# My solar powered indoor led lighting part 2

##### Newly Enlightened
Brlux, this is bloody excellent. Many thanks for showing what you've done.

I'm in the process of doing the same, and your posts inspire me to get going. The Luxeons came last week ...

Like Veto, I'm interested in all the details, all the dirt, and any pitfalls. Nothing replaces on-the-ground experience.

Doug

#### Brlux

##### Enlightened
I used 2 resistors for two reasons. First it made for an easy connection between the LED's and second because 1 ½ watt resistor at the desired value would have come close to dissipating to much power for the 1 resistor to handle. By by dividing up the resistance between 2 resistors I was able to achieve the voltage drop I wanted without having to use higher wattage resistors. The theoretical maximum resistance for a ½ watt resistor with 350ma running through it .5/(.35^2) is about 4 ohms. This is a great little Ohms Law reference table.

The resistor values for each lighting block varied slightly. I epoxied down the 3 LED's and then after they had set up I connected them together in series using alligator clips. I would then hook them up to an adjustable 12V power supply with an amp meter in series and play with different combinations of series resistors to achieve my desired drive current for that particular set of 3 LED's. Almost all of my light blocks ranged between a total resistance of 2-5 ohms. The VF of an LED will change slightly at different drive currents and every LED will have a slightly different VF. This makes it hard to just calculate an exact resistor value, though the calculators will get you close and that is maybe close enough. Resistors are cheep and I would recommend you get your self a variety of low value ½ watt resistors.

One important thing to take into consideration is the maximum and minimum voltage the battery will reach when in operation. For my particular charge controller it seems to cut off the charge once the battery reaches about 13.9V. A discharged led acid battery is in the high 10.xV range. The more resistance you have the less change there will be in output current as your battery voltage changes. There is really no substitute for playing with it your self.

I hope this sheds a bit more light on things.

#### Weylan

##### Enlightened
So what sized batteries are people using?

Are people putting in extra large batteries or are people just ifinh batteries to go over night?

I have heard the scale to use is about 3 days\nights, but was wondering what practicle sized batteries people are really using because of what is actually available?

Any one have the dusk to dawn thing worked out so the lights are not on all the time?

#### Vermonter73

##### Enlightened
I've always kept the "eir-pie" table in my head for remembering Ohm's Law

E
---
I R

Draw a circle around it and it's a pie

This gives you E=IR, I=E/R, R=E/I

E is volts, I is current, R is resistance

Last edited:

#### Brlux

##### Enlightened
The larger you make your battery the better off you will be. I use 2 6V 225Ah golf cart batteries in series for my 12V system. There are also 40-100Ah deep cycle marine batteries that you can get from the automotive store which work great. You don't want to use a regular car battery as they are not designed for being discharged much past 50% without being damaged. These batteries I have mentioned are called flooded cells because you have to be maintained by removing the caps and keeping them filled with distilled water. You should not put flooded cells inside your home as they vent a very small amount of hydrogen when being charged which creates an explosion hazard. If you want to put your battery inside or don't want to have to maintain it then you want a Sealed Lead Acid (SLA) battery. These came in all sizes, but are much more sensitive to over charge damage. I have used the 7Ah one out of my Thore spotlight with one of the VW solar panels for running my older LED lights for a few weeks. U1 electric wheel chair batteries are usually about 35Ah and should give plenty of capacity for running lots of LED lights.

I have built a night time sensor for my brothers indore solar led lights. It is basically a large p channel mosfet with a pull down resistor on the gate and then the gate is connected to the + solar source. It uses the solar panels as your light sensor.

#### Brlux

##### Enlightened
My wife has a desk in a rather dark corner of the house and she has been wanting me to install some of my new cool lights for her to use. I was struggling with how to mount them until I found an old black powder coted aluminum bar about 4 feet long in the back yard. I don't know what you call it but it is the kind that is bent at a right angle like an L shape. Well I drilled and taped it so that I could mount 2 light bars to it. It seems to be working great an now all is well again in the Brlux household again.

#### Cnote

##### Newly Enlightened
Very Interesting!

#### rizky_p

##### Flashlight Enthusiast
a Very Nice Indeed.

#### ensile

##### Enlightened
i think this stuff is pretty cool, hats off to those able to create things they design, it must be a really nice feeling.

keep it up.

#### mitaccio

##### Newly Enlightened
Brlux. I just got a panel from my local VW dealer for free. It's the newer kind with a charger controller in line and connects to the OBDI? instead of the cigarette plug. I want to make some yard lighting and wanted to find out about what batts you suggest. I want to keep it cheap. A SLA or can I make some NiMh? I have tons of R/C batt cells around to make 2 12v and run them parallel to get about 5aH. Can the panel charge both types and what do you recommend?

#### Brlux

##### Enlightened
Ya it will charge either type but the charge controller is designed for lead acid. It's a low enough charge rate < 1/20C for a 5Ah Nimh pack that I don't think it could do much damage to a pack in the roughly 5 hours a day of of useful sunlight.