Quote:
Originally Posted by Al Skierkiewicz
Keith,
The skin effect caused by AC currents in copper wire is about 8.5mm at 60 Hz or about twice the diameter of #10 wire (~4mm). At the switching frequency of the Victor of 150Hz, skin effect is not much different and at full throttle surely does not exist. At 15kHz, (the switching frequency of Jaguars) the skin effect is about the diameter of #17 wire. The difference between solid and stranded conductors is still minimal.
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Who said anything about the switching frequency of the Jaguars? I don't think I did. I'm talking about the variable load presented by the entire robot. I'll tell you what, bet you a dinner (if we are ever in the same town) that I can vary the load (might cost me a motor or 2) in such a way that there is a nice several volt AC signal modulating the DC supply provided by the battery. And that component (if over 400Hz or so) would travel more on the outside of the #6 AWG wire than the inside, more and more the higher the frequency. I never claimed this is a primary or even secondary factor, just something worth knowing about.
And the skin depth numbers you are talking about refer to the depth at which the current density decays to 1/e (0.37) of the surface density. It is a relative measurement and not a threshold, there is not zero decay under that depth. Indeed there is some decay at lower frequencies and with more constant loads (but not with zero load and/or a perfectly static load). We tend to think of the robot as a static system just because it uses a battery as a power source. That is not strictly true, often times not even close.
HTH