amplified zener? for charger circuit

[MrDEB]

In need of a very simple battery charger using solar cells.
Planed cells produce 7.2v
Found this schematic but trying to sim in LT spice? using a 4.7 zener **broken link removed**
Want to charge 4 AAA rechargeable batteries(4.8v)
Maybe use a larger zener but this schematic seems to simple to actually work
Found similar but it has an LM317 included.
any suggestions

 

[Nigel Goodwin]

Looks fine - but do you need it?, how big are your solar panels?, and what output will you actually get from them?.

Unless you are using substantially larger panels from most people, you can simply connect directly to your batteries via a blocking diode, the panel probably isn't big enough to overcharge?.

 

[MrDEB]

according to the website https://www.electro-tech-online.com/custompdfs/2010/07/solar_cells_list_prices.pdf
#228161 the cells output 100ma at 7.2v
Having never worked with solar cells I assumed that I needed to have some sort of regulation?
The 4 AAA batteries add up to 4.8 I believe?(most rechargeable Ni Cads, looking at cost compared to Nihim
still waiting to hear back from OK solar as the price list , if I am reading it right, says 3 for $44.89

 

[colin55]

You will find the 100mA rating will only be produced when the sun is shining very bright. In most conditions the output will be less than 50mA.and this can be directed straight to the AAA cells via a diode without any fear of overcharging

 

[Nigel Goodwin]

You will find the 100mA rating will only be produced when the sun is shining very bright. In most conditions the output will be less than 50mA.and this can be directed straight to the AAA cells via a diode without any fear of overcharging

Yes, the rated current is highly imaginary - except perhaps for a few minutes a day in the sahara desert? - as long as it's accurately aligned.

 

[colin55]

$445.00 is inordinately expensive for such as common solar panel as this. Look at some of the other suppliers and ebay: 18Volt 1.2W SOLAR CELLS 18Volt SOLAR PANEL US $4.30

 

[MrDEB]

This solar charger idea may go along the wayside as locating a solar cell that is encapulasted (weather proof) and able to provide 7.2 volts to charge 4 -AA batteries yet not exceed 1.5"x5" in size. Could use two of same size but the price for NEW looks way out in left field.
Will keep looking but ??

 

[Nigel Goodwin]

This solar charger idea may go along the wayside as locating a solar cell that is encapulasted (weather proof) and able to provide 7.2 volts to charge 4 -AA batteries yet not exceed 1.5"x5" in size. Could use two of same size but the price for NEW looks way out in left field.
Will keep looking but ??

You small size requirement is really crippling any decent output levels, you certainly won't need any kind of regulation.

What sort of performance are you looking for?.

 

[MrDEB]

just to maintain the charge on batteries.

the battery powered unit only needs 5v. The present PIR units only draw 5ma at 5v
the new PIRs only need 3.4v but thats taken care of if using a 9v battery pack and then use a LDO voltage regulator for 5v(PIC) and a zener for the 3.4v(or a voltage divider.
here is the present schematic that is powered by 3-AAA batteries
Piezo output is jp2

 

[Nigel Goodwin]

Four AA NiCd (or NiMh), solar panel feeding directly to the batteries via a blocking diode, easy as that.

 

[MrDEB]

But will the batteries charge durring the day seeing how the batteries are 4.8v and the cost of available solar cells for 6volts.
If I could depend on the batteries to stay charged then a lower voltage solar cell.
As I mentioned, I have no experience with solar cells and charging of batteries using solar cells.
My worry is going higher than 5v then a voltage regulator is needed.

 

[colin55]

This circuit will produce 5v from 2v supply:
**broken link removed**

 

[ronv]

I think what's missing is this:

The battery load will keep the solar cell output from going over about 5 volts. The solar cell will put out as much current as it can (100ma max) to charge the batteries. You won't need to drop the voltage from the solar cells, the batteries will hold it down while charging. Just don't remove the batteries in bright sunlight.

 

[Nigel Goodwin]

But will the batteries charge durring the day seeing how the batteries are 4.8v and the cost of available solar cells for 6volts.
If I could depend on the batteries to stay charged then a lower voltage solar cell.
As I mentioned, I have no experience with solar cells and charging of batteries using solar cells.
My worry is going higher than 5v then a voltage regulator is needed.

As we've repeatedly told you, NO REGULATOR IS REQUIRED - just a blocking diode. The batteries will regulate the voltage.

 

[MrDEB]

No regulator but what size solar cell? voltage wise. 4.8 I assume.
Now to find a good supply of solar cells. The ones on Ebay are either chipped, large quantities, and then being it is going to be outside, must be encapsulated for weather protection.

 

[Nigel Goodwin]

No regulator but what size solar cell? voltage wise. 4.8 I assume.

No, you need higher than that to charge it - but solar cells don't provide a single simple voltage anyway - but aim at 7.2V or 9V, or a panel specified for charging 4.8V.