# Solar LED Flood light . questions..



## frankber

Hello CPF Community ! 
I am new here, it's actually my 1st post. 
and the purpose of this message is to get some help ( classic..)

First, please note I am not LED expert, 
The story is like this : 
I have made a small solar PV offgrid system to power a LED flood light at home. Here the details:

*INTRODUCTION*
-I use 2x 3.2V 20Ah Lithium 0.33C LiFePo4 batteries togeher in serie 
it gives me 6.4V 20Ah 
-I use a solar controller 5A 6V
-The LED flood light I use is rated 6V 6W 1A. ( but I have some doubts)

So I connected everything together to light my garden at night. The controller is set for 6 hours. It has been a while since the 1st trial..about 7 months running everyday.. Some facts : 
- The LED is still very bright at the beginning of the night. 
- 2-3 hours later it starts dimming. when we reach almost 6 hours of use, it's hardly on..it's very very weak

*QUESTIONS*: 
what is wrong with my system ? why the LED cannot be bright 6 hours ? 
in terms of safety of discharge, i feel we are good : 
- Battery 0.33 x 20Ah = 6.6A and I use only 1Ax6hours = 6A in the night.

in terms of watts, I feel we are good too..
6Wx6hours = 36 Watts per night . 
Battery has 6.4V x 20Ah = 128A
If I draw 50% of the battery i can run 2 nights ( 2x 6hours) without charging but everyday it does ( may be not fully, but I assumeI get 3-4 hours of sunshine at least, which gives me 3 hours x 5A = 15A everyday. and LED only uses 6A everynight..

in terms of solar panel:
I use 3x 6V 10W solar panels in parallel . so total is 30W 6V ( and 5A)
Today , at noon, it was cloudy and my charging voltage was 6.17V ( solar panel side) 
the charging voltage for batteries was 5.84V 
I measure directly on the solar controller's bolts.

At the beginning of the night, when the LED is bright, the measured voltage is 5.77V
When it dims and is very weak, the measured voltage is 5.14V

How is it possible ? 

My solar controller is supposed to have a discharge cut off voltage of 5.4V. So, how come the LED is still on with a voltage of 5.14V ?

I try to understand what is wrong but I cannot see throught .. 
is my battery dead ? I doubt it..and it's Lithium LiFePo4..
is it not enough solar power to charge ? 

What would you change to get 6 hours of brightness everyday ? 

Thanks : )

Frank


----------



## ssanasisredna

I assume it is a 6V lead-acid charge controller? Any idea what the full-charge cut-off value is? A good charge controller would cut off at 7.4V which is good for lead acid and LiFePO4. Cheap ones tend to cut off at 7.1-7.2V. That should still be most of the capacity of the cell, but without a proper charge profile, the cells do not charge linearly.

5.84V at the battery is virtually dead. Heavy clouds can reduce the panel output to next to nothing so you were likely getting very little charging as well.

Not all X volts solar panels are created equal. Most 12V panels are 17-20V open circuit, but can deliver full amperage at battery charging voltages, but not full watts. The same will be true of your 6V panel, but if targeted at 5V USB charging, its voltage may be lower. Can you count how many cells are in series?

Note 10W does not mean 10/6 Amps ... it is probably closer to 1-1.2A per panel and that is bright sunlight 90 degrees to the panel. 

I would try charging the batteries several days with the lights off and see how high the voltage gets on the batteries.

You also did not say where you are located. If it's cold where you are, then the capacity of those batteries is greatly reduced ... and your estimate of 3-4 hours of sunlight could be grossly high on average.

Yes your light could be drawing too much as well.

Without knowing where you are, its impossible to make an estimate of what you need for reliable lighting.


----------

