wt happen if 3 led in series with 12 vdc

[mamun2a]

Whhat happen if i use 3 White LED series with 12 vdc, is it consume more current than parallel??

 

[Nigel Goodwin]

Whhat happen if i use 3 White LED series with 12 vdc, is it consume more current than parallel??

No, considerably less (in fact only a third as much, assuming you run the LED's at the same current) - calculate the series resistor accordingly.

 

[Aily Sajjad]

LEDs will consume more current when put in parallel. In series, the current will be equal to a single LED's current while the voltage when measured with reference to ground will be different for each LED.

Be sure to take care of the series resistor.

Aily
----
MoM!!!! My transistor is suffering from fever. It heats up!!

 

[mamun2a]

aily brother do u clarify me the switch system (combination switch's off on HL connections point to point) of the CT90 s wiring diagram. pleaaaaase...

dr do ask for resistor in every LED?? do u mean that LED consume more current in parallal connection. if so why maximum lowvolt Led flash light use LED in parallal connection, because it reduce battery life faster. confused??!!!

 

[evandude]

dr do ask for resistor in every LED?? do u mean that LED consume more current in parallal connection. if so why maximum lowvolt Led flash light use LED in parallal connection, because it reduce battery life faster. confused??!!!

Because putting LEDs in series requires a higher voltage. the forward voltage of an LED is typically 2-4 volts depending on the type (especially the bright white ones you'd see in a flashlight which are often around 4V), so to run three of them in series, for example, you'd need around 12v at least. A small flashlight is probably only going to have 3 batteries in it, ie - around 4.5v, so the only choice would be to run them in parallel.

Just because the total current draw is lower when they're run in series, DOESN'T mean the total power is different. power is voltage times current (P=VI) so running them in series you get high V but low I, and in parallel you get low V but high I. The total power would then be the same either way.

 

[RODALCO]

LED's

Power depends upon if you run a single LED wirh correct resistor from 12 Volts, or 3 LED's in series from 12 Volts with a series R.

1. If you put 3 single LED's drawing 20 mA each, with their own resistor on the 12 Volts supply the power usage will be higher.
2. Put the 3 LED's in series, drawing 20 mA with a single dropping resistor, usage will be lower.

In the first case each resistor will have to dissipate about 8 to 9 volts at 20 mA in heat. (taken 3½ to 4 volts per white LED)

In the second case the LED's consume about 10.5 volts and the series resistor only has to dissipate about 1.5 - 2 volts at 20 mA's.

 

[Hero999]

Put the LEDs in series for optimum effieiency and use an appropriet value series resistor.

 

[evandude]

Power depends upon if you run a single LED wirh correct resistor from 12 Volts, or 3 LED's in series from 12 Volts with a series R.

1. If you put 3 single LED's drawing 20 mA each, with their own resistor on the 12 Volts supply the power usage will be higher.
2. Put the 3 LED's in series, drawing 20 mA with a single dropping resistor, usage will be lower.

In the first case each resistor will have to dissipate about 8 to 9 volts at 20 mA in heat. (taken 3½ to 4 volts per white LED)

In the second case the LED's consume about 10.5 volts and the series resistor only has to dissipate about 1.5 - 2 volts at 20 mA's.

Yes, that's true, assuming you use the same supply voltage in both cases. I was referring to using parallel LEDs on a lower-voltage supply, versus using series LEDs on a higher-voltage supply, since he was asking one question about series LEDs with a 12v supply, and another question about parallel LEDs in a small flashlight which likely had around a 4.5v supply.
Assuming you have control over what supply voltage you want, it doesn't really matter whether you use series or parallel in terms of power usage. If you are stuck with a certain voltage, you quite simply put as many LEDs as you can in series such that the sum of forward voltages is lower than your supply voltage, and then put several of these series combinations in parallel if you need more LEDs.