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Harness the power of the sun.

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I want to make a solar charger for my cell-phone or other devices that can be charged on a usb circuit. I also want to put batteries in this kit so it can hold the charge and be used for later. So my questions are as follows.
>How big will the solar cell have to be to charge two 18650 Li-ion batteries?
>Will these batteries explode on me for some unholy reason?
>Will this project even work?
This is my first real DIY project and I know very little about electricity, so I'm going to need some serious help. Thanks in advance.
>>
>>904725
How big will the solar cell have to be to charge two 18650 Li-ion batteries?
>pretty fuckin'. Certainly won't be a cute Altoids Tin size

Will these batteries explode on me for some unholy reason?
>If you a noob, then by God YES

Will this project even work?
>anything is possible

Just buy a solar charger/powebank.
>>
About this big.

https://youtu.be/MgRloFSeWoE?t=97
>>
>>904725
>charge two 18650 Li-ion batteries
how fast do you want to charge them?
where do you live?
solar charging is highly innefective.. to charge those batteries in a reasonable time would take a solar panel the size of a small car.

I have a solar charger that has one 3.x V 2000-3000 mah battery in it and it takes about 24 hours of direct sunlight to charge it, panel is abou the size of a credit card.
Ive stuck it in the window for a few days and the battery bar never went up. I think Id need to take it outside and lay it proped up facing the sun to actually charge it.

I am looking forward to the advancements that should be comming is solar tech though.

when you buy your pannels pay attention to the voltage AND the current (amps(a)/milliamps(ma)).

>Will these batteries explode on me for some unholy reason?
if you dont have a proper charging circute, hook the batteries up wrong, over charge them(?), or just generally fuck shit up.. then yes.

>Will this project even work
if you get yourself a good pannel that is very efficient and has good current, and get a good charging circute then yes absolutly.

if you use a panel that is half the size of an altoids box then you are going to stop using it after the first couple of uses because of how damn long it takes.
>>
>>905245
>voltage AND the current (amps(a)/milliamps(ma)).
pro-tip: voltage x current = power
>>
>>905252
protip: knowing the voltage AND the current when he is charging 3.7V batteries and making a charging circuit is more important than knowing some autistic simplified "how guds it werk" number.

12v @ 2A = 24 w
10,000V @ 0.0024A = 24W
>>
>>905268
>how do switching regulators work
you going to collect all of that measly sun energy and piss it all away on an inefficient charger?
boy that sounds real smart.

if you have a 10000v solar cell for sale i would be very interested
>>
>>905270
either you are baiting or you are autistic enough to compete with /g/.
just incase you are actually retarded that was an example of how unreliable "wats" are when making something.

5V @ 4.8A (480 ma (retard)) = 24W
10V @ 2.4A (240 ma) = 24W
12V @ 2A = 24W
10,000V @ 0.0024A = 24W
>>
>>905285
>4.8A (480 ma (retard))
you have some real issues buddy
>>
>>905245
>solar charging is highly innefective.. to charge those batteries in a reasonable time would take a solar panel the size of a small car.

No, it isn't, and, no, you wouldn't and, yes, you are an idiot. It isn't going to work well with something that easily fits in your pocket for day-to-day use, but certainly something small enough to carry around easily.

Most anything you'd want to charge this way is built around the USB standard. Any device also designed around this standard will be expecting a number of different current levels, but 99% of them will work fine with a 5V 1A supply. Let's call it 2A, because that's also typical and many devices can utilize the extra power to charge faster.

So, 10W.

Being generous for inefficiencies in the panel's regulator and less-than-ideal sunlight, let's say you need a 30W panel to actually get a semi-reliable 10W on your output.

An average 15% efficient solar panel will, conveniently enough, produce approximately 150W per square meter on a sunny day. You only need 1/5 of that, or 2000cm^2. A fold-out panel with two 40x25cm sub-panels or something similar covers this nicely. You can cut that size in half if you're okay with just a 1A USB port. Further still if you use high-efficiency (read: more expensive) solar cells.
>>
>>905298

(con't.)

As to why you're an idiot for harping on about I/V:

Solar cells are primarily rated in watts because their voltage and current capability fluctuates wildly. The listed voltage of a cell is virtually useless, because that's only at open-circuit or extremely light loads. The listed current of a cell is virtually useless, because that's only at short-circuit, where the current has sagged so far that the cell isn't actually producing much power. They're relevant characteristics, but mostly inconsequential in real-world applications; voltage rating is useful insofar as that you can get a rough idea of what kind of voltage range to expect out of a string of cells.

What you want to find is the amount of current you can draw from the cell right before the voltage starts falling faster than the increase in current can make up for in terms of overall power output. This is called the "maximum power point". Any good solar system will have some form of MPPT (maximum power point tracking) included, which, one way or another, monitors the characteristics of the cell and load on it. It can then adjust the regulator (or inverter) to ensure that you're actually getting as much power as the cell/panel can produce for the given weather conditions.
>>
>>905289
You have to understand Im talking to somene that doesnt understand an example of how two very different equations can get the same answer. people like him are the same kind of people that give out dangerous advice.. not that this is dangerous, but still the same person thats going to go tell someone that a shipping container makes a great bunker.

>>905298
yes.. it is ineffective and inefficient(time), especially to what the average person and typical young city hippy kid thinks it is.
Those batteries he is wanting to charge, I have the same ones. in this light in particular they last about 30 minutes.. factor in atleast 1-2 days of charging in perfect sunlight and pause for night and multiply the time for morning and evening, yea.. fuck solar panels.

you want to talk shit to me based off of the first sentence without reading the whole post. go read what I said after the last greentext, I clearly say it will work if he gets a good panel.

the car thing was not meant to be interpreted literally.. + Ive seem some really tiny cars.

>>905303
The reason I told op about the current is because people will sell shitty solar panels and try and pass them off as good.
Just a couple months ago in a store I found a solar car battery charger that advertised "12 volts" in big letters, the solar cell area was the size of half a pizza box and it actually looked decent.. no mention of watts anywhere and on the back in tiny letters it says that it was only like 50ma.. fucking worthless.
yea it might be acceptable if you found it in a post apocalytpic world where the last powerplant shut down over 100 years ago but lets be realistic.. would you rather use that for a day or let the engine run the alternator for less than a minute?
And before you jump back to "power ratings" op clearly has no clue what hes doing.. understanding voltage and current is allot better than learning "is x watts enough to charge my batteries".

measuring electricity in watts isnt always a good idea..
>>
>>905328
>You have to understand Im talking to somene that doesnt understand an example of how two very different equations can get the same answer.

His issue is with the fact that 4.8A and 2.4A is 4,800mA and 2,400mA, respectively, not 480 and 240mA.

And then you called him a retard.
>>
>>905353
oh, I see my mistake now. thats funny..
I had read his response as saying I have issues for calling the other guy retarded, like Im just mean..
I know that the it changes on 1000.. my mind was a bit clouded at the time probably due to messed up blood sugar or something and I just typed them out wrong.

still everything I said stands.
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