4ga. cables. does it matter how many strands?

[JohnnieB]

Gentlemen,

I subscribe to the theory that it is the fluctuations in flux density of the magnetic field surrounding a conductor that causes the skin effect, rather than reversals of that field. Granted, the amplitude of the fluctuation is far greater when the magnetic field reverses, but I believe the skin effect does exist with pulsed DC.

More importantly, there is a consensus of opinion amongst the learned people I have spoken with over the past few days that the total skin effect within cables with stranded conductors is about the same as it is within cables with a single solid conductor, unless the individual strands are insulated from each other.

Therefore, the electrical properties of a 4 Ga cable with single 4 Ga conductor would be approximately the same as a 4 Ga cable whose conductor was made up of 1831 strands of 36 Ga wire. (The difference being in the fact that the combined circular mils of 1831 strands of 36 Ga wire does not equal the circular mils of a single 4Ga conductor.)

This effectively renders whether or not pulsed DC has skin effect, a moot point.

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Of course, a high strand count is still needed for flexibility as well as a jacket material impervious to the acid laden atmosphere in the battery compartment. The lugs should be the closed end type and the gap between the lug and cable insulation should be sealed air tight.

Being old school, I prefer soldered lugs.

[scottyb]

I had to put my tin foil hat on just to read that But I think I agree

[Sergio]

Originally Posted by JohnnieB

........
This effectively renders whether or not pulsed DC has skin effect, a moot point.

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Of course, a high strand count is still needed for flexibility as well as a jacket material impervious to the acid laden atmosphere in the battery compartment. The lugs should be the closed end type and the gap between the lug and cable insulation should be sealed air tight.
.....

Wow, this thread has been all over the place... I just wanted to say that I absolutely agree with both of those two points you made.

[beach cart]

Tin foil didn't even work for this one.

[radioman]

I don't think any possible loss due to skin effect in golf cart applications would make any real difference because a DC motor wouldn't be able to convert the type energy lost to skin effect to produce any work. The whole golf cart system of controlling a DC motor speed with pulsed voltage is inefficient anyway, especially at slower speeds. But I can't think of a better way to do it.

[yurtle]

I've questioned skin effect on non litz cables, but never got a clear answer. I play with 65 kHz and have played with over 100 kHz at hundreds of amps and tens of thousands of volts, where I used hollow conductors, but that's hard to do with flexible cable. Litz will bankrupt you. If your cables aren't getting hot, they're adequate.

[JohnnieB]

Originally Posted by yurtle

..................... If your cables aren't getting hot, they're adequate.

I think you've hit the nail on the head.

Earlier this summer, I made a 13+ mile run, driving my cart as hard and as fast as conditions allowed while logging data from the controller.

The max amps logged was 504A, but my 42V battery pack was loaded down to 39.9V at the time, so only 20.1 kW of energy was passing through the cables rather than the theoretical max of 22.5 kW.

Anyway, the cables/connections were barely warm to the touch and the controller was a little warmer at 106°F, while the motor was hot enough to boil water.

[radioman]

A 2.1 volt drop across your batteries at 504 amps indicate your batteries internal resistance and jumpers have a total resistance of .00417 ohms or a conductance of 239.808 mhos which is very good. A loss of only 1058 watts.

[JohnnieB]

Originally Posted by radioman

A 2.1 volt drop across your batteries at 504 amps indicate your batteries internal resistance and jumpers have a total resistance of .00417 ohms or a conductance of 239.808 mhos which is very good. A loss of only 1058 watts.

It is bit more than a 2.1V drop.
The at-rest voltage on my 42V pack (Seven Exide GC-145 -245AH) is 44.68V at 100% SoC, but I was about an hour into the run, so I had already sucked quite a few AH out of the pack by then.

A few seconds prior to the 39.9V/504A data point, the throttle position was -0- and the voltage was 42.5V, so you numbers are probable very close to reality.

The lowest under load voltage I recorded on that trip was 35.5V (1.69VPC), but that was near the end of the 1 Hour 40 Minute trip and I was on a long uphill climb. I was only drawing about 250A at the time, so the motor's energy input was about 12HP.

I've got to figure out a way to monitor and record the Armature and Field Amps and Voltage along with battery pack Amps and Voltage. Monitoring is just a matter of connecting some ammeters and voltmeters, but recording it is going to be a bear. Data loggers would break my limited budget while taking a video of the readouts and copying the frame by frame info into a spreadsheet sounds like too much work.

[yurtle]

Originally Posted by JohnnieB

I think you've hit the nail on the head.

Dang. I guess the sun really does shine on a dog's arse every once in a while.