# led

Discussion in 'The Projects Forum' started by handydragonfly, Jun 4, 2014.

1. ### handydragonfly Thread Starter New Member

Jun 3, 2014
3
0
Hey Everyone,

I am about to embark on a new project and would like some guidance if possible, please forgive the post if its missing information as electronics and circuits is all new to me.
I need some assistance with a project and will post the details as follows. I am trying to create a rechargeable led strip light that comes on at dusk for the outside deck. I want to make itself contained so I dont have to run power leads

Now this is where I need some help, trying to work out the most cost effective method that produces the longest light up time.
So this is what I am thinking:

1x 30cm - 50 cm strip 5050 12v LEDS (approx: 30 LEDS for 50 cm and 20 LEDS for 30cm)
Power: YUASA - Y1.2-12 - BATTERY, LEAD ACID, 12V, 1.2AH
I think this would power these for around 1200 hours???

I am also going to integrate a lamp adapter circuit that switches on when its dark. I am going to up cycle from this

http://www.ebay.com.au/itm/281257881002?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

It seems cheaper than making my own circuit.
I would just like to know if I am on the right track.

2. ### Papabravo Expert

Feb 24, 2006
11,163
2,185
Your math is faulty. 1200 hours would imply a current drain of 1 milliampere. I can tell you from long experience that 1 milliampere will NOT even make the LEDs turn on let alone glow in the dark.

At 10 milliamperes PER LED, a strip of 20 will require 200 milliamperes and a strip of 30 will require 300 milliamperes. This is because they are connected in parallel. They cannot be connected in series because there is not enough voltage. They might be parallel strings of series connected LEDS but you need to look deeper into how they are constructed.

You should also plan to have a mains connected charger to recharge the battery during the day.

3. ### #12 Expert

Nov 30, 2010
17,899
9,317
I think I see another problem. Up cycling a 120 volt AC lamp adapter will require a 120 volt AC power supply. You can do that with a battery powered inverter to avoid installing a power wire, but it will require some more battery power.

Apr 30, 2011
1,426
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Those strips are usually 3 LEDs per series so a strip of 30 is 10 parallel strings of 3. At 20mA each that's 200mA for the strip of 30 and 370mA for both together. Your lights will run for 3 hours from a fully charged battery with no other loads.

5. ### handydragonfly Thread Starter New Member

Jun 3, 2014
3
0
Can I not just use the circuit with the LDR, replace the incoming power terminals with the battery and the output termiinals with my LED chain at 12v

6. ### AnalogKid AAC Fanatic!

Aug 1, 2013
5,658
1,607
No. When the switch device is an electronic component rather than a relay, you can not mix AC and DC devices. The night light is not a generic power controller. It is designed to do exactly one thing, run three LEDs off of house power. It certainly has all of the functions you need, but it will not work with a low voltage DC circuit.

ak

7. ### handydragonfly Thread Starter New Member

Jun 3, 2014
3
0
Do you know of a device that will do this, building my own circuit is quite expensive and would rather up cycle a product with a part that I can purchase at a lower cost

I bought a \$2 solar garden light but it uses a transistor and solar cell to switch the device on/off and charges an AA battery during the day..I would need 8 of these to power my lights and then how long would 2000mah last if a 1.2ah will only last a few hours?

8. ### k7elp60 Distinguished Member

Nov 4, 2008
509
90
You do not need to run the strips at a full 12V as they may produce enough light with less voltage, and if you mount a small solar panel on the deck you can use the solar panel to charge the battery and also detect darkness and daylight. I have two systems installed at my house that do exactly that.
One system has been installed for about 3 years and has not needed maintenace. The other one has been installed for about two years and same story no maintenance.
I use a pulse width dimmer circuit of both of them. I have done some experiments with the 12 light strips and with pulse width dimmer a human eye can still see them illuminated when there is only power to for about 10% of the time.
The circuit I use consists of a dual timer(NE556N) to monitor the voltage from the solar panel and also the battery voltage.
This part turns on the LED's at dark and then off at daylight and monitors the battery voltage and turns of the LED's if the
battery voltage is to low. I use another timer (NE555) with a p-channel mosfet for intensity of the LED's. The mosfet serves
a dual purpose, it also is used to turn on/off the LED's

Last edited: Jun 5, 2014