Today's Message Index:
----------------------
1. 08:21 AM - Re: Blowing fuses on B&C BC433 alternator (Robert L. Nuckolls, III)
2. 09:00 AM - Re: Blowing fuses on B&C BC433 alternator (Bob Verwey)
3. 11:36 AM - Re: Conductor interface enhancements (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Blowing fuses on B&C BC433 alternator |
About 50 flight hours ago, one of the fuses blew. Really blew, it
partially melted
the plastic coating. I couldn't really find anything wrong, but I
thought possibly
there was a short from one of the butt connectors to the firewall, nothing
definitive though. Last week, 50 flight hours later, another fuse blew.
I don't know if it was on the same leg as I didn't record it the first time
it happened. All the wiring from the alternator to the VR seems to be 100%.
I put my VOM on the leads and they all checked out per the B&C service
manual. https://bandc.com/wp-content/uploads/2018/05/pmr3a-trouble.pdf
It would be interesting to see the carcasses of
the blown fuses. A design goal for fuses is to
provide a benign mitigation to an overloaded
wire. They are electrical 'weak links' in the
energy conduction chain. Fuse (and breaker)
manufacturers design and test their products
striving to bring a potentially catastrophic
failure to a ho-hum conclusion.
If a blown fuse presents with a compromised
enclosure then it seems likely that some condition
other than fault current is in operation. Especially
when two such events are widely spaced in time.
Electrical connections inside holders for
these fuses are close cousins to the fast-on
style terminals. They depend on very high
pressure mating to achieve gas-tight integrity
at the interface between blade and terminal.
As we've seen and studied on switch failures,
loss of gas-tightness, over TIME, can produce
electrically induced heating at the joint that
contributes to a slow but ever increasing
degradation that ends in rather spectacular
failure of the whole assembly.
This may well be what we're seeing here.
The fuse didn't simply open up in response
to some over-current, rather it may have
failed in response to a precipitous heating
event at the blade-to-terminal interface.
Suggest you replace all three fuse holders
and see how it goes.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 2
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| Subject: | Re: Blowing fuses on B&C BC433 alternator |
Bob N,
you posted
"The fuse didn't simply open up in response
to some over-current, rather it may have
failed in response to a precipitous heating
event at the blade-to-terminal interface."
Years ago, a sage at E.I. gave me a tip on said problem; this may be heresy
in your eyes, but I am yet to suffer ill consequence as a result of this
bit of advice...
He suggested a drop of ACF 50 or equivalent on mating connections as a
prophylactic to calendar driven corrosion events which lead to "hot"
joints, even in crimped connections.
Your thoughts?
On Tue, 17 Aug 2021 at 17:26, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> About 50 flight hours ago, one of the fuses blew. Really blew, it
> partially melted
> the plastic coating. I couldn't really find anything wrong, but I thought
> possibly
> there was a short from one of the butt connectors to the firewall, nothing
> definitive though. Last week, 50 flight hours later, another fuse blew.
> I don't know if it was on the same leg as I didn't record it the first time
> it happened. All the wiring from the alternator to the VR seems to be 100%.
> I put my VOM on the leads and they all checked out per the B&C service
> manual. https://bandc.com/wp-content/uploads/2018/05/pmr3a-trouble.pdf
>
> It would be interesting to see the carcasses of
> the blown fuses. A design goal for fuses is to
> provide a benign mitigation to an overloaded
> wire. They are electrical 'weak links' in the
> energy conduction chain. Fuse (and breaker)
> manufacturers design and test their products
> striving to bring a potentially catastrophic
> failure to a ho-hum conclusion.
>
> If a blown fuse presents with a compromised
> enclosure then it seems likely that some condition
> other than fault current is in operation. Especially
> when two such events are widely spaced in time.
>
> Electrical connections inside holders for
> these fuses are close cousins to the fast-on
> style terminals. They depend on very high
> pressure mating to achieve gas-tight integrity
> at the interface between blade and terminal.
>
> As we've seen and studied on switch failures,
> loss of gas-tightness, over TIME, can produce
> electrically induced heating at the joint that
> contributes to a slow but ever increasing
> degradation that ends in rather spectacular
> failure of the whole assembly.
>
> This may well be what we're seeing here.
> The fuse didn't simply open up in response
> to some over-current, rather it may have
> failed in response to a precipitous heating
> event at the blade-to-terminal interface.
>
> Suggest you replace all three fuse holders
> and see how it goes.
>
>
> Bob . . .
>
> Un impeachable logic: George Carlin asked, "If black boxes
> survive crashes, why don't they make the whole airplane
> out of that stuff?"
>
--
Best Regards,
Bob Verwey
082 331 2727
Message 3
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| Subject: | Re: Conductor interface enhancements |
>Years ago, a sage at E.I. gave me a tip on said problem; this may
>be heresy in your eyes, but I am yet to suffer ill consequence as
>a result of this bit of advice...
>He suggested a drop of ACF 50 or equivalent on mating
>connections as a prophylactic to calendar driven
>corrosion events which lead to "hot" joints, even in
>crimped connections.
>
>Your thoughts?
I can recall at least two times I was tasked with
researching some form of contact enhancement/
preservative treatment for use on connectors
while at Beech.
Some of the products came with impressive
presentations and credentials. Without a doubt,
all of them performed as claimed . . . none
of them were found to have deleterious effects.
In each case, the products were found not to
add value to our production processes. All
of these products were tailored to
enhancement of LOW PRESSURE interfaces
where gas-tightness cannot be achieved.
Connector pins/sockets are the most prolific
examples of this condition.
Our findings in no way suggest that one should
not need/use these products given situations
where benefits are inarguable. But at Beech,
virtually all of our pin/socket connectors
were specified and qualified to requirements
that demonstrated resistance to the ravages
of climate and time.
All other connections strove to achieve
gas-tightness in current carrying interface
of a connection. By definition, gas-tightness
prevents ingress and effects of moisture/
oxygen/contaminants.
EVERY instance of joint failure analysis
by this writer had root cause in failure to
achieve enduring gas-tightness where materials,
tools and processes were expected to achieve
that goal.
The fact-sheet for ACF-50 echoes risk
factors like cracks, joints, seams, etc.
It also claims effectiveness of up to 24
months. I cannot argue with anyone who
has observed 'zero failures' for having
used this product but I can argue for
the gas-tight condition that renders the
product unnecessary.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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