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Posts: 4
Reply with quote  #1 

I currently am using a small SLA 12V battery to power the following in our screened-in back patio:

1.  CURRENT USE:  A small 12VDC audio amplifier that I use for internet radio, listening to my mp3 collection, and as a sound system when we use our video projector to watch a movie outside.


2.  CURRENT USE:  LED lighting strips from IKEA (LEDBERG model) that provide switched lighting.  Mostly for intermittent use to safely transit the dark patio to our two doors into our house ('our side' and 'mother-in-law's side).  Occassionally we spend time in the porch on a nice evening, though, and the lighting is perfect.  The attached picture is pretty true to life on the lighting.


3.  FUTURE USE:  To power the intermittent (1-3 times per day) water pump in this amazing home gardening system that I would build just outside the long wall on the right side of the above picture.


Currently, I just throw a small trickle charger onto the small SLA (1.2 AH) battery every now and then.  What I'd really like to do is convert this to a PV solar system.  I want/need to succeed on the first try, though, and not end up with a system that will fry the battery prematurely from overcharging or overdischarging.  I'd like to know that if I hadn't used the lights or amp in a few days that they'd work when I went to use them, too.  There's not much point if I have to get out the trickle charger at the last minute for movie night.

I've determined that I would like one decent small wattage (10-50 watts?) monocrystaline panel, to be mounted at near ground level.  But I'm having a hard time deciding exactly what charge controller / discharge limiter compnent(s) to buy that will work best for this very small system. 

Any suggestions?  Advice?  Comments in general?  Much like I discovered first-hand that motor scooters are not cost efficient after your first $60,000 in medical bills from an accident, I believe it would be very easy to have this hobby cost more than needed if I have to replace things because I bought the wrong item or if I don't get the best life out of whatever next 12V battery I end up with.



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Posts: 2,881
Reply with quote  #2 
I think you're on the right track, and I agree that hobbies can sometimes get out of hand.

How long does your little 1.2 ah battery last on the current load, and how much do you expect to expand?

You can buy a small 12v "U-1" battery at Big Box for maybe $30, probably less than many smaller batteries. They're commonly used to start lawn tractors, about 30 ah.  You can run a whole lot of LED lights with it.

Solar panels get cheaper per watt as they get bigger, but there's no point in getting silly about it.
You can get some pretty nice solar panels online for about $30, and a small charge controller for about the same.   All told about $100 US.

But be VERY, VERY careful what you wish for; the solar bug has a nasty bite, and I don't know of a cure.  It's into me for more thousands than I like to think about. [frown]

Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay

Posts: 4
Reply with quote  #3 

I just hooked up an ammeter to my patio battery and saw the following:

The lights:  0.19 amps
Adding the stereo amp at a normal listening level brought that up to 0.27 amps.  The efficiency of that T-Amp circuitry is amazing.  8 AA batteries will fill a room with home stereo quality sound for several hours.

If I increase the amp to 'movie night' level, the combination draws about 0.35 amps.  But the lights would go out when watching a movie, so really I guess the design max as it stands now would be about 0.9 amp-hours over a three hour evening with the lights on and the stereo playing....too much for the current small 1.2 AH battery, but fine for a common 7 AH sealed lead acid battery, like this one.


I've been debating adding one more LED strip to each of the three existing light strips.  That would run me another $15 at IKEA, and bring the lights-only load up to about 0.3 amps.

The kicker will be adding the pump for that hydroponic gardening system referenced in my original link.  I see that a readily available 12VDC submersible pump uses 5 Watts, or about 0.5 amps when running, and would need to run about 1.5 hours total during the day.  I'd also need some kind of programmable timer to switch it on and off.   That timer may be something I'd need to power with regular batteries, like I do my Bluetooth receiver.  But, hey, I could add a NiMH charger to my solar load....

Right now, I'm considering this:


along with this:


or a premier model like this:


I kind of want the discharge limiter functionality included in the charge controller because I realize there might be occasions where we forget to turn the lights off overnight.


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