=>Now that is what I call a cable!

[Bison_69]

The cable is an AmerCable’s 2000V Diesel Locomotive Cable (DLO) on a single conductor.
We used this type of flexible cable at work to assemble power drive systems for our marine applications.
(see the enclosed pdf spec. sheet)

[CamLight]

Perfect! I've been wanting to lower the resistance of my cabling and I just got a shiny, new 15W Radio Shack soldering iron.
I can use that for soldering 1111kcmil leads to my controller, right? The cable brochure says "Extremely flexible stranding used for
increased flexibility and ease of installation" so it must be easy to solder.

[Edit] It worked! I was able to use my 15W iron to solder on those almost-2" diameter cables but they're finally on. I had to sit there for over 30 hours until the iron heated the cable up enough.

Oh, and I had to use 2 spools of solder.

And the controller weighs 8 pounds more.

And I can't find connectors for 1111kcmil cable to hook them up to my motor.

Hmm...perhaps I can drill 2" holes into the motor casing and just replace the existing wire! Yea, that will work. I don't think it will take longer than 40-50 hours before my iron can heat up those connections. Time to buy some more solder!

[John in CR]

It looks good, but I bet it costs a lot more than the 90°C rated wire 6awg I picked up at the hardware store for about $2/meter. It's thick stranded, but I like my high power wires to stay in place, so stiff is fine. At what electrical rpm do we need to start worrying about skin effect on our phase wires?

John

[texaspyro]

A friend of mine built some jumper cables out of started cable used for tanks. The stuff was huge, weighed a ton, but was as flexible as wet spaghetti. The conductors looked like litz wire.

[lazarus2405]

At what electrical rpm do we need to start worrying about skin effect on our phase wires?

Math to the rescue!

Let's say we're pretty conservative and say you want your wire radius r to equal skin depth δ, so that current density in the very center of your wire is still ~.37 (1/e) what it is on the outside of the wire. It's more or less an approximation for at what point skin effect starts to manifest itself; below that point the difference between any AC and DC resistance due to skin effect would be immeasurably small.

In my case I use 10AWG stranded THHN from the hardware store for my phases, which we can approximate as a solid wire since the strands aren't insulated from each other. Diameter D of that conductor is ~2.6mm, so let r=δ=1.3e-3m

δ is approximated by sqrt(2*ro/(omega*µ)), where ro is the resistivity of the conductor, omega the angular frequency, and µ the magnetic permeability. For copper, ro=1.68e-8Ω*m and µ=1.25e-6H/m. Solving for frequency, omega=2*ro/(µδ^2). Omega is just 2π*f, so f=ro/(πµδ^2)

Plugging in numbers, f=(1.68e-8)/(pi*1.25e-6*(1.3e-3)^2), f=2.57e-3=2.57KHz, or about 150,000 electrical RPM - 150k! You would see a 10% increase in resistance at about 5.4khz (~325k ERPM). For a point of reference, a 5300 (12 poles) in a 20" wheel at 50mph will run at 10k ERPM. If you put a BMC in the same wheel and the same speed, you're looking at ~67k ERPM. Hell, you have to pay extra for a special firmware to get a Kelly controller to handle that. So at full speed, there is no reasonable hub motor setup that could possibly make us worry about skin effect in our phase wires, at least from commutation from one phase to the next at cruising speed.

One possibility, though, might be at low speeds under high-frequency PWM. I don't know how most other controllers switch, but Kellys' FET choice and driver circuits seem to be optimized for fast switching (as opposed to low Rds), and they claim a 16KHz operating frequency (and imply it has something to do with higher efficiency). Maybe at that frequency it makes a difference - in 1 meter of 10AWG at 100 amps and 16.6KHz, the increase in effective resistance from skin effect would cost you ~19w over the length of that wire, which if you think about it is a lot of heat in a wire, but not even worth thinking about when you're throwing 100a into a hub for a few seconds at a time. But I don't know enough about controllers and switching and PWM to know if "operating frequency" necessarily has anything to do with the frequency of current in the phase wires.