Strips question

Mak'er Grow

Well-Known Member
Prob a silly and easy answer...I just can't seem to wrap my tiny brain around this.
Why do strips not follow regular electronic 'laws'?
Example:
In the picture I have used resistors as strips...1 resistor=1 strip...since we stated in another thread/post that they are basically resistors...anyways.
If we do the math for parallel it would basically be R = 1 / (1/R1 + 1/R2 + 1/R3 ... 1/R10) and each resistor = 10 ohms (value is just for easy calculating...not actual)
We should get 1 ohm total across the + & -.
In series they add together so it would + 100 ohms.
So why does the resistance go up in the middle in parallel and down in series...or as I've been told it does?
examples.png
 

cobshopgrow

Well-Known Member
dont worry the strips do follow ohms law.

the problem is you daisy chained the strips in your example in the other thread.
so according your suggestion there 10ohm + 10ohm + 10ohm--- and so forth, R1+R2+R3...
the resistance added up.
a strip just have a thin layer copper, not much compared to a propper sized cable.
in your recent example for parallel wiring youre not going throgh each strip, no daisychain.
practically thats very fine when the main lines are thick enough.

an example
10 strips each at 10V and 1A drive current to make it simple.
thats a 100 watt.

so we drive them in parallel, each strip connected directly to the driver (not daisy chained).
our driver needs 10V and 10A , 100W
the current will divide to all strips in parallel (the wire lenght plays no role as the resistance is too to low to matter if the right diameter is choosen).
10V 1A at each strip, 10W.
it wont be a 100% 1A on every strip but more then close enough that we can work with that, it will be even hard to measure differences.

we drive now the 10 strips in series, 100W.
each strip is still 10V 1A, 10W.
now our driver need to delive 100V and only 1A, lower ampere mean lower resistance, thats the point.

you increase the resistance putting more leds, resistors whatever, in series but in our usecase we lower the ampere/resistance therefore.

the load to resistance ratio isnt linear,
for 1 Amp on 1 inch wire trace you need 0.39mm width.
for 10 Amp on 1 inch (same parameters) you need 9.36mm wide traces.
you see that this is more then 10 times, its not linear.

you need to consider that your voltage goes up when you use them in series but as you still use the same wattage, your amperes go down, this you need to take in to account.
 

Mak'er Grow

Well-Known Member
the problem is you daisy chained the strips in your example in the other thread.
so according your suggestion there 10ohm + 10ohm + 10ohm--- and so forth, R1+R2+R3...
the resistance added up.
daisy chained/parallel is not added. It follows the top pic. Since each strip is basically connected to + & - and not + to - that makes it parallel...+ to - would make it series and then they get added....this is where I'm getting lost...lol
I get how they are powered and all that...its this parallel/series and resistance that is throwing me off for some reason. :)
 

cobshopgrow

Well-Known Member
best is if you take a practical example and try to calculate it to get a better feeling.
volt x ampere = watt

to get a feel what wire you would need for distribution.

to get a idea of how wide a trace need to be for the ampere you use.

and probably also good would be to understand how a strip is made.
as an rough overview.

practically parallel and series wiring and mixes of it are fine for what we do, dont bother too much just dont daisy chain too much and consider traces on PCBs can be thin.
 
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