Need expert advise on a build

[martialmedia]

I am looking to use a laser to heat a 4 mm diameter dark copper plate that is about 1 mm thick. The plate will be positioned about 2" from the laser. I would like to hit it with about a 3 mm beam. It needs to heat to about 250 degrees F in 2 seconds. I'd like to use the lowest mw laser that I can, for longer battery life. Can someone give me an idea of a laser that would be best to achieve that?

Thanks

 

[jander6442]

What are you powering a TEC?

 

[martialmedia]

I'm not powering anything, just heating a little copper plate. I ordered a 1.25w blue laser. I figure that will do it, but I'd prefer to go lower if possible to keep it in the class 3 range.

 

[CheeseHasLeafs]

Does it absolutely have to be a laser? Seems to me there are better ways to achieve this.

 

[martialmedia]

There are definitely more efficient ways, but none are more fun or cooler to watch. :drool: I'm gonna give it a shot at 1.2 watts and take it from there.

 

[BShanahan14rulz]

Keep in mind that the best case scenario, 1.25W of heat would be transferred to the copper disk. This would basically look like the laser beam stopping when it hits the disk, i.e. no spot, just laser beam stopping.

I'm too lazy to google the maths, and too dumb to know this off the top of my head, but you should look into calculating how much power you would need to heat that mass of copper up to that temperature in 2s. You know the mass and you can find thermal capacity of copper, and I'm sure there is a fairly simple equation that relates those variables to power and time.

Keep in mind that it isn't a one way valve; you are pumping energy into the copper, yes, but the copper is also radiating heat, and if it is touching something, conducting heat out.

I also discovered, apparently I like to say "Keep in mind" a lot. Keep in mind, I don't actually talk like this.

 

[Photonz]

You need the heat capacity of copper, mass of the copper piece (in grams) and initial temperature(assuming room temp)

solve for q in the following equation to figure out how much energy is needed to heat it to 250 F (121C):
q=mC(Tf-Ti) and you would plug in 121 for Tf and 25 for Ti(room temp)
so the final equation would be:

q=mass x .385 x 96
Solve for q which is in Joules

once you have the value for how much energy is required to heat it to 121C or 250F then use this equation to find out how many W or how long it will take: J=W x s

so assuming it absorbs all 1.2W then it would be J=1.2 x seconds (solve for seconds) but because you want 2 seconds then it would be better to solve for how many watts you would need.

so J=W x 2

If you have the mass of the piece I could solve it all out and calculate the minimum number of Watts you need to heat it up.

If you want to do it then use this combined equation: W=(mCΔT)/s
and solve for W
where W is watts, m is mass(in grams), C is heat capacity of copper(which is .385), ΔT is change in temp in celcius(which is 121-initial temp), and s is time in seconds.

 

[martialmedia]

Thanks for all your input! I think a 1w will be a little light, so to speak haha! I'm glad I took remedial math!

 

[Photonz]

If you could mass the copper piece I would find out how powerful of a laser you would need. Anyway, glad to help:beer: