Solar cemetery candle led lamp

[Lucky-Luka]

Hi all
Just an unusual topic.
My parents occasionally ask me to recharge 2 AA batteris for cemetery candle led lamps they use for their dead parents.
I would like to turn those lamps into solar one. I know I can buy them already solar powered but it's just a way to improve my knowledge.
Can you suggest me a circuit to follow?
Cheers

[Twoflower]

The one I opened used a QX5252F (or something like that) for doing that.

[JackJones]

YX8018 is another common one. There's a bunch of different ICs for this, including surface mount versions. I haven't found surface mounts for sale though, and the cryptic part numbers on them don't reveal anything. I've got some solar corks with SOT-23-5s with markings Aj7R4, but haven't found anything relevant with searches.

They are stupidly simple to use though, just basically an inductor, solar cell, LED and NiMH battery and you're good to go!

I've modified the solar corks I have by adding a resistor in series with the LED, it gives it a little bit more battery life without sacrificing brightness. You can also modify the output current by adjusting the inductor value.

[Lucky-Luka]

I think I will go with QX5252F since I have found a nice datasheet.
What solar panel and battery should I use?
I have 3.7V lipo batteries at home but I don't know if it's the right choice.
A solar panel like this one https://www.amazon.it/gp/product/B073Y4BJH3/ref=ox_sc_act_title_1?smid=AQ1IBDB6G2RRD&psc=1 can be used?

[JackJones]

Li-ion is not suitable for these, they are designed for NiMH rechargeable batteries.

The solar panel should be about 2V panel, and the current rating depends a bit on the size of battery you are using. There is no cutoff for the charging current, the battery is continually being trickle charged so if you use a too big solar cell you can put too much strain on the battery. You can get away with quite a small one, for example the solar cork thingies I have have a 2.5cm diameter 2V solar cell. Probably gives 20ishmA, and it works fine with a small 80mAh NiMH coin cell, even near the arctic circle.

[opampsmoker]

Yes, to use Li-Ion.....then put a charger between the panel and the Lipo cell.
2V is very low voltage, so use a little monolithic boost converter to give you a ~5V rail to run things off. (you can "do stuff"  with 5V).
Then you can use say a little sepic to charge your Lipo from the 2V output of the solar. Add a large-ish capacitor to the 2V solar cell output.

Bear in mind that the SEPIC  (or whatever), will have to use logic level switching fets that can get well enhanced by the 5V.

You can then run a micro on the 5V...and get it to sense the Lipo voltage as you charge (use   the micro's  ADC) ...when the Lipo voltage gets to 4.1v......stop charging......make it stop charging for say 10 mins before you again sense the Lipo voltage to see if you need to replenish it. (start re-charging).

By the way...this method only charges you up to 80% capacity, but thats probably ok i imagine?......if you want 100%, then you have to put a voltage regulation loop in there, and keep charging after 4.1v is reached until charge current goes right down.

[Lucky-Luka]

@opampsmoker

looking at the datasheet I don't need all these things if I use a Ni-MH battery...

[Lucky-Luka]

I've decided to resuscitate this post because I've noticed that when the light hit the solar panel QX5252F keeps the LED turned OFF while in darkness it turns the LED ON.
I would like to have the LED always turned ON.
Any sugestion?
Thanks

[Twoflower]

I think for this the QX5252E will do. This one has a LS pin used for a light sensor. If you pull it to GND (Uls < 0.22 * VIN ) it will drive the LED all time (see https://www.mikrocontroller.net/attachment/158139/QX5252.pdf; page 3).

[Lucky-Luka]

QX5252E are almost impossible to find

[Twoflower]

Yes, you're right. How about the PR4403? But this one needs an additional external (Schottky-)Diode.

[Lucky-Luka]

Looks at its beautiful datasheet and compare it to chinese quality one regarding QX5252 IC... There is a bold price difference between the two solutions. You have to pay for quality.
I will try this solution for sure!
Thanks