I should add that my comments are in no way a reflection on the quality of
Airpax products. We used Airpax breakers almost exclusively in the
Apollo/Saturn program for both flight vehicle use and ground support equipment
applications. Airpax breakers are definitely "top-drawer" components.
> From: n4uc@hotmail.com
> To: tentec@contesting.com
> Date: Tue, 14 Dec 2010 10:18:41 -0600
> Subject: Re: [TenTec] Airpax Breaker Part and Source
>
>
> Yes they do, but you have to look past the marketing and look at the data
> sheet. According to the trip curve for their "instant" breakers, the typical
> operating time for current of 2X the breaker rating is just over 100
> milliseconds, where the "non-instant breakers can hang in for over a second
> at the same current. Definitely faster, but far from "instant". In fact the
> fastest time they are guaranteed to operate is 10 milliseconds and that's at
> currents at least 8 X the breaker rating (i.e. 160A for a 20A breaker).
>
> > From: Mike_N4NT@charter.net
> > To: tentec@contesting.com
> > Date: Tue, 14 Dec 2010 10:49:16 -0500
> > Subject: Re: [TenTec] Airpax Breaker Part and Source
> >
> > Airpax calls some models "instant," don't they?
> >
> > ----- Original Message -----
> > From: "art davis" <n4uc@hotmail.com>
> > To: "TenTec reflector" <tentec@contesting.com>
> > Sent: Tuesday, December 14, 2010 1:24 AM
> > Subject: Re: [TenTec] Airpax Breaker Part and Source
> > >
> > > I'm no expert, BUT...
> > >
> > > be very careful with the use of the term "instant trip" when referring to
> > > a circuit breaker or fuse. All circuit protection devices take a finite
> > > amount of time to operate, no matter what type they happen to be. Look at
> > > the response curves (i.e. trip curves) for any breaker or fuse and you'll
> > > see that it may be very quick indeed (less than a millisecond in many
> > > cases) if the fault current is high enough, but not "instant". And in the
> > > world of semiconductors very quick might not be fast enough. And look at
> > > the curves to see the level of current that can flow through the device
> > > without it tripping at all. You might be surprised. I may be wrong but I
> > > doubt that there is any circuit breaker on the market that, when located
> > > upstream at the power supply, can operate fast enough to protect
> > > semiconductors from damage due strictly to overcurrent. If the fault
> > > current is high enough (many times the circuit breaker rating) they may
> > > offer some limited protection from the heat generated
> > > by the overcurrent flowing through the device, but the semiconductor
> > > itself must be capable of surviving the current in the first place.
> > >
> > > The primary reason to specify different response time characteristics
> > > (trip curves) for circuit breakers (slow blow, fast, etc...) is to make
> > > sure that the power feeder circuit maintains proper trip coordination
> > > among the various circuit protection devices in the circuit in case of a
> > > fault in the wiring upstream of the load. In most power distribution
> > > systems the fuses and circuit breakers upstream of an end user (i.e.
> > > radio) are there only to protect the wiring between the power source and
> > > the load. The load (in this case, the radio) must protect itself
> > > internally. My guess is that there could be significant damage done
> > > inside a transceiver long before a 20A breaker all the way back at the
> > > power supply knew what was happening.
> > >
> > > Of course, the flip side to all this is that it couldn't hurt, right? You
> > > certainly won't have any protection if you don't use something, so put
> > > the
> > > fastest breaker in there that you can find and keep your fingers
> > > crossed!
> > > Just don't call it "instant"
> > >
> > > Art, N4UC
> >
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|