# Solar Lighting Project

Thread Starter

#### jonny_tinslecat

Joined May 30, 2006
7
Hey All!

Im looking for some help / advice at the moment. Im a complete newbie to the world of electronics so i need as much help as possible.
Im just building a nice decking at the back of my house, and would like to inset a series of Super bright LED's around it for night lights. I have seen the little individual units that are availible, but would like to make a large scale version powering up to 50 LED's.

I have bought myself 50 superbright LED's, (10,000MCD - dont know what the significance of that is), and all the fixtures for the walls. I have been looking for a solar panel, and found a plethera of different ones, at different prices. Ideally i would like to spend as little as poss, but enought for it to be effective.

I have found a panel that i think may be suitable, but do not really understand what im looking for, or how much power these LED's are going to take to power. I guessed that the 12v is suitable, but i am unsure as to the wattage.

ONE NEW AMORPHOUS SILICON SOLAR PANEL, (12 VOLTS , 5 WATTS, 320MM x 250MM) METAL FRAMED WIRED WITH ABOUT 1 METRE LENGTH OF CABLE + BLOCKING DIODE

EXCELLENT FOR VEHICLE BATTERY MAINTENANCE AND GREAT FOR USE OVER WINTER TO AVOID BATTER DRAIN. IDEAL FOR INDOOR OR OUTDOOR USE. EXCELLENT FOR USE IN GARDEN LIGHTING, WATER FEATURES, CARAVANS,BOATS,SHEDS,OUTHOUSES OR FOR ANY POWER PROJECTS.

Also if anyone has any suggestions for wiring / battery usage i would be so unbelievably grateful!

I know i sound useless, but cant find anyone to help me with this problem.

#### kubeek

Joined Sep 20, 2005
5,765
First we need to know the parameters of the diodes - forvard (supply) voltage and current.

As for the solar panels, I suppose you are going to use the LEDs during the night and recharge some battery during the day. Am i right?
If yes, for how long shall it be working during the night?

Thread Starter

#### jonny_tinslecat

Joined May 30, 2006
7
ok the specification i have been given is DC forward voltage typical 3.2v max 3.6 v

DC forward current 20mA.

Ideally i would like the lights to work for 3 hours a night in the summer (obviously dependant on amount of sunlight) i dont know if this is being a bit ambitious of the british summer sun!

my idea was to possibly have a double battery affair, a general battery that gave a couple of hours a night, and a second that could be used if the deck was being used at night for longer periods. the other option would be a back up 12v feed from a 12v constant source (stepped down from mains)

If anyone has any good ideas im always willing to hear them!

Thanks for the help kubeek!

#### kubeek

Joined Sep 20, 2005
5,765
Originally posted by jonny_tinslecat@May 30 2006, 09:12 PM
ok the specification i have been given is DC forward voltage typical 3.2v max 3.6 v

DC forward current 20mA.

Ideally i would like the lights to work for 3 hours a night in the summer (obviously dependant on amount of sunlight) i dont know if this is being a bit ambitious of the british summer sun!

my idea was to possibly have a double battery affair, a general battery that gave a couple of hours a night, and a second that could be used if the deck was being used at night for longer periods. the other option would be a back up 12v feed from a 12v constant source (stepped down from mains)

If anyone has any good ideas im always willing to hear them!

Thanks for the help kubeek!
[post=17407]Quoted post[/post]​
the set of led´s would then require 3.4V*0.02A*50=3.4W. There are many ways to power thees LEDs, probably the best would be 12V lead-acid battery with constant current source, so I suggest wiring pairs of LEDs in series, connected alltogether in parallel, the whole thing connected to an 0.5A current source and a battery.

The battery should be 0.5Amp*3hours = 1.5Ah, but better bigger.

The charging supply is a bit more complicated to count, but if I take empty battery and say 10 hours of sunlight, the panel(s) then have to provide cca 13V and current at least capacity_of_battery_in_Ah/charging_time, --> 150mA.

But I guess there won´t be 10 hours of sunlight all the time, so you should get also some lead-acid battery charger.

