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Newbie construction TL battery maths help required http://forum.timescapes.org/phpBB3/viewtopic.php?f=12&t=12214 
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Author:  ruebenad [ Wed Sep 03, 2014 12:41 pm ] 
Post subject:  Newbie construction TL battery maths help required 
Hi I have a calculation I’m having difficulty comprehending. I need to establish what 12v deep cycle battery I need to last 5 days. I want to make a timelapse for 14 hours per day Monday to Friday. My camera (canon 30d) says it uses 7.4v but actual reads 8.1v. The camera uses 1w in standby and 4w’s when taking a photo and to write to card (5 seconds max). I will ask it to take a photo every 6 mins for 14 hours per day. To go from 12v to 8.1v I will use a stepdown board (LM2596S, I don’t know how much this uses?). How many 12v Ah will this consume over 5 days…and if you have time can you explain it like I’m a 5 years old so I can work out how to do it myself in future? Thank you in advance Rueben 
Author:  photosentinel [ Sun Sep 07, 2014 8:31 pm ] 
Post subject:  Re: Newbie construction TL battery maths help required 
Hi Reuben, This from our electronics engineer: This link should explain it in detail. Start from step one. http://www.powerstream.com/batterycapa ... ations.htm Quiescent Current of the LM2596 is 10ma (worse case). So you need to add 10ma as a constant duration. Also the LM2569 only switches at 73% efficiency (worse case, although from 12V to 8 it’s probably not that bad). But to be safe, once you’ve done all the maths you should take the 73% efficiency into the consideration as well. (just multiply the final Ah x 1.27) Sorry the calculation isn’t actually that simple, I don’t have time to explain it in much more detail bit you should have enough to get started. Matt 
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