First steps in using the Sun's energy

[birrbert]

Hi SeanB!

I did a search for capacitors and found various types. For instance there are two types of 16V/10000uF electrolytic capacitors advertised based on 'working temp': 85 degrees Celsius (0.81 USD) and 105 degrees Celsius (0.96 USD). Also there's a third type called 'low impedance' (15 mOhm): this one costs 3.59 USD for one piece of 16V/8200uF.

And of course there are super capacitors that I could afford: 22F/2.5V/5.5A regular barrel shaped which costs 2.84 USD and 10F/2.5V/3.8A flat shaped which made me think whether it's nicer to mount in a charger and costs 9.43 USD.

So, which one should I go for? And I have to mount this "in parallel with the solar panel" which is before the regulator. Is this correct?

edit:
In the same time I'm searching for a good LDO and I think I found one. Would you please comment it or recommend a better one?
MCP1703A-5002E/DB (output 5 V, max input 16 V, max output current 250 mA, SOT223-3 case) or MCP1703AT-5002E/MB (everything the same just SOT89-3 case).
To be honest I don't know the practical difference between the two cases.

edit2:
Another question that just popped into my mind is, what happened if I connected my solar cells to put out 600 mA at 6 Volts instead of the 300 mA at 12 Volts? That way I probably wouldn't have to worry that much about over-voltage and anyway it seems that my primary problem is low current rather than low voltage. I will probably try this configuration out too, but first I would like to achieve result with current one.

[SeanB]

In this application either of the cheap ones will definitely work fine. In the interim look in some old computer motherboards for high value capacitors ( non bulged ones) and unsolder them and try them out in the interim.The supercaps will work as well, but you will have to stack a few in series so that the total voltage of the stack is higher than the open circuit voltage of the solar panel, which would mean you have placed a rechargeable battery across the panel output.

As to the LDO regulators, they both will work, but you will have a hard time soldering on to the packages, and they will need a heatsink. Look for a premade board with them on, or one in a TO220 package which will make it easier to connect in circuit.

[birrbert]

So, I started hunting components again for this project and I found some interesting ones. For instance:
- This Li-Ion Battery Charging Board which uses the TP4056 IC or;
- This very simple booster step-up module with USB output. I couldn't identify the chip that it uses. I actually have two types, please see photos.

I made a drawing how I imagine the cell phone charger as of today. Please find it attached. It's based on the idea that it's much better to store the energy in a rechargeable battery and then - by boosting the voltage - use that as a source to charge the cell phone. What do you think? Would I need other components?

[SeanB]

Will work, you will just need a switch to turn off the inverter to the phone when not in use so it does not kill the battery during non use.

[birrbert]

Thank you very much Sean! You're a true gent! I can hardly wait for the parts to arrive and put it together!

By the way, I bought a 300 mA analog current meter and I shorted the solar cells into it. With one cell it showed 100 mA and with three cells 300 mA. I was outside, the cells were exposed directly to the Sun and of course I aimed a bit. It's good to know that these cells produce what they claim. For instance, behind the window no matter how much I tried to aim, the cells could only produce half the current.

[MJLorton]

Great stuff, look forward to seeing how it goes...have fun with it!

Cheers,
Martin.

[birrbert]

Thanks! I'm certainly having fun.

I'm still waiting for the Li-Ion charge controller. In the meantime I charged the batteries with my "almost-ready-PSU". The disadvantage in my case is that the PSU doesn't have "real" current limiting. This is a special case of mine, but it might happen to others as well, especially with DIY power supplies.

- Let's say I set the Voltage to 4.2 Volts and apply no current limit, then I have the feeling that the battery pulls as much current as it can from the PSU. In one case it drew about 700 mA in the beginning and in time the value slowly decreased; in another case it pulled 1.2 A in the beginning and again with time the value slowly decreased. I disconnected the batteries when they were pulling only 50 mA.

- Now, if I limit the current (the goal would be to charge at a slower rate, e.g. 0.5C-0.8C) then the voltage output of the PSU drops too, meaning that I can't maintain the 4.2 Volt charging (to give the battery a full charge). I don't know if it matters for the Li-Ion battery if it's charged slower or quicker... I will have to experiment with this a bit more. By the way, the batteries I bought are small 1200 mA Li-Ion cells made for Nokia 8210/7210.

