Help with a school project on solar power

[Charly]

Hi. I have a science fair coming up in May and I would really appreciate some help. 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? Do these DC splitters connect devices in series or parallel? How many Ah would you guys recommend? Although I suppose it doesn't matter too much 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? The solar panel should have a diode inside it. I see a lot of solar charge controllers that don't say what types of batteries they support.

A charge controller isn't necessary if I use SLA batteries, 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. Do you think I can afford the power draw of the LED on these toggle switches and two of these? 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.

Thanks a lot, I appreciate it.

[Sunking]

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?

You tell us. A 12 volt 10 AH lead acid battery cost roughly $25 and a lithium 12 volt 10 AH will cost you $150. Which one will you buy?

Do these DC splitters connect devices in series or parallel? How many Ah would you guys recommend? Although I suppose it doesn't matter too much 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.

Splitters? Why on earth would you need them for as they serve no purpose.

What about diodes? Do I need them? How will I make sure that the device charging doesn't get fried? The solar panel should have a diode inside it. I see a lot of solar charge controllers that don't say what types of batteries they support.

You do not need any diodes as the charge controller prevents the battery from back feeding the panels. All charge controllers tell you what kind of battery they charge as they only charge one type, lead acid. No one would be foolish enough to use a lithium or nickel based batteries because of cost.

A charge controller isn't necessary if I use SLA batteries, is it?

Wrong, dead wrong, charge controllers are extremely important if using SLA batteries to prevent over charging and thermal runaway.

When you get done try to think about economics. If you use a 10 watt solar panel, 2 amp charge controller, and a 12 volt 10 AH battery over the life of the product, about 2 years, will generate roughly 10-cents USD of electricity. Is it worth spending $100 to make 10 cents of electricity? That may be the lesson you do not want to learn or hear about.

[Charly]

You tell us. A 12 volt 10 AH lead acid battery cost roughly $25 and a lithium 12 volt 10 AH will cost you $150. Which one will you buy?



Splitters? Why on earth would you need them for as they serve no purpose.

You do not need any diodes as the charge controller prevents the battery from back feeding the panels. All charge controllers tell you what kind of battery they charge as they only charge one type, lead acid. No one would be foolish enough to use a lithium or nickel based batteries because of cost.






Wrong, dead wrong, charge controllers are extremely important if using SLA batteries to prevent over charging and thermal runaway.

When you get done try to think about economics. If you use a 10 watt solar panel, 2 amp charge controller, and a 12 volt 10 AH battery over the life of the product, about 2 years, will generate roughly 10-cents USD of electricity. Is it worth spending $100 to make 10 cents of electricity? That may be the lesson you do not want to learn or hear about.

Thanks for the advice. I'm not really making this for the purpose of saving electricity. I'm doing it for a science expo which can () get me through to the regional and national science expo. I found this 8Ah lithium battery for £25.25 (42.29$). I also found this solar charge controller for £125 that supports sealed, gel, flooded lead acid and lithium. That's way more than I want to spend on a charge controller.

[Sunking]

OK lets back up a second. This is a science fair project right?

If that is correct it does not have to be real life functional. It is make believe right? Only thing that has to be real is the battery and a LED or whatever low powered gizmo you want to run. Makes no difference if the panel and charge controller actually work or not. So why go to all that expense, especially buying a lithium battery?

Secondly with a 10 watt panel, and that is large enough for a 8 to 10 AH 12 volt battery only requires a 1 amp. You do not need a 15 amp controller. A 15 amp 12 volt controller is made for a 200 watt panel. Just use a LM 7812 voltage regulator for $1 if you want to use a real panel that can actually charge a battery.

There is no reason to go to all that expense.

[Wy_White_Wolf]

Why are you set on a Lithium battery? Here's a SLA battery and charge controller.

http://www.amazon.co.uk/Mobility-Scooter-Battery-AGM-12v-12Ah/dp/B002USO09W/ref=sr_1_1?ie=UTF8&qid=1393617376&sr=8-1&keywords=sla+battery

http://www.amazon.co.uk/Solar-Charge-Controller-Regulator-Control/dp/B00A34SQQI/ref=sr_1_6?ie=UTF8&qid=1393617304&sr=8-6&keywords=6amp+solar+controller

WWW

[Charly]

This is a science fair project right? If that is correct it does not have to be real life functional.

You do not need a 15 amp controller. A 15 amp 12 volt controller is made for a 200 watt panel. Just use a LM 7812 voltage regulator for $1 if you want to use a real panel that can actually charge a battery.

I need to be able to show, with a multimeter, that the solar panel charges the batter. I knew that I never needed a 15 amp charge controller but I didn't think there was any other solution. If I drew 2.1A at 5v and small-ish 12v lamp (not sure how much power these typically draw) how long would a 5Ah battery last (Assuming the solar panel isn't charging)?

[Charly]

Why are you set on a Lithium battery? Here's a SLA battery and charge controller.

http://www.amazon.co.uk/Mobility-Scooter-Battery-AGM-12v-12Ah/dp/B002USO09W/ref=sr_1_1?ie=UTF8&qid=1393617376&sr=8-1&keywords=sla+battery

http://www.amazon.co.uk/Solar-Charge-Controller-Regulator-Control/dp/B00A34SQQI/ref=sr_1_6?ie=UTF8&qid=1393617304&sr=8-6&keywords=6amp+solar+controller

WWW

Thanks. I would have liked the amount of space a lithium battery would have saved but it only makes sense to go for a SLA setup.

[inetdog]

Thanks. I would have liked the amount of space a lithium battery would have saved but it only makes sense to go for a SLA setup.

And the biggest reason for you to go with SLA rather than FLA (Flooded Lead Acid) is to make the whole system more portable and safer in case it gets pushed off the table.
In the practical world, except in specific circumstances FLA will be more economical in both the short and long run.

[Sunking]

I need to be able to show, with a multimeter, that the solar panel charges the batter. I knew that I never needed a 15 amp charge controller but I didn't think there was any other solution. If I drew 2.1A at 5v and small-ish 12v lamp (not sure how much power these typically draw) how long would a 5Ah battery last (Assuming the solar panel isn't charging)?

OK looks like WWW did your work for you and found you a battery and charger.

As for how long would a 8 AH battery last with a 2 amp load on it is pretty simple math. 8 AH / 2 A = 4 Hours

[inetdog]

But if you discharge the battery to that level regularly or without recharging it soon after, the battery will not last very long.

[Charly]

Thanks everyone. One final question: what type and gauge of wire would you recommend?

[Charly]

What would I do if I get a charge controller without a positive and negative terminal for load like this?

[Sunking]

Use the battery

[axis11]

I helped a neighbor's son on his science project a few months back. He was tasked to deal with solar power( no specific goal mentioned). What we did was connect a 15 volt 10 watt panel directly to an automotive grade 12v led. Hanged a 250 watt halogen lamp on a pole to shine over the panel. Plugged the halogen on a wall outlet inside the classroom and work is done. He could have also used a dc fan but he preferred the LED because it is readily visible when it lights up.

[SunEagle]

I helped a neighbor's son on his science project a few months back. He was tasked to deal with solar power( no specific goal mentioned). What we did was connect a 15 volt 10 watt panel directly to an automotive grade 12v led. Hanged a 250 watt halogen lamp on a pole to shine over the panel. Plugged the halogen on a wall outlet inside the classroom and work is done. He could have also used a dc fan but he preferred the LED because it is readily visible when it lights up.

How could you tell that the 12volt LED was working with that 250 watt halogen "resembling the sun" being so bright. They should have done the experiment outside with the real sun but if he got a good grade on his project then no harm done.