I v/r
Ohms law
I have measured 100ma through circuit using ammeter getting 100ma but my math keeps coming up with it= 338ma
This is a parallel circuit with
12.70v battery
Connecting 14 LEDs total
4 resistors each 150ohm
4 strings of LEDs running series-parallel
S1= 2.2x4 LEDs / 150ohm
S2= 2.2x4 LEDs /150ohm
S3= 3.2x3 LEDs / 150ohm
S4= 3.2x3 LEDs /150ohm
My math says 37.5ohms for R-req
338ma
Somethings not right please help
As your photo.. Each string is series connected so after calculating the vf of the three / four LED's you have @ 4v.. 4v / 150 ohms is around the 25mA.... The results you obtained seem to be right!! 4 x 25mA is 100mA...
Just been thinking!!!! Are you are totalling the mA across each LED? There are 4 circuits, each circuit consumes 25mA regardless of the amount of LED's.... Each string ( including the 150 ohm resistor ) totals 508 ohm... All four together total resistance of 127 ohms or a total power of 1.27 Watts
Each red string: I=(12.7-4*2.2)/150=26mA.
Each white string: I=(12.7-3*3.2)/150=21mA.
For the 4 strings in parallel, total current = 2*26+2*21=94mA.
Combined 'effective resistance' = 12.7/0.094 = 135Ω.
Bear in mind that a LED is a non-linear device so its resistance is current-dependent.
508 ohms is the total resistance in the led string + the 150 ohm resistor.. Each LED has internal resistance.. (2.2v / 25mA = 88 ohm ) ..
Remember these figures are the ideal!!
i in a circuit is always the same.. So you have 12.7v and 150 ohm...measure the V across the resistor ( will be about 4v )
4v / 150 = 26mA.. Once you have the current..... Jobs done..