9V Solar Battery Charger

Did you know that you can buy 9V rechargeable batteries?  You can, but they're rare in stores.  I recently bought some off ebay to use on projects and loved them.  Only downside is that I don't have a 9V battery charger and all the ones I found on ebay are quite expensive.

Luckily I'm resourceful and decided to build my own.  The entire project only cost me $10 and didn't take that long.

Cost: $10
Time: 1/2 Hour
Difficulty: Easy

Step 1: What You Need

Supplies:
Solar Cells - Read the next page for lots of details
1N914 Diode
9V Battery Holder
Wire
Enclosure - Optional

Tools:
Soldering Iron
Tape
Cutting Tool

All the supplies for this project can be found on my website, http://www.browndoggadgets.com.  I even have a 9V kit of everything you need.  90% of all sales go towards more fun projects.  The other 10% goes to doggy toys.

Comments

[Schmidty16]

Dang i wish u were my 8th grade science teacher

[bdailey2]

How do you avoid over charging the battery?

[JoshuaZimmerman]

The method we're using is only a "trickle" charge, which means we don't have to worry about over charging. We're not throwing enough current at it to do any damage. They'll just stay topped off.

[JeenJogi]

Commercial Solar Panels are Expensive!
Fact: It will take you more than 10 years to pay back
Solution: Using Surplus Solar Cells You can get pay back in 1-2 years
There is an Engineer from Chicago his name is John Sommer
He explain it All in his diy solar panels Blog Search for him using Google
Type "top diy solar panels" Open the first Result.
Note: Ignore the adds at the top.

[rosebudfarm]

Awesome design! Those solar lamps are dump fodder for sure and easy to come by.

I am looking for a way to trickle charge 9v irrigation timers. Would this set-up be adequate and could I just piggyback the leads from the timer battery to the charger?

[NickFiya]

Does this work with only 3 of the solar cells?

[JoshuaZimmerman]

Well 3.5V x 3 = 11.5, which is not going to be enough to charge up your 9V. You'd need at LEAST 12V, but more like 16 to play it safe.

Joshua

[NickFiya]

Thanks bud

[jim_2000]

How much current do you get out of these cells?

[JoshuaZimmerman]

Something like 20mA. Usually less.

Thats what we need though. These 9V batteries are rated at only 280mA, and we don't want to throw more than 10% of their capacity at them at once or they'll die.

[JoshuaZimmerman]

If you're having issues finding solar cells, you may just wish to buy three 6V cells. I do have some small ones on my website that work wonders.