designing traces for a PCB heater

[Alex Hornstein]

Hello,
I'm putting together a circuit board with a PCB heating trace a la Makerbot/RepRap's heated build platform. I'm looking for tips or (heaven!) a set of design rules on sizing the traces for my heater. I don't need a lot of power--I'm trying to get a tiny enclosed space (~.25 in ^3) up to a max of ~70C

This project doesn't have anything to do with 3D printers--it's the control/heating board for a 3D printed micro-incubator for ~3 petri dishes, but the idea of integrating a heater onto the PCB is inspired by the HBP, and I'm hoping there's some designers on the list who've had experience with these heaters.

An initial googling was foiled by pages of results talking about heating equipment for processing PCBs. I'd welcome any tips or pointers.

Thanks,
Alex

[Joheinz]

Hi Alex,

not hundred percent sure, but it should go along these lines - more
googling required.

When you design the PCB, you can calculate the resistance of the
traces. Let's say 5 Ohm.
You know your supplied voltage. Let's say 12V.

You know your target Temp and room temp, lets say 70 °c and 20 °C.
So, you need to warm up by 50 °C.

There is a formula which says dT = P / R.
That would imply:
50 °C = P / 5 = 10

P = U * I => 10 = 12 * I hence you know that you need to supply a
current of 10/12 A in order to heat up by 50°c.
(in German: http://de.wikipedia.org/wiki/W%C3%A4rmewiderstand#Elektronik)

And here you have a resistance calculator for your PCB:
http://circuitcalculator.com/wordpress/2006/01/24/trace-resistance-calculator
You probably need to get some values from your Fablab.

Please note, that what I wrote should be taken with extreme care!
There are others here on the list, who hopefully can verify some of
the stuff. I would be willing to learn here too.

Markus

2011/11/27 Alex Hornstein <bridge...@gmail.com>:

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[Brent Crosby]

You would be better off using a resistor. A 1210 size SMT resistor
soldered to large pads would be much more predictable than counting on
trace width (pretty well controlled) and thickness (less well
controlled).

[James McCracken]

Don't let them poo-poo your work!

I say just make a heater trace design, put it into copper, and fire that bad puppy up.  For the use you say, you'll want to insulate the chamber well and use thinner more tightly packed traces - maybe of the 8-12 mil width...