Solar recharge circuit not working

Hi Hardware Experts,

I bought a solar rechargeable LED key chain light from eBay, a few months ago, here:
  http://www.ebay.com.au/itm/Mini-Solar-Power-Black-3LED-Light-Keychain-Torch-Flashlight-Key-Ring-Useful-/181743115934

It's about half the brightness that it was months ago when I bought it, so I tried to recharge it by sitting it in direct sunlight for probably 10 hours total now, but the brightness doesn't seem to be improving at all.  I confirmed this by comparing the brightness to that of a new one.

As you can see on eBay, it's very cheap, and I could easily replace it, but that is not my point.  I wanted a solar rechargeable light, and I'm wondering if this device is even designed to recharge the battery or if they are advertising it falsely and the solar cell is just for show.

I dropped it a couple of days ago and it fell apart.  It still works, but this allowed me to take some photos, which I have attached.

Questions:
Q1. Is there an easy way to confirm whether the CR2016 lithium battery is really rechargeable?
Q2. Does the circuit look capable of recharging the battery?
Q3. Any other ideas on why it might not be recharging?

Thanks.
tel2
LED_Key_Chain_Cell.jpg
LED_Key_Chain_Circuit.jpg
LED_Key_Chain_Batt.jpg
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viki2000Commented:
It seems someone else had a similar experience as yours and found out that the battery is not rechargeable and from here less light after a while.
http://www.dutchforce.com/~eforum/index.php?s=6647bd540ed0d433a796252a299419b6&showtopic=33583

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Mal OsborneAlpha GeekCommented:
A CR2016 is not designed to be rechargeable. Having said that, all primary cells can be charged to some extent, you might get a couple of part recharges out of it.
rindiCommented:
The idea behind the solar panel is not to charge the battery, but rather to use the sun's power rather than the battery's when you use the LED's when you have daylight. This would extend the life of the battery. But it is a bit hard to see any reason to use the lights while there is ambient light around, so the positive effect will be minimal and you'll probably have to replace the battery almost as much as if there were no solar panel.
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tel2Author Commented:
@Viki - good link - thanks!

@Malmensa - yes that confirms what someone at Viki's link said.

@rindi,
"The idea behind the solar panel is not to charge the battery..."
1. How do you know that?
2. If that is the case, then how would you explain the "Description" half way down the eBay page, which includes:
    "Solar Powered Re-chargeable Built-in Battery"
    "Charging Time: 3-6 hours (in the Sun is ok)"
viki2000Commented:
CR2016 - most of them are not rechargeable, but there are also rechargeable:
http://eu.mouser.com/ProductDetail/Renata/LMR2016/?qs=%2fha2pyFadug2tHXiIUuRhvc%252brnl%252bEpUk8GZJ%252btIgL6ZTmoccGb%2fi5q%2fBuBQDmjji
It is only your bad luck that yours seems not rechargeable, that's why is cheap, with a false claim.
Could you make a photo with opposite part of the PCB?
I see no diode, at least one to block the current from battery to solar panel and/or the other way around.
There is no charge circuit on the photo 2 "Circuit board".

If you want to go deeper, then you have to identify proper your battery.
You have to make photos or good scanning of the battery on both sides, eventfully you have to take the yellow cover around it and also on bottom side to see if there is additional marking and upload here.
rindiCommented:
The ebay description is wrong. Maybe the seller doesn't know his product and just said it was rechargeable because it had a solar panel? Rechargeable Batteries would have another product number, like VL2016 or ML2016.
viki2000Commented:
I tried to translate the text from the battery on photo 3 "Lifted up back of battery", but is only a general warning to keep safe and away from children because they can swallow such small button battery.
If there is no more text on the bottom covered side of the battery to identify it, then  we can simply rule out CR2016 is not rechargeable. As my link above from Mouser shows (LMR2016) and as rindi suggested too , there is another code instead of CR for a rechargeable battery of the same size and voltage.
The ebay seller has no clue what is inside the key-chain, is just a trader.
Even so, with a proper charging circuit, a normal battery may be charged a bit, with very low current, several times, even if it is not indicated. By the time the key-chain does not work properly anymore, few months have past and for a cheap light like that, it does not matter if it works or not anymore. On such thinking is based the production in China and the manufacturer rely on the fact that being so cheap for western countries, it does not matter anyway and you buy a new one.
tel2Author Commented:
@Viki,
Thanks.  I might try to remove the circuit board from the solar cell sometime, so we can see the other side.
"CR2016 - most of them are not rechargeable, but there are also rechargeable:"
The label on the one you linked to is not CR2016.  It is "LMR2016".  Which leaves me wondering, is there such a thing as a rechargeable lithium "CR2016".
"You have to make photos or good scanning of the battery on both sides, eventfully you have to take the yellow cover around it and also on bottom side to see if there is additional marking and upload here."
My 1st has photos of both sites (see "Circuit board" for the -ve side).  Is the quality sufficient?  But I haven't taken off the yellow cover yet.

