Simple Solar Battery Charger

This is a simple little project I used today.  I've been working on my car the past couple weeks (complicated project and very little time).  Well, I had concerns that I might need to freshen up my battery a little.  It was already out of the car and it was a sunny day so...

Simple Solar Battery Charger:  This is a "45 Watt" solar charger kit from Harbor Freight (normal retail about $140, which includes panels, charge controller, lights and battery hookups).  I purchased mine at a Flea Market for $100 (yeah, a blocking diode burned out a week later). 

These are great kits if you like to experiment with solar electricity.  They are convenient and practical.  I actually pass a house on my way to work that uses one of these to light their yard shed (a bargain in my opinion).

Here is the setup (remember I'm still down a blocking diode, more on that later).

Now, the battery was not really discharged.  It was about 13 volts, which a fully charged battery is technically 12.6 volts "at rest".

Here is a picture of a voltmeter hooked up to measure the solar energy capture!

This is the battery without solar juice:

The voltmeter reads: 13.31 volts.  Now hooked up to "the juice":

Reading 14.36 with strong sun.  This is right in the "sweet spot" for charging a 12V battery.  I am not so worried about amps.  The max for this set up is around 2 amps.  Now a word about the blocking diode.  This is an important part of any solar set up.  Think of it as a "one-way valve" for the charge.  If we don't have one (like this) and say I forgot about it over night...well that would be bad because at night the battery could discharge!!  For now I'm just more attentive to the set up.

What about if the sky is overcast?  Well:

Reading 13.55 volts with clouds in the sky.  It was not too dark but overcast enough so that you did not have a shadow. 

Now if I fix the blocking diode I could leave the battery hooked up for several days (in case it were really discharged).  Either way, next time I crank my car I'll have used a little (OK, OK, infinitesimal) renewable energy.