I have tested many many 1' strips wired in parallel on a 80-20A, and wired in combo S/P on a 185-36A with amazing results.
At 20v every strip hits a bulls eye with a handful pulling only 15mA more constantly.
In 2s3p every pair is on point at 39v-39.2v with equal split current.
I was most interested in testing the voltage between the 3 different batches iv ordered each with a different Lot#. Each of the three lots tested the same.
For circuits that go from strictly parallel to a combination of series and parallel then the series component takes your voltage tolerance and doubles it.
If your voltage tolerance range for the strip in question is 24V with a +or-1 V
A 2sx3p voltage tolerance would now be + or - 2 V
A 3sx3p voltage tolerance would now be + or - 3 V
I guess this means that the more you put in series on a combination circuit the higher risk you run of having larger differences in current.
The min/max comes from a strips datasheet. From the Vesta at 1000ma and 25C its Vf min is 23.6V, avg is 24.8V and max is 26.0V. If you build in series you add voltages, in parallel you add current and in combination circuits both.
Lets say you build a 2s x 3p. You series two strips that are the average, 24.8+24.8 = 49.6V but you could also series two strips that are 23.6 + 23.6 = 47.2V and you could also series two strips that are 26+26 = 52V. And when you parallel these 3 sets of two strips you get current divided by each leg. But when you have each leg looking at 47.2V, 49.6V and 52V your getting current wanting to take the path of least resistance so most of current will be in the 47.2V leg and the least in the 52V leg.
I think in practice, with quality LEDs of the same part number, there's not enough variation in voltage to matter. As it is, the fear of thermal runaway is already greatly exaggerated.
I very much disagree.
This is extremely hypothetical, and unlikely in my opinion, and from my personal experience.
Like Shim said, these fears are exaggerated.
We are all aware of these ranges.
In the highly unlikely event that you are faced with this situation, Retest and contact the supplier. Digi-Key has been extremely helpful with some concerns Iv had regarding strips Iv recieved.
Test test test. Test all your equipment in various configurations to learn as much as you can about it is always a good thing.
The min/max comes from a strips datasheet. From the Vesta at 1000ma and 25C its Vf min is 23.6V, avg is 24.8V and max is 26.0V. If you build in series you add voltages, in parallel you add current and in combination circuits both.
Lets say you build a 2s x 3p. You series two strips that are the average, 24.8+24.8 = 49.6V but you could also series two strips that are 23.6 + 23.6 = 47.2V and you could also series two strips that are 26+26 = 52V. And when you parallel these 3 sets of two strips you get current divided by each leg. But when you have each leg looking at 47.2V, 49.6V and 52V your getting current wanting to take the path of least resistance so most of current will be in the 47.2V leg and the least in the 52V leg.
Never mentioned thermal runaway, I am going with strips to get an even spread and understanding what effects that is my goal.
Its cool if you disagree with some of what I say but when you deal with numbers and tolerances its pretty hard evidence of what can occur, otherwise they wouldn't post their tolerances and we'd be none the wiser.
We are in agreement in one thing in that test, test, test which in a round about way is exactly what I am saying with testing voltages of strips before slapping them together in a combo circuit.
Strip voltages correlate directly with current. And every data sheet will have a tolerance for their tested values.
What your suggesting will never happen. If your strips are not closely following the I/v curve within tolerance supplied in the data sheet then contact your supplier.
The min/typ/max values are all measured at specific currents and correspond with such. You won’t see two strips verifying in +/- 3v if they are both given the same amount of current.
Have you ever built a light with mid power strips? Or are you just suggesting what your interpretation of the data sheet is?
Your confusing useable voltage range with tolerance.
All three strips will receive the same current and be almost exactly the same voltage (+/- allowable tolerance stated in the data sheet usually in the form of a foot note at the bottom of a page)
What your speaking of is min/max.
a strip will only pull the current it needs at any given voltage (+/- tolerance)
The MIN V has a particular current it will pull at said V
The TYP V has a particular current it will pull at said V
The MAX V has a particular current it will pull at said V
In series all three strips will be supplied the same current and therefor the same voltage.
The voltage range is not tolerance and does not add up in series chains.
From datasheet at 1000ma 23.6v min 24.8v avg 26.0v max. Tolerance would then be 24.8 +1.2/-1.2V This states that at 1000ma the voltage can range from 23.6-26.0V.
I think the confusion starts when you assume what others are thinking. If your asking what is +/- then I suggest you find out what mfg tolerances are and how they apply. Then ask yourself how they apply in your build.
Series circuit - not important unless your running near the max or min of the driver.
The example in the previous post's is not for a standalone series circuit, its for a combination series parallel build regarding tolerances, sit on it and then digest it.
