Metku.net

MetkuMods
It is currently 20.10.2018 16:26

All times are UTC + 2 hours [ DST ]




Post new topic Reply to topic  [ 5 posts ] 
Author Message
PostPosted: 28.05.2010 16:49 
Offline
Regular Modder
Regular Modder

Joined: 26.05.2007 10:06
Posts: 128
Location: Texas
Grin, Yes i know it's been a while but I have been still checking up on one of my favorite sites on and off...

Anyway, this is one that may seem simple, but I still want to make sure.

I have a small project that the 3v 200mA transformer is about 25-30 FEET away from the actual placement of the Amber/Yellow LEDs.

I have already done the ledcalc.com option of

Supply Voltage 3 VOLTS
Voltage Drop Across LED 2.1 VOLTS
Desired LED Current 24 MILLIAMPS
How many leds connected 1

and came up with the resistor value of 37.5 or 39ohm

I have a possible two part question. (You know I can't ask anything simple)

I am going to make 3 single LED's with resistor to run off this power supply. There is going to be 1 pair of wires running in an enclosed underground PVC pipe that has been sealed with PVC glue so that (I HOPE) it gives it a water tight seal. Once the length of the wire from the transformer through the pipe underground is ran the 25-30 feet I am then going to take each of the three LED's (with Resistor) and run them from that 25-30 foot wire. The LED attached wire is NO MORE than 3 feet each.

#1 Does the 25-30 foot of wire matter as far a drop in current / voltage (?) from the start of the wire to the end (no mater what the size.)

#2 How do I figure out the difference if it does?


Thank You for looking,

Dan


BTW - Can you see any problems with this build. It's for LED's to light the bottom of a Tree.

Image


Top
 Profile  
 
PostPosted: 28.05.2010 17:57 
Offline
Site Admin
Site Admin
User avatar

Joined: 24.01.2002 10:09
Posts: 4683
Location: Finland
Hmm... hard to say but this should be easy to test if you still have the wire coiled up. Just hook up the leds with that long 30 wire and power them up. See how bright they are. Now take a shorter wire with two leads and use that to make a "shorter" connection between the leds and the transformer. You can connect the long and the short wire to the transformer together. Then just hook and un-hook the short wire's leds side repeatedly to really spot the difference (bypasses the longer wire).

I don't see any problems other than a small fire hazard... if a lighting strikes near the wire it could fry the transformer and start a fire. There are special transformers that are meant for outside use and they have better over voltage and short circuit protection.


Top
 Profile  
 
PostPosted: 29.05.2010 20:09 
Offline
Regular Modder
Regular Modder

Joined: 02.11.2006 19:30
Posts: 249
30 foot of very thin wire (for example 30AWG = 10mil = 1/100 inch diameter) will have resistance of just couple of ohms and you'll have two of these in series. I'd say we are talking about less than 10ohm.

Ofcourse that 30AWG wire is very thin and I wouldn't use that in this project. 18AWG would be good IMO to be used between transformer-project box. With that wire size wires' total resistance (2x30foot wires) would be 1ohm or less (quick calculation in mind). 24AWG would be good between project box - led.
Temperature might affect on that resistance.
And can't help about burying wire in a pipe underground. But two questions that could help other users: How much does it rain in Texas? What is lowest and highest air temperature over there?

So: 30foot shouldn't affect too much in this case, as long as you use decent sized wire.


Top
 Profile  
 
PostPosted: 20.05.2011 18:49 
Offline
Regular Modder
Regular Modder

Joined: 26.05.2007 10:06
Posts: 128
Location: Texas
Cool, and Thanks yall... Am just not getting back to where I can HOPEFULLY start tearing things apart to see whats inside... Grin...


DanTheMan


Top
 Profile  
 
PostPosted: 20.05.2011 22:21 
Offline
Site Admin
Site Admin
User avatar

Joined: 24.01.2002 10:09
Posts: 4683
Location: Finland
Hi, nice to see you back! :)

_________________
Metku | AlltheMods | LedCalc | Teknolelu | AndroidCoding
Main Computer: Intel i5, MSI H55M-ED55, 12 Gigabytes of DDR3, 3 Terabytes of HDD, GTX295 and Benq 27"


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 

All times are UTC + 2 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 6 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group