12V solar power « Jee Labs Talk

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12V solar power

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e_lexy

I have some 12V 7Ah gel batteries and solar charge controllers (steca pr2020 20 Amp is silly but I don't use it) laying around and some small 12V 1.8Wp panels came on sale at Leroy Merlin , here in Spain for 19,95. Since I need to power a Jeenode outside to measure and transmit temperatures on a set of solar water heaters, I thought of putting all of it together to power the jeenode (overcapacity but hey, letting that stuff do nothing and buy new is also silly).
Now the output terminals on the steca will put out what is being put in the batteries. this could reach over 14V. As I understand it, this may damage the jeenode.
As an electronics newby i found the LM2841 which looks like it may be able to protect the jeenode. Can anybody confirm or correct/help me. They provide a circuit design help with parameters, so the design would be quite easy to do.

Posted 02/06/2010 19:44:29
e_lexy

I read on instructables that a cheap and reliable solution would be get a cell phone car charger from some dollar store. They are most likely built around a MC34063 which would step down nicely to 5V. I think I still have some from expired cell phones. I'll open them up and see what's in there.
This does, however, not help me gain any desperately needed experience in circuit design...

Posted 02/06/2010 21:29:39
jcw

If all you want is to reduce the max 14V or so to the max ? 13V allowed for the JeeNode, then 2 or three simple diodes (such as 1N4148's or 1N4001's) in series will do the trick - each of them will drop the voltage by 0.6 .. 0.7V.
Note with linear regulators, 75% of the energy will be turned into heat (i.e. 12V -> 3V, roughly) before the JeeNode does anything. Basically, everything you feed a JeeNode over 3.5V just gets turned into heat inside the regulator.
If you want to actually use most of that energy, then a step-down switching regulator is indeed the way to go. It's a lot more complicated than adding a few diodes, though.
As it so happens, here's a recent video from the EEVblog. Lot's of useful info about how it all works.

Posted 02/06/2010 21:57:42