Discussion in 'General Electronics Discussion' started by rabi, Jun 11, 2013.

1. ### rabi

3
0
Jun 11, 2013
need a help ... i have 10 white bright led lights
and a battery of 6v 4.5ah (cycle use :7.25~7.45v (25 degree Centigrade ))
(initial current :less than 1.2a)
standby use :6.8~6.9v (25 degree Centigrade))

the leds are glowing fine with 3.5 v battery ....
but i have 6v 4.5ah battery
so if i connect the leds in parallel ....
which resistor should i use in each led to glow fine

i used 1 k resistor (as directed by a frnd) in each led but the light is too low (very dim )

2. ### jrote1

7
0
Jun 11, 2013
About 150ohm should fine if they are standard white leds (3.3v ~20ma). 270ohm would do it if your battery reaches about 7v.

3. ### rabi

3
0
Jun 11, 2013
the battery is ( sealed lead acid rechargeable battery )

i dont know weather it reach 7 v or not ...... .

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,482
2,830
Jan 21, 2010
See the tutorials section and look for the LED tutorial.

If these are high power LEDs you should be looking at a constant current source. For longest life, a switchmode constant current source is the way to go.

5. ### rabi

3
0
Jun 11, 2013
i checked and find that the battery is giving 6v output ..so which resistor should i used

6. ### KrisBlueNZSadly passed away in 2015

8,393
1,271
Nov 28, 2011
What current do you want to run through the LEDs?
What is the forward voltage of each LED at that current?
Do you have a part number for the LEDs so we can view the data sheet?

Have you read the LED driving tutorial that Steve mentioned in post #4?

7. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,482
2,830
Jan 21, 2010
We can't tell you unless you can tell us the Vf of the LED and the current you wish to operate it at.

And if you know these, the tutorial tells you how to calculate it (or to find an on-line calculator to do so).