How much resistance?


Dec 19, 2007
Those could be not resistors but inductors and could be 0.2 Microhenrys, +/-5%.

Resistors in PCBs are marked R(x) and Inductors as L(x).
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Newly Enlightened
Dec 14, 2008
Remember that the ammeter has some internal resistance too, at least in the order of 0.2V/20A = 0.01 Ohm.

Those things are not inductors, by the look of them, and by the description of the circuit. But yes, inductors can look quite similar.

You have a multimeter, so why don't you just measure the current that passes through the lamp's switch? Then you can measure the voltage across the resistors and see if the currents and resistances add up.
Measuring the off-load & on-load battery voltages, and knowing the current passing, you can calculate the internal resistance of the batteries. Ri=(U1-U2)/I.

LED's can be modelled somewhat simplified to work within certain limits & accuracies in equations. They can be said to have a turn-on voltage & an internal resistance. The turn-on voltage being found from the extension of a straight line towards zero current, from 700mA through 350mA. The turn-on voltage can then simply be subtracted from the battery off-load voltage. The results would be reasonably accurate between say 250 & 1000 mA.

Of course the real world has a more gradual turn-on and also temperature coefficients etc.