This is kind of a hard question to word, so bear with me...
I currently have a string of 10 LEDs wired in parallel. I am using 3 - AA rechargeable batteries (1.2v rated) wired in series to power them. The LEDs all draw 30mA each. I have a plug on the end of the LED string that hooks up to a ~5.2v power source to recharge the batteries. The jack disconnects power from the ground side and uses an alternate wire when charging so that the LEDs are not on when the batteries charge, but the switch has to be (since I have it connect inline with the positive side of the battery).
It's kind of a pain to make sure the circuit is on when I go to plug the batteries in. So, I've run another connection from the positive side of the battery that bypasses the switch. The problem I'm going to have is that when I give a 5.2v charge to the batteries, I get a 4.8v output. I've used the LED calculator just for giggles to see what size resistor it would tell me to use (5.2v input, 3.6v forward current, 300mA draw), but it comes back with 5.6Ω. Since I know that can't be right, and I suspect my methodology is flawed, can anybody shed some light on what I need to make sure I don't fry my 3.6v LEDs when connected to a 5.2v power supply? Keep in mind that I have 3 batteries connected at the same point.
Thanks a bunch!
I currently have a string of 10 LEDs wired in parallel. I am using 3 - AA rechargeable batteries (1.2v rated) wired in series to power them. The LEDs all draw 30mA each. I have a plug on the end of the LED string that hooks up to a ~5.2v power source to recharge the batteries. The jack disconnects power from the ground side and uses an alternate wire when charging so that the LEDs are not on when the batteries charge, but the switch has to be (since I have it connect inline with the positive side of the battery).
It's kind of a pain to make sure the circuit is on when I go to plug the batteries in. So, I've run another connection from the positive side of the battery that bypasses the switch. The problem I'm going to have is that when I give a 5.2v charge to the batteries, I get a 4.8v output. I've used the LED calculator just for giggles to see what size resistor it would tell me to use (5.2v input, 3.6v forward current, 300mA draw), but it comes back with 5.6Ω. Since I know that can't be right, and I suspect my methodology is flawed, can anybody shed some light on what I need to make sure I don't fry my 3.6v LEDs when connected to a 5.2v power supply? Keep in mind that I have 3 batteries connected at the same point.
Thanks a bunch!