@rindi,
OK, you've answered my 2nd question to you.  Please answer this rephrased 1st question to you:
"The idea behind the solar panel is ... to use the sun's power rather than the battery's when you use the LED's when you have daylight."
1a. How do you know that is the idea behind it?
1b. How do you even know that the solar panel is functional and electrically connected?
viki2000Commented:
My 1st link points indeed to LMR2016, which is not CR2016, but the size and voltage are the same.
If it is marked CR2016, then it should not be rechargeable. A rechargeable one must be marked different. Nevertheless, from China you may have suprises:
http://www.alibaba.com/showroom/rechargeable-cr2016-battery.html
Your photos have good enough quality, but they do not show all the needed info: the other side of the PCB and the other side, uncovered, of the battery.
rindiCommented:
I don't know that, but it is the only logical function of the solar panel, it must be the idea behind the whole thing. Why would you waste a solar panel on a device without any charging circuitry (there isn't any circuitry on the board besides the on/off button and the contacts that connect everything) or a rechargeable battery. It can only be of use when there is light available.
tel2Author Commented:
Hi all,

I have now separated the circuit board from the solar cell, and attached is a photo.  It seems that all that was holding them together is the glue (that you can still see on the circuit board).
I can't see any components on that side of the circuit board.

I tried contacting a multimeter to the contacts in the corners of the cell (above the "+" & "-" symbols), and I can get upto 7.7v in direct sunlight.
However, from looking at my original "Circuit board" photo, you can now see that those solar panel contacts will not connect with anything on the circuit board, so it looks as if the (genuine) solar panel is all for show.  What a waste.

Why do you think they put the yellow thing around the battery?  To reduce the chance of leakage?  I guess it would be for insulation, but I can't see what it would contact that matters.

tel2
LED_Key_Chain_Unglued.jpg
rindiCommented:
The yellow plastic around the battery protects against short circuits if the metal of the battery touches a component on the circuit board. Those batteries with solder points like yours usually come that by "default" from the manufacturer.
tel2Author Commented:
OK - thanks rindi.

I measured the "3V" battery, and with the light off it measures 5.6V (tested on 2 different meters), and with the light on it drops to 2.7V (probably significantly lower than 3V because it's already getting a bit flat).
I've never seen a 3V button cell show such a high voltage even when not under load (apart from the load of the meter, of course).  For example, I've got some new CR2032's here which read 3.3V.
Have you seen such high voltages from a 3V button cell before?  Any explanation as to why?  (Somehow I don't think it's because of my charging, since the solar cell seems to be not connected to anything.)  (There's so much "scope creep" in this question, eh?)
viki2000Commented:
Well, at least now we know it. Your mini-solar panel was not even connected and also did not have the diode installed.
I would say is a genuine fake :)
But don't worry, you are not the first one, neither the last one.
Here is a similar analysis. I hope it will answer to all your questions.
http://sebastianschaper.net/index.php/archives/118

And as for the plastic ring around battery, just try to remove it. Maybe you will have the surprise to see  two "CR2016 cells stacked on top of each other, resulting in a 6V disposable battery rather than something rechargeable" - to quote the above link, then you will understand how come you measured 5.6V, meaning 2x CR2016 in series discharged.
tel2Author Commented:
Very interesting link, thanks Viki.  I should have found that (and did, but you beat me to it).

Any comments on the 5.6V I'm getting from the battery (see my last post)?  Just tested a new keychain and it's batt is measuring 6.14V with light off, and about 3.3V (and slowly dropping) with light on.  It is also a "CR2016 3V" lithium battery.  Why such a huge difference between the voltage with & without load with these particular batts, while my CR2032 3V batts are about 3.3V without load?
viki2000Commented:
Any comments on the 5.6V I'm getting from the battery (see my last post)?
I thought I did, 2 CR2016 in series.
And as for the plastic ring around battery, just try to remove it. Maybe you will have the surprise to see  two "CR2016 cells stacked on top of each other, resulting in a 6V disposable battery rather than something rechargeable" - to quote the above link, then you will understand how come you measured 5.6V, meaning 2x CR2016 in series discharged.
tel2Author Commented:
Sorry Viki - I somehow managed to miss that part of your post.

And you're absolutely right!  I took the yellow cover off and there are 2 x CR2016 batts on top of each other!

And that's strange because as I mentioned above, my 2nd (new) keychain and it's batt is measuring 6.14V with light off, and about 3.3V (and slowly dropping) with light on.  So the voltage under load is only about half the voltage without load.  Would you expect such a voltage drop in this scenario?
viki2000Commented:
The new CR2016 has between 75-90mA, depending from manufacturer to manufacturer, if it is a good quality.
Your 3 LEDs do not have any resistor in series to regulate the current, therefore the battery goes from constant voltage mode, as supposed to be when a resistors is used, to constant current mode, meaning the voltage across the battery will be equal with the voltage of the 3 junctions of the LEDs in series, indicating 1.1VDC for 1 LED.
To answer your question: yes, it is logical. I would have expected.
Just measure the current through the LEDs with a DC ammeter, then you find the working point of the LEDs and we can calculate a small resistor to regulate the current, so you do not see the same voltage drop.
But even now, if you consider 6V-3.3V=2.7V and around 20mA for LEDs, then you get 2.7/0.02=135ohms, just try something between 120-150ohms in series with your LEDs.
Then you will not see that voltage drop anymore, because a part of the voltage will be on LEDs (3.3V) and a part on the resistor (2.7V) and the battery becomes a constant voltage source, as supposed to be.
tel2Author Commented:
Thanks for that, Viki.

