Free portable power
You can build in one hour

Let’s say you are on a road trip, maybe camping or staying in a mud hut in the middle of the Amazon basin.

What if your bug zapper is the only thing standing between you and biting flies the size of canned hams?

You want some source of electricity. Free electricity is even better. That’s where your portable solar electric generator comes in.

What is a portable solar electric generator?

A portable solar generator provides both household (120-Volt) and automotive-type (12-Volt) current. It has a battery which it charges with a photovoltaic (PV) panel, and an inverter which converts the 12V from the battery to the 120V that we all use for our stuff. By “stuff”, I mean all the conveniences of home, such as laptop computers, satellite transceivers, boom boxes, TVs, short-wave radios, fans, and electric cucumbers. (I don’t even know what that means).

ALERT: If you know what an Amp, Volt, Watt, and Amp-Hour is, you can skip this next block.

Where do we get one?

$429 buys you a solar power pack like this one, and it would be well worth it. But anyone who knows me knows I always think I can build better, or at least cheaper on my own. Let’s see if I can.

The commercial model

This model weighs 20lbs, has a 21 amp-hour battery, and a 300 watt inverter, which means you can plug

in AC equipment up to 300W. (An X-Box 360 plus a 19-inch TV would use 240W).

The unit has a charge controller which takes the power from the photovoltaic panel and charges the built-in battery. It can handle up to 40w at 2.5 amps from the solar panel.

The stock solar panel with this unit is a 10w panel, but we are spending the extra hundred dollars to upgrade to 30W, which will charge the battery three times faster.

Important Questions to Ask

Real world information you want to know about your generator is:

— What is the battery capacity in terms I can understand?

— How long does it take to re-charge the battery from the PV panel?

How long will it power my PS2? (and 19-inch TV)

We know the Playstation 2 uses 50 W and TV uses 80W. That totals 130W.

If the battery is rated for 21 Amp-Hours, then it’s 21AH x 12V = 252 Watt-hours (Wh). The inverter is 80% efficient, so 252Wh x .8 = 201Wh available for use. 201 / 130W = 1.5 hours of play.

Therefore, I recommend, if you are going to play video games, at least take along an LCD TV, which will get you 25% more play time.

How long does it take the 30-Watt PV panel to charge the battery?

The battery capacity is 21 Amp Hours. The 30W Solar panel provides 1.8A in direct sun. If you run that battery flat, then it’s going to take 21 / 1.8 = 11.7 hours to charge it all the way back up. You’ll actually do much better, though if you charge WHILE you play.

The Home-Made Model

Credit where it’s is due. I get FULL credit for stealing borrowing this design from Phil Heiple at http://www.rain.org/~philfear/how2solar.html. On his page, Phil notes copyright Boa Boy Press 1996 free for non-profit use, so we have permission to reproduce it here. I found the same exact design over at http://www.minifarmhomestead.com/homestead/solargen.htm, so this information has really gotten around.

What I’ve done is taken their general design, done the research, and gotten specific with the type, brand, model, and price of batteries, inverters, and other parts. I also added a Charge Controller to the circuit because it prolongs battery life and solves other problems.

Since I got a major deal on the PV panel, I was able to upgrade to an awesome battery with more amp-hours, get 4 times more wattage out of the solar panel, and still save a ton of money on the original DIY design.

Parts List

What are the charge controller and inverter?

The charge controller
Takes electricity from the solar panels, makes sure it’s coming in at the right voltage for the battery, and can handle up to 5A. It keeps juice from flowing in reverse at night, when there’s no power coming from the solar panels. Finally, it keeps the voltage correct so it doesn’t overload the battery, and has an LED panel that shows you whether it is overcharged, undercharged, or charging. This solves a lot of problems for only $20 from http://www.gameinfinity.net/index.php?l=product_list&c=40.

The inverter
That’s the gizmo that converts 12V battery power to 120V household current, and has the nice 3-prong outlet that all your stuff knows and loves.

I’m truly proud of this one I found on line. It’s a good name, Black and Decker, handles 800W surges, and provides 400W continuous instead of the 300W for the commercial model, is fused, and has some smart electronics to shut off when the battery is low. All for $34 from http://www.invertersrus.com/pi400ab.html. That’s cheaper than Wal Mart, and a much better product.

Very simple wiring diagram

from http://www.minifarmhomestead.com, which shows you how to hook everything up. Note: Instead of a voltage regulator, we are using a charge controller, which does the regulation and a few more nice things for us.

Assembly Instructions

1. Drill holes in the top of the battery box and attach velcro so you can install the Charge Meter, charge controller, and triple outlet to the top, and pass the wiring down through the holes.

2. Use insulated wire like “Zip” or extension cord to attach the DC Meter to the positive and negative terminals of the battery. Handle only ONE wire at a time, or you could light up like Christmas.

3. Attach the OUTPUT connectors of the charge controller to the battery the same way with zip cord. (The inputs are for the wires coming from the PV panel, which we will do last. Note this takes the place of the Voltage Regulator in the wiring diagram, and does a better job of looking out for the battery.

4. Same thing with hooking up the triple DC outlet with zip cord.
5. Use the heavier battery cable to connect the battery terminals to the inverter. (Positive to Positive, Negative to Negative).
6. Finally, use the zip cord to attach the solar panel to the INPUTS of the charge controller. Optionally, but recommended, would be a two-pin connector available at any popular electronics store, so you could have a quick, easy way to disconnect the solar panel for storage or travel.

That’s all there is to it. After obtaining the parts, you can build this thing in an hour. I discovered the best way to find deals on parts is to go on line and Google. Someone on either e-bay or Craig’s List or SOMEWHERE has an awesome deal for the finding.

Best wishes,

E.J. Wilson (Zehaas)

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