Peltier Cooling System Part 6. “It’s alive”
Finally I finished this cooler! A quick summary:
Six 60 watt Peltiers = 360 watts with an estimated actual calculated output of 252 watts of cooling.
A small reserve tank of slightly less than 2 liters with a total system capacity measured of 2 1/4 liters.
The pump is an inline “Little Giant” 2-MDQ –SC Water Pump.
The cooling line and pump is insulated with closed cell foam 9 to 12 mm thick with a few areas of only about 3mm. The reserve tank box varies from 12mm to 38mm thick.
The system is temperature controlled with a JLD-612 Temperature Controller and there is an inline thermocouple also an inline flow switch linked to the laser switch and a visual type flow paddle wheel.
Panel lights show that there is power to the Peltier’s six fans on all the time when the main power switch is. There are also lights for each the two Peltier banks that go on when power is applied (turning on and off) to them through the temperature controller. The Temp Controller lights up when it cycles the relays but that is not telling the power got there.
Each Peltier bank has its own 30 amp power supply and each has a line fuse of 20 amp on the 12 volt side. The power going to the Peltiers is of course turned on and off by the Temp Controller and through solid state relays for each bank.
At this point it appears that the Peltiers are doing fine without me coming up with some sophisticated current controlling device as the efficiency is great. I’ve ran the system twice for at least 6 hrs (without the laser) each time and they are performing fine. Note that the Temp Controller pulses the power to the Pelteirs for the first 5 mins or so then the pulsing slowly fades over the next 7 mins to almost completely gone then turns on and off to maintain the programmed temp needs. The cool down plot is not linear but cools faster toward the end. Makes sense with the way the controller pulses. If it was powered on full time at first I’m sure it would cool the water down in less than half the time it is now. I’m not sure I want to mess with it until I understand the Peltiers current draws and needs better.
I learned a lot about planning wire runs as the bundles can add up really fast and also about calculating wire sizes for current needs. Also planning the coolant line flows and addressing the filling and draining of the water problems. I found out the hard way to pretest ALL water line connections BEFORE closing it all up. I can write up something about draining and refilling the water later if there is an interest as it’s not as simple as it seems.
System performance so far is excellent. It takes about 20 minutes to cool the system down to the programmed temperature 20C from 29-30C. Today was a mild day and it was about 10 or 12 minutes to go from 25C to 20C. At this point the system has not had any problems keeping the water cool and the temperature has only fluctuated a degree or so staying within the programmed limits easily. However, this is based on the 6 runs one raster or 20min and 5 vector cuts of 4 min each back to back. Limits are set to 20C plus or minus 2C right now as we have had a few days of 40 to 45% humidity. Later I’m going to reprogram it to about 16C nominal.
The Temp Controller works this way, it pulses the power to the Pelteirs for the first 5 mins or so then the pulsing slowly fades over the next 7 mins to almost completely gone… then when it reaches the programmed temp it turns on and off to maintain it… The cool down plot is not linear but cools faster toward the end. Makes sense with the way the controller pulses. If it was powered on full time at first I’m sure it would cool the water down in less than half the time it is now. I’m not sure I want to mess with it until I understand the Peltiers current draws and needs better. Given the cutting and engraving I’ve done so far, once its reach temp, it’s not even noticeable that it is doing any work to control the temp while running.
One thing I noted is that my notes is that say I was cutting 6.5mm thick Popular at 12ma (300mm/min)…now I’m getting the same cut at 7ma. I’ll have to do a few more test to be sure but this observation suggest better performance at a lower power with the cooling and with the CD3 board. (no re-alignments of the mirrors or lens cleaning has been done).
I’ll try to post some schematics of the wiring later and a parts list but for now here are some final pictures.