I have a couple of questions about that:
  1. What is the practical advantage of adding a resistor?  Battery life?
  2. What is the practical disadvantage of adding a resistor?  Brightness?

Thanks.
viki2000Commented:
Basically yes.
If you look at the discharge curve of the Cr2016 batteries:
http://data.energizer.com/PDFs/cr2016.pdf
http://www.sony.net/Products/MicroBattery/cr/pdf/cr2016.pdf
http://www.varta-microbattery.com/applications/mb_data/documents/sales_literature_varta/HANDBOOK_Primary_Lithium_Cells_en.pdf

then you see that they have around 90mAh capacity and the curve is based on 30K resistor to give 100uA at 3V start voltage.
You should measure the current in LEDs when batteries are new.
There is a working point of the LEDs (voltage, current) given by the LED exponential curve.
The brightness is direct proportional with the LED current.
In your case, we can assume 20-30mA for the LEDs, then is max. 3-4hours until the battery will be discharged, but the brightness will be reduced as the battery voltage drops to lower values.
The resistor sets the current for LEDs and automatically you know the discharge time a bit better.
That drop of voltage on resistor may be seen as reduce efficiency, because some of the energy from battery will be dissipated on resistor, but at this simple circuit does not matter anyway. Just try and see by yourself.
tel2Author Commented:
Thanks for that, Viki.

Going back to a previous post of yours, where you wrote:
> "...meaning the voltage across the battery will be equal with the voltage of the 3 junctions of the LEDs in series, indicating 1.1VDC for 1 LED"
Are you aware that the LEDs are powered in parallel, not in series?  It's a bit hard to tell, this can be seen on the "Circuit board" photo.  So that would be 3.3V (not 1.1V) for each LED, right?
viki2000Commented:
I checked your photos one more time. It seems you are right, the LEDs are in parallel.
tel2Author Commented:
Thanks to all of you for all your comments, especially Viki who was most helpful.  (I clearly should have done more googling before posting this question, as some of Viki's links prove.)
viki2000Commented:
Hi tel2,
Thank you for the points. They helped me to get a new rank and also a new T-Shirt; not that I am chasing them, but will be my Christmas present :)
Let me tell you a "secret", why I believe I found those links and you didn't. I did not search the web for words, but I used visual search. I used Google images, I tried the solar keychain, then I looked over the images. Then I opened some of the webpages which contained those images and "voila"...
Hope that helps you in further searches.
Cheers.
tel2Author Commented:
Thanks for that, Viki.  

And don't worry - you're secret's safe with me (and everyone else on EE who may see this).

I've used Google images to search for people before, but not objects.  One time a Nigerian 419 scammer sent me "his" photo, so I searched the web and found it was some priest, so I sent him the link and told him that I'd found his identical twin.  He didn't want to talk to me after that.  8(

When you say:
"I used Google images, I tried the solar keychain..."
What solar keychain did you try?  Are you saying you searched by one of the images I supplied?  If so, which one?

Also, how can I confirm how much current the solar cell puts out when it's in the sun?  I measured the voltage (7.7V), and my multimeter can measure amps, but don't I have to add some load or something?

Thanks again.
viki2000Commented:
When I used Google Images, I used something like keywords "inside solar keychain" or "teardown solar keychain" for search and not your images. Important is always to find the proper keywords.
This is "free of charge":
http://tarkus-notes.com/en/mini-chinese-solar-power-flashlight/
And by the way, sometimes is good to try also search videos, Youtube. You will be surprised what you find:
https://www.youtube.com/watch?v=uAmXudEA_HE
https://www.youtube.com/watch?v=546bIjc4pes

Here is the real thing:
https://www.youtube.com/watch?v=QyzHa8q5bgQ

To measure the solar panel output power, which is a curve that depends by load, you need a set of of various resistors values. Then you measure the current and the voltage and make a graphic.
http://www.voltaicsystems.com/blog/solar-charger-tutorial-part-2/
http://www.instructables.com/id/How-to-Measure-a-Solar-Cells-Power-Output/
http://www.reuk.co.uk/Measuring-the-Power-of-A-Solar-Panel.htm
tel2Author Commented:
Hi Viki,

Sorry - when I said Google images I meant something else, i.e.: images.google.com.  Have you used it?
But yes, I have used Google to search by key words then check the associated images, but it's not something I thought of for this keychain thing.

Interesting that you posted those 3 YouTube links, because I watched all 3 of them only hours before your last post.  Unfortunately, the seller mentioned in that 3rd link doesn't sell them anymore, but I may be able to find another who does.

Thanks for the tips on measuring the current.  Not as simple as I had hoped.
viki2000Commented:
I used "images.google.com", but with words, not uploading images, not this time.
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