Wire size maximum apms
metron9
Posts: 1,100
Please confirm this is ok to do
Using the table below I calculate I can run 36 Lumileds at 320 mA using a standard 24AWG ethernet cable
I only need 4 wires to each device. (12V+,Ground, and two signal lines fot the electronics on board each device)
Each device will have three Lumileds in series. I will dasichain up to twelve devices so that
12V DC Voltage
Lumiled 3.5 to 4V Forward Voltage
(I will be using a current source onboard each device to hold maximum 320mA per device)
320 mA per device * 12 = 3.84 Amps
SO BY USING 2 wires for +12V and 2 wires for the Ground return I can use up to 4.2 Amps.
Two connectors on each device to dasychain 12 devices (with 3 Lumileds in series each) in parallel
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Think outside the BOX!
Using the table below I calculate I can run 36 Lumileds at 320 mA using a standard 24AWG ethernet cable
AWG Dia Inch enclosedAmps ----------------------------------------- 24 0.020 2.1
I only need 4 wires to each device. (12V+,Ground, and two signal lines fot the electronics on board each device)
Each device will have three Lumileds in series. I will dasichain up to twelve devices so that
12V DC Voltage
Lumiled 3.5 to 4V Forward Voltage
(I will be using a current source onboard each device to hold maximum 320mA per device)
320 mA per device * 12 = 3.84 Amps
SO BY USING 2 wires for +12V and 2 wires for the Ground return I can use up to 4.2 Amps.
Two connectors on each device to dasychain 12 devices (with 3 Lumileds in series each) in parallel
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Think outside the BOX!
Comments
Don't forget to figure in the voltage drop in the length of wire you will be using. To be safe, I would double the wires in the power loop.
If I remember right, the optimum specs for a Luxeon is 3.6 v at 350ma, using suitable heat sinking.. A 12v supply using individual regulators for each string of 3 might not be enough overhead if you factor in the loss you get ( regulator, wire length )..
Bob N9LVU
· Have you turned on one of these yet?· I don't know what your level of expertise is, but I suggest a step-by-step approach instead of going whole-hog from the get-go to be followed by the "nothing works... and I burn my finger when I touch..." Reply post.· Does that make sense?
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When you get 1st Place in the "Darwin Awards", you're a Winner & a Loser.
How true, I have trashed some regular leds by using wrong resistor value (math error)!
I used some old cpu heatsink/fans when I "experimented" with my 5W units, worked like a charm!!!
Bob N9LVU
Yes I will be making just 2 devices to start with.
WHen you say double the wires you mean use 4 wires instead of 2?
Any suggestions on 4 wire connectors that would work for this application?
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Think outside the BOX!
Sure, use the same connectors found on computer power supplies to HD/CD/DVD's
Bob N9LVU
Yes I am thinking of these connectors as well however they do not have a positive lock clip on them
I am looking for off the shelf wires/connectors if possible. We were using the regular rj11 phone connectors when the devices used only a few LED's each but now that we have gone high power in the design the wires and connectors are on the front burner so to speak now so we are just exploring options.
We are looing at these as well: http://www.action-electronics.com/ampcpc.htm
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Think outside the BOX!
You not only need to look at the ampacity of the wire, but the temperature rating of the insulation.
You can safely pass lots of amps through a conductor until it melts!!! But you have to think of the insulation rating.
I dont know about the type of cable you are thinking about, but most network cable is not rated to take much internally generated heat. It is a good size conductor, so there will not be much signal loss over long runs.
The resistance is given as ohms per unit distance. The longer the cable the more heat you will generate.
Here is a link for single conductor wires and the safe ampacities.
www.alphawire.com/PAGES/383.CFM
You have to derate the wire for multiple conductors, and low temperature rated insulation.
The money you save by using the wrong type of wire you will spend in making the power supply big enough to light the leds after heating up the wire. Remember the losses come first!
Alan Bradford
Plasma Technologies
www.plasmatechnologies.com
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When you get 1st Place in the "Darwin Awards", you're a Winner & a Loser.
You have the wrong person here, I was replying to "metron9"....
And if he uses say 3 or more wires on slupply and on ground legs, based on his calculations, he should be safe.
Bob N9LVU
The length of wire between the units will be at most 6 feet
The units will only be used at most 50% duty cycle each and it would be impossible to light all of them at once.
But I still want to make sure if for some reason they all did hold in the on position it would take the heat.
So with that, I will continue and run some tests.
I see one of the cat-5 cables I have has a 75c printed on the wire.
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Think outside the BOX!
·
This is actually incorrect. It can still catch fire. The only thing that plenum states is that it won't produce "as much" smoke as pvc coated cables. Exactly how much isn't known. [noparse];)[/noparse] (At least to me, anyways.)
Knight.
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www.powerwerx.com/
If you're looking for a smaller profile, I use the old keyboard style connectors. I'm not sure the amperage ratings, but they are fairly high, probably at least 40-50 watts. Digikey, Mouser, Jameco, just about everyone carries them for decent prices. For this kind of stuff just look around in the digikey and mouser catalogs, there are TONS of connectors with any size power rating needed.
Knight.
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-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=-=-=-=-=-=-=-=-=-=-=-
This message transmitted with 100% recycled electrons.
-=-=-=-=-=-
Gravity doesn't exist. The Earth sucks.
-=-=-=-=-=-
Make a man a fire, and he will be warm for the night.
Light the man on fire, and he will be warm for the rest of his life.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=-=-=-=-=-=-=-=-=-=-=-
So 16.6 * .2A = 3.32 Watts Times 10 = 33.2 watts On the first 5 foot length of wire to the first unit and 3.32 watts less for each of the remaining connections.
We will use 2 wires each for ground and the 16.6V feed
At no time will all of the units receive full power at the same time. I estimate less than 20% of the power will be used on average so this part is done.
I did smoke some resistors (1/4 watt) when my wires from my dual 9V batterys crossed and shorted, (note to self, tape bare wire ends on battery when testing stuff and buy some higher wattage small resistors)
We will be using a self resetting fuse on the main power distribution for short circuit protection.
Hmmm, guess I will add another led and pnp transistor on the power distribution box to show short circuit condition....
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Think outside the BOX!