George Tyler via EV wrote:
An alternator is very different to a Dc-Dc converter in this respect. Modern
high frequency DC-DC conv. Have very small inductors storing very little
energy. An Alternator has a HUGE inductor storing a lot of energy, and this
is not on the output but in the control side! So has much more effect! You
won't get much overshoot from the DC-Dc converter.
Yes, a DC/DC is different; but the same principles apply. An alternator
has no output filter caps, but has lots of inductance. When you
open-circuit it, you get a tremendous voltage spike.
A DC/DC has negligible inductance, but huge output filter capacitors.
When you short it, you get a huge current spike. Since there is always
wiring inductance, this high current "charges" the inductance. When the
short suddenly goes away, you still get a huge voltage spike.
Suppose something momentarily shorts the DC/DC output, and its
capacitors deliver a peak current spike of 1000 amps; which almost
immediately burns out the short. The wire between the DC/DC and that
short has a mere 1 microhenry of inductance. V = L x di/dt. 1 uH x 1000a
/ 1usec produces a 1000 volt spike.
Lee
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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