Electrical – LED Christmas lights without limiting resistor


My LED Christmas light strings do not have a series limiting resistor, how is this achieved? They are 70 LED strings with two 35 bulb sections. I have carefully checked and there are no provisions in the plug or inline with the wire. I measured resistance from sockets back to plug and measured no impedance. What am I missing? Can the the LEDS be made (doped) so the internal resistance be high enough that as a group they provide sufficient impedance?

Best Answer

If you are willing to watch "Big Clive's" vlog, he uses the "easiest" method of finding the resistors, a thermal imaging camera.

In the 220V set he found 3 resistors in 3 of the LED bases, the rest had no resistor. Each resistor was 510R for a total of 1530\$\Omega\$. He also says he found a bridge rectifier molded into the bit where the wires split.

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That was for an apparently Polish made set. It's certainly possible that other sets use variations on this theme but you get the idea. Bridge rectifier plus a few hidden resistors distributed out among the LEDs (to spread out the heat dissipation, otherwise they could use just one resistor).