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Topic: How to modify the voltage of solar charger? (Read 5938 times) previous topic - next topic

falexandru

May 24, 2018, 07:23 am Last Edit: May 24, 2018, 07:32 am by falexandru
I  want to charge one 3.7 LiIon 18650 battery using a photovoltaic panel.

The panel is rated 6V.

The project has two stages:
a) to charge the battery - no matter how
b) to charge in sunlight and light one white LED during dark time

For the a) I think a  0,5W 4,7V DO35 Zener Diode coupled directly to the panel may suffice.

For the b) stage I need an automatic charger/commuter

+++

For the b) stage I found only a couple of schematics on internet - 2, attached.

Both are stated to work on 2V panel - which I cant understand, because I could not find a 2V panel, but only 1V, 6V and above). I know I will not get 6V but only 3-4 V under regular daylight and using not-oriented panel, but still a 2V looks excessively pessimistic.

Question is: although these 2 circuits are  stated to work on 2V solar panel  - is it safe for the 3.7 battery to charge from the 6V panel?

Thank you very much for your kind opinion and for any hint to an alternative simpler schematics!

This is education project (kids).


septillion

Mm, charging LiPo is not simple. At least not to do it reliable and hazard free. What's wrong with using a LiPo charger IC/breakout?
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

falexandru

This project is education-centered. Kids to learn how it works and to see what they do.

LiPo are more expensive.

I can think to NiMH (2 x 1.5 V) instead - cheap enough.

septillion

NiMH is pretty easy to use indeed. Just supply it a voltage with limited current (resistor) and you're done. Can also sustain trickle charging so no need to disconnect etc.
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

falexandru

Thank you!

NiMH is a kind of old. But well- cheap .

One NiMH is 1.2 V x 2 = 2.4V. Then it can be charged by the circuits I found - is the provided voltage is still 3 V when I connect it to 6 V panel (panel working voltage will be probably around 4V).

If this 2.4 V(in practice I think it will be some 2 V) would b e sufficient to open an white LED, that is to be checked.

+++

I cant figure out: are those circuits regulated (or limited) to 3 V, or their output will increase with the input voltage? Thank you!

wvmarle

White LEDs tend to have a forward voltage of about 3V. So you'd better take a set of three NiMH batteries, then you have a voltage of about 4.5V (fully charged) dropping to about 3.6V when nearly empty. That should be good enough, and your solar panel can still charge them.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

falexandru

3 x 1.2V = 3.6V (NiMH) - according to the labels of the units I have in hand (perhaps they is another type of 1.5 V, I will have a look  in the store).

In any case, I can connect the 3 units directly to  the panel - no circuit at all. Even the panel will go as high as 6 V (which I doubt), then the NiMH old sheep will be OK (I hope, communication by smoke is another project :-)).

wvmarle

Batteries always have a voltage range: when fully charged usually more than the nominal voltage, dropping to below nominal when almost empty.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

falexandru

#8
May 24, 2018, 07:01 pm Last Edit: May 24, 2018, 07:02 pm by falexandru
Oh, I get it now.

I measured my 3.7 LiIon units by multimeter and it was 4.2V when fully charged. I did not  know it is normal

 

ted

Oh, I get it now.

I measured my 3.7 LiIon units by multimeter and it was 4.2V when fully charged. I did not  know it is normal

 
For this batteries you need a voltage regulator with output 4.2V and current limiting resistor approximately 50 ohm.
4.2V is normal.
For 3 batteries 1,2V you can use also above mentioed voltage regulator

falexandru

My panel is 6 V 3.5 W 384 mA according to its description (mono-crystal).

I wonder whether I can use a simple Zener regulator like the one in the attachment to charge 3x  1.5 V NiMH batteries.

+++

I am a bit concerned about adapting this charger to a wind turbine (Savonius vertical axis). 

ted

#11
May 24, 2018, 08:34 pm Last Edit: May 24, 2018, 08:38 pm by ted
Link to your batteries 1.5V or picture will help.
Zener 5V =ok

falexandru

The batteries are supermarket (Auchan) NiMH labelled 1.2 V 800 mAh (blister of 4 units - 3USD). There is no picture available. Something similar is:

http://www.shoptimise.fr/p/2742149361285/piles+rechargeables+ni+mh+aa+x4+auchan+x4

falexandru


ted

#14
May 24, 2018, 08:49 pm Last Edit: May 24, 2018, 08:50 pm by ted
This are 2500mAh batteries with current charging 384 mA it is take to charge them you need about 7 hour, AAA have less capacity so willb faster.

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