Hi; I feel like a twad for asking as this seems a ridiculously simple question...
I started on a prop which has 5 LEDS in parallel. They are blue LEDs, so they draw 3.3V and each uses 20Ma of current.
Power is coming from a battery pack which on paper outputs 3.7V; but I've measured it and it outputs 4V.
Naively I thought it'd work without a resistor and well... for five minutes I was right, now one of the LEDS started flickering. So, time for a resistor.
The formula for this is:
R = (Vinput -Vused)/drawnCurrent
so R = (4 -3.3)/(5*0,020)
R = 0.7/0.1 = 7
7 ohms seems like such a small number that I start to doubt if I'm correct. The prop itself is fairly small, and I'm not that practiced when it comes to soldering. So I was hoping to use only one resistor in stead of putting one in series in front of each LED (hence the 5*0.02)
Am I actually correct that I need one resistor of 7 ohms to balance it all out? What will happen if the batterypack drains out more power and actually outputs the value it should(3.7V or oven lower) rather then the measured 4V?
All the best!
I started on a prop which has 5 LEDS in parallel. They are blue LEDs, so they draw 3.3V and each uses 20Ma of current.
Power is coming from a battery pack which on paper outputs 3.7V; but I've measured it and it outputs 4V.
Naively I thought it'd work without a resistor and well... for five minutes I was right, now one of the LEDS started flickering. So, time for a resistor.
The formula for this is:
R = (Vinput -Vused)/drawnCurrent
so R = (4 -3.3)/(5*0,020)
R = 0.7/0.1 = 7
7 ohms seems like such a small number that I start to doubt if I'm correct. The prop itself is fairly small, and I'm not that practiced when it comes to soldering. So I was hoping to use only one resistor in stead of putting one in series in front of each LED (hence the 5*0.02)
Am I actually correct that I need one resistor of 7 ohms to balance it all out? What will happen if the batterypack drains out more power and actually outputs the value it should(3.7V or oven lower) rather then the measured 4V?
All the best!