First steps in using the Sun's energy

[gording]

Hello Birrbert

Well, actually it is done like you say. The Li-ion battery is charged directly by the charger unit. One step up converter (the selectable one) is used to increase voltage coming out from the battery to supply the meters, other is used to convert voltage , also coming out from the battery to charge the phone. Could I use there one converter, and supply 2 meters and charge mobile phone from this one converter only? Probably I could. Maybe I'll try to get rid of the green converter at the very end and instead use the selectable one with voltage on the output selected to 5V.  Adafruit gadgets are not cheap, and I prefer to learn by myself even if I discover something that was long ago already discovered

[birrbert]

Out of curiosity: can you calculate how much you spent until now?

[gording]

If you calculate how much energy in terms of cost would I use by using factory charger and plugin it into wall socket, then probably for 100 years of using it I would pay less than the costs of building my solar charger.
 But first of all: This charger was NEVER meant to be financially viable project. For most it's hobby for spending free time, secondary it's learning platform.  My another project after this will probably be a laptop power supply. A flat where I live in limits me very seriously as of the size (power output) of solar arrays, cause all the windows face north-east direction.
Until I move to a new place I have to live with what I've got.  My energy harvest time is from sunrise until around 11 a.m. And that's it. With this conditions none solar project can be financially viable. However, keeping in mind it's mainly a hobby project I still do this. Now next step is to calculate how much window area would I have to use to supply laptop, and deciding if it is feasible. Most probably it's not. Still waiting for a socket meter to check exactly how much my laptop consumes.

Coming back to costs of current project. All the wiring, switches and converters were actually very cheap. The step up converters AFAIR were about 2-3 $ each, Li-ion charging module similarly. The greatest cost was the part that sits outside of the window. First solar panels I bought in Polish web site were very expensive. The next panels I found later on eBay were much much cheaper, however still the greatest cost was actually the silicone for encapsulating the panels. It cost me around 30$, for 1 litre bottle, out of which I used half - but it was the smallest bottle available. There aren't many electrotechnical  silicones on the market, so not much to choose from.

Probably if in future I'd decide to build a bigger project I'd go for factory made panels. But for now, for learning how to solder and basics about Voltage, Amps, Watts parallel and series connections, it was a great, great lesson.

[birrbert]

Don't get me wrong, I wasn't criticizing your goal to learn or the viability of your project. I wanted to know about your expenditures so that I could compare with mine later when I make a calculation. Also, you wrote that Adafruit is not cheap. Well, I think it's affordable. As you say, when you hunt for components and do stuff yourself, you spend more than the cost of a ready made product and the only reassuring thing about it is that you learn (I consider it a school-fee).

[gording]

You're right. At the the very end the most important for me is satisfaction. I can get no satisfaction if I buy complete project from Adafruit. This one I've done from top to bottom by myself and I'm proud of it   Many of complete projects have a box with all the electronics and a solar array joined together. I specifically needed to hung the array outside of the window and because of the unfavorable geographical direction make it way bigger than it would come with of the shelf projects.

[birrbert]

Some updates on this project

The solar cell phone charger started to take shape. At the moment I'm using my award winning DIY power supply to simulate the solar cells. I'm following the drawing posted earlier: Li-Ion batteries are being charged through the TP4056 regulator and a step-up converter provides 5 Volts to charge the cell phone. I made a battery bank out of four cell phone batteries, wired them in parallel, each around 1000 mAh capacity and charged it all the way up.

The 1350 mAh battery of my Nokia X1-01 was down to the level of 1 bar and with the first try I charged it up to 5 bars out of 6. Then I waited to go down to 1 bar again and with second try I gave it a full charge. After this the battery bank still had 3.6 Volts in it so I took a Samsung cell phone which barely turned on because of the low battery and I gave that one almost a full charge. That's when the battery bank depleted. Now I'm charging it back again to do some more testing.

I also encountered some problems or I should say "birrbert wasn't paying attention.
First, I killed one step-up converter. I didn't pay attention and I connected the battery bank to the converter the wrong way and it didn't work anymore. It's allowing electricity to pass, but it's not boosting. I went online for information and discovered that indeed they don't have reverse polarity protection. That's that. Luckily I had two: the green one is dead, the blue one is till OK so I'm using that now.
Second, I think I damaged the charge regulator. I wanted to check its temperature by putting my finger on the board, but unfortunately I was charged with static electricity and there were some serious sparks upon contact. Since then the LED of the regulator is green, which normally indicates that charging is done, but in reality charging is not done, the battery bank is still being charged, because I can see current draw on the LCD of my power supply. So, the LED should be red and turn green only when charging is finished. The LED remains green even when battery bank is not connected; in this case it should be blinking. Again, lucky that I have two more of this regulator, though they are different versions and this was the one I liked most.

