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about cable gauge

camilozk

Apr 20, 2014
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hi!

I have a system in which I have to send 12v to some led strips, around 20 meters away from the PS. I need 5 Amperes at the end so I calculated that a cable 2.5mm2 should do the job.

My question is the following: Because of how I built my controller (and I am not saying it is the right way to do things), there is a short section (10 centimeters) of 20awg cable. Would this have a great impact on the amount of power reaching the led strips?

thanks for sharing!
 

AnalogKid

Jun 10, 2015
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10 cm is only 2.5% of the 40 m round trip distance, so right off the top it will not have a huge impact. Calculate the voltage drop at 5 A and include that in your calculations. It's all Ohm's law:

What is the absolute minimum output voltage of your power source?
What is the absolute minimum voltage you must maintain at the far end?
What is the voltage drop across the piece of #20?

Start cranking the numbers to get the max allowable voltage drop in the 40 m loop, convert that to an equivalent resistance, and see what the wire tables tell you.

ak
 

Bluejets

Oct 5, 2014
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2.5 sq mm is 14 gauge.
100mm of 20 gauge is hardly going to be noticed.

Edit:... enclosed wire chart might make life a bit easier for you.
I'd be putting the ps a lot closer.
 

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(*steve*)

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And using a constant current driver (assuming the load will always be 5A) will mean you don't need to worry about the resistance of the wires (for sensible amounts of resistance).
 

camilozk

Apr 20, 2014
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the load will not remain stable at 5A. it is addressable led strips displaying different programs.
 

(*steve*)

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In that case, you could consider regulation closer to the load. At the very least I would place some capacitors across the supply rails at the load.
 

camilozk

Apr 20, 2014
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If I could place the PS closer, I would definitely do it.

How would it work out with the capacitors? I have no experience on this.
how do I calculate which capacitors and where?

thanks in advance
 

(*steve*)

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I would use a 16V capacitor with a capacitance between 2200uF and 4700uF. Higher voltage or higher capacitance would also be ok.

Capacitors of this size are polarised, so be sure to connect then the correct way around.
 

(*steve*)

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They have two purposes. The first is to help prevent the voltage from sagging when brief high current pulses are drawn.

The second reason is that the long cable run can have significant inductance, and it is possible that you will see even greater voltage variations sure to this. Additional capacitance will damp this out.
 

camilozk

Apr 20, 2014
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thank you so much for the info. I will be reading more on these regards
 

Bluejets

Oct 5, 2014
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If I could place the PS closer, I would definitely do it.

I would give it some serious thought.
If you looked at the chart, the cable size for 5A @12v is 7.9 sq mm
As there is no such size then one would have to decide whether 6 sq mm would suffice given the lower load you mention or bite the bullet and go for 10sq mm
Either way, big bucks.
 
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