# RJ45 Connections



## spinman1949 (Jun 29, 2009)

So I made these nifty little boards made from little conversion boards I got from Spartfun. They take the odd pin pattern to a straight 8 pin connection perfect for a circuit board. When I looked at the traces on the board they appeared pretty small. Of course usually an ethernet connection carries very little current. So Halloween night my Tot Greeter worked perfect. Some after Halloween testing showed evidence of some damage though. Got a stripped tooth in the horiz eye servo. Not sure how that happened. But as I was testing, all of a sudden I have nothing. No servo's, no LED's, nada. What a pain to try to unsolder the RJ45 connector. Note to self. Get solder sucker or solder braid. Well I was correct. The trace on the positive on the board in the skull is open. Likely others have discovered this and make their own trace for the positive and negative to handle the current. Just thought I would pass on as a FYI.


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## HomeyDaClown (Oct 3, 2009)

spinman1949 said:


> Likely others have discovered this and make their own trace for the positive and negative to handle the current. Just thought I would pass on as a FYI.


I've used those SparkFun RJ45 breakout boards also but only for data. I guess you could double up on the wires to run power but I prefer to run two separate heavy power leads alongside the CAT-5 since a single servo can draw more than 1 Amp of current. What you have to watch for is when multiple servos are moving, they can pull a lot of current. Some have used a second CAT-5 cable with four wires tied to ground and four wires tied to V+. Even then a single 24 gauge wire is rated less than 600 milliamps capacity and thin PC board traces become fuses.


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## spinman1949 (Jun 29, 2009)

*Makes sense !!*

Homey,

Now that I think about it, it is really incredible they did not fail right off the bat. 6 servos running off that tiny thin trace. Not to mention eight led's. I sent a message to Sparkfun asking if they could beef up the traces on pin #1 and #4 since they match up well to the ssc32 board. I am going to run an external trace for these pins.

I think using the counter springs helped reduce the load. Still amazed they lasted well over 200 50 second routines.


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## HomeyDaClown (Oct 3, 2009)

spinman1949 said:


> Homey,
> 
> Now that I think about it, it is really incredible they did not fail right off the bat. 6 servos running off that tiny thin trace. Not to mention eight led's. I sent a message to Sparkfun asking if they could beef up the traces on pin #1 and #4 since they match up well to the ssc32 board. I am going to run an external trace for these pins.
> 
> I think using the counter springs helped reduce the load. Still amazed they lasted well over 200 50 second routines.


The servos would have to be under a load and firing simultaneously to pull the maximum current but it is always good to design for that. It is more likely that the trace was getting warm all along until it was pushed over the edge by a current surge. The hotter the trace gets the more resistance it has and more current it draws kind of a self destruct feature. This even happens in house wiring where the copper lead has been kinked or bent sharply and unfortunately can cause a fire.


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## spinman1949 (Jun 29, 2009)

*Heat degradation.*

Yup heat means resistance which means more current, which in turn creates more heat. Vicious circle in the land of conductance.

My routine had all 6 servos involved at times. I think for next year where I expect to have 3 axis units at various locations, that I will put battery packs at the unit for power to the servos.


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## spinman1949 (Jun 29, 2009)

*Update*

I wired some 22 guage wire as jumpers on the two RJ45 connectors. I actually jumped from the wires that are exposed running down the front of the connector to the solder points where the sparkfun board is soldered to the interface board. Bypassing the traces is the result. Wow what a difference ! The servo's respond much quicker and the led array's only dim slightly in conjuction with the jaw movement. So my entire unit was current starved no doubt. Live and learn.


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## fritz42_male (May 5, 2009)

Just one thing to bear in mind. When it comes to current capacity, it's the surface area that counts. A decent sized trace can carry a fair amount of capacity compared to a wire. I remember being taught this ages ago by a tutor - he used to rail against people who would bypass fuses with silver cigarette paper - he showed the students how bypassing a blown 13A fuse with this stuff could be fatal. We did a test and the silver paper carried 40+ amps before starting to burn.


