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How many LED can a 9 V battery power?
To ensure full current over a reasonable range of battery voltages – 9.5 V down to 8 V – you can only have two LEDs in series on a 9 V supply. These will drop about 3.4 V each and 6.8 V in total. A series resistor will drop the remaining 2.2 V to make up the 9 V battery voltage.
What is the maximum current output of a 9 V battery?
Since you haven’t specified, I’d assume that you mean a household, commercially available 9V battery. A standard 9V battery has about 400-600 mAh capacity. In the most basic terms, these batteries can supply about 500 milliamps for one hour before being “dead”.
How much current does a 9V led take?
Let’s say for sake of example you have a typical 20 mA green LED that drops 2.1 V. The battery puts out 9 V, so that leaves 9V – 2.1V = 6.9V accross the resistor in series with the LED. These LEDs can take 20 mA of current, but unless you expect to use it in a bright environment that will be overkill. Let’s aim for about 10 mA LED current.
Which is better an AA or 9v battery?
If efficiency is a concern, then use two AA batteries. They will be closer in to the LED voltage so proportionally less power will be wasted in the resistor. They also have higher capacity than the 9V battery. For best efficiency, use a switching power supply.
Is a resistor required to power a LED strip with a 9v battery?
With 3 LEDs and 9V the resistor is going to be very efficient because the forward voltage will be very close to 9V. efficiency will improve as the battery voltage drops. This strip was intended to draw about 60 mA @ 12V and would likely be fairly bright. At 3-4 mA not so bright but should be visible.
Can a 9V alkaline charge 3 LEDs at 4 Ma?
With 3 LEDs and a 39Ω Resistor the LEDs will draw about 3-4 mA @ 9V. At this load a 9V alkaline will have a capacity of about 600 mAH as it discharges to 5V. At 4 mA the forward voltage is likely to be below 9V. So it should be visible for a while.