David Kerzel wrote:
The concern about a DC high current circuit breaker is the maximum
interrupting current at the operating voltage. If a fault or a turn-off
happens under load there will be an arc. The speed the contacts open,
possibly a magnetic arc deflector all determine if the arc will maintain or
be broken. If it is maintained the circuit is still closed by plasma inside
the breaker.
If the short circuit current of your battery system is less than the maximum
interrupting current the breaker, preferably less than half, and the nominal
voltage is under the breakers rating, it is properly applied.
I.e. it WILL successfully open, and stop the current, as long as it is
operated within ratings.
Unlike a relay, there is a lot of opening and closing force in a circuit
breaker and they are designed to protect the circuit even if they are
destroyed.
Yes. A good circuit breaker is designed to ALWAYS fail open, even if it
is destroyed in the process. A switch or contactor can fail with its
contacts welded closed. But a circuit breaker (or fuse) will always fail
open. You pay big money for them to guarantee it!
However, this rule is broken if you ask it to interrupt too much voltage
and too much current at the same time. The exact border is somewhat
fuzzy. As you go higher in voltage, you have to considerably reduce the
current it is asked to interrupt.
By the way: You may not think your batteries can supply over 1000 amps.
But remember that they also have significant capacitance. You also have
many thousands of microfarads of charged low-resistance capacitors in
the controller. These capacitors can supply much higher peak currents
than the batteries alone. So the peak current for a few milliseconds can
be extremely high.
When a breaker or fuse interrupts it maximum current and voltage (like
160vdc at thousands of amps!), all hell breaks loose inside it. Much of
the insides are vaporized, and white-hot plasma shoots out of every
opening. Do *not* mount them in a location where this plasma can set
fire to surrounding materials!
Always remember Murphy's Law: A fuse will only protect something only if the
fuse costs more than what it protects.
Ain't THAT the truth! :-)
--
For every complex problem, there is a solution that is simple, obvious,
and wrong. -- H.L. Mencken
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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