Questions and situations to experiment with:
- How much charge can I transfer from these cells into different types of mobile phones, using the cheap DC-DC step-up converter that I bought from eBay?
- Try to determine the efficiency of the step-up converter.
- Why doesn't the iPhone 3G S start charging if connected to the USB port of the step-up converter? Can the converter be modified?

Websites that I found helpful after browsing them for hours and hours:
- Battery University. I recommend checking out the article about charging lithium-ion batteries that provides a nice theoretical background in this topic.
- Brown Dog Gadgets. Especially interesting the Single USB Boost + Lithium Charge Controller Board that they sell.
- Adafruit Learning System. They have very nice documentation of the stuff they sell, easy to understand explanations, detailed discussion about challenges and possible obstacles that need to be taken into consideration when somebody makes this kind of charger.

edit:
A few minutes after writing this post I found this product on DX.com: Portable 5V "30000mAh" Li-ion Battery Solar Power Bank w/ Dual USB + LED - Black + Whitewhite-240475.
Well, if one engages in a project like I did, he needs to have a lot of motivation and a lot of fun to keep up and deliver some kind of result. I have to admit that seeing this product got me thinking. For one, the price is unbeatable (i.e. in my country the solar panel alone would cost more than the whole thing, not to mention the battery or other components); two, I started my project to learn about electronics by doing, but one might be able to learn the same way through buying a ready made product, examine it, disassemble it (if possible), etc. Maybe. Possibly. Just a few thoughts I wanted to throw in here.

[MJLorton]

I think you'll learn far more doing exactly what you have been doing. Don't let that stop you from investigating a retail product but many of them don't deliver on what they say they will.

[birrbert]

I agree with you! I will buy this charger sometimes and test it.

In the meantime I did a couple of things. I connected one Li-Ion cell to the boost converter and started charging a fully discharged Samsung cell phone. It didn't do much; the cell discharged quite fast (went down from ~4 Volts to ~2 Volts) and the phone showed only one bar of charge. Then I took three cells in parallel and used those to charge the phone furthermore. These ones discharged much slower (obviously) and the phone showed all five bars, though it didn't display the "battery full" message. Interesting thing that I didn't keep an eye on these three cells and by the time I "woke up" they went down to 0.8 Volts; still the phone was charging with a steady ~4.9 Volts which gives me the impression that this boost converter does a good job.

This was one step in determining the efficiency of the converter. Next, I have to check the Amps too (from the cells to the converter and from the converter to the phone separately), but it's damn hard without proper equipment.

And here's something I don't understand. When everything is connected and the cells are charging the phone through the converter, if I take a Voltage measurement with the multimeter at the cell terminals I see the Voltage (typically 3.7-4 Volts), but when I take the same measurements at the input terminals of the converter I usually see 1.9-2.1 Volts. What gives? I mean there's nothing between the cells and the input side of the converter, only the cable that connects them.

edit:
1. During usage the converter gets quite warm. I hope that it will do it's job later too when I put it in an enclosure.
2. Is there a way to add some kind of charge state indicator to my system? For example three LED's which turn on for 10 seconds at the push of a button: one LED would show that the battery bank is low, two LED's that it's halfway charged and three LED's that it's fully charged. The idea would be to keep power consumption minimal, hence the LED's and the push button. Do you guys have experience or an idea for this?

edit2:
Regarding the charge state indicator, I just remembered that the charge controller I have chosen has some LED's on it so maybe I can use those, but those light up only when charging is in progress.

[gording]

Hello Birrbert

I'm glad that I found this forum and your thread. Now there's two of us! I live in Poland - Warsaw. By coicidence I've started exactly simillar project like you do.
Not knowing about you and this forum I've come to allmost exactly the same solution and project as you did.However im still on much earlier stage of construction. I've spend couple of weeks completing my solar panels. I've made them of single wafers wich I've solderd by myself, then I've bought a frame and encapsulated the wafers in a electrotechnical sylicone. The panel alltogether produces around 6V and 2Amps open circut. Theoretically. Why 2A? Well I live in a flat with windows on one side of the world only. And the side is north-east. :/ Putting panel on top of the roof is out of case as the community in my building would'nt allow for this. So I had to put it outside my window. By making it 2Amps i hoped i will secure myself against all the hours when my windows are shaded. Fev days ago measurments showed 6,5 Volts open circut and 1,1Amps at bright sunny day but with the sun around 50 degrees to the side of panel face. Didn't check it yet with shaded conditions. Only 3 days ago I've made a mounting frame and hung it outside the window. Now all i got is panel outside and bare cables inside
I've allready orderd both blue and green step-up converters. I do allso already have a nice LDO voltage regulator in 220 type body. I also ordered such a meter:

http://www.ebay.com/itm/181214038738?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