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## fritz42_male (May 5, 2009)

Oh, for anyone interested in lighting or prop control, I'm playing with some 4 output SSR boards from the group buy on DIYXMAS - I plan to use these to control 240V pneumatics on next years props. The Sparkfun breakout board is ideal for the controller end of the setup. No current capacity issues with what I'm doing as the SSR boards pull 30mA for the trigger!


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## spinman1949 (Jun 29, 2009)

*240 Volt ?*



fritz42_male said:


> Oh, for anyone interested in lighting or prop control, I'm playing with some 4 output SSR boards from the group buy on DIYXMAS - I plan to use these to control 240V pneumatics on next years props. The Sparkfun breakout board is ideal for the controller end of the setup. No current capacity issues with what I'm doing as the SSR boards pull 30mA for the trigger!


Fritz,

Typo? 240 volt pneumatics. Thats one powerful solenoid !!!


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## spinman1949 (Jun 29, 2009)

fritz42_male said:


> Just one thing to bear in mind. When it comes to current capacity, it's the surface area that counts. A decent sized trace can carry a fair amount of capacity compared to a wire. I remember being taught this ages ago by a tutor - he used to rail against people who would bypass fuses with silver cigarette paper - he showed the students how bypassing a blown 13A fuse with this stuff could be fatal. We did a test and the silver paper carried 40+ amps before starting to burn.


This is really good to know. So for instance if you take a piece of copper wire and flatten it to say 5 thousanths of an inch thick which is paper thin, it will still conduct the same amount of current. So can we assume that many of the descriptions of electricity traveling down a wire are invalid? IE it is common for such graphic descriptions to show electrons bouncing within the confines of the wire. Your description would indicate the electrons travel on the surface of the wire. Would a piece of copper tubing provide the same conductance as a piece of copper wire the same diameter? Or is the area you refer too, the entire area as in volume of the wire?

Inquiring minds or in my case half minds want to know. LOL !!!


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## fritz42_male (May 5, 2009)

As far as I am aware, copper tubing would actually have a higher current rating than a wire of the same diameter due to the higher surface area (outside surface and inside surface). However, I'd like to check up on this and to make sure what I said was accurate - my tutor was good but did occasionally make mistakes.

I'll ask my sister - she has a BSc and Phd in high energy physics!


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## fritz42_male (May 5, 2009)

spinman1949 said:


> Fritz,
> 
> Typo? 240 volt pneumatics. Thats one powerful solenoid !!!


Nah not really, just a low current rating. Sometimes easier to get stuff like this in Oz than 12 and 24V solenoids.


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## spinman1949 (Jun 29, 2009)

*cryogenic cooling*



fritz42_male said:


> As far as I am aware, copper tubing would actually have a higher current rating than a wire of the same diameter due to the higher surface area (outside surface and inside surface). However, I'd like to check up on this and to make sure what I said was accurate - my tutor was good but did occasionally make mistakes.
> 
> I'll ask my sister - she has a BSc and Phd in high energy physics!


I would think that if tubing provided a higher level of conductivity it would be a natural for cryogenic cooling which of course can bring resistance down to nearly zero.

I found this link which may clear things up a bit.

http://www.allaboutcircuits.com/vol_1/chpt_1/2.html

I wonder if your tutor was elluding to the possible aspect of the number of free electrons increases as well as the available paths for them to flow as the diameter of the wire increases. The way the above link describes conductivity, it seems to me that the electrons flow through voids in the conductive material. Since air is an insulator, I would suspect a tube would provide less conductive material and thus not be as efficient based on diameter as a solid wire of equal diameter.


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## bradbaum (Jul 26, 2008)

I was always told stranded wire could carry more current then solid of the same gauge.

And it had to do with surface area.

However, stranded wire and a tube are two different things.


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## spinman1949 (Jun 29, 2009)

*Stranded wire.*

Hmmm ? Perhaps electrons flow with less resistance as they approach the surface of the conductor. That would explain your statement. Many small wires would likely provide more surface area than one large wire.

