It looks like quite a few people have built Peltier cell based laser power meters. I’ve seen different approaches to the heater for calibration and black paint.
One approach to the heater is to attach a couple of resistors to the front side of the cell. The problem with this approach is that only the part of resistor that is in direct contact with the cell transfers the heat directly to the cell and the rest of the resistor dissipates the heat via radiation in all directions so god knows what percentage 60, 80… get actually transferred to the cell. Another approach is to attach looped resistive wire which probably transfer more heat to the cell. However the biggest question what to use to glue the wire. Any type of glue will be a heat barrier unless the glue is heavily loaded with good heat conductive fillers silver, cooper… but still even with this approach the efficiency of heat transfer will be less than 100% because the heat conductivity coefficient of best TIM materials on the market is less than 15 W/m*K and that with more than 95% loading rate of the filler. So with the silver powder and 60% loading rate it will be less than 5W/m*K and probably close to 2 W/m*K.
Another issue is the black paint. I’ve seen people using markers and spray can paint which can create a problem as both paints use dies that usually absorb more light in certain wavelength range. Some people are using graphite discs cut from battery’s electrodes glued to the cell. The problem is the same as with the wire heat loses in the glue and heat conductivity of carbon is pretty low. Some people are making paint in which they use activated carbon die in some sort of glue. This seems more valid and I’d like to try this approach but I’m not sure what type of glue to use. In industrial thermal pads the most common polymer is silicon but it is very thick for the paint even if it is highly diluted.
I wander how people on this forum solved the problems?
One approach to the heater is to attach a couple of resistors to the front side of the cell. The problem with this approach is that only the part of resistor that is in direct contact with the cell transfers the heat directly to the cell and the rest of the resistor dissipates the heat via radiation in all directions so god knows what percentage 60, 80… get actually transferred to the cell. Another approach is to attach looped resistive wire which probably transfer more heat to the cell. However the biggest question what to use to glue the wire. Any type of glue will be a heat barrier unless the glue is heavily loaded with good heat conductive fillers silver, cooper… but still even with this approach the efficiency of heat transfer will be less than 100% because the heat conductivity coefficient of best TIM materials on the market is less than 15 W/m*K and that with more than 95% loading rate of the filler. So with the silver powder and 60% loading rate it will be less than 5W/m*K and probably close to 2 W/m*K.
Another issue is the black paint. I’ve seen people using markers and spray can paint which can create a problem as both paints use dies that usually absorb more light in certain wavelength range. Some people are using graphite discs cut from battery’s electrodes glued to the cell. The problem is the same as with the wire heat loses in the glue and heat conductivity of carbon is pretty low. Some people are making paint in which they use activated carbon die in some sort of glue. This seems more valid and I’d like to try this approach but I’m not sure what type of glue to use. In industrial thermal pads the most common polymer is silicon but it is very thick for the paint even if it is highly diluted.
I wander how people on this forum solved the problems?