Modify 240V AC LED buld to work on 12V DC Battery

Thread Starter

salai ezhil Mathi

Joined Jan 24, 2017
20
Hello,

240 V AC LED bulbs are cheap compared to the 12V DC bulbs we can buy. I am thinking I can modify the bulb to work on a DC battery 12V.

I know we might have to remove the internal bulb circuits and just keep the LEDs and move from there. but really not sure.

Need your help please.
 

DickCappels

Joined Aug 21, 2008
10,152
You are on the right track. Inside the lamp is a power supply that drives the LEDs. The power supply probably would not work at all at 12 volts, so you will have to remove or at least bypass the power supply.

An alternative to hacking up the lamps is to use an inverter to get 240 VAC for the unmodified lamps.
 

Cmanila

Joined Jan 24, 2017
4
you can do that by removing the power supply inside the bulb, that is for 220v operation. I have modified lots of ac led bulb to work on 12v dc. I have 12 led connected in series, powered by 36 volts internal supply. To make it operate on 12vdc, group the leds by 4 as shown below
6w led 220vac.png 6w led 12vdc modified.png
 

AnalogKid

Joined Aug 1, 2013
10,987
Yes, but it might be nothing more than a few resistors. The AC/DC power supply had a current-limited output designed specifically for driving LEDs. If you know the approximate LED current needed, you can limit the battery current to that value with a resistor. If you have multiple strings of LEDs in parallel as in post #3, each string gets its own resistor. An alternative is a constant-current limiting circuit, but that is a more complex design.

ak
 

Cmanila

Joined Jan 24, 2017
4
The LED bulb I use to modify for 12vdc use a step down board at 36 volts output connected to 12 leds in series. Bulb rating is 5 watts so from that current I=5/36 = 138.89 ma. Each LED is rated approx .4 watt @ 3 V so that would be 1.67 watts per string of 4, if you want to insert current limiting resistor on each string then you can compute for the resistance value I=1.67/12 = 139 ma per string, Total current 139 x 3 = 417.5 ma or .4175 amp. Actually the additional diode D13 also provide some sort of current limiting because of the voltage drop it introduce to the whole circuit, be sure to use diode that can handle the total current. You can also insert a 10 ohms 1 watt resistor on each string or insert additional diodes per string and try to experiment on that depending on your actual supply voltage.

By the way I have been using my modified LED lamp for quite some time now and it is working just fine. Hope this help
 

Thread Starter

salai ezhil Mathi

Joined Jan 24, 2017
20
Can you please give me a circuit to limit the voltage to 12V DC. because the battery (Lead acid) voltage would be 14 to 15 V DC, I believe that would fry the LEDs.

Please also provide the values for the components like: Capacitors, resistors. I can build a board from scratch.
 

LesJones

Joined Jan 8, 2017
4,174
A method that I have used to drive strings of LEDs in series from a nominal 12 volt supply (11V to 14V) is to use one of the cheap switch mode step up regulators sold on ebay modified to be a constant current source. The output voltage limit is 35 volts so I would suggest limiting each string to 9 LEDs . This is the modification I made. http://lesjhobbies.weebly.com/led-driver-01.html
The zener diode is to prevent the regulator destroying itself if the chain of LEDs goes open circuit. It should be about the same voltage as the string of LEDs. It will limit the output voltage to the zener voltage plus 1.25 volts. Do not use a zener diode with a voltage above 33 volts. I have also found some 12 volt 4 watt MR16 LED bulbs for about £2.00 each in the "Home Bargain " chain of stores. They seem to have a proper switch mode current regulator as the current decreases when the supply voltage is above 12 volts and increases when it drops below 12 volts.

Les.
 

Dodgydave

Joined Jun 22, 2012
11,285
Hello,

240 V AC LED bulbs are cheap compared to the 12V DC bulbs we can buy. I am thinking I can modify the bulb to work on a DC battery 12V.

I know we might have to remove the internal bulb circuits and just keep the LEDs and move from there. but really not sure.

Need your help please.
Take pictures of the leds pcb, and measure the voltage across it if you can, that way you can determine which psu to use.
 
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