Bad dumb nodes

[chrisatpsu]

ok, but even with 18mA  it pushes 4A to about 74 nodes...

[davron12]

So we must be under powering all of our nodes - smart and dumb. Yes/no?

[chrisatpsu]

don't know what the smart string resistors are

[rm357]

As stated, we don't know the values of the resistors used, but I would expect that we are not hitting the maximum rated current as that would tend to reduce the life of the LEDs. You want to get close for maximum brightness, but you also want a margin for safety...

The number one enemy of LEDs is internal heat buildup. The maximum rated current is determined by the manufacturer based on the heat dissipation of the part at some ambient temperature, which is probably around 70F. Too much current will generate too much heat and damage the light producing region.

[davron12]

Ok, so trying to tie this back to our problem at hand... we're not hitting the maximum rated current per led in our dumb strings. With the resistors used, it should be using a max of 20mA per color at 12V. I'm saying max of 20mA, because the red resistor is on the high side, probably only supplying 18mA. Further, a 100ct string is drawing under 4A, so the current per led is definitely under 20mA on average per color.

Chris brought up that we should only be using 66 bulbs because that should be 4A. If we add another 34 bulbs, that wouldn't increase the current per led. That would either cause our wiring to heat up and melt, or possibly damage our dsc, or cause a voltage drop near the end of the string and affect the colors of those nodes. Either way, it wouldn't over power and destroy the led.

[chrisatpsu]

I was finally able to cut apart one of the bad nodes, and unfortunately I don't think there's anything wrong with it. The resistors used are

Blue - 430 ohms (3.4V)
Green - 430 ohms (3.4V)
Red - 560 ohms (0.8V)

I took apart a bad ss node today to compare...

the smart string nodes resistor values are... (at least from the first batch last year)
Blue - 510 ohms
Green - 510 ohms
Red - 560 ohms

which leaves me scratching my head, b/c then that leaves 17.86mA + 17.25mA + 17.45mA for the three colors which don't add up to the 29mA that the node is supposed to be using...

[davron12]

Yeah, something about that doesn't add up, but unless that has something to do with over powering the reds, that's probably a different thread. Sorry, just trying to keep us on track of figuring out what's wrong with the dumb strings.

510, 510, 560 is good to know though. That means the red should definitely be fine in the dumb nodes. 510 and 510 may explain why occasionally a blue or green might go bad. That is a pretty big difference.

I had a hunch that may explain what's wrong. Can you measure the size of the resistors as close as possible so that we can determine their power rating? I measured the ones in the dumb strings and they're about 2mm x 1mm. Which would indicate that they're 1/8 watt resistors being used at twice their rating. I haven't taken apart a ss node, but they look bigger to me, like 3mm x 1.5mm, or 1/4 watt resistors. I'm not sure how much their values would change with twice the current running through them, but it wouldn't take much to over power the reds.

[davron12]

That wouldn't explain why those using MR16s are reporting no problems and us using the dsc are reporting problems, unless those using the MR16s are using a different batch of dumb strings and the parts were swapped to make them cheaper. That's just a guess.

[chrisatpsu]

i don't have anything to measure millimeters but they are the same size as the ones on the plastic rectangles, metal squares, and flex strips...

also the flex strips use
470 & 510 ohm resistors (for comparison, even though they power 5050's instead)

[davron12]

That's what I figured. If they're the same ones on my flex strips, then they're bigger than the ones used on the dumb strings, so that could possibly be the problem.

[rm357]

The blue and green LEDs have different voltage drops than the red, that's why their resistors are smaller.

None of this explains why they are burning out though...

[chrisatpsu]

he was talking about physical size, like they might be a different wattage resistor.

[davron12]

And the power usage for the blue and green resistors would be .172 watts, running at only 38% over their rating, causing not too much of a change of their resistance, and thus not burning out many of the blues or greens.

[sittinguphigh]

I ordered 3 smart strings and had the last one had four bad strings.
The one of the wires came off the nodes coming out of the box.
I hope the new style will be better. The square ones.

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I have been thinking how the fix the round ones.
Rap tap around the the node leaving about 1/4 inch on the wire side.
Get some hard rubber sealant in a tube and inject it into the wire end around the wires.
I think if we can find the right sealant rubber that would work.

[zwiller]

Anyone resolve this? 

My interpretation    of the thread is that there seems to be an issue with DSC's causing failures but not with MR16's.  Also, you should not connect more than 66 nodes to a DSC but that does NOT cause the failure of leds.  Am I way off?