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Registered Member #4274
Joined: Mon Dec 19 2011, 03:10AM
Location:
Posts: 47
I have a 55 watt solar panel behind my shop, and I recently ran a romex cable from it to inside the shop to charge a small 12v lead acid battery. The battery will basically serve as a constant 12v power supply for me, but I need a way to keep it charged if the load exceeds the output of the solar panel for the day. I want to be able to use my normal 12v battery charger, but I only want it to be on once the battery drops below a certain voltage. How can I do this without buying anything commercially made? I believe they have this for grid tied solar systems (or something like it), so it shouldn't be too hard should it?
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
Are you familiar with microfontrollers? You could run up a quick level detection pcb with a microcontroller on it to read battery voltage, solar output, etc. if you arn't comfortable with the "hardcore" uC single chip stuff, then go and buy an arduino. It's an extremely easy to use and program development board for atmels atmega328p ic chip.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
You won't be sensing more than a couple channels of analog data, so any atmega8/168/328 will do fine as long as it can hold you're full program data. I suggest a duemillinove or uno version with the 328. All you need is the IDE from arduino.cc, the board itself and a USB cable. Take a look at the example programs to getting a feel for it. The great(or bad) thing about it is that all the normal register setting, interrupts, etc that are necessary are all dealt with in the bootloader. So all you need to do is: analogRead(0); to read an analog signal on analog0.
I honk you can handle all the logical operations needed to complete the hop at hand, it's just basic c/c++
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
If you don't like microcontrollers, you'll find a design for a PV system charge controller using old-fashioned components in appendix F of my thesis.
It had one channel dedicated to a backup charger: this was a regular car battery charger, and the controller was set to turn it on at 10V and off again at 15V or suchlike. The effect was that it would kick in when the batteries got dangerously low, and give them a full equalising charge.
I installed this nearly 10 years ago and nobody ever complained about it.
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Backup 12v Charger for Solar System