Lastly, I did a quick research on the Internet about step-up converters. Please find attached the .txt file which lists the boost converters I think can be useful. There are cheap ones that say they work even with an iPhone and then there are two more expensive ones from engineers I already mentioned in this topic. If you think I missed some, please post here.

In the next round I will prepare everything for a test out in the sun. I'll be back with photos too (my camera is not working at the moment). Cheers!

[SeanB]

Smoke let out...... Probably cheaper to buy a new boost converter than to change out the chip on the board, which is the likely failure. Best is to place a 1n400x diode across the input to provide some reverse polarity protection, along with a fuse of around 5A. That will provide a reduced chance of blowing the module with reversed polarity.

Static damage is a problem, you need to look at doing static control, and if you have carpeting I would suggest taking a sprayer ( like a garden sprayer) and filling it with a solution of fabric softener ( 5l of warm water and 2 measures of softener) and spraying the carpeting with this. It works well to handle static build up, and makes the whole place smell nice. Clean carpets before hand, and if you can rent a wet extractor and do them you will pull out some brown soup as well. The softener also works on wooden or vinyl flooring, but there you will be best applying with a mop.

[birrbert]

Thank you very much for the advice! I must take measures. As of yesterday, I wasn't concerned about static electricity, because I never did any damage with it, but now that I experienced it myself I have to be more careful.

The diode should be on the positive side or the negative side or it doesn't matter?

[SeanB]

Across the power input so that it does not conduct unless the input is reversed. If you have old PC power supplies use the Shottky rectifiers from the 12V side as the diode, the low forward voltage drop and high current capability in a TO220 package will help to protect and blow the fuse, but in normal operation it will draw no power and effectively not be there. If you put it in series with the input you will have a loss across the diode which will be a concern in low voltage inputs like here, where you want all the power out of the cell.

If you look up you can also use a MOSFET as a protection diode, where it is run in reverse ( funny though that looks) and the gate is used to turn on the device when correct power is applied and short out the body diode. Simple and works with low loss. Old PC supplies will also have the MOSFET in them on the 3V rail.

[birrbert]

Hi! Yesterday and today was a great day. I got sunshine and time to play with the solar cell phone charger. To be precise, I tested only the first part which is the battery bank charger. It's working as expected. In unobstructed sunshine the panels provide 580 mA which is great because it's very close to the claimed 600 mA. The Voltage was at around 4.5-4.6 V, which is a bit lower than the claimed 6 V, but I don't mind until the TP 4056 based charge controller is OK with this.

When I started charging today at around 10 AM the battery bank was down to ~3.3 V and now after ~3 hours is closing up to 3.9 V. Yes, it's not so great, but there wasn't full sunshine because of them clouds. I'll have to invest in some more powerful solar panels or cells. Since I don't have any image recording device at hand that's all I can present for now. Enjoy the rest of your Sunday!

Cheers!

[MJLorton]

Hello Robert,

Good to see you are playing with the solar charger again...I've started playing with my solar powered Kindle again and will be posting some videos about it soon.

Cheers.

[birrbert]

Wow, that's great news! Looking forward to it!

[birrbert]

I'm getting around 20 mA on cloudy days at around 4 PM. It's slowly decreasing, 15 ... 13 ... and finally 0 until it get's dark, I guess.
I will let the panels charge right until the evening because I'd like to see how does that charge controller act in darkness.

[birrbert]

After two and a half days testing I can say that the system is working well. The panels needed this amount of time to charge the battery bank from ~3 V to the full 4.15 V. One full day was cloudy and the rest was sunny. Now at least I know what the situation is in the area where I live. It would've been nice to log some data that I can present here, but for now that's not possible. Also, I must mention that I'm not sure how many mAh's can my ad hoc battery bank hold (four cells used in Nokia 7210).

OK. That's about it for now. I'm a bit unsure which way to go from here. I'm planning to buy a good 4400 mAh rechargeable battery and I'll put the cells in a fabric casing thingie. Oh, and of course I would like to try out more powerful solar panels, e.g. three 500 mA @ 6 V wired in parallel.

[MJLorton]

Interesting Robert. I have to say, it is frustrating finding a reasonably priced device to measure power and energy (Ah and Wh) and log it. I've been chatting to someone about designing such a device...will see where that leads.

Cheers,
Martin.