How much current/power though a specific cable??

[capetonian]

Hi guys,

I have a question. I am looking at options for connecting my MIP to my Overhead. I need to run power from my pc powersupply, mounted on the MIP to the Overhead. I want to do several things:

Power Supply on/off (green)
Ground wire (black)

5v+ (red)
Ground (black)
12v + (yellow)
Ground (black)

That's 6 wires. I know that I can use one ground for both the 12v and the 5v rail but I would prefer each to have it's own ground cable.

I have been looking at what kinds of cable I can use, I will be connecting the cable to both the MIP and overhead with a 7pin DIN plug and chassis mount socket on both the MIP and the Overhead.

I was thinking of using an old VGA cable as it has about 13 wires in it or, and my preference goes out to this one, a serial cable. Inside an old 25 pins serial/parallel cable there are 25 wires plus an unshielded ground cable. Can I pump 12v and 5v down a cable like this or is that asking for problems? I am not too up to speed on electronics and stuff so I'd rather ask a question screw up something.

Thanks in advance for your input.

Andrew.

[Sean Nixon]

http://en.wikipedia.org/wiki/RS-232#Voltage_levels

[capetonian]

Thank you Sean,

I honestly did not think about looking at WikiP first. Well, that answers my question, up to v25+. That makes life a whole lot easier. And since I have 25 wires to play with I might use the other wires and switch my Sixpaxk and Caution lights from my overhead setup .... hmmm .... Building a cockpit is so much fun!! :)

[fordgt40]

Andrew

The key factor here is what current are you expecting to draw and what is the diameter of the wire. There are other factors such as voltage drop across long distances. If in doubt, and you have a meter, then measure your current drain. It might be surprising, particularly on the 5v rail. On my 12volt feed to the overhead, I use nearly 3 amps alone for backlighting. Also you should check the current rating of your connectors. This link will provide some help

http://www.emrg.ca/dc_wiring.htm

Regards

David

[fordgt40]

Andrew

I have just seen your latest post. Please be careful here, with due respect to the link that Sean provided, the information re RE232 standards is related to largely digital signals/protocols. You must establish the likely current drain and then choose the cable - else it could get very hot indeed!

Regards

David

[flatlandpilot]

http://www.epanorama.net/documents/wiring/wire_resistance.html

fuserate of some cables:

Cross- Overload
sectional current
area rating

0.5mm² 3A
0.75mm² 6A
1mm² 10A
1.25mm² 13A
1.5mm² 16A

using fuses to protect youre power supply and wiring, is a good thing.
big currents in case of a short circuit over a thin wire is not (fire) save.

the power lost (heating) in the cable P = I^2 * R

[capetonian]

Thanks for the information everyone...

I need to det to grips with this stuff. Backlighting is not going to happen with Version of the Overhead so I don't have to worry about that at the moment.

[Sean Nixon]

http://www.epanorama.net/documents/wiring/wire_resistance.html

fuserate of some cables:

Cross- Overload
sectional current
area rating

0.5mm² 3A
0.75mm² 6A
1mm² 10A
1.25mm² 13A
1.5mm² 16A

using fuses to protect youre power supply and wiring, is a good thing.
big currents in case of a short circuit over a thin wire is not (fire) save.

the power lost (heating) in the cable P = I^2 * R

Whilst I'm not desputing that all electrical circuits should be designed carefully, the above is aimed at mains voltages (220-240v AC). Your not going to get into too much trouble at 12v DC (other than continuous fault finding). You certainly won't catch fire.

Having said that, the RS232 serial cable is probably not a good choice for drawing much current throught it. It will work, but I'm not sure how much you could run off it.

Sean

[fordgt40]

Whilst I'm not desputing that all electrical circuits should be designed carefully, the above is aimed at mains voltages (220-240v AC). Your not going to get into too much trouble at 12v DC (other than continuous fault finding). You certainly won't catch fire.
Sean

Try telling that to my wife! There is a big (in my wifes eyes) burnt section in our dining room carpet caused by an accidental short on a 5 volt supply from a pc - its not the voltage but the current that kills. Mind you, I should have used a fuse!!

Regards

David

[Sean Nixon]

Try telling that to my wife! There is a big (in my wifes eyes) burnt section in our dining room carpet caused by an accidental short on a 5 volt supply from a pc - its not the voltage but the current that kills. Mind you, I should have used a fuse!!

Regards

David

LOL!

Still, 5v DC is not going to kill you.

[flatlandpilot]

the heat in the wire = I^2 * R
(and is not "aimed" at 220v, the formula works with all voltages)

[Sean Nixon]

I was suggesting that the link in your post is not that relevant to the posters original question, that's all.

[capetonian]

No please .... feel free to elaborate on this as much as you all want , ... all info is welcome and interesting

[fordgt40]

Andrew

Now see what you started! LOL

But as you say, it is all knowledge

Regards

David

[flatlandpilot]

in the question was asked for "current/power"

The maximum current for a certain cable is:


0.5mm² 3A
0.75mm² 6A
1mm² 10A
1.25mm² 13A
1.5mm² 16A

you can make the current to power conversion like this: P = I * V
So the maximum power a 1mm² wire can carry at 12V is 120W.

When using a power supply bigger than lets say 10 A (12V)
every wire has to be 1mm² or better else you damage youre wiring
in case of a short circuit, for this reason it's better to use fuses.

flatcables and flatcableconnectors are usually rated for 1A.