Amps in a wire...

[n1ist]

Looking at a chart on line, 18AWG copper wire has a resistance of 0.00639 ohms per foot.  Multiplying by 40 (2 conductors (+ and -) times 20 feet) gives a resistance of 0.2556 ohms.  At 20A, Ohm's law says that you will drop 20 * .256 = 5.112 volts in the wire.  That means your lights will only see 6.9V, which may be an issue.  Also, your wire will be dissipating 20 * 5.112 = 102W.  It will get warm; each foot will dissipate 5W.

Retrying this with 14AWG (.002525 ohms per foot) gives a 2V drop and 40W dissipated in the wire. 

/mike

[animal]

I ran spt 2 to my gutters from the hub to 3 break away boxes with 4 port passive hubs. This powered 92 feet of flex strips along all the gutters. I probably had maybe 60 to 70 feet run to the furthest break out box. Everything ran cool including the 750 watt power supply, but I did feel it wasn't as intense as it should have been. I'll be running seperate power supplys per box next year.

You can check it out here. I have done a behind the sceans video I'll post soon. (work  )

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      animal

[zwiller]

This is one of the tradeoffs for working with 12VDC vs. 120VAC.  I did some research for a using 350W 12VDC power supply for a MR16.  IIRC I needed 10AWG to properly feed a MR16...  OR double up...  The spade connectors for power don't really allow doubling. 

(Highjacking thread - GET YER HANDS IN THE AIR!) 
If my spider senses are tingling right there is gonna be ALOT of people planning on using MR16s this year for dumb gear.  I also think most of these folks will use Ray's connectors too.  It would real nice to update the board for better input and output power connectors, like those on the LE since they are going to be popular.  Maybe same input power connector and 2 rows term strips to keep same form?  Am I alone?  One of the weakest areas of my hardware was bad crimping or spade connectors coming off my MR16 during setup. 

[Steve Gase]

This is one of the tradeoffs for working with 12VDC vs. 120VAC.  I did some research for a using 350W 12VDC power supply for a MR16.  IIRC I needed 10AWG to properly feed a MR16...  OR double up...  The spade connectors for power don't really allow doubling. 

(Highjacking thread - GET YER HANDS IN THE AIR!) 
If my spider senses are tingling right there is gonna be ALOT of people planning on using MR16s this year for dumb gear.  I also think most of these folks will use Ray's connectors too.  It would real nice to update the board for better input and output power connectors, like those on the LE since they are going to be popular.  Maybe same input power connector and 2 rows term strips to keep same form?  Am I alone?  One of the weakest areas of my hardware was bad crimping or spade connectors coming off my MR16 during setup.

I used a combination of MR16s and Ray's 27-channel DMX controllers.  In each I attached 4-pin water-proof connectors.  For the MR16s I attached the spade connectors, for Ray's I just screwed them down to the board.


I created water-proof extensions (to extend to the RGB lighting elements) using the 4-pin connectors and 20-awg wiring, using soldering and shrink tubing.


I also use a lot of power-over cat5 and 3-channel DMX controllers to light elements when having embedded controllers makes sense.




This thread about diminished power levels has me thinking now...  but I don't know if I'll do anything different.  I will probably notice the difference in intensity (now that it has been mentioned), but I'll add it to the list of things that annoy me about my display (but are not noticed by anyone else).

[zwiller]

Wow Steve, thanks.  Never knew the 27 channel controllers were 12/24VDC, thought they were 120VAC... 

Just did some digging and I didn't realize how many folks are using them.  I guess they must be decent.  Must be used in first universe, right?  Also about half the output capacity as the MR16.  Not they I need it.   

[chrisatpsu]

dmx devices you can use in any universe

[zwiller]

Great.  I will explore that.