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Heated Bed Calculation

Posted by Ray

Ray

Heated Bed Calculation
September 18, 2014 11:13PM

Registered: 9 years ago
Posts: 25

Good Evening,

I was reading about Robert's Heated Bed and about Conductive Materials but I didn't find how he calculate a resistance of 1.3 Ohms:

32 loops x 220mm = 7040 mm= 7m

R_s=0,0168/1,5= 0,0112Ohms/m

R=0,0112*7= 0,0784 Ohms

and with the other wire value given in the post:

R=7(0,0168/(3,14*(0,56/2)²))=0,47 Ohms

What did I do wrong?

Reply Quote

Ray

Re: Heated Bed Calculation
September 20, 2014 09:36PM

Registered: 9 years ago
Posts: 25

As Mr Kuhlmann kindly solved my problem in MP, I share the solution so everybody can benefit.

Quote
Robert
Hi Ray,

easy: There are 32 nails on each side. Each nail can be used for two loops/lines, giving 64 lines of app. 14m length + some extra length for the curves around the nails.
For a specific resistance of 0.0175 this would result in a calculated 0.98 Ω resistance.

Isolated copper wire can have a slightly higher specific resistance and standard meters aren't very accurate at low resistances. I measured 1.3Ohms though. The very low specific resistance of 0.0168 you've used in your calculation would only fit for pure copper, which you won't find in standard wires and cables.

I'm using only 32 loops for my 18A heated bed (calculated) and I'm very satisfied with that. Printing with 110° C on plain 3 mm thick aluminum with hairspray works great.
Feel free to ask any further questions. But you should ask in public so others can benefit from the answers as well.

Greetings
Robert