# Help A Newbie Make His First Circuit; Solar Battery Charger

#### woodjac

Joined Nov 11, 2008
2
My Background
I have really been trying to grasp circuits but admit I have a hard time applying what I know to actually design and make a circuit. I took a basic circuits class for mechanical engineers but it was all in theory. We didn't have a hands on lab to physically see how it all works. So I have basic circuits knowledge but don't know how to apply it. For the past couple months I have been trying to apply what I've learned in my spare time, but I am not really getting anywhere. Help would be greatly appreciated.

Project Background

What I have
I have three (3) Coleman 50002 1-Watt Solar Powered Trickle Charger with Maximum Wattage: 1 watt; Ip = 80 mAmps@15 volts. The adapter is via the cigarette lighter in a car. The panel is used to maintain a vehicles 12V battery charge.

What I would like to have
I would like to make a circuit that can charge various types of batteries using the three solar panels. Specifically; AA 2650mAh NiMh batteries, 9V 400 mAh NiMh Batteries, and a 12VDC 7Ah lead acid battery.

Project Details

What I think I know

So my guess is that I will need to setup three seperate circuits and use a three way switch to determine which circuit will be active.

For the AA battery charging circuit I could probably charge up to six batteries in a day if I could get the voltage down to about 10.8V with the current at about 320mA. This is using an assumption that it is possible to break the voltage down to four parts of 3.6V @ 80mA within each of the three solar panels, wire the four parts each into parallel so that one panel produces a total of 3.6V @ 320mA, then wire the three panels in series for a final 10.8V @ 320mA. The batteries would then be charged in series?

Similar operations as above but respective to each battery type for each of the three circuits.

What I Don't Know/Current Problems/Questions

The problem is that each panel is one solid piece of glass, so I cannot break one piece into four pieces.

Is there a way to design a circuit that will convert the approximate 15V @ 80mA solar panel output to an approximate 3.6V @ 320mA output for the AA battery portion?

I have never made my own circuit board from custom designed circuit, but have a majority of the tools and hardware that may be required. I have been practicing using the Evil Genius Circuits book, but it covers basics and I am still unsure what types of components are needed for a given application. Any help on how to go about this circuit design would be GREATLY appreciated, sincerely. I really want to understand this stuff and feel the best way is to try and make things I can use.

Sincerely,
Jake Wood

#### thingmaker3

Joined May 16, 2005
5,073
What you'll need is called a "buck converter." There are several websites which can describe boost converters and buck converters more eloquently than I.

#### woodjac

Joined Nov 11, 2008
2
Thanks for the info! I'll take a look at this "buck converter" on the web and post an update to what I found.

#### Audioguru

Joined Dec 20, 2007
11,251
Energizer's website has details for all their batteries. They have a Ni-MH Applications Manual that you should download and read.

A Ni-MH cell is about 1.5V when fully charged. Then three in series need a charging voltage of 4.5V, not 3.6V. Three of these in series need 13.5V plus about 0.8V for a series diode then your solar panel cannot supply the required 14.3V at its rated current.

The solar panel will produce its rated output only when the sun is directly overhead at noon in summer. In the morning and afternoon and in winter the current is much less.

My solar garden lights glow fairly brightly all night in the summer. Now they glow dimly for about 1 hour after charging all day in the sun. I am not far North. I am close to America.

#### thingmaker3

Joined May 16, 2005
5,073
and in winter the current is much less
The solar panels actually work better when cold. They do, of course, produce more current with more light.

#### Audioguru

Joined Dec 20, 2007
11,251
Solar panels work a little better when they "follow" the sun across the sky.
But in winter when the sun is shining on the other hemisphere the amount of light is low and for a short duration each day.