solar charging

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ed
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#1 solar charging

Post by ed »

Has anybody got any experience with solar panels charging a 12v battery in a caravan scenario?

I set up a remote weather station at a local flying field last April with a solar panel(25watt) and 12v battery powering an avr setup which uploads weather data to the web via a G2 mobile link. All has been well until 2 weeks ago when the battery went flat. Measurements say the panel produces between 30ma and 120ma in low light conditions. The avr wants 70ma with a 1 second burst requirement of 240ma every 47 secs(average 72ma). Not to forget an extra little bit to keep the battery charged.

It obviously wants a bigger panel(possibly 100watts). But in the meantime I want to adjust the charge controller to switch off the load during the hours of darkness(don’t need a weather report when it’s dark!).

Here’s the question...the charge controller has a very scant instruction sheet and it hints at being able to turn off the load for a certain period during every 24 hours. It just doesn’t explain how.

The controller:

https://www.ebay.co.uk/itm/10-20-30A-So ... enEEYc4ILA


I’ve spent a week trying to find a better instruction manual for the thing, unsuccessfully!

Last resort is to buy a new controller that has the function AND a workable instruction manual.

Anybody done this?
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Nick
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#2 Re: solar charging

Post by Nick »

I know the avr is far from the most frugal controller out there, by 70ma seems a hell of a lot. can't you get it to spend most of it time asleep?

Which avr is it? how are you generating the 5v or 3.3v for the avr from the 12v? Maybe a more efficient converter?
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#3 Re: solar charging

Post by ed »

I haven't given this a lot of thought since I set it up, especially as it's been working without a hitch for 6 months....

it's a 328 with a real time clock, a 433mhz am receiver board, a GPRS mobile transmitter board. The receiver listens in real time for a packet from the weather station mast, decodes the packet and re packages to upload via the GPRS board. Most of the time is spent rejecting spurious transmissions on the 433mhz band(you would not believe how busy that band is). Even with a fairly tight checksum it's still possible to get fooled by a rogue packet.

The 12v is taken directly from the charging controller and dropped via a 7805 regulator.

what has caught me out is the drop in supply from a 25watt panel during winter light periods. There is very little experiential info on the net from caravan types and the panel experts. The best I could find was that panels produce 4 to 5 hours in summer and 1-2 hours in winter at uk latitudes.

edit: and an on-board atmospheric pressure guage
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#4 Re: solar charging

Post by Nick »

So the cpu could sleep while its not being nagged by the receiver. Maybe the receiver is pulling most of that current. If it is there is not much to be saved I guess unless you can find a lower power receiver.

This one seems to need 10ma or less if its waiting

https://www.rfsolutions.co.uk/radio-mod ... odule-p350
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#5 Re: solar charging

Post by ed »

appreciate the thoughts

my current receiver is rx4mm5 high rejection and runs at about 7ma so it really isn't the culprit here.

No, I'm fairly happy I'm in the right ball park for all that's going on with 70ma. Back to the original post...If I could turn the load off during the hours of darkness(or at least when there is nothing coming out of the panel) when it's not needed I would save in the order of 18 hours x 70ma which is 1.26 Ah.

I could turn the unit back on in April to run 24hrs a day cos I know that there's enough sun for full operation from this years experience. Maybe I should have installed a 100watt panel in the first place then this would all be academic. But a chap needs something to worry about otherwise he might be tempted to the dark side. At least that's what granny told me.
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