Building a DIY solar charger instead of using a plug-in charger is a great way to save money, save the environment and reduce our dependence on foreign oil. This article will tell you about the different kinds of solar battery chargers, which type is best and how to build your own.
A battery charger can be as simple as a power supply that provides electricity at the correct voltage for the battery you wish to charge. You connect the power supply to the battery until the battery is fully charged and then disconnect it. Say, for example, you have a 7.2v rc car battery. You can plug it into a 9v power supply and then when it is fully charged, disconnect it. Unfortunately, though, using this simple system, there is nothing to prevent you from overcharging the battery.
Overcharging will decrease the life of a battery. If you overcharge too much you can actually damage the battery. A charge controller will make sure that the correct voltage is applied to the battery and that the battery is not overcharged, even if you leave it connected to the charger for long periods of time.
The most common type of charge controller for smaller batteries is a Pulse Width Modulation or PWM charger. Basically, it turns the power to the battery off and on very fast to provide the correct voltage and current to the battery. Over time it provides more “off” than “on” until finally, it is providing no power to the battery at all when the battery is fully charged. These types of charge controllers usually have a small microprocessor to control and monitor everything. You can leave this type of battery charger plugged in all the time with to problems because the microprocessor continually monitor the battery and will only allow current to flow to the battery when the battery starts to discharge. This type of monitoring and “topping up” of the battery is called trickle charging and can be very handy for situations where you use don’t use a battery very frequently, but always want it fully charged for when you do use it. Solar battery chargers of this type are often used on boats and RVs, for example.
OK, that’s all there is to a battery charger – power source and charge controller (and even the charge controller is actually optional). So, what a DIY solar charger different? The only difference between battery chargers that are plugged into the wall and solar battery chargers is the power source. Instead of plugging the charge controller into the wall, we plug it into solar panels.
Standard solar cells that go into the solar panels you usually see on house roofs or in large installations typically produce about one half of a volt each. Many solar cells are connected together to produce higher voltages. You can find small solar panels of many different voltages, however. It is important to match the solar panel voltage to the requirements of your battery and charger controller. The charge controller should tell you what voltage is required. If you aren’t using a charge controller, get a solar panel that is a bit higher voltage than the batteries. For example, for 7.2v battery, you will want about 9v. For 12v batteries, you will want 15-18v. Remember, though, if you are using a charge controller, go with whatever voltage the charge controller requires. The power input to the charge controller will tell you what it needs.
How to wire your solar panel to the charge controller depends on the controller. You may need to solder on whatever type of connector your charge controller has to the wires coming from your solar panel. If you are not using a charge controller, put a connector on the wires from your solar panel that matches your battery. For an rc battery, you can buy connectors or cut them off of an old battery or wall charger. For AA batteries, you can buy a small battery holder with leads at Radio Shack. If you are charging a larger 12v battery, it is best to use spring loaded clamps for easy connection. You can twist the wires together and then apply electrical tape to attach a connector to the panels or charge controller, but it is much better to solder the connector on. Don’t worry, this type of soldering is very easy to do and is hard to mess up. You can buy a soldering iron and solder at Radio Shack. Just twist the wires together, heat up the wire with the soldering iron and then touch the solder to the wire until it melts. The only things to watch out for are don’t burn yourself and make you you touch the soldering iron to the wires and not to the solder. You want the wires to heat up enough to melt the solder, you don’t want the soldering iron itself to melt the solder.
That’s about it! A DIY solar charger is pretty simple and can be built fairly inexpensively. First, you need to know what kind of battery you want to charge. Then buy a charge controller appropriate for that battery. Next, get a solar panel that matches the voltage required by the charge controller. Finally, wire the solar panel to the charge controller. Once you have the solar battery charger assembled, you get free power forever! You are helping your pocketbook since you won’t have to pay for electricity to charge the battery any more, you are helping the environment by using renewable energy and not adding to greenhouse gasses, and you are helping the country by reducing dependence on foreign oil.
I built the DIY solar charger you see in the picture above using a home solar guide called GreenDIYEnergy. It includes ebooks, spreadsheets and videos. I especially liked the videos. They are DVD quality and show the whole project, step-by-step, from start to finish. It was really easy to follow along with the videos as I built my solar charger. Now I can charge my rc car batteries, iphone and even my laptop for free. If you’re interested in building your own DIY solar charger, I highly recommend GreenDIYEnergy.