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Heated Bed....

Posted by Lucastar 
Heated Bed....
June 17, 2012 06:09AM
Hi, can anybody give me a bit of guidance with respect to heated bed resistors?

I understand that the ally clad resistors are reliable.

I have a sanguinololu controller with an Atx PSU, and wish to heat an 4mm Ally bed to about 60degrees directly from the board.

I was thinking that 4 resistors would be enough, (like a Mendel-parts machine)

what rating would I need to select? 1 Ohm?

also what thickness wire would I need to connect these together? I had a look around, but cant find any advise on these....

Any advice would be very much appreciated!

Thanks
Re: Heated Bed....
June 17, 2012 11:54AM
Have a look here....
bed link
Re: Heated Bed....
June 17, 2012 05:31PM
As a side note, I used JB Weld to attach my Al-clad resistors to my heated bed. I have an oversize machine though, the heated bed of which draws 24 Amps (through a relay). I used 10 5-Ohm resistors in parallel to get 0.5 Ohm total resistance, which is 12V/0.5Ohm = 24 Amps. If you want your bed to draw 10 Amps like the Prusa heated beds do, you need a total resistance of about 1.2 Ohms, so 1 Ohm should be fine. If you were to use 4 resistors in parallel, that would be 4 Ohms each. 9 resistors in parallel would be 9 Ohms each. Easy math when you need 1 Ohm total resistance smiling smiley

I used the following resistors, but any similar ones should be fine:
http://www.digikey.com/product-detail/en/AHA10AJB-5R
They are rated for 10W.


Cameron

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Re: Heated Bed....
June 18, 2012 01:27AM
I use 4 2.2 ohm alu housed resisters to heat 5mm thick alu bed, could do with a few more on it as it takes 20 mins to get up to 60C and I just put a dob of thermal paste on them the stuff you use on CPU heatsinks and bolt them on


__________________________________________________________________________
Experimenting in 3D in New Zealand
Re: Heated Bed....
June 19, 2012 09:08AM
Thanks everyone for that info -

NewPerfection: I've noticed that all the ally clad resistors being used are the HS10 watt or HS15 watt type - does anyone use the HS25?


Glyn, I had never seen the Bed link before. Thanks for that.
Are the modifications to the Sanguinololu necessary? or will it power the heated be directly?

NelsonRap, are you powering directly off a sanguinololu?

I've not chosen my ally plate thickness yet - was going to do it 4mm until I saw Adrian's 3mm ally with 4mm glass on top.
I guess that the 5mm will take a lot longer to warm up than the 4mm - not sure about the 3mm with the glass though...
Re: Heated Bed....
June 19, 2012 03:38PM
Quote
Are the modifications to the Sanguinololu necessary? or will it power the heated be directly?

You can power the resistors directly from the board which I do. Going through the mosfet will allow more current and quicker heating ( I presume).
Re: Heated Bed....
June 19, 2012 04:10PM
I'd go with the thinnest flat AL plate you can, the flat part means you really should buy cast rather than rolled AL even at the increased cost.
Rolled stock is never flat.

For point of reference one of my printers has a 1/8th inch rolled AL heated bed, it wasn't until I put the glass on it I realized how not flat it was, and it's not flat enough that in places it doesn't contact the glass well.
Re: Heated Bed....
June 19, 2012 04:22PM
Yes straight off the sanguino,. By using the the thicker 4 or 5mm alu plate I find it's fairly flat well flat enough to use with glass. I have a good supplier who picks out the flattest bits for me


__________________________________________________________________________
Experimenting in 3D in New Zealand
Re: Heated Bed....
June 19, 2012 04:58PM
As long as you aren't drawing more than 10 or 12 amps, you can draw directly from the sanguinololu. My over-sized heated bed is 3mm aluminum, and is plenty flat. It all depends on what you can find though.


Cameron

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Re: Heated Bed....
June 19, 2012 06:16PM
I'm going to try 3mm ally first, and see how it comes out. I will also drive it straight off the sanguinololu. I'll keep it to 10amps+-

I guess it's one of those things that you just need to try.....


Thanks for the help!
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