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nuckolls.bob(at)aeroelect
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 Posted: Sat Jul 16, 2016 8:50 am Post subject: breaker as switch for aux alternator? |
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At 08:15 AM 7/16/2016, you wrote:
| Quote: | | You might want to also look at the rated lifetime operations of the pull-able breaker vs a plain switch or a 'circuit breaker switch'. It's unlikely any of us would ever wear any of them out in a homebuilt, but those ratings are at least some indication of expected life. Most breakers aren't designed for multiple actuations during every use of the 'appliance' they protect, so their number of rated operations is typically lower than a switch. Sometimes by a lot. |
While switches are generally rated in the tens of
thousands of operations, our favorite little breakers
are only rated in mere thousands.
You're not going to wear it out in the life time
of your airplane . . . and even if you did . . .
it should be operated once per flight-cycle in
pre-flight . . . you'll detect the failure for
an easily replaced component.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sat Jul 16, 2016 9:17 am Post subject: breaker as switch for aux alternator? |
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At 11:52 AM 7/16/2016, you wrote:
| Quote: | Hi All;
The rated life of the Tyco W31-X2M1G, which is a toggle switch/circuit breaker available from 1 to 50 amps is stated to be equal or greater than 10,000 mechanical cycles, or 6,000 cycles at 100% rated load. The push pull type is similar. Enough for my limited life-span.
Cheers! Stu. |
These devices were problematic in the Barons and Bonanzas.
Furhter, their i(squared)T constant is larger than the
legacy, miniature breaker. If you want to use a breaker
upstream of crowbar ov protection, please consider the
miniature, push-pull breakers.
Bob . . .
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ashleysc(at)broadstripe.n
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| Posted: Sat Jul 16, 2016 10:40 am Post subject: breaker as switch for aux alternator? |
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Hi Bob;
How far back in time is your experience with these devices in Barons and Bonanzas? In other words, has there possibly been time for improvement? I know of many in use without complaints.
Cheers! Stu.
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Saturday, July 16, 2016 10:16:18 AM
Subject: Re: Re: breaker as switch for aux alternator?
At 11:52 AM 7/16/2016, you wrote:
| Quote: | Hi All;
The rated life of the Tyco W31-X2M1G, which is a toggle switch/circuit breaker available from 1 to 50 amps is stated to be equal or greater than 10,000 mechanical cycles, or 6,000 cycles at 100% rated load. The push pull type is similar. Enough for my limited life-span.
Cheers! Stu. |
These devices were problematic in the Barons and Bonanzas.
Furhter, their i(squared)T constant is larger than the
legacy, miniature breaker. If you want to use a breaker
upstream of crowbar ov protection, please consider the
miniature, push-pull breakers.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jul 17, 2016 1:43 pm Post subject: breaker as switch for aux alternator? |
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At 03:55 PM 7/16/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: Kelly McMullen <kellym(at)aviating.com>
While the Beech aircraft did result in an AD, I have heard reports of as many problems generated by taking things apart and replacing before failure as those that generated the AD. A lot of other brands used the exact same units such as Mooney that do not have AD. Don't know if there is any difference, or just luck of the draw that any failures didn't catch the FAA attention. |
Excellent observation. This was a rather strange
cause/effect/response . . . perhaps the least satisfying
'fix' I had occasion to observe.
[img]cid:.0[/img]
The 'problem' first presented as a 'smoke in the
cockpit' event which gets everyone sitting upright
in their chairs. Seems that at least one . . . and
perhaps one or two others . . . don't recall now
. . . experienced smoke squirting out around the
control handle of the Prop DeIce switch/breaker.
I seem to have lost the teardown photos but suffice
it to say that all strands of flexible, multi-strand
wire (intended to carry current across the axle joint
of the upper moving contact) had parted. This
forced the switched current to find a new path . . .
which was the spring. The relatively high current
draw of the prop de-ice heaters caused the spring
to get really hot causing adjacent, interior surfaces
of the plastic housing to char and emit smoke . . . most
of which squirted out around the control handle.
What's a mother to do? There were thousands of these
switches in service on thousands of airplanes
including ships other than Brand B going back a
long time. I'm not sure anyone ever researched
a fully detailed history of that switch/breaker's
biography but I do recall some conversations wherein
speakers alluded to a number of changes to internal
design over the years . . . ostensibly without
Beech (or anyone else) taking notice.
The root problem was failure of the fine-wire
bundle that carried current across the axle
joint. Surely this component had not be subject
to operating cycles exceeding life specifications . . .
on the prop de-ice switch?
Changing that material would be a major design
effort. But wait, suppose we stick a little
piece of insulator under the spring? Then,
when the wires do fail, the device being
controlled simply fails to come on yet risk
of smoke in the cockpit is averted.
Hmmmm . . . no doubt, there are thousands
of airplanes flying with those wire strands
compromised . . . but on smaller loads were
the spring happily carries the load. Now what?
Anyhow, powers that be decided on an AD that
forced replacement of lots of switches . . .
replacements that created new problems in
airplanes that had been operating just fine.
A point of consideration took notice that
unlike the breaker on a panel driving a switch
someplace else, the breaker-switch was the ONLY
control device in the circuit. One had no
breaker to be pulled when the associated
control switch poured smoke.
The short consideration is that the W31
breaker switch has a lot of monkey motion
going on inside. It demonstrates a vulnerability
to what must be a combination of operation
and vibration stresses. I think a stress
analysis of the physics would suggest that
a BRAIDED jumper strap has superior performance
under vibration because the strands 'brace
each other' while the individual strands used
in the W31 design are vibrationally independent
of each other. The wires failed, one by one, right
at the point where they are spot welded to
the frame.
So, the 'fix' became a 'non-fix' . . . the switch
is still subject to failure to perform, it is simply
prevented from making smoke. Further, lots of
switches were forced into replacement in spite
of the fact they presented no risk.
Sure glad I didn't have to make that decision.
It was a classic damned-if-you-do, damned-if-
you-don't situation. Beech made no friends
with their customers that day . . .
Bob . . .
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