hello all,
I would appreciate any help/schematics for a simple circuit I would like to make - my aim is to have a red LED constantly flash by using a solar panel and rechargable battery.
I need the solar panel to charge/keep the battery topped up so I dont have to tend to it/keep it charged via a normal battery charger.

I have a small solar panel (one from a LED garden light),
a 9v flashing led (one with the resistor built in),
and a 280mah pp3 rechargable battery.

Any help would be much appreciated as I have connected the panel & led straight to the battery and it doesnt work.

Thanks,
Lionalcook.

 

Does the led flash when connected to the battery? I assume you connected the led the right way round...

Is the battery fully charged?

Does the solar panel have a voltage at its connections when measured with a dvm...? What level is it?

You will need more than 9.0v to maintain the charge in the battery...

To charge the battery, you will need a constant current charger with a charge current set to 1/10 of the Ah rating of the battery...28mA in this case...You can do this simply with an led, a transistor and a couple of resistors....

Come back when you have answers for the above....

__________________
Eccentric millionaire financed by 'er indoors

 

hello,
yes the LED does flash when connected to the battery.

yes the battery is charged.

I dont know the voltage of the panel - i will know in a couple of hours as im waiting for my friend to get home from work so that i can borrow his multimeter - i will let you know then, but in the meantime it is the small type that charges a AA 1.2v 600mah battery, from a solar garden light (dusk to dawn type)

Thanks for your help

 

I doubt it will charge your PP3 then...You may need to use several panels to achieve a voltage high enough to charge the battery

__________________
Eccentric millionaire financed by 'er indoors

 

ok thanks,
have you got a diagram for this please?

thanks,
Lional.

 

See the attached sketch....

Assume the output voltage from each cell is 3volts...4 in series will give approx 12volts...

To charge a PP3 battery you will need around 13v...So adjust the number of cells accordingly...If the cell output is more than 3v then reduce the number in series, if the output is less then add more...

The solar cells need to feed the current regulator that is charging the battery and needs an isolating diode to prevent the bettery back feeding into the cells....

Attached Thumbnails

   

__________________
Eccentric millionaire financed by 'er indoors

 

excellent - thanks mate!

I have just found a 6v 280mah ni-cd battery that i could use instead of the pp3- would i be able to use just the one solar panel for it or would i need 2?

or is there a lower voltage flashing led i could use? the ones i have got only work from about 6volts and upwards.

also could you please tell me what the bd140 and 1n4148 components are in ur schematic please, i assume the other 2 components are resistors? thanks - im still a newbie LOL.

thanks again.

 

Ok we sorted that bit...

You need to determine how much voltage is output by the solar panel...that will determine how many cells are needed...

Whatever voltage Nicd you use, the supply for a charger needs to be at least 3-4 volts higher...

But you said your led is 9v..Now you want to use a 6v battery?..

It may flash, mebbe slower and not as bright..

__________________
Eccentric millionaire financed by 'er indoors

 

when i bought the flashing led's they were advertised as 9v - so i assumed they would only work with 9v but i've just been testing it and using various batterys with the flashing led and these are my results =

1.5v - no flash
3v - flash - not as bright
6v - flash
9v - flash

 

No problem then....You could use the 6v nicd and use less solar cells for charging..

__________________
Eccentric millionaire financed by 'er indoors

 

thanks mate,

could you please tell me what the bd140 and 1n4148 components are in ur schematic please, i assume the other 2 components are resistors? thanks

 

BD140 is a PNP power transistor and the 1N4148 is a general purpose silicon diode....

__________________
Eccentric millionaire financed by 'er indoors

 

If it comes to it, there are lower voltage flashing LEDs available. You might try allelectronics.com or bgmicro.com (I forget which I got mine from) ... good luck!

__________________
Michael Shimniok
http://bot-thoughts.blogspot.com/
Microcontrollers can solve world hunger, too!

 

maybe im thinking too simplistic. get ahold of rechargeable garden light, replace the led with one with a built-in flasher, and off you go

 

I made a solar flasher recently, using a super capacitor: ZZTools: Simple, Battery-Free, LED Flasher
This keeps flashing for many hours after charging in the sun. Certainly enough to keep going over night. Super capacitors cannot store as much energy as a rechargeable battery (currently) but they last much, much longer.