I bought a small string of 20 LEDs (the kind that use SMD LEDs soldered in parallel to copper enamelled wire and then covered in resin) and I'm planning on connecting them to another project I have, through USB, so I don't need to continually buy CR2032 batteries for them.
Now, the weird thing is that they use two CR2032 batteries, i.e. 6V. The LEDs are warm white, so I'm assuming their forward voltage is somewhere between 3.2-3.5V. As I said, they're just wired in parallel and there's no resistance I can see (unless it's built in to the LEDs themselves), so I'm not sure why they need two 3V batteries and I'm not sure where the extra 3V are actually going.
So I hooked them up to my variable voltage DC power supply and I found out that once the voltage gets up to around 3.2V (which is the beginning of the forward voltage threshold I had in mind) it plateaus and stays there. If I set the voltage at 6V to start with and then hook up the LEDs my voltage readout drops to 3.2V. So the actual voltage that's being output by my variable power supply is limited to 3.2V, no matter how much I ramp it up (I haven't gone too far over what I calculate are 6V when turning the pot, as I don't want to burn out the LEDs in the name of exploration, because I need them!)
I then got out my breadboard and hooked them up to a couple of resistors there (47, 100, 150 ohms —because I wanted to regulate their brightness anyway) and even though I had 2 more extra LEDs (5mm, single LEDs one normal yellow, one super bright warm white) hooked up to the same circuit there's no voltage dip in my power supply.
Now, I'm wondering why this is happening? Is it normal (although I haven't seen a drop like this before when using LEDs) or is there something I can't see in the string that's actually regulating the voltage?
Now, the weird thing is that they use two CR2032 batteries, i.e. 6V. The LEDs are warm white, so I'm assuming their forward voltage is somewhere between 3.2-3.5V. As I said, they're just wired in parallel and there's no resistance I can see (unless it's built in to the LEDs themselves), so I'm not sure why they need two 3V batteries and I'm not sure where the extra 3V are actually going.
So I hooked them up to my variable voltage DC power supply and I found out that once the voltage gets up to around 3.2V (which is the beginning of the forward voltage threshold I had in mind) it plateaus and stays there. If I set the voltage at 6V to start with and then hook up the LEDs my voltage readout drops to 3.2V. So the actual voltage that's being output by my variable power supply is limited to 3.2V, no matter how much I ramp it up (I haven't gone too far over what I calculate are 6V when turning the pot, as I don't want to burn out the LEDs in the name of exploration, because I need them!)
I then got out my breadboard and hooked them up to a couple of resistors there (47, 100, 150 ohms —because I wanted to regulate their brightness anyway) and even though I had 2 more extra LEDs (5mm, single LEDs one normal yellow, one super bright warm white) hooked up to the same circuit there's no voltage dip in my power supply.
Now, I'm wondering why this is happening? Is it normal (although I haven't seen a drop like this before when using LEDs) or is there something I can't see in the string that's actually regulating the voltage?