SparkFun Forums

[docwisdom]

Hey everybody.
I am working on a metal sign right now for my company and it will be set off from a backing board. I would love to throw some LED light strips behind the metal to shine on the backing board (bright green). Anyway, I was wondering if anyone could help me on the control unit.

The sign will only need to operate starting at dusk and for a few hours thereafter. I would like to run it off of a 12volt lead acid battery with a solar charger. Does anyone have any simple, efficient designs already in existence that I could use?
I think a simple PIC and a light sensor circuit with some mosfets will work fine for the operation of the LED's. The thing I'm mainly stumped on is the charging mechanism.

thanks much
-brian

[wiml]

Lead-acids are pretty forgiving when it comes to charging. (Is it a sealed or a non-sealed type?) You might be able to get away with just connecting the PV panel to the battery through a diode (to prevent the battery from discharging through the panel in the dark). If the panel is big enough that it could possibly overcharge the battery, you'll need a charge controller. The commercial ones basically consist of a PIC and a few mosfets.

To get more power from the cell, you can use a maximum-power-point tracking controller. This is basically a switching regulator (aka DC-to-DC converter) that, instead of regulating its output voltage, regulates its input voltage (by drawing more or less current) in order to operate the PV cell at max efficiency. Somewhere recently I saw a clever all-anaog circuit to do this, but I can't find it now.

[Jaylimo84]

My company too works with lead-acid charged by solar panels.

You DEFINITIVELY have to look at the UC3906 by TI for your controlled charging needs. Simple design procedure explained in datasheet, and work very well with few components.

By the way, if charging solar battery is not intuitive to you, www.batteryuniversity.com has good documentation for you.

[kb0thn]

In my solar powered wind data loggers I use a morningstar Sunguard SG-4 charge controller. It is a simple device that can have up to 75 watts of solar panels connected. It's cheap and plug and play.

Northern Arizona Wind and Sun is a cheap place to get them at:
http://store.solar-electric.com/sg-4.html

Not as much fun as doing it yourself!