Small street light system -Starting with test results

[human011]

I am designing a system of 6 street lights .
initially opted for 10watt floods but i further searched and optimized to 3Watt flood lights .

They provide enough brightness for small street .
There was a issue of cloudy days, i down sized the battery capacity .
So initial units can get grid power as charging from grid is now cheap(low WH battery) .

Initial test:
Tested the led 230V driver out voltage :10.1V
230V-->driver-->floodlight
But i want to run the full set on DC , removed the driver and tested via linear dropping
resistor:
12V battery-->44Ohm dropper-->flood light


This gave current of approx 0.1Amps for a suitable brightness ,voltage across flood led 9.3V
[i know the dropper with electronics will be best,i will come to that]


As i didnot had 5W ,44OHM resistor so test resistors (.25Watt ) got heated and i had to abort the test
!

So I calculated


12V 7.5AH battery can source ...7hour approx @1AMP
same battery will give .............9hour approx @1AMP when led voltage is 9V
same battery will give ............15hour approx @.6AMP when we use six No.s LED [per led current .1A]

Conclusion:
Practically 10hour backup is possible ,cloudy days it will get a feed from grid.

Questions
a) is the calculation correct ?
b) 20Watt solar panel should be fine for the job as battery is just 7.5AH?
c) Will it be good to use a basic charger circuit, MPTT tradeoff may be 10%?

d) please suggest a dropper for 12V to 9V @.1AMP ,I am eyeing on options
- LM317 as CCS (tidy )
- few 1N4007 as dropper (cheapest)
-Fexible FET CCS http://bit.ly/1elYzGp :the FET ccs can also have a dimming via dumb 555circuit

[Shockah]

3watt street lights?! Narrow street.
If there is "an issue of cloudy days", you should up-size the panel or down-size the bulb,,, not down-size the battery.
A 3watt LED burning 13 hours (=39wh) winter nights would require a 16.25ah (5 day) battery... 7.5ah will not last long.
Be aware, don't trust the advertised watt rating on bulbs. All of the 3watt E27 bulbs I have been thru draw closer to 4watts.
A 4watt LED burning 13 hours (=52wh) would require a 22ah battery.
20watt panel is sufficient for 39wh, if you have a minimum of 4 sun hours, and a decent CC.

FYI: I am speaking in terms of 12v.

[human011]

3watt street lights?! Narrow street.
If there is "an issue of cloudy days", you should up-size the panel or down-size the bulb,,, not down-size the battery.
A 3watt LED burning 13 hours (=39wh) winter nights would require a 16.25ah (5 day) battery... 7.5ah will not last long.
Be aware, don't trust the advertised watt rating on bulbs. All of the 3watt E27 bulbs I have been thru draw closer to 4watts.
A 4watt LED burning 13 hours (=52wh) would require a 22ah battery.
20watt panel is sufficient for 39wh, if you have a minimum of 4 sun hours, and a decent CC.

FYI: I am speaking in terms of 12v.

yes these are narrow roads that can pass a small car and a man .
->There will be SIX lights ,for 6hours total time
->LEDS taking very less current for some good light output (.1Amps)
->cloudy days the central unit will charge from grid,as battery is small
the electricity bill will go minimal and can be paid from community funds.

instead of mounting on L shaped posts they will be on straight posts at 12Feet from ground .

1) so cutting cost by reducing distance from ground.

That was surprising to me seeing these 3watt marked ones throwing 400lumen approx(roughly)

2)the expected light hours are cut to 6 hours like 5pm to 11pm mainly to help walking people .
after 11Pm walkers can trigger a 10Min light on timer by pressing any of the push switches in the poles .
I am thinking of doubling the battery just to add flexibility as the panel can charge both .


Some more idea on the project
*
battery and controller will reside at one place for all 6 LED lights
,low maintenance , safe fast debugging
wires will carry dc to all
*

What do you think the system will work within desired hours ?

[Sunking]

Would be a whole lot less expensive just sticking with grid power some 90% less expensive. Your panel wattage is too low and battery way too small.

[human011]

Would be a whole lot less expensive just sticking with grid power some 90% less expensive. Your panel wattage is too low and battery way too small.

people are unwilling to pay full year(although the cost may be say 10$ full year,they suspect it may be 200$)..2-3months bills , all ready

secondly the project can be scaled for a eco home model ..3LED1FAN(dc fan)/house,
the lights will teach basic issues and fixes

for eco home battery and panels will have 10x ratings..

[Shockah]

Check your specs again,,,
3 watt LEDs should be drawing .25amp current @ 12volts, .1amp if @ 30volts.

(6) LEDs, with (1) 7.5ah battery and (1) 20watt panel?
Even @ 6 hours each, you are still looking at 108wh... You believe in miracles?

How far apart are these (6) LEDs?
You imagine running the wires above the posts or under the ground?
That is a lot of heavy wire you'll be using.

3watts putting out 400lumen? Sweet...

Where are you located?

