You have 4.99V from a 5V regulator?

That's perfectly acceptable as the tollerence is normally about 5%.

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YEah, the cheap battery quickly fell to 7v, so I just bought some duracells.

Ugh, this is all so confusing.


I believe the battery is 400 mah.

 

The Energizer datasheet for their alkaline 9V battery shows that its voltage drops to 6V in 20 hours when the current is 25mA which is a capacity of 500mAh. If the current is 200mA then it is at 6V in 1.5 hours and its capacity is only 300mAh.

Energizer has curves on their datasheet for their 9V alkaline battery that has the voltage quickly falling to 7.2V then slowly dropping lower. Your voltage regulator will not regulate for most of the life of the battery.

Attached Images

9V alkaline, 75mA.PNG (7.5 KB, 2 views)

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Uncle $crooge

 

Im so ****** confused its not even funny. Can you explain all this MAH and crap. What does this mean? I dont get this. All Im doing is hooking up a 9v battery, to a 5v resistor, then I have the 120ohms resistor to the LED.

 

MAH is the current capacity of a given battery, it tells one how long a given battery can supply a load before being discharged. You can wire 8 AA cells in series for 12volts total but it won't have the same MAH capacity as a large 12volt car battery. Make sense?

So a battery has two main specifications, it's nominal voltage rating in volts and it's current capacity rating in MAH (milliamp/hours) or AH (amp hours).

Batteries come in two main types, primary types (non-rechargable) and rechargable. There are many different types of batteries that have different benifits Vs costs, esp in the rechargable types.


Lefty

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Measurement changes behavior

 

Yes it can be confusing, do you want to learn all this stuff or do you soally just want to make a charger???

mA(milli Amps) is what your application (LED,or any other load) will draw from the battery, the resistor, "resists" the amount of current(mA) passing though the LED.

if you use a resistor that does not "resist" inuf current(mA) then the LED will be really bright and burn out.

LED's have a milli Amp rating
and a voltage

eg: if your LED is rated at 3Volts and 25mA of current.
then you will need to find a resistor to suit 25 mA of current

and this is how you find the correct resistor

say your power supply is 5V

and your LED is 3V

and the mA (milli Amps) needed to light the LED is 25mA

so you do the followong:

5V - 3V (LED) = 2V

so now

2V / 0.025A(25millAmps) = 80

so you would need a 80ohms resistor to get 25mA supplied to the LED

i hope this makes sense, iv tried to explain it as noob friendly as possible

 

Yeah, it kinda makes sence. I just gatta keep at it

 

Hi!

I’m glad, that you are interested in electronics. The LED must be fed with current generator. The LED drop voltage is 1,9…4V depending on it’s color. If you connect the LED directly to 5 Volts, the LED and the source supply may damage. Always use a serial resistor for LED’s. R=(US-UL)/I. US=supply voltage (5V from USB), UL=LED voltage (2,7V in your project), I=LED current (in general 10…20mA => 0,01..0,02A). In your project R=(5V-2,7V)/0,02A=115 OHM. The nearest standard value is 120 OHM. If you want to charge your portable device from battery, you must use a higher opacity off batteries then the portable device. Use 6pcs batteries of 1,5V connected serial. Use R14 or R6 batteries, or sealed lead-acid battery of 2…10Ah.

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Eddy