We've got a new mission for this academic year called ‘Sun Chaser'. The team’s aim is to capture footage of the Sun’s rise over the horizon of the planet from the Stratosphere. In order to achieve this, they will construct a mathematical model which can predict the time of sunrise from altitude. They will also design and build two new probes (names to be announced). The launches will take place in the dead of night in Wales and will be timed so that as the probes are reaching their peak altitude, the Sun’s disc will just be visible over the horizon. We're planning to use a new camera, a Canon IXUS 140, alongside a reliable old Canon A810. Both will have CHDK Firmware loaded and an intervalometer script. The IXUS 140 is a little more tricky as the Li-ion battery won't work due to the extreme cold so we're looking at an external power solution. I'm thinking about getting a third party ACK-DC90 for the battery adaptor but what we need then is a power pack which supplies the 3.7V of the original Li-ion. We've got to use Energizer L91 Lithium's as they are the only batteries proven to work at -30-40C. Has anyone seen an adaptor or circuit that can turn 3V into 3.7V? I'm concerned as with two batteries in series we get 3V which at cold temperatures will be too little to keep the camera going. With three batteries in series we get 4.5V which will be too much and will probably damage the camera if it works at all. Any help you can offer would be much appreciated! If you want to find out more about the mission pop over to: http://horizon.qmgs.walsall.sch.uk/ (there's a good YouTube Channel as well).
I can point to lots of things that will step voltage up to 6v or down to 5v, 6v or 12v. I cant find anything that will go to 4 or 4.2v (Li-ION is 4.2v fully charged.) http://www.racing-cars.com/pp/Product_Category/Full_List/HW30600400001.html http://www.amazon.co.uk/XINTE-Telem...e=UTF8&qid=1424085241&sr=8-6&keywords=12v+bec
normal AA rechargeable are 1.2 V, 3 of them will provide the required voltage. otherwise a resistor in series will provide the correct voltage
AA non rechargeable battery's are 1.5 out the box but they drop to 1.2 fairly quickly - I quite often need to make 4xAA battery's into 5v ish (up to 5.5) so I just stick a 1N148 diode on the positive as it's got a voltage drop of about 0.7v accross the diode, and that lowers the voltage fine for me. I would run 3 in series and stick a diode on the end, that will get you 3.8ish when the battery's are fresh. test it with a meter though - I just stick little circuits in kids toys so I wouldn't be too upset frying anything your case might be different (but I have tested this with a meter before)
Rechargeable AAs are out as they stop working -5C. The diode idea is good but how does it compare to using a resistor? How do we calculate the best resistor value?
Right, I'll dig through the tech specs for the camera to find idle and peak draw. Thank you so much to everyone for your suggestions, it's given us lots of new leads for our research.
