Let me try a simple analysis with no specs
- my initial reading was you had two 39 in series = 78Ω, so I will show Rev B
- let 14.4W / 60LEDs = 0.24W /LED including 1/3rd of Pd in 78Ω
- let's assume they "cheated" ( or exaggerated marketing with no specs)
V+=14.4V ( car alternator = 14.2V nom) e.g. 14.4V*1A = 14.4W
thus 60 LEDs in 20 strings = 50mA per string
- and Vdrop on both R is 50mA*78Ω = 3.9V
- with Vf = (14.4-3.9)/3led=3.5V (cheaper quality LEDs)
12V will never achieve rated power for these StripLeds, you need a battery and charger or a 15V or 14.4V power supply, because they are rated for Cars but still work on 12V since the LEDs add up ~9V at low current.
These will also be running near maximum temp so suitable for semi-trailer trucks with forced wind cooling. lol.
Analysis with updates on Rs current limit using two 39Ω in parallel=20.5Ω
- Given 60 5050 LEDs/m in parallel(P), series(S) array 20P(3S + 20.5Ω)
- your results of 2.0A at 12V for 2.95 meter = 8W/m and not 14.4W/m
Now what would we expect at 14.2V with 2.9V/LED?
- or a rise of 2.2V or almost 20% in power source to match opt. alternator voltage in cars
- do we expect a linear incremental rise in power due to series R? no but,
- a 20% rise in voltage, results in a 40% rise in power if it was linear
- we need almost 6.4/8W=80% rise to achieve 14.4W, so it is quasi-linear
- this is because the most of the voltage rise is across Rs=20.5Ω
- You measured 2.9V/Led @ 8W/m thus If= 8W/(20S * 12V)= 33.3mA /string
- thus V across 20.5Ω * 33.3mA= 0.68V
- my trick is knowing LED ESR is due to incremental V/I above 2.7-2.8V
- i.e. (2.9V-2.7V)/33mA=6.7Ω assuming your reading was accurate
now I can estimate power vs voltage for arrays in two ways, Can you?
- such as 20S(3P+Rs) using LED ESD & threshold Vth or from specs