white led

[pier1]

So should i put a resistor across it to discharge it when it is put off ?

 

[audioguru2]

So should i put a resistor across it to discharge it when it is put off ?

Yes, but I can't remember the voltage across it and the capacitance value to calculate the resistor value and power rating.

 

[pier1]

Hello AG
             Do you mean the voltage across the led string when the mains voltage is disconnected and the led's are put off ?

 

[audioguru2]

Hello AG
             Do you mean the voltage across the led string when the mains voltage is disconnected and the led's are put off ?

Yes. I can't remember how many volts is across the capacitor that bites you.

 

[pier1]

when the mains is off and all leds are also off the voltage across the capacitor is 117 volts DC (reducing very very slowly) . The capacitors i used is 10uF/450volts, 3nos in parallel which makes 30uF.

 

[audioguru2]

A 100k resistor will nearly fully discharge 30uF in 15 seconds.
It will use only 1.2mA and dissipate only 137mW with the power connected. Use a 1/2W resistor for its high voltage rating.

 

[audioguru2]

Hi Pier,
The circuit has 300mA, not 960mA.
A 2N3055 power transistor can dissipate up to about 70W if it has a huge heatsink.

Why do you have battery-powered LEDs in your room? Don't you have electricity?
Or do you live in a tree? :

 

[pier1]

Hi AG
;D I dont live in a tree. I have a 13.5 volt 1.5A battery charger so that charges the battery and also lights up the leds. So when the power goes off it lights for some time taking back up from the battery. My previous image had some wrong calculations. In the image shown here i plan to have 4 such modules(led board 4nos and current regulator 4 numbers). So which would be the best power transistor to use ? the current of one module is 240mA.

View attachment 40512

 

[audioguru2]

If the LEDs are actually all 3.0V and divide the current equally then each 33 ohm resistor will have a voltage drop of 0.99V. Then if the battery is max at 13.55V the power transistor has a voltage drop of 13.55V - 9V - 0.99V= 3.56V. It will dissipate 3.56V x 0.96A= 3.4W. Any power transistor will work fine with a small heatsink.

Why does your power go off? Can't they fix it so it is on all the time like mine?

 

[pier1]

Due to summer season there is power cuts here . They call it load shedding. So need to prepare for it.

 

[audioguru2]

Due to summer season there is power cuts here . They call it load shedding. So need to prepare for it.

It must be difficult to live in a tree.

My home is on the ground and my electrical utility company keeps the electricity running for 99.999999% of the time. They also keep the voltage and frequency accurate.
Of course it is not as hot here in summer as it is in your country but we still use air conditioning in summer.

Our electricity use was maximum just before Christmas because of millions of old high current incandescent Christmas tree lights. So the electrical utility traded new low current LED Christmas tree lights for the old ones and now the electicity use is less.

 

[pier1]

Me too live on the ground  ;D. Water here reduces a lot in summer and Hydro stations are affected.

 

[audioguru2]

My electricity is supplied by a hydro generator station between the largest lakes in the world (The Great Lakes) at Niagara Falls. The lakes never run out of water.

There are two or three nuclear generating stations nearby.
My electrical utility company plans for future growth.