LED's how much power and how to calculate

[SBSP]

Hi Everyone.
Sorry this is not entirely got to do with PC' mods, But i'm sure someone can help.
I want to help build someone lightning for their house in marloth park.
The house has got no power and they will not be putting in power.
But having some lights its always welcome cus using candles are messy and dangerous and
using a torch its a shlep.

there are 2 rooms downstairs, 2 bathrooms a kitchen a living area , stoop and a 2 arias upstairs with a lookout deck upstairs.

So i need about 15 LED lamps with about i would say 10LEDs in each lamp.
they will all work with normal house light switches which was installed when they built the house.

IF we hide a truck/Bus or 2 car battries(Parallel) in a cupboard and connect a 150 LED's to the battery how long will it last about ? and the battry will charge during the day from a removable solar panel (if its not the monkeys messing with it its the Mozambiquers stealing it.)

Will the battery charge quick enough on a normal sunny day to have power for the night , the panel is a decent size.
and if we put in a few of those movement detectors to switch power off in in about 15mins to save power, will those units
use power or save power ?

[Samaya]

Hi Everyone.
there are 2 rooms downstairs, 2 bathrooms a kitchen a living area , stoop and a 2 arias upstairs with a lookout deck upstairs.

So i need about 15 LED lamps with about i would say 10LEDs in each lamp.
they will all work with normal house light switches which was installed when they built the house.

IF we hide a truck/Bus or 2 car battries(Parallel) in a cupboard and connect a 150 LED's to the battery how long will it last about ? and the battry will charge during the day from a removable solar panel (if its not the monkeys messing with it its the Mozambiquers stealing it.)

Will the battery charge quick enough on a normal sunny day to have power for the night , the panel is a decent size.
and if we put in a few of those movement detectors to switch power off in in about 15mins to save power, will those units
use power or save power ?

Good idea but there are complications. The problem with LED's are that they use quite a bit of current for the amount of light they give out. Your standard high bright LED can use more than 50mA when running continuously (I found an LED yesterday that uses 2.8A, is rated at 11.8W and has a luminance of 700lm!!!). If you calculate, for your application using 50mA LED's, it would work out to
approx. 7.5A for full load. If you have a 100Ah car battery then you will run the battery completely dead in 13.3 hours and you can't do that. You can only use about 60% of this charge which leaves you with 8 hours of useful LED light. You then have to charge this battery with enough panels so it can charge within 6 hours to full capacity. You will have to add a couple of panels for days when the sun doesn't shine brightly. South Africa has THE highest amount of sunshine of any country including those in the Sahara, which is a good thing. That figure sits at 6.5 hours average per day of usable sunlight.

There are ways to reduce the amount of continuous power that is used, by almost a third if you know what to do. It is quite a bit of work to do but you can use a PWM signal in each lamp to switch the LED's on and off very fast. The power saving part is when the LED is off (duh...) you are switching it fast enough that the switching is not noticed yet the LED is off for say half the time, saving you half the power. The biggest problem with this type system is if it is done wrong you will get half the brightness of the LED's. You have to set the LED's resistor so that it does not cause the LED damage yet allow the LED to radiate enough light. The best formula I can give you is for the LED's resistor. Rled = (Vsupply - Vled)/Iled. This will calculate the resistance for the LED. One thing that you need to know is that an LED can handle a higher current for a shorter period of time. example: LED continuous current = 20mA @ 3.5V. 1ms pulse current = 200mA @ 3.5V. IOW the LED is on for 1ms using 200mA. The brightness will be on par with the continuous current but only for 1ms. Proof is done by using the electric charge formula of 1Coulomb = 1A * 1s. So for the 200mA pulse you will require 0.0002 coulomb of electric charge transfered but for the 20mA continuous over 1s it becomes 0.02 coulomb transfer.

So you can figure out for your self that using the pulsing method could save you quite a bit of power. Now I can already answer your question about the pulsing part. You use a stupid little circuit with a NE555 timer (for pulsing) and a FET with resistor (for each LED) to drive this whole story. If you need more help I am a PM away...

[SBSP]

Thanks! Verry cool.

Bit technical but cool

Oh wanted to ask, a friend of mine is having a 21st
he wants LED on his Bday he bought like R200 worth of LED from communica for 5 bucks each.

But he never did some research, the guy told him the LED will work from a 3v supply
and he doesnt have one but he as a 9volt supply can you put 3 LED's in serie ? then a bunch of 3leds groups in parallel ?

[Samaya]

That could work. But when the 9V battery's output drops the last LED will start to dim first. Like you say place 3 in serie to light it up. You can then make 66 clusters of 3 LED's in series and place them all in parallel. You'll have 2 LED's left over. I hope his battery is large though because he will be drawing very close to 6A for all those LED's...

[SBSP]

Thanks, Its not going to be on battery he want to use it at his party, so it will be connected to a 220->9VDC plug