Developing a Solar Powered Charger for Mobile Devices!

[frasierdog]

Imagine a bi-folding portable solar charger the size of a small novel. It collects solar energy by day and stores it in a high capacity internal battery. At night you can access your energy via a high powered 5V 2.5A USB port, enough to power any tablet or smart phone!

This week I am going to order the parts to assemble the first prototype of my DIY solar charger. I am pretty new to the DIY world. The basic design has already been created, but I am not totally sure which circuits and components I will need to make my project function the way I want it to. I suppose it's easiest to describe what I want it to do and work backwards from there. Below are some pictures I have done in Sketchup and Google Draw to give a rough idea of what this thing will look like!

**broken link removed**

Don't laugh! It was my first time using Sketchup!



Functions: - ultimately I would like it to...
- Charge any USB device
- Support power draw up to 2.5 A
- Have a single button and 4 LEDs to indicate charge level and charging status
- Be able to power directly from the Sun, and fall back on stored energy only if the solar voltage isn't enough


Components - to achieve the above end, what pieces will I need?
- 2x high power solar panels (probably monocrystalline)
- 8000 mAh battery capacity
- Voltage controller for solar panels
- MPPT tracker
- USB Port (in and out)
- LED light piece


Well that is the basic idea. Yes, I know, it's far from electrically complete. That's why I have shared this idea with electro-tech. Perhaps you can help me fill the gaps in my knowledge (more like canyons)

Questions: - this is what I know I don't know, but does not include what I don't know that I don't know!
- Can a USB port support a 2.5A output?
- What kind of voltage booster would I need from the battery to the USB port?
- I would like to shoot for a sum total of 6000-8000 mAh of battery storage. Is it more efficient to do this with one large battery or two smaller ones? Is there a voltage advantage to wiring two smaller batteries in parallel?
- How do I build in a mini-usb in for 5V wall charging?
- What kind of circuit do I need for a charging status/capacity indicator?
- What kind of solar voltage controller can manage two solar panels? Do you wire them in parallel and then attach a voltage controller or is there a model that can accept two inputs simultaneously?
- What type of battery do I want to use? It must withstand prolonged charging and many hours spent outside basking in the sun.
- I would like the folded unit to be about the size of an iPad mini (5.3"x8"). With two solar panels approximately that size, is it possible to draw enough power to charge the battery fairly quickly?



I know it's a lot to digest! Thanks electro-tech! If anyone could point me in the direction of the right components it would be much appreciated - can't wait to build it and take a dream into reality!

- frasierdog

 

[Mr RB]

It looks useful, but you should be aware there are already a LOT of solar power gizmos for portable devices very cheap already on ebay. I'm not sure if any match the features of your design.

Also if you open it like a book, you are better off with two solar panels one on each side. This gives better power output AND protects the battery etc from sitting in full sun.

Or maybe some design change that leaves the battery shaded, folded safely under the solar panel somehow when charging.

Have you done research on the solar panel of that size and how much power it produces? I think you will find it is not very much, so you may be trying to charge a 8000mAh battery from a solar panel only producing 60-80mA or so...

With the hassle of putting it out in full sun each day, and the fact you might only get peak charging for 3-4 hours a day, that could take 45 days of hassle to charge the 8000mAh battery once.

 

[frasierdog]

Right, I guess I wasn't perfectly clear on my diagram. Two solar panels, one on each side, with the battery underneath the unit.

I understand it's not going to be a lot of power, but how did the Joos Orange do it? (https://solarjoos.com/) That panel couldn't be more than 5 Watts but manages to charge the unit successfully within a reasonable time frame. The entire unit is approx 5.7"x8.5" with an even smaller solar cell in the middle. With this design I could have more than twice the surface area.

 

[ronv]

Here is a low cost cell.


The trick now is going to be getting from a few hundred mv to 6 or 7 volts.

**broken link removed**

 

[ronv]

Hmm. Maybe this one.

https://www.electro-tech-online.com/custompdfs/2013/05/TPS612.pdf

 

[blueroomelectronics]

Not worth the effort IMHO, as mentioned solar cells just don't have the energy for such a small surface. Plus you need to point them at the Sun or somehow focus the Suns rays at them. They're more gimmick than practical.

For about $70 you can buy a relatively small 60WH (Trent iCarrier) charger that can be topped up in a few hours. This is enough to charge a typical phone 6x.

PS building one will cost far more than buying one.

 

[Mr RB]

Right, I guess I wasn't perfectly clear on my diagram. Two solar panels, one on each side, with the battery underneath the unit.

I understand it's not going to be a lot of power, but how did the Joos Orange do it? (https://solarjoos.com/) That panel couldn't be more than 5 Watts ...

It's not even close to 5W. I have a proper 12v 5W glass solar panel which is about 15x12 inches solid. In peak sun, for 3-4 hours near noon (if lucky) if puts about 280-350mA into a 12 battery, when pointed directly AT the sun. That's <4W. To make it's claimed "5W" output it needs to source current to a load at about 17.5v.

That little "Joos" cell would be about 6 times smaller, and make barely 0.5 to 1W under ideal PEAK SUN conditions. Then you take another hit from battery charging efficiency.

I think you are confusing marketing hype with how well these devices might work in the real world. And it's not really your fault, some marketing claims are outright lies.