Need some help calculating what wire gauge I should use?

[Gershy13]

Not sure if this is the right place to post, but I'm trying to make a project which involves 5v LED strips...

I need to power them, but not sure how thick the wire should be.

It's going to be around 4m of strip, and it consumes 18w/m, so that would be 72w total. Which is 14.4a... 

The strip is going to be around 2m away from the power supply.
What AWG would you guys reccomend for these conditions? 

Not sure if this makes a difference, but the wires are going to be run behind a wall...

The power supply I'm planning to use is something like this:
http://s.aliexpress.com/VrMnUbmE

The voltage can be adjusted slightly up and down on it...

Any ideas?

Thanks

Gershy13

[Valkyrie Lenneth]

i run 5v leds just from a USB cord stripped ( powered usb hub works too for higher loads )

 

u can also connect them through molex ( stripped if needed ) , u can set molex so that its only outputting 5v,7v or 12v, with molex just check what kind of watt room u got on the psu ^^

[Gershy13]

1 minute ago, Valkyrie Lenneth said:

i run 5v leds just from a USB cord stripped ( powered usb hub works too for higher loads )

Unfortunately these are really power hungry RGB leds?

[Valkyrie Lenneth]

12 minutes ago, Gershy13 said:

Unfortunately these are really power hungry RGB leds?

edited post with more info , u can connect them through molex on 5v ^^, u can also use the 12v rail ( WHICH CAN TAKE A HUGE AMOUNT OF WATTS ) and use a volt regulator to reduce it to 5v

 

i somtimes just use an extra old pc powersupply to power stuff around, u can connect a paperclip in the 24pin cable to keep the powersupply turned on without somthing connected C:

 

my recommendation is, just get a MOLEX POWER ADAPTER ( its just a seperate adapter with a molex port that powers up to X amounts of watts , its quite small and will do the job easily, just connect the molex and get some longer cables ( that u require )  5v doesnt need very thick cables ( take the molex cable thickness for example , per cable ofcourse , it runs high amounts of watts through that aswell

 

a standard single molex can deliver up to 132 watts

 

https://www.amazon.com/inch-Molex-Extension-Cable-Sleeved/dp/B0014XDBIA

 

u can just connect those together x)

[themctipers]

spare electrical wire

the one you use to wire a light or something if you have that.

 

you must have it somewhere.. right? 

[Enderman]

I would personally use some 16awg +/- 2 for this task.

[mariushm]

You have the basic formula : V = I x R  ( voltage equals current x resistance )

 

You have here a list of wire gauges : https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes

 

So let's say you go with AWG24, which is common in USB cables and ethernet cables. That would mean you have  ~ 84 mOhm per meter of resistance.  So, with 2 meters of wire between power supply and first led of the strip, you have 2 x 2 m = 4 meters of wire, because electricity has to reach the device and come back, so overall you have 4 x 84 mOhm = 336 mOhm or 0.34 ohm

Therefore  V = I x R = 14.4A x 0.34 ohm = 4.896v ... so you'll have 5v - 4.896v = 0.11 v at the strip.

Obviously, that's not gonna work.

 

Let's go with AWG 18 wires (typical for power supplies) with their 21 mOhm per meter, so your resistance drops to 0.08 ohm (across 4 meters) and therefore voltage drop will only be 14.4 x 0.08 = 1.152v, so your leds will get 3.8v  ... it's still too low.

You'd probably have to either use AWG16 or AWG14, or just double the wires, use 2 pairs of AWG18 or something like that.

 

Because the voltage drop over the wires is proportional to current, that's why most led strips are 12v or higher. It would make sense to split your 4 meters of led strips into chunks that need less than 3A of current, and then simply use tiny dc-dc converters that convert 12v down to 5v ( 5v 3a or lower dc converters are cheap, maybe less than 2$ each)

 

 

[Gershy13]

9 hours ago, mariushm said:

You have the basic formula : V = I x R  ( voltage equals current x resistance )

 

You have here a list of wire gauges : https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes

 

So let's say you go with AWG24, which is common in USB cables and ethernet cables. That would mean you have  ~ 84 mOhm per meter of resistance.  So, with 2 meters of wire between power supply and first led of the strip, you have 2 x 2 m = 4 meters of wire, because electricity has to reach the device and come back, so overall you have 4 x 84 mOhm = 336 mOhm or 0.34 ohm

Therefore  V = I x R = 14.4A x 0.34 ohm = 4.896v ... so you'll have 5v - 4.896v = 0.11 v at the strip.

Obviously, that's not gonna work.

 

Let's go with AWG 18 wires (typical for power supplies) with their 21 mOhm per meter, so your resistance drops to 0.08 ohm (across 4 meters) and therefore voltage drop will only be 14.4 x 0.08 = 1.152v, so your leds will get 3.8v  ... it's still too low.

You'd probably have to either use AWG16 or AWG14, or just double the wires, use 2 pairs of AWG18 or something like that.

 

Because the voltage drop over the wires is proportional to current, that's why most led strips are 12v or higher. It would make sense to split your 4 meters of led strips into chunks that need less than 3A of current, and then simply use tiny dc-dc converters that convert 12v down to 5v ( 5v 3a or lower dc converters are cheap, maybe less than 2$ each)

 

 

Thanks, this is what I needed to hear..m I think I'll end up using 14 gauge, or 2 sets of 16-18 gauge. As I might need to power both ends of the strips, it might be better to get two straight from the PSU.

[Pixel5]

i guess you are using ws2812b LED´s ?

 

unless you have them turned on white and full brightness on all LED´s you will not have that high current draw.

i have a 5m roll here with 300 LEDS on it and the total power draw when cycling through different patterns including one where they are all on and fade between colors was max 2.5A

 

i bought a 12A powersupply because i was also expecting a gigantic power draw but it turns out its not that bad.

[Gershy13]

Just now, Pixel5 said:

i guess you are using ws2812b LED´s ?

 

unless you have them turned on white and full brightness on all LED´s you will not have that high current draw.

i have a 5m roll here with 300 LEDS on it and the total power draw when cycling through different patterns including one where they are all on and fade between colors was max 2.5A

 

i bought a 12A powersupply because i was also expecting a gigantic power draw but it turns out its not that bad.

Yeah how did you guess?

 

They'll be on full brightness all the time, but not always white...

I think I'm going to go with a 20a PSU just incase, and also that means at lower loads the fan won't turn on...

And I'll go with 14 gauge wire...

[rodrosenberg]

I use an app on my android phone to quickly check some of these calculations. The one I use currently is called ElectroDroid and has so much info in it including wire ampacity and voltage drop along with stuff like pin outs 

 

https://play.google.com/store/apps/details?id=it.android.demi.elettronica&hl=en

[Gershy13]

1 minute ago, rodrosenberg said:

I use an app on my android phone to quickly check some of these calculations. The one I use currently is called ElectroDroid and has so much info in it including wire ampacity and voltage drop along with stuff like pin outs 

 

https://play.google.com/store/apps/details?id=it.android.demi.elettronica&hl=en

thanks, thats awesome.