Interesting !


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## HomeyDaClown (Oct 3, 2009)

spinman1949 said:


> Hmmm ? Perhaps electrons flow with less resistance as they approach the surface of the conductor. That would explain your statement. Many small wires would likely provide more surface area than one large wire.
> 
> Interesting !


Electrons flow on the surface of a conductor and since stranded wires have more surface area than the same gauge solid wire, they carry more current. To electron flow, solid copper wire is the same as very thin walled copper pipe of the same diameter. In in practical applications, the current carrying capability of solid versus stranded wire is negligible. Surface effect has little impact on DC. At high frequencies though, skin effect has big impact.


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## spinman1949 (Jun 29, 2009)

*Deeper answer.*



HomeyDaClown said:


> Electrons flow on the surface of a conductor and since stranded wires have more surface area than the same gauge solid wire, they carry more current. To electron flow, solid copper wire is the same as thin walled copper pipe of the same diameter.


Homey,

Your answer has an aspect of truth, but I believe this explains with more detail. The flow of electrons migrate out to the skin or surface of the conducter as Frequency increases. This is not the case it would appear with 60 cycle AC circuits. Of course this is a WIKI response.

Do electrons flow on the outside of a wire rather than through it?
In: Science, Physics, Chemistry, Wiring and Electricity [Edit categories]

Normally, no. But at really high frequencies they do. 
As we increase the frequency in AC (alternating current), the current begins to shift from an "evenly distributed" flow to something else. The center of the conductor will begin to carry fewer electrons and the outer surface or "skin" of the conductor will begin to carry more. It isn't surprising that we call this phenomenon skin effect and we see it in high frequency applications. In really high frequency circuits, particularly high power circuits, we see "wire" being substituted with a wave guide to carry the high frequency, high amperage currents used in applications like radar. The household microwave oven uses a waveguide to carry the power into the cavity where it heats what you put in.

For anything the AC power grid, which works at about 60 cycles per second (60 Hertz) in America, there isn't a substantial problem with this phenomenon. A link is provided to the Wikipedia article on skin effect.

I would imagine that since frequency is a part of this skin effect, that DC circuits are not included in this flow issue. Thus unless other proof can be provided, I believe that if a piece of copper tubing is matched against a piece of copper wire of equal diameter, the wire will prove to capable of providing a higher current flow based on equal voltage input and equal load.


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## HomeyDaClown (Oct 3, 2009)

Surface area is the electron conducting zone; or, the outside and the inside surface is the only place the valance electrons are released by the copper atoms to move and attach to neighboring atoms.

At high frequencies, a conductor has both a resistance property and a self-inductance that oppose current flow, this self-inductance is referred to as skin effect. 

Skin Effect:
The apparent resistance of a conductor is always higher for alternating current than for direct current. The alternating magnetic flux created by an alternating current interacts with the conductor, generating a back e.m.f. which tends to reduce the current in the conductor. 

For a given cross-sectional area the skin effect ratio for a thin copper tube is appreciably lower than that for any other form of conductor. Copper tubes, therefore, have a maximum efficiency as conductors of alternating currents, particularly those of high magnitude or high frequency.

That's why copper bus bars (copper pipes or groups of copper plates with spacing) are used for large industrial applications. A conductor will fail (as you have seen) when the current running through it generates enough heat to melt the conductor, copper bus bars are easily cooled.

These things can also influence pulsing DC in much the same way (pulse width modulation used in DC motor speed controls).

You'll just have to build a few thousand skulls, grab a huge power supply and do some testing


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## spinman1949 (Jun 29, 2009)

*That is more detail.*



HomeyDaClown said:


> Surface area is the electron conducting zone; or, the outside and the inside surface is the only place the valance electrons are released by the copper atoms to move and attach to neighboring atoms.
> 
> At high frequencies, a conductor has both a resistance property and a self-inductance that oppose current flow, this self-inductance is referred to as skin effect.
> 
> ...


