk3 heated beds which give me 8x16 and I have a custom milled aluminum plate specifically made for this setup. I usually don't print 1 large print but, I commonly print a bunch of smaller objects. The two heated beds are wired through a solid state relay and I'm currently running 3 power supplies due to the fact that I have dual extruders as well. I've tested out the setup to make sure it would work and then recently ordered my own set of parts to complete this build.

I have a printrbot plus v2 with extended y and Z axis's. I also added aluminum bearing blocks on all axis's to accomidate the added weight. I'm also replacing everything above the base with custom milled aluminum. A lot of work has gone into but, running two heated beds was the cheapest and most effective way to do it for me. I would agree with others to say that it's not realistic to use that much space to print a single object. It's a lot better to print several smaller items and assemble them after prints.

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Re: Dual Hotbed
February 28, 2014 06:27PM
If one was to use two 8.5" ( MK2a ) hotbeds side by side creating a 8.5" x 17" bed
Would one connect the bed in parallel or series

I have a 300W power supply.

Thanks in advance

Edited 2 time(s). Last edit at 02/28/2014 06:27PM by TheBearF8.
Re: Hotbed
March 01, 2014 04:24AM
With a 300w psu, neither.

Assuming it is a 12v psu. In series you would have a total of about 75w, no where near enough to reach usable temperatures. In parallel you would have 290w, far more than you want to be drawing from a 300w psu, even if it was only running the heated bed. You add your other electronics too and bye bye psu
Re: Hotbed
March 01, 2014 07:40AM
To Lazzymonk

Thanks for the feedback Yes it is a 12V PSU
could you go into more details, how did you get the 75W and 290W figures ?

Also if this was a 500W or 600W PSU which then would be best ?

Thanks in advance

Edited 1 time(s). Last edit at 03/01/2014 07:42AM by TheBearF8.
Re: Hotbed
March 02, 2014 05:22PM
Its all about resistance. A mk2a has a resistance of 1.0 - 1.2 ohms. 2 beds in series have a resistance of 2 ohms ( worst case ). 2 beds in parallel have a resistance of 0.5 ohms.

You can use ohms law to calculate the wattage or you can use something like this [www.ohmslawcalculator.com]

the best bet would be a 24v psu and run them in series. 290w at 24v is 12amps. But 290w at 12v is 24amps. Thats a lot of current, would need large cables to supply it. Would need a relay to control it as is far too much to run directly through any electronics that i know of.
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