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Help with a school project on solar power Answered

Hi. I have a science fair coming up in May and I want to do my project on solar power but I really don't know too much about electricity. This is my plan, please correct me where I'm wrong and tell me if there's a better way to do certain things:

I am going to buy a 10w 12v solar panel (I might be able to get a 40w for a bargain) which will charge a battery. Would it be better to get a 12v lead acid battery or a 12v lithium battery? Lithium batteries have DC jacks instead of normal terminals on lead acid batteries so how would I connect the battery in parallel to the 2 devices I want to power? A splitter like this would work but it connects it in series? Although I suppose it doesn't matter because I just need to show that it works at the expo but I'd like to use it now and then. The battery will connect to a 12v LED light and a 12v to 5v USB charger.

What about diodes? Do I need them? How will I make sure that the device charging doesn't get fried?

Thanks a lot, I appreciate it.

EDIT: A charge controller isn't necessary, is it? I'd also like to add in a switch to cut off power to the USB ports, power to the light and power to the battery from the solar panel. This would cause a problem if everything was connected in series.


Also: which gauge wire would you guys recommend? Would a 10 or 20 watt panel be enough?

To charge a lithium battery you will need a special charge controller. The panel itself can be directly connected to an SLA battery but it's still best to use a charge controller with it as well.

Most panels have built in diodes. Make sure it does. If not then you will need to have one between the battery and the panel. Otherwise the power from the battery will fry the panel.

As long as the devices connected to the battery can handle the 12V from the battery you won't fry anything.

Nothing in your setup should be connected in series. Everything should be connected in parallel. Otherwise the devices you connect to the battery will not get full 12V they need. If you connect 2 devices in series with a power source they get about half the voltage. For example to 6V lights can be connected in series and put on a 12V source and won't blow. If you have 2 12V lights in series on a 12V source they will be about half as bright as they should be. You put those 12V lights in parallel on the 12V source and they will shine with full brightness. They just end up drawing more current.

Hi, thanks for the help. I see a lot of solar charge controllers that don't say what types of batteries they support. If I can't find a lithium solar charger would it be possible to find a lithium battery charger with DC input and connect the panel to it?

That's because solar power systems all run on SLA batteries. Most solar power systems are made to run into an inverter so you can have mains power. This is a huge current draw on the batteries which Lithium can't support for long periods of time. You should be able to find a lithium charge controller easy enough. Just be sure it uses a 11V - 15V input otherwise the panel may be too much for it.

The cheapest charge controller I can find is £65.93 which is about 3 times the price of my 6800mAh battery. Is this right or am I just not looking in the right places. I would have liked to use Lithium because of the space I'd save but it doesn't seem like I'd be able to if the charge controller costs 3 times the price of the battery.