Electronic Circuits and electronic circuits, electronic schematics plus an extensive resource for hobbyists, inventors and engineers

DiscoverCircuits.com has links to 45,000+ electronic circuits, cross-referenced
into 500+ categories.    We have searched the web to help you find quick design ideas.

HOME Schematics Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches
Welcome to DiscoverCircuits.com - online since 2002

See Media Kit for
Advertising Opportunities

Attention Designers:  Please alert us by eMail if we have linked to sites
where your original material has been copied without your permission.
We will change to the LINK to your site.  
Thank you.

 

Circuits designed by David Johnson, P.E.
Last Updated on: Wednesday, October 18, 2017 05:04 AM

Master Category List - Dave's Circuits

Text & Graphics Copyright David A. Johnson, PEALL Rights Reserved.
LINKING to Dave's circuits is permitted but DO NOT COPY to ANYWEB SITE server!


More  Solar Cell Circuits 

Solar Powered Flood Light Using NiMH Cells
December 20, 2013

Solar Powered Flood Light Using NiMH Cells  There are many solar powered garden lights available.  Most of the devices offered at the home improvement stores have very poor performance. Their batteries are too small, the light launched is weak and the solar panels are undersized. None of the devices I have tested would operate through a typical night. 

Over the years, I have modified several garden lights to make them more practical.  In this design I show how to build a light which uses 3 AA size rechargeable NiMH cells and a 4v eight cell solar panel to produce a useful light, which launches a nice broad flood pattern and will operate through the longest night.

A typical white LED needs about 3.2v at a current of about 20ma. If the light used five LEDs wired in parallel, they would draw a total of 100ma of current from the battery.   A long winter night might last 16 hours so the battery would need to store at least 1600ma-hours.

If we added another 50% for cloudy days, that would put the needed battery Amp-hour size at about 2400ma-hours.  Several battery configurations are possible to power this kind of light.  A 3.6v rechargeable lithium ion cell with a 2400ma-hour rating would be nearly ideal but they are hard to and are expensive.  Another option is to use three very common AA size 1.2v NiMH cells, wired in series, to produce a 3.6v supply. Most AA cells have a capacity of about 2500ma-hours, so they would be a good choice for this application.  NiMH cells also have a fairly low internal resistance, keeping the available voltage high during the discharge process.  NiMH cells would not need any charge control if the charging current is about C/10, where C is the Amp-hour capacity of the battery.

Three series wired NiMH cells need about 4 volts to insure they are full charged. Assuming about 0.5 volts per cell, the minimum number of solar cells to charge the battery is eight.  However, the charge control circuit will need to be very efficient with a very low voltage drop, since there would not be much of a margin between what the solar panel can deliver and what the battery needs.  Also, during the night, the current pathway from the battery back to the solar panel needs to be blocked, so the battery is not discharged when there is no sun.  These two requirements can be met with a quality p-channel MOSET wired backwards.  During the day, the device is turned on, providing a low resistance path between the solar panel and the battery.  At night, the device is turned off blocking any discharge current.

A typical day should provide about 8 hours of sunlight.  Working backwards, if the 2500ma-hour battery is nearly fully discharged, and only 8 hours of sunlight is available, then the solar panel should be rated at about 300ma.

An inexpensive phototransistor is used to detect sunlight.  A small Schmitt trigger inverter is used to turn on and off the p-channel FET linking current from the solar panel to the battery.  The same signal also turns on and off the LED current.

An op-amp is used to control the LED current.  With components shown, the circuit only requires a 0.05 volts across a shunt resistor to maintain current control.

8 Solar Cell 250ma Solar Panel    AA 1.2v NiMH Cell Modified Solar Garden Light
 

Click on Drawing Below to view PDF version of Schematic

5 LED Solar Garden Light by David A. Johnson

 

More  Solar Cell Circuits 

Dave's Circuits


eMail David A. Johnson, P.E. about this circuit

 

 


Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches



 About Us   |  Advertise on DiscoverCircuits.com   |   Report Broken Links  |    Link to DiscoverCircuits.com  |   
Privacy Policy


Discovercircuits.com endeavors to credit original designers.   Please alert us by eMail so we can
delete links to material that have been copied without your permission
.   Thank you.


Copyright of all original material on this website is the property
of David A. Johnson, P.E. (Dave Johnson & Associates ) unless otherwise noted.  

Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.
All material is provided "as is" without guarantees or warranty of any kind, either expressed or implied.