What circuit? These measurements were done with a lab setup and using a Fluke thermal-cam to get average hotside and coldside temps. (Quicker than finding the hot probed blocks, or making some.)
I am only supplying power to the heater to simulate heavy power input.
(And supplying 12v to my cold-side fan for consistent readings.)
What I wanted to show, was the load on the peltier by "shorting" it with a resistor, although dropping the sensitivity will also cool the hot side.
I think the effect is related to the seebeck effect but I can't really explain the physics behind it. It is real though.
On my comment of actually cooling the hot side (making it in essence the cold side but only too room temp): That would use power. In fact, it would require about 30% more power than the input laser power due to less than 100% efficiency in the TEC. I guess it wouldn't work well either as it appears it's not the actual laser-power that is the problem, but the fact that it has to be absorbed by a thin layer on the surface of the TEC and lasers are good at burning stuff... Fun thought experiment though.
On a different (slightly) note: I did test the TEC with blackened surface as a detector today. Defocusing the beam to be about 90% of the width of the TEC and placed the TEC under it with it's HSF cooling the back-side.
I used a diode from a SH-S223Q Super Writemaster 22x DVD-RW drive (silly diode that needed lots of work to fit a normal 5.6mm host) and ran it at a few fixed resistor-values. Here's the raw data:
Code:
Id(mA) Vtec(mV)
139 2 (lasing error/flicker)
192 12
227 16.3
288 17.2
312 16.7
340 17.7 (flickering again)
I used a standard linear reg setup as constant-current.
Looks like I should have used a few more values between 139 and 227, but based on the curve I think the diode peaks there? From what I read here on the forums theoutput goes down again after you reach max out and from there it's not far to ruin. I guess I better stay below 300 mA?
The high current needed for stable lasing was odd to me too, but I firt noticed it when testing the laser the first time. I couldn't get it to light stabely at 50 mA. In fact it didn't light at all. Luckally it just needed more...
I must say that the TEC as sensor principle works quite well.
Cudos for that! I guess I'll settle for using an avr to deliver serial data as I want to log it.
Using my power inputs earlier I estimated a "ideal world max power" for the laser. If my 3.6w today produced 262 mV and the losses there were about equal % wise as what I have with the laser, then 17 mV should equal 233mW.
Most likely that is optimistic and I may not even be beyond 200.
All I know is it's barely enough to cut my stencils, but it does actually work.
