Another formula: Voltage from Current in Lux3

Another formula: Voltage to Current in Lux3

This won't work for every Lux3, but for my Jbinned models it comes extremely close.

I took actual measurements of my J binned Lux3 and plotted current v voltage.. I then created a function to close-fit the curve and came up with this:

oops.. original formula V=(I-2.6)^2*0.76 I had V switched with I..

the correct formula is I = (V-2.6)^2*.76

thanks to the help from the peanut gallery for helping me out on that one.

the 2.6 is an offset for left/right and the .76 is a multiplier to stretch the curve up vertically... if you plotted your own measurements you could modifiy to exactly match yours.

The point you may ask?

Well i needed to figure out what resistors to use for my 3-stage AAA switch.. and i wanted to run it at 2W, 1W, .5W... so i needed to know the voltage and current based on the Wattage.. so i made a spreadsheet that i can calculate current voltage or power based only on ONE of any of them.. from there i can figure out the voltage drop on a resistor to get the power level i want..

Much less trial and error.. especially when it's so difficult to get accurate current measurements.

when combining some parallel and some series resistors in a switch 9mm diameter 4mm tall.. not much room for error.. want to have the right value to start with.

Hope this can help somebody out there, it was extremely useful for my current project.

-awr

Re: Another formula: Voltage to Current in Lux3

Hmmm..., I plug in I=0 and get a voltage of 5.14V. something ain't right.

Re: Another formula: Voltage to Current in Lux3

Big oops on my part i have voltage and current reversed..

The correct formula is I = (V-2.6)^2*.76

reality check: (3.5V-2.6)^2*.76 = 608mA.. and 608mA x 3.5V = 2.12W.. sounds right.. thanks for catching my oops.. it was after an alnighter that i posted this..

note.. obviously this formula will only work for values over 2.6V since it's a quadratic it'll say you get more current when you start going less than 2.6V It also gets farther 'off course' as you approach 1A and more, but it's still really darn close..

(3.9V-2.6V)^2*.76 = 1.28A x 3.9V = 5.00W.. and that's about exactly what i measured when i run my micromighty on a full charge.. so far the formula worked exceedingly well for estimations.