#### Gadget

Joined Jan 10, 2006
614
Dunno about using a Lead Acid battery unless you have a circuit to shut of the LED's when the voltage drops below about 11.5 - 12 volts. Lead Acids and SLA's don't like being too deeply discharged. NiCads and NiMH's are OK to discharge however.
Most Cheap (10 for $20) solar lights use a single NiCad charged by a small cell that also doubles as the light sensor, with a voltage Step Up circuit to power the 3.5v LED. Perhaps a 12v Lead Acid, with the LEDs in Series strings of 3 LEDs with Low voltage cutout would be the method I might use as the cheapest alternative however. 17 strings of 3 LEDs @ 20 mA would draw 0.34 amps. A 5 Watt solar panel should give nearly an Hours storage for every hour of full sunlight, depending on your Charge method.. (float charging may yield less as a Lead Acid tends to take less and less charge, as charge time increases). Also, remember a 5 Watt solar panel will never yield a 5 watt output in the Real World, and any Rechargable battery requires More power to charge, than what is actually stored. You may also want to think about the pre-assembed 12 volt LED bulbs already easily available, and more than capable of putting out a reasonable light. Thread Starter #### jonny_tinslecat Joined May 30, 2006 7 "You may also want to think about the pre-assembed 12 volt LED bulbs already easily available, and more than capable of putting out a reasonable light." i think i know what you mean by these, but they are well expensive, the ones ive seen are around £10 per 3 or 5 LED unit!, i want to do some serious lighting but on a tight budget! (the decking cost me an arm and a leg!!). i found individual chrome LED holders (like annoying kids screw their number plates on their car with)got 100 for £5! thses should be ace for mounting them into the decking. do you think maybe i should be looking at a higher wattage of solar panel then? i havent bought it yet. i have found one circuit on the net that doesnt use a DC voltage, but a high frequency pulce (?!?!?!) apparently it gives the same brightness from the LED (as a constant DC voltage) while needing less than 50% of the energy. What are your thoughts? i really dont understand this, but sounds like a good way to prolong the use i get from a limited charge. I am unsure whether this method would work on such a large circuit. I have attached the circuit diagram if it is of any use to you! Thread Starter #### jonny_tinslecat Joined May 30, 2006 7 "You may also want to think about the pre-assembed 12 volt LED bulbs already easily available, and more than capable of putting out a reasonable light." i think i know what you mean by these, but they are well expensive, the ones ive seen are around £10 per 3 or 5 LED unit!, i want to do some serious lighting but on a tight budget! (the decking cost me an arm and a leg!!). i found individual chrome LED holders (like annoying kids screw their number plates on their car with)got 100 for £5! thses should be ace for mounting them into the decking. do you think maybe i should be looking at a higher wattage of solar panel then? i havent bought it yet. i have found one circuit on the net that doesnt use a DC voltage, but a high frequency pulce (?!?!?!) apparently it gives the same brightness from the LED (as a constant DC voltage) while needing less than 50% of the energy. What are your thoughts? i really dont understand this, but sounds like a good way to prolong the use i get from a limited charge. I am unsure whether this method would work on such a large circuit. I have attached the circuit diagram if it is of any use to you! [attachmentid=1447][attachmentid=1448] #### Gadget Joined Jan 10, 2006 614 Originally posted by Gadget@May 31 2006, 01:51 AM Most Cheap (10 for$20) solar lights use a single NiCad charged by a small cell that also doubles as the light sensor, with a voltage Step Up circuit to power the 3.5v LED.
[post=17415]Quoted post[/post]​
And the circuit you posted is pretty much the circuit they use. If the 1.2 volt nicad were used without this circuit, there wouldn't be enough forward voltage (3.5 v) for the LED to draw a current and illuminate. As well as charging the battery when the solar cell is in sunlight, you will notice that the cell also turns the BC547 hard on, stopping the circuit from Oscillating thereby switching the LED OFF until it is dark.

Thread Starter

#### jonny_tinslecat

Joined May 30, 2006
7
So could i use exactly the same circuit for my decking project?

would the increased voltage not affect the performance of the circuit?
if i put the 17 x 3LED's in instead of the one LED, and the solar pannel i have seen instead of the single cell?

#### Gadget

Joined Jan 10, 2006
614
No. That circuit is designed to drive 1 (or possibly 2 LEDs in series). It is the same circuit found in those $3 solar lights..(or 10 for$20 on special here at present).

Thread Starter

#### jonny_tinslecat

Joined May 30, 2006
7
Originally posted by Gadget@Jun 2 2006, 08:31 AM
No. That circuit is designed to drive 1 (or possibly 2 LEDs in series). It is the same circuit found in those $3 solar lights..(or 10 for$20 on special here at present).
[post=17456]Quoted post[/post]​

So what would i have to do to the circuit to "beef it up" for my little project? im guessing all the ratings of the components would need altering?

Would the same principle still work for my larger scale project. Im assuming that by using a frequency instead of a direct current the power usage is far less?

#### Gadget

Joined Jan 10, 2006
614
If you want pulses, then feed your 3 LED strings with a square wave from the 12 volt gel cell. You may get a slightly higher brightness... doubt if you will have much less current draw, as now you have added some extra complexity to the design. try it with both, and see. Nothing like experimenting.

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