On 10/5/19 1:41 PM, Jan Steinman via EV wrote:
From: Lee Hart <leeah...@earthlink.net>
"wireless charging" is fundamentally just a transformer.
With an extremely lossy core!
It's been decades since I worked in RF engineering, but they don't change the
laws of physics very often.
Electromagnetic coupling between two coils depends on the frequency of the
signal being propagated, proximity of the coils, and permeability of the
material between the coils. All three factor seem to be challenged in
rapid-charging EV batteries.
Frequency is at odds with high currents, which means larger conductors, which has a "skin
effect" at higher frequencies. Proximity is an obvious problem with contactless charging,
unless one coil is inserted into another, which sorta loses the main advantage of
"contactless." And the permeability of iron is about 1,000 times more than that of
nitrogen (the major component of air), which is actually an inhibitor — you're better off using a
vacuum than nitrogen!
So, how does modern "contactless" high-power charging work? Seems like an intractable
design problem to me! I'm guessing it involves "contact" between hefty iron cores at
moderate frequencies. But I admit, I don't know.
Jan
Not lossy at at all. This is a focused magnetic flux, which is captured
by litz wires on top of ferrite. The efficiencies (plug to battery) are
between 92 and 93%. Best I've seen for conductive charging is 96%.
They are using several different frequencies for different solutions:
85 kHz for small autos, 20 or 40 kHz for larger truck chargers.
For how this is working, check out the website I posted earlier.
Cheers, Peter
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