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The battery cells are so small that if a few LEDs are turned on together then you will see them dimming as the battery cells quickly die.
They are designed for much less current than your LEDs will use, unless the LEDs are very dim.
A dim little tea light uses a much thicker CD2032 battery cell and its battery lasts for 70 to 100 hours.
They are designed for much less current than your LEDs will use, unless the LEDs are very dim.
A dim little tea light uses a much thicker CD2032 battery cell and its battery lasts for 70 to 100 hours.
Brightness of an LED depends on the color and the specific construction of the LED and also on your perception of intensity vs. color. If you want to match brightness, you'll have to experiment with different resistors to.
A series connection will barely help in prolonging the on time: 2 batteries in series will require a higher series resistance to limit the current through the LEDs. Thus the higher voltage from 2 batteries in series will drop across the series resistor and the energy will be dissipated as heat. The current through the LEDs will be the same as for a single battery and lower series resistance. The batteries will be drained at the same speed. The only advantage is that due to the higher initial voltage it will take longer for the LEDS to fade gradually to dark.
A coarse calculation of battery life can be done this way:
A = battery capacity in mAh (CR2032: ~210 mAh) --- note that the capacity of 2 batteries is the same as for a single battery (same mAh) at twice the voltage, thus the effect I explained above
E = battery efficiency (typically around 80 %)
I = total LED current (5 LEDs at 5 mA each -> 25 mA)
T = useable uptime of the battery
T = (A × E) / I = (210 mAh × 0.8) / 25 mA = 6,7 h (approximately)
If you need a longer duration, go for batteries with more capacity.
Hi, the trouble is space, I only have a small area to put the batteries in and it's going to be a lot tighter now I have to wire in some resistors. As I said battery life isn't the issue as the leds will only be on for a few seconds at a time and not that often, it's getting all the lights on and roughly the same brightness.
Use 0402 smd resistors for space savings.
bertus
Moderator
Hello,
Do you have details on the used leds, like datasheets?
For the SMD resistors, you could have a look at Farnell:
https://uk.farnell.com/w/c/passive-...sistors?resistor-case-style=0603-1608-metric-
I have choosen the 0603 style for the 100 mW power.
You will have to buy multiples of 10 pieces.
Looking at other places, they even sell in multiples of 100 pieces.
Bertus
Do you have details on the used leds, like datasheets?
For the SMD resistors, you could have a look at Farnell:
https://uk.farnell.com/w/c/passive-...sistors?resistor-case-style=0603-1608-metric-
I have choosen the 0603 style for the 100 mW power.
You will have to buy multiples of 10 pieces.
Looking at other places, they even sell in multiples of 100 pieces.
Bertus
bertus
Moderator
Hello,
0402 is really small.
http://eastbay-rc.blogspot.com/2012/09/smd-led-sizes.html
Have a look at these videos:
Bertus
0402 is really small.
http://eastbay-rc.blogspot.com/2012/09/smd-led-sizes.html
Have a look at these videos:
Bertus
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So far I've got the 0402 leds in place and I've got some resistors but I have no idea how to wire this lot up. There are 5 leds of various values and I want to light them at the same time. Do I wire in series, parallel or does each light need it's own power supply? As I said earlier I would like to use 2 x2032 cells in series to power this lot as I haven't got a lot of room. If anyone can come up with a wiring diagram I would be very grateful.
bertus
Moderator
Hello,
Did you read the resource that @Harald Kapp gave you:
"Got a question about driving LEDs?"
In there you will find this picture on leds in parallel:
As you can see each led has its own resistor.
As you are using different colors of leds, the resistors will have different values.
Bertus
Did you read the resource that @Harald Kapp gave you:
"Got a question about driving LEDs?"
In there you will find this picture on leds in parallel:
As you can see each led has its own resistor.
As you are using different colors of leds, the resistors will have different values.
Bertus
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