Will an 18 AWG aluminium wire carry 5A of 12VDC?

[nyoo]

This is a beginner asking, and it feels like a general question. If it should be in another forum, please let me know.

I have a 250W computer power supply unit. It advertises 13A on its 12VDC rail. Most of the 12VDC wires coming out of the PSU are 18 AWG aluminium, with 30-35 strands in the bundle.

I'd like the PSU to power a 2.1A 12VDC pump. Through some primitive op-amp control logic. The pump has a starting surge of 5A.

The Handbook of Electronic Tables and Formulas, quoted at American Wire Gauge table and AWG Electrical Current Load Limits, gives "very very conservative numbers for power transmission", based on 700 circular mils per amp. For solid copper AWG gauge 18, maximum amps for power transmission are 2.3.

Now, I have seen 18 AWG copper wire claiming anywhere from 5.4A to 16A, never as low as 2.3A.

For 12VDC work, what is your experience? Will 18 AWG stranded aluminium wire support a sub-second surge of 5A, and normal running of 2.1A?

Thanks very much for your help.

 

[crutschow]

If you go to the bottom of your referenced page there is a voltage drop calculator which can be used to determine the resistance of Al wire. The resistance of 18 AWG Al wire is about the same as 21 AWG copper wire. Based upon this, the maximum recommended steady current for chassis wiring would is 9A, which is applicable to your useage.

18 AWG Al wire has a resistance of .013Ω/ft. so you may need to take that into account for the voltage drop generated by longer wire runs.

 

[Hero999]

Are you sure it's aluminium wire?

It's probably tinned coper which is silver coloured and looks like aluminium.

Sizing cables isn't as easy as you might think. The maximum current rating depends on the acceptable voltage drop and the temperature rating of the surrounding insulation and material. The voltage drop is fairly easy to calculate using Ohm's law but the conductor temperature is much harder because it depends on how well the heat can escape.

Here in the UK we measure wire sizes i by their crossectional area, mm². Calculated using the values in your table 18AWG is about 0.82mm² and the maximum current is listed at 16A.

No mention is made of the ambient temperature, the temperature rating of the insulation and other influencing factors such as the number of neighbouring conductors and surrounding material.

Assuming an ambient temperature of 30°C and an insulation temperature rating of 70°C and the conductor is in free air 16A sounds far too high. From memory the maximum sized fuse you're allowed to use for flexible 0.75mm² PVC cable is 5A, 16A flexible cable is normally 1.5mm².

 

[nyoo]

Chassis wiring, and not power transmission, is applicable to pumps? That's good to know.

The wire is flexible, not brittle, so it could very well be tinned copper. If it's tinned, though, it's tinned the whole length of the wire. When I said "aluminium", I was going naively by the silver colour.

From both your discussions, it sounds like my plan would not be a gamble, long term. I'll do it. Giving the PVC insulation as much breathing space as possible. The PSU wiring, by the way, will be barely a foot in length.

Many thanks.

 

[Hero999]

Chassis wiring, and not power transmission, is applicable to pumps? That's good to know.

That's right the application isn't important.

P = I²R is true however the cable is used.

The wire is flexible, not brittle, so it could very well be tinned copper. If it's tinned, though, it's tinned the whole length of the wire. When I said "aluminium", I was going naively by the silver colour.

Some aluminium alloys are quite flexible but it does sound like coper wire to me and it is normal to tin it through the entire length.

From both your discussions, it sounds like my plan would not be a gamble, long term. I'll do it. Giving the PVC insulation as much breathing space as possible. The PSU wiring, by the way, will be barely a foot in length.

Many thanks.

That sounds sensible to me, it should be able to carry 2A continuous and 5A peak with no trouble.

 

[GonzoEngineer]

Just hook the damn thing up......if the wires get hot you have a problem.

If they don't get hot.....no problem!

Seriously.....a computer power supply has copper wire....and they say it can deliver a certain number of Amps, they mean that the wires coming of it are also good for that same power!

Just duplicate the wire gauge of the power supply and you are good to go.

 

[Leftyretro]

This is a beginner asking, and it feels like a general question. If it should be in another forum, please let me know.

I have a 250W computer power supply unit. It advertises 13A on its 12VDC rail. Most of the 12VDC wires coming out of the PSU are 18 AWG aluminium, with 30-35 strands in the bundle.

I'd like the PSU to power a 2.1A 12VDC pump. Through some primitive op-amp control logic. The pump has a starting surge of 5A.

The Handbook of Electronic Tables and Formulas, quoted at American Wire Gauge table and AWG Electrical Current Load Limits, gives "very very conservative numbers for power transmission", based on 700 circular mils per amp. For solid copper AWG gauge 18, maximum amps for power transmission are 2.3.

Now, I have seen 18 AWG copper wire claiming anywhere from 5.4A to 16A, never as low as 2.3A.

For 12VDC work, what is your experience? Will 18 AWG stranded aluminium wire support a sub-second surge of 5A, and normal running of 2.1A?

Thanks very much for your help.

Some good information and advice given above. Just as a side bar, wire current specification is all about the wire gauge, it's material, length and frequency of operation if in AC service. Voltage specification on the other hand is all about the insulation used to cover the wire. The wire cares not about the voltage, just current, but the insulation most certainly does as well as the amount heat being generated by the voltage drop in the current carrying wire. 12vdc is a easy specification for any common insulation material.