LED Lights

[jldavis1969]

Anyone found any with Resistors built in?

I think i have. The LED set I have has one of what is pictured below on each end. I cut the Green Shrink tubing away to find green plastic with a little bit of a resistor showing. I see one color band of brown. wish I could see more.


Attached files

[jldavis1969]

Here is the front of the box of lights.

Attached files

[Roman A. Gurule Jr.]

I have about 90 strings of the walmart m5's from last year, I think about 90% of those are identical to what you have pictured!
And by the way they have been going strong now for about 2 weeks, with rain and 10 degree weather.

Roman

[-klb-]

LED strings should always have resistors built in. LEDs in series by themselves have their current increase exponentially with voltage. Adding resistance in series causes a more nearly linear current response, so that the string does not fry itself on an otherwise minor voltage surge.

[jldavis1969]

I was thinking that these strings do not need a snubber if using 2 or more strings especally when fading. Am I correct?

[-klb-]

The resistor built into the string is not a "snubber". A true snubber is actually a filter that goes next to the triac, to prevent high dv/dt from causing the triac from switching on, without a gate signal. The "snubbers everyone talks about here, PC, and elsewhere are resistors in parallel with the LED strings, rather than in series with them, and the resistors perform different functions in those two settings.

The ones in series allow the current in the LED's to be reasonably constant over the range of voltages that may normally be applied to them.

The ones in parallel may be doing several things. They assure that there is some minimum linear load on the channel to help prevent the triac from switching off early. They help offset any reactance from the capacitance that a large number of strings can generate. They can drain capacitively induced voltage off the strings, to keep them from lighting with the channel off.

So, a whole different set of functions between the two ways the resistors get wired in.

[Rafter Bar R]

Resistor values vary depending on the color and the number of LED's used in the string. I would say that the string that was pictured is probally using a 1K resistor.