[Sunking]

people are unwilling to pay full year(although the cost may be say 10$ full year,they suspect it may be 200$)..2-3months bills , all ready

secondly the project can be scaled for a eco home model ..3LED1FAN(dc fan)/house,
the lights will teach basic issues and fixes

for eco home battery and panels will have 10x ratings..

You are way off. Anything you take off grid is going to cost many multiples more than commercial power for the rest of your life. There is no justifiable reason you should take anything off-grid if you have commercial power.

[human011]

Shockah,
Yes you are correct , I had suspicion on my measurements .
One possibility is LEDs light with full current @10.1V from the driver [the 230v grid usage]
they may be used at lesser current @some lesser brightness .
I just used series dropper to get comfortable light , in side room ,need to check outdoor performance.
still .25Amp practically can never be 0.1Amp unless error ... i will buy a new multimeter to verify .
Street has posts so wiring is no issue , waterproof telephone scrap wires should do,


Here in india 5-6Kilometre or more covered with heavy TV cables , the small street is no issue just 300Metres .

Anything you take off grid is going to cost many multiples more than commercial power

here people will rather use dim mobile phone LED than street light if they know it needs grid power , question is
who will bear the cost ,practically no one.

If i say i am engineer who made a solar system that is 70% of the time takes sun power..people will appreciate .
The learning from this tiny system i can use to make some bigger products .
Believe me off grid system is cheap

panel=20$
Battery=5$..etc

full system come near 90$
which is like 2 pairs of my shoes .
so donating this to my neighbourhood.

Let elderly walk with ease ..great feeling isnt it!!

Check your specs again,,,
3 watt LEDs should be drawing .25amp current @ 12volts, .1amp if @ 30volts.

(6) LEDs, with (1) 7.5ah battery and (1) 20watt panel?
Even @ 6 hours each, you are still looking at 108wh... You believe in miracles?

How far apart are these (6) LEDs?
You imagine running the wires above the posts or under the ground?
That is a lot of heavy wire you'll be using.

3watts putting out 400lumen? Sweet...

Where are you located?

[human011]

Beam shot from 3w led 12feet

Here is a beam shot from *JUST 1 LED unit * in full dark
The screen is 12feet away


you can see my DIY movie screen is lit pretty bright , as if i can use it as teaching board , just kidding

actual pics of the LED unit i cant provide as someone can replicate the Idea.

[Shockah]

waterproof telephone scrap wires should do, ......................
the small street is no issue just 300Metres .

http://www.calculator.net/voltage-drop-calculator.html

Congrats on your DIY progress, your intentions are good....

However, your system needs fine-tuning, starting with heavier wire to deliver current 300meters.

[bcroe]

300 Meters and 10.1 Volts

One possibility is LEDs light with full current @10.1V

the small street is no issue just 300 Metres.

If you do this, I see 2 problems. Battery voltage is wrong for LEDs, and voltage
won't be maintained for 300 Metres. You can solve both of those problems, and
extend your battery performance. Set up your system to run at something like
24 or 48 VDC. This will solve getting power out 300 Metres. Then put a $2 DC-DC
switching converter at the LED, set to supply 10.1 V. This will be the most efficient
way to use your power, and give correct voltage everywhere. Bruce Roe

[human011]

If you do this, I see 2 problems. Battery voltage is wrong for LEDs, and voltage
won't be maintained for 300 Metres. You can solve both of those problems, and
extend your battery performance. Set up your system to run at something like
24 or 48 VDC. This will solve getting power out 300 Metres. Then put a $2 DC-DC
switching converter at the LED, set to supply 10.1 V. This will be the most efficient
way to use your power, and give correct voltage everywhere. Bruce Roe

What if I use a 12vTo24vdc pump circuit keeping wires thin and batt at 12v??


This way i will eliminate heavy wire (=cost,hassle) and battery change to 24V again adds cost.
24battery is difficult to procure, then again 24 panels will be more costlier .

[Sunking]

At 300 meters there is no good solution.

[bcroe]

What if I use a 12vTo24vdc pump circuit keeping wires thin and batt at 12v??

This way i will eliminate heavy wire (=cost,hassle) and battery change to 24V again adds cost.
24battery is difficult to procure, then again 24 panels will be more costlier .

That will work at far smaller overall loss than 12V. The tiny cheap converters I see are
only rated up to 40VDC input; after that you go to a much more expensive class. I would
say, set your buck converter to 38 VDC out, then see just how much copper it is going to
take to make this work. You might need double or triple parallel conductors at the feed
end where the current is highest, to minimize drop. Feeding it from the center would be
a huge help. You may still not make it out to 300 meters. What gauge wire is available?
Bruce Roe

[Shockah]

At 300 meters there is no good solution.

Ditto...
Even if the battery was in the middle, 150meters each way is not doable with 20ga wire.

What gauge wire is available?
Bruce Roe

Scrap telephone wire... isn't that 20ga-24ga?