Jos Okhuijsen wrote:
>
> We can't rely on the pump's CB to trip (a fast-acting fuse i
>
> And the non-technical assuming continues as happy as before. . Why
> cant's we rely on the pump's CB?
It comes from a Potter & Brumfield data sheet for its popular relay sold
by AC&S and Wicks. The only case which will cause the thing to pop
quickly is an amp draw assumption that appears (simple Ohm's Law math)
can never happen in the scenario here.
>>supply 7 amps to the pump after the OV trips, it can take up to one hour
>>to trip the recommended 5A breaker.
>
> Asumming a failed regulater feeds 7 A to the pump? Or where, in which
> documentation did you find this 7 A exactly? Let me guess: You assumed it.
You missed the point. If OV protection pops and full unloaded, ~100V of
rectified AC goes only to a 14V DC fuel pump, what the pump will draw,
whether the pressure kills the engine, or if it will pop the hose off
spraying fuel inside the cabin, and how the CB will perform are all
indeed pure guesses. We really shouldn't assume anything other than
potential disaster!
> I am very interested to see the numbers, again. What is the chance that
> a regulator, or this particular regulator will fail in the first place?
> MTBF please!
MTBF is irrelevant to safe aircraft system design. Bob Nuckolls has
written a short treatise on this; the FAA considers it irrelevant to
certification also.
> While assuming, why don't we assume there is some kind of
> kill-dead system in the regulator itself?
If there is such a system, whose components will fit in the tiny
regulator case, I haven't found one in dozens of tech papers by the
regulator mfr's and semiconductor application notes, and two texts on
power supply design.
> And please don't come up
> with an assumption, these things are measurable! What is the maximum
> safe charging load for the battery in low and high ambients? > This should
> be in your batteryies' documentation.
It's 15.0 volts at room temp, +/- a few tenths depending upon type of
lead-acid battery, and battery docs say beyond that don't go there. The
current to do that is a function of amp-hour capacity, and time of
course. For this reason, CPS, Inc (a Rotax dealer) says the simplest
protection against a Rotax regulator gone wild is enough AH capacity in
the battery need it or not.
Regards,
Fred F.
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