Finally have found some time to make a start on this project.............so, went to dick smith, the 12volt fridges were $19.95, so 5 of them, 3 x 10amp switches with red l.e.d, some cable connectors to try and clean things up a bit (sorry asimov, but John K and Mike are neat people) and a $49.94 jump starter to power things.
Over on SCP we decided saturday night / sunday morning, we were imaging saturn no matter what the weather was like.........so i left my scope out in the pouring rain and shorted the battery charger..........soooo, $49.95 for a jump starter just like Mike's was the way to go.
John K's will be the lid design ie cooling the mirror from above and needing 3 peltiers. Mike's will be like mine and cooling from below.
Paul Haese is also making one with 5 peltiers for his 18" SDM and will be a lid type.
Here a few piccies, more over the next couple of days
Davo, remember that peltiers are about $11 ea. from Jaycar... might be a better bet if you're buying a few of them?
I had a chat to Paul about this 5-peltier beast, made sure he knew that the best system (IMHO) was one that only cooled the mirror about 3 or 4 degrees below ambient, so that there was no danger to the mirror and also it didn't take too long to come back to equilibrium when the power's turned off.
Peltiers can be very efficient if you insulate the cold side - it's easy to go 20 or 30 degrees below ambient, this is not what's wanted for this application, so I deliberately built a very lossy system (metal tube, minimal insulation) so I couldn't accidentally cool the mirror too far.
Paul is now reconsidering that he might only need 3 peltiers, and I reckon that's enough for just about anyone :-)
Will watch this space to see how you put it all together David, looks very interesting thus far especially from an economy point of view.
Rain and scopes just dont get along do they..lol
Davo, remember that peltiers are about $11 ea. from Jaycar... might be a better bet if you're buying a few of them?
the beauty of the Dick Smith firdge is that get the peltier in a great piece of insulated housing with small cold plate with threads for attaching the main cold plate, a fan and heat sink all for the $19.95.
Just out of curiosity, do you guys manually control these peltier units, as in, do you keep an eye on the temp and just switch off the unit or do you have a proper thermostat switch to set it to follow ambient temp?
us tough, rough, manly and ready blokes just use our eyes and switch off.
those propellar heads use auto shut offs.
or to put it another way,
bird and wombat have the brains to build data loggers and sensors that feedback and switch off / on automatically. the rest of us are just plain lazy!!!
i switch off say at least 1/2 degree ambient and then let it settle. Birds is the ultimate in the way it monitors the lot and automates everything.
A much easier solution - a PC power supply. The +12v rail is rated at 20A or more on any modern supply, and they cost about $50, and are nice and lightweight. The marvels of mass produced switchmode units.
And yes, peltiers draw a lot of current. My cooler with 3 peltiers draws about 10A, the heavy duty 12v wire that runs from my power supply to the scope gets quite warm while it's running.
A much easier solution - a PC power supply. The +12v rail is rated at 20A or more on any modern supply, and they cost about $50, and are nice and lightweight. The marvels of mass produced switchmode units.
Yes even better.
Just make an enclosure to protect it from dew etc.
hmmmmm....music of mission impossible......do i cut the red or the yellow.........the world's future depends on this.......must concetrate..........1.....2.....3.. ...aaaaaaaaaaaaaaaarrrrrrrrrrrgghhh hhhhhhhh... ccccccccrraaaaaaaaaaaappppppppppp!
ok red reads 5.4 volts
yellow reads 11.4 volts
and the funky green one.................11,000,000..... ................................... .........boom!