Homey,

I asked for more proof and you provided it. I do find it interesting that much of the descriptions of electron flow indicate that electrons flow throughout the conductor. Perhaps many explanations are designed as a generic description and not intended to get to the depth that you have provided.

So bottom line. If I take a 14 guage piece of common household copper wire and hook it up to a load utilizing 24 volt DC. IE a motor. And then take a piece of copper tubing the same diameter as the 14 guage wire and hook it to another motor of the same HP rating, I will see a higher stall torque from the motor attached to the copper tubing. This of course presumes that the molecular structure of the tubing and the wire match, and that both circuits are provided with an identical rated power source.


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## bradbaum (Jul 26, 2008)

I believe this to be true, but the the difference will be so minimal that you probably won't see the difference.


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## HomeyDaClown (Oct 3, 2009)

spinman1949 said:


> Homey,
> 
> I asked for more proof and you provided it. I do find it interesting that much of the descriptions of electron flow indicate that electrons flow throughout the conductor. Perhaps many explanations are designed as a generic description and not intended to get to the depth that you have provided.
> 
> So bottom line. If I take a 14 guage piece of common household copper wire and hook it up to a load utilizing 24 volt DC. IE a motor. And then take a piece of copper tubing the same diameter as the 14 guage wire and hook it to another motor of the same HP rating, I will see a higher stall torque from the motor attached to the copper tubing. This of course presumes that the molecular structure of the tubing and the wire match, and that both circuits are provided with an identical rated power source.


Exactly, and if you were to draw more than it's maximum current capacity, you could pump some air or better yet liquid nitrogen through the copper pipe greatly extending it's capacity by reducing heat. Can't do that with wire unless you surround it with a pipe. But over long runs copper wire adds a strength component to the game and I would think it is less expensive to manufacture wire than pipe.


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## spinman1949 (Jun 29, 2009)

*Cryogenics*



HomeyDaClown said:


> Exactly, and if you were to draw more than it's maximum current capacity, you could pump some air or better yet liquid nitrogen through the copper pipe greatly extending it's capacity by reducing heat. Can't do that with wire unless you surround it with a pipe. But over long runs copper wire adds a strength component to the game and I would think it is less expensive to manufacture wire than pipe.


I would think that long distance transmission would warrant this tubing or buss approach. Of course there is the issue of insulation from ground when high voltage is transmiited subterra. And above ground tubing would likely collapse from its own weight unless some fairly high pressures of cryo fluid were maintained in the tubing.

Talk about a thread going well beyond the original discussion. From MA to Mega Watts. LOL !!!


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## fritz42_male (May 5, 2009)

OK, the answer IS to do with heating - here's the question I asked and the reply from my sister:

ME: Quick question - I remember being told that in a conductor, the current carrying capacity is based on surface area of the conductor NOT the diameter of the wire - is this correct? This is why a flat piece of thin foil carries more current than the same amount of metal as a wire?

SISTER: In that it is to do with how much heat it can radiate without melting yes. Since resistance is inversely proportional to cross sectional area, and heat produced depends on resistance, and a flat sheet has a larger surface compared with a cylindrical wire, the sheet will get less warm so can carry more!

Incidentally, from what I remember of high voltage cabling, you usually find that you have the current carrying core of copper or aluminium surrounded by high tensile steel cable to provide the strength. Copper is very ductile and will stretch and distort if tension is put on it so the steel core is there to stop the cables from sagging.


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## HomeyDaClown (Oct 3, 2009)

fritz42_male said:


> Incidentally, from what I remember of high voltage cabling, you usually find that you have the current carrying core of copper or aluminium surrounded by high tensile steel cable to provide the strength. Copper is very ductile and will stretch and distort if tension is put on it so the steel core is there to stop the cables from sagging.


I once worked at a manufacturer of that cable (the now defunct Copperweld Steel) and still have a roll of it around here somewhere. It's the same diameter as #12 copper wire but very strong. The copperweld wire I have has a steel core with a copper skin.


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