Why would you use serial wiring?

[arthurbarnhouse]

I'm doing some minor wiring in my apartment, but I'm just trying to figure out something. If I'm understanding parallel wiring correctly, the use of, say, five LED's vs 10 LED's uses the same amount of power, whereas serial wiring adds a level of resistance equal to the voltage of each LED. So why would I use serial wiring? Is there something I'm missing, or some scenario that I'm not familiar with that might require it?

 

[IanP]

If I'm understanding parallel wiring correctly, the use of, say, five LED's vs 10 LED's uses the same amount of power

No, mate, power equals {voltage * current}, and as each LED draws I[led] you have 10X or 5X of I[led] in the equation .. power = {10 * I[led]} * U[led] or power = {5 * I[led]} * U[led] ..

If you connect 10 LEDs in series you have {10 * U[led]} x I[led], still 10 * U[led] * I[led] ..

Same thing ..


As far as wiring is concerned, the only advantage of serial connection is that the current is n-times smaller (where n is the number of LEDs connected in parallel) as oppose to parallel connection, and therefore you can use thinner wires, that’s all ..

Rgds,
IanP

 

[arthurbarnhouse]

Yes I'm sorry I knew that. I was mixinng my terms, I'm a little new to this. I meant that parallel wiring doesn't require additional voltage, but of course requires additional power.

Thanks for the explination, I apprecate it.

 

[betwixt]

Parallel uses the same amount of power as serial. Power is V * I, in serial connection V is the sum of all the LED voltages but the current is the same through them all. In parallel, the voltage is that of one LED but the current is the sum of all the LEDs.

It's a case of high current with low voltage or the other way around, when you multiply the two you get the same result.

However, if you have the voltage available for a serial connection, you need fewer components. As the current is the same throughout the loop, you only need to regulate it once. If you wire in parallel you have to regulate it for every LED. You can't reliably just connect LEDs across each other, the one with lowest forward voltage will divert current away from the remainder and you will get different brightness from them.

Brian.

 

[arthurbarnhouse]

You can't reliably just connect LEDs across each other, the one with lowest forward voltage will divert current away from the remainder and you will get different brightness from them.

But if all the LCDs are of equal voltage, then no currency is diverted, correct?

 

[betwixt]

Incorrect. Even LEDs from the same batch will have slightly different forward voltages. The only way to ensure the current is evenly distributed is to add a series resistor to each LED.

Remember that LEDs are current driven, if the data sheet says Vf is 1.5V and you just put 1.5V across them they will probably burn out, you need to set the current to the recommended value using resistors or regulators. Vf is the voltage the LED will drop when the current is set correctly, it isn't the voltage you are supposed to put across them.

Brian.