I already know from Martin films that there are better meters but I think I should be quite satisfied with this one keeping in mind the good price of it.
Now next step will probably be to buy a 3,7V li-ion battery. Perhaps i will go into a 18650 type.
My Samsung galaxy s3 battery is 2100mA, 7,98Wh
So i will probably try to buy a few18650 batteries to make something around 5000mA of them so I could charge my and my wifes phone as well in one night.
I need to find out some more about the  charge controller which you bought. Would it prevent our li-ion external batteries from being overcharged?
Are there any other options to protect external battery from being drained by step up converter in no use time than a on/off switch. I'd like to make it as simple as possible and don't quite like the fact that one have to remember to switch toe switch off after disconnecting the phone - a thing easy to forget. Especially that probably it won't be just me using this charger.

Well I'm very glad we could exchange our experiences and learn together. Cause actually all the thin is about learning and having fun from it at the same time isn't it
If you'd like i can post some pictures of my panels outside my window later when i get back home from my work's trip I am on now.

edit: I looked at your scheme. Noticed there's no LDO voltage regulator between solar panel and charge controller. On the ebay auction also theres nothing about output of that charge charge controller. I think I could on a shiny day get over 6,5Volts under load conditions. Is that not to much to the 3,7V battery? Also if this charge controller doesn't lower the voltage then the 6,5v would go straight to our step up converter and then  directly to a phone.

edit2: I think I saw somewhere on our Polish websites a protection circuit which prevents 3,7 battery from being drained if we charge to many phones in poor light conditions We could implement it between external battery and step up converter. 
Yep, actually it was here.
http://www.batimex.pl/towary.php?idzastosowania=1253&idzastosowanianad=1050&search=&selectLanguage=en&selectCurrency=2
Probably we could find something similar on ebay for a better price. However I will probably buy it from them as they are just a few kilometers from my home. I know they also have a Li-ion batteries with protection boards already installed in battery's casing so I will hesitate from buying a battery on ebay until I pay them a visit and talk to them.
Cheers
Konrad Hanc

[birrbert]

Hi gording! Welcome to the forum! Please post photos with explanations about your progress!

To address a couple of your concerns:
- The charge controller I chose was made specifically for 3.7 Volt Lithium-Ion rechargeable batteries. It has overcharging protection, because it will stop when the batteries are at 4.2 Volts. Also, it uses 1/10 of the charge current as termination current.
- Here is a review of the charge controller using the TP4056 chip. The reviewer guy states that " When charger is disconnected from power, but with a battery in, it will draw below 1uA from the battery." While this is valid for the charge controller, I have no clue about the current consumption of the step-up converter, so it's a thing worth looking into sometimes.
- There's no need for an LDO regulator. The TP4056 can handle a maximum of 8 Volts input, so you should be fine because your solar cells will produce a maximum of 6.5 Volts. The output is a stable 4.2 Volts.
- Your concern about draining the battery too low is valid. I forgot to check on them once and they went down to 0.8 Volts, as I mentioned in my previous post, but I immediately charged them up and hoped they not got damaged. I bought two protection boards for testing: this one and this one. These are good for testing and learning, but otherwise it's best to buy the battery with built-in protection board, in my opinion.

Right now I'm waiting for info regarding the issues I raised previously. I'm especially interested in an explanation regarding the difference in Voltage at the battery terminals and the step-up converter. I also couldn't find info about the technical requirements for charging an iPhone 3G S through USB.

Regarding batteries, I found one locally for a good price: Swing 4400 from Boston Power. It would be great to test it, but don't have the funds for it yet (I just spent some money on silicone cables from Franky's shop)!

[gording]

Hi Birrbert
Thanks for your reply.
I'm still waiting for some main components to arrive, like step up converter. But in the meantime managed to make a simple circuit. I connected solar panel output to a pcb board. As I have no battery yet, I placed an LDO voltage regulator. And on a very cloudy day I had with cell phone connected 5,5v from the panels. And only 4,7 coming into phone. I write "only" because I thought LDO will always give 5v on the output. However it did gave 5v on output on open circuit, under load conditions I only got 4,7. Around 0,8v drop. The phone didn't charge at all because all my "was-to-be-mighty" panel gave was 70mA on open circuit. Probably I would do better today if I connected solar panel straight to the phone, avoiding LDO. But I had no time to play with it for longer. Do you have any experience with LDO voltage regulators?  On a product card I've found that they require to mount two at least 22micro farads capacitors. One on source-negatve, and other on load-negative. I've mounted two 100 micro fahrads, however I have no idea if it has any influence on my circuit. The only I can think of is that it would support voltage for a few seconds when suddenly disconnecting solar panel. But I don't think that is the reason of mounting them on. BTW I had a little fire on my pcb last night when at the first time no knowing what I'm reallly doing I connected the capacitor other way round. Lesson learned!
Thanks for the TP4056 details. I will certainly familiarize myself with them.
Will post some photos in couple of days, when I'll find some spare time.
How about if you dismantle some old usb charger if you have one and connect it to the iPhone and use an multimeter on it? I had an old Samsung charger - the one you connect to the wall socket. I cut the phone plug out and mounted usb socket in there. I also have a Usb cable so by using it i managed to connect a phone and check that the wall charger gives constant 5,05v both open circuit and with load on/phone connected. I also checked the current a phone drains. Now I know that with empty battery it drains around 480mA which drops some much lower amperage when almost fully charged. (I don't remember the value now, but I have it written somewhere). If you do the same you will at least know what the original charger produce and could then compare it with what your solar panel gives and see if you can do anything to change the solar panel or the step up converter into what the original charger gives.
Bye

[birrbert]

I found my answer about charging Apple gadgets through USB on Adafruit Learning System. It's well written, detailed and for the most part easy, so all I need now is some brain activity (i.e. wisdom) and testing to fully understand it. Great people these folks over at Adafruit!

Link: http://learn.adafruit.com/minty-boost/icharging

gording, you didn't specify what type of LDO you are working with, but please DO NOT AVOID IT! Don't connect the solar panel straight to the phone, because you will damage it! You have no control over the Voltage output of the solar panel, thus you have no way of knowing how much Voltage is going into the phone. I don't know if cell phones have any kind of over-voltage protection, but I know one thing for sure: they aren't as cheap as a capacitor that you popped the other day.

edit:
I just watched the video that Ladyada posted and I realized how important resistors are. They play a huge role in every electronic device or circuit. I have the impression that everything is circulating around resistors.

edit2:
Guys, is there anybody here who could help understand how the blue and green Chinese step-up converter work? I typed into Google what is written on the components, but couldn't find any usable piece of info.
The green one has an inductor labeled 220, a resistor labeled 222, three SMD capacitors, two diodes (one SMD and the other  labeled SS14) and one small-black-IC looking-chip labeled E5 00. The blue one uses mostly the same components, except for the inductor which is labeled 470, the resistor labeled 102, plus it has one less capacitor and instead of SMD the one capacitor is electrolytic.

[dr_p]

SMD resistors are usually marked with 3 (or 4) digits. The first 2 (or 3) are straight up value, the last is multiplier (power of 10).
So:
 153 is 15*10^3=15*1000=15000=15k
 4701 is 470*10^1=470*10=4700=4k7

Other Rs are coded in a "nasty way", so you better read this.

Inductors are marked the same way, but the value is in micro-Henry (uH).
So a 470 inductor is 47uH, a 331 is 330uH. I have also seen inductors marked 4R7 and I presume it means 4.7uH, as there is no way of marking it with the 3 digit code.

Now, regarding your boost converter: I've recently been interested in these. I bought THIS module and the IC was marked AL205. Other eBay pictures showed it as AL289. So I realized this is not the IC name, but a code. I finally suspected the IC used is a FP6291, based on the pinout and specs (1MHz, 1A) etc. The datasheet also states, under "marking information", that the package is coded with ALxxx, so this is definitely it.
What I'm saying is that it can be difficult to find an IC from what is written on it. But in your case I don't think it's that important what IC it is.

You were asking how they work. They are classic "boost converters", you can google that.
I still have one of the FP6291 modules, so if you're interested you can have it, no charge.

[gording]

Under the link below is my film with my attempt to charge my phone using 4 AA batteries and LDO regulator - failed. If you have any idea what am I doing wrong I will appreciate your suggestions. Sorry, I've tried for over one hour to post a youtube film directly in here instead of a link but failure again. None of "posting youtube video into a forum" worked for me. 

http://www.youtube.com/watch?v=Au4tL3gGnz4