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rnjcurtis(at)charter.net
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 Posted: Sun Jun 26, 2016 11:54 am Post subject: Master contactor temp? |
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Sent from Mail for Windows 10
From: Roger (rnjcurtis(at)charter.net)
Sent: Sunday, June 26, 2016 2:50 PM
To: Eric M. Jones (emjones(at)charter.net)
Subject: RE: Re: Master contactor temp?
If the can is 120 deg F and the surrounding temperature is 0 degrees. What is the temperature inside the can? It depends on the rate of heat removal, but it's more than 120 deg F for sure, and a device rated for 122 deg F would be in trouble.
The ambient temperature here is 0 degrees! If the device fails
here from high temperature, then I would suggest that there is
a faulty design or application. The ambient temperature is not
120 degrees.
Roger
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jun 26, 2016 11:54 am Post subject: Master contactor temp? |
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At 10:03 AM 6/26/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Eric M. Jones" <emjones(at)charter.net>
"Ambient" refers to the contactor temperature. But keep in mind that "ambient" doesn't refer to the temperature someplace outside, but AT and ON the contactor can. |
No . . . ambient means SURROUNDING conditions . . .
| Quote: | | Furthermore the type to is G-position sensitive |
Yes . . . more G's than it takes to pull
the wings off your airplane . . . as is
every other metallic contactor.
| Quote: | | vibration sensitive |
Non-quantified . . . how many g's at what
frequency? Levels SMALLER than those found anywhere
on a light aircraft? I've never analyzed a
Type 70 failure that I could attribute to a
vibration stress . . . LOTS of failures attributable
to dripping water . . . a few failures due
to manufacturing defect . . . and none that
posed high-risk scenario.
Show me ONE contactor used on any TC light aircraft
that is liquid proof . . .
| Quote: | | and has many undesireable characterists |
Many implies more than one . . . I'd settle for
just two . . .
| Quote: | . . . compared to other solutions.
As for my choice? I go with the Flaming River Battery Switch, or any of the several electronic contactor offerings, unless your mission doesn't take you far from home. |
Can you cite any instance in the literature
where a contactor failure "far from home"
figured in elevation of risk to airframe
or people in it? If so, what were the circumstances
that promoted that failure?
| Quote: | | Factoid: No NASCAR vehicle uses a type-70 contactor. |
For what reason(s) . . . can you cite conditions
on these vehicles that are analogous to conditions
on our airplanes?
| Quote: | | Factoid: Very old Type-70's were made from far better stuff. |
Really? I've done some teardowns several
variations of 70 series contactors. See pictures
of inspected articles here:
http://tinyurl.com/kcc26jt
. . . they may be useful in explaining how the
materials illustrated in picture A of a failure
are 'better' than those in picture B. How
did they contribute to the failure?
One failure in a 'modern' 70 series contactor
had nothing to do with selection of materials
and lots to do with failure to solder a joint
on the production line . . .
http://tinyurl.com/zs42jpj
| Quote: | | Please, can we do better than "hot to the touch" |
I will suggest that 'hot to touch' is more
definitive to stress boundaries than several
of your assertions above. "Too hot to touch" at
least says somewhere more than ~130 degrees.
I like "sizzle-spit" as being greater than
212 degrees. "Sticking your tongue to the flag
pole" says a whole lot colder than 32 degrees.
But 'sensitive to vibration' offers no bounded
image.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jun 26, 2016 5:52 pm Post subject: Master contactor temp? |
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| Quote: |
If the can is 120 deg F and the surrounding temperature is 0 degrees. What is the temperature inside the can? It depends on the rate of heat removal, but it's more than 120 deg F for sure, and a device rated for 122 deg F would be in trouble. |
Exactly . . .
If you take any 70 series device apart you
will find a collection of materials.
Threaded, copper terminal studs upon which
stationary contacts are formed.
A washer-like movable contact mounted to the
end of an iron armature that moves freely
within the cylindrical 'bore' of a coil
core.
The core has evolved a lot over the years.
But suffice it to say, that whether the
solenoid wires are (1) simply wound on a tube
and captured between disks of phenolic, (2)
embedded in a solidly potted assembly or (3)
wound on a complex molding that forms the
tube, end confines, terminals and mates with
contours of the shell . . . ALL materials used
must first hold components in their intended
positions while withstand expected internal
operating temperatures.
I used to work in a facility that specialized in
the design and manufacture of numerous electronic
and motor driven components . . . including the
actual motors.
I can tell you that ALL materials used in the
manufacture of a brushed DC motor including insulated
magnet wire, insulating varnishes, paper and molded
plastic insulators and components were RATED to
perform as advertised while enduring "Class H"
thermal conditions.
http://www.marathonelectric.com/generators/docs/manuals/thermal-life.pdf
Of course, these are INTERNAL conditions which
are expected to be hotter than external conditions.
122F is 50C . . . a rather benign condition for
many qualification levels in aircraft. 70C ambients
for black boxes are not uncommon. At the same time,
I can tell you that 100C ambients for most electronic
assemblies not dissipating a lot of power is no big
deal. An engineer I've worked with for years will often
throw his brass-board assemblies into the lab oven at
100C just to make sure he didn't overlook an unusually
vulnerable part in the design.
I trust this little dissertation goes to an understanding
that 'proper' temperatures for operation with limits
of design goals can be all over the map. Certainly
your cylinder heads will 'sizzle spit' under perfectly
normal conditions.
The contactor illustrated in
http://www.marathonelectric.com/generators/docs/manuals/thermal-life.pdf
demonstrates a temperature rise of ~50C with no air
flow over the device. Were we to operate this contactor
in its RATED 122F environment (70C) then we might expect the
contactor surface to go up to 120C . . . which will
sizzle-spit.
I can tell you that we didn't build a single motor
that could not be operated with surface temperatures in
sizzle-spit range . . . VERY much too hot to touch.
Hence I can assert confidently that while the observed
surface temperature for an operating 70 series contactor
is unfriendly the touch, the device is NOT being
unduly stressed internally. The 122F limit to operating
environment suggests something less than class-H ratings
for stuff inside . . . at the same time, it
poses no practical operating limits on how we use
the contactor.
Bob . . .
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alec(at)alecmyers.com
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| Posted: Sun Jun 26, 2016 6:44 pm Post subject: Master contactor temp? |
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Is there any evidence it's actually a limiting temperature?
| Quote: | >and the only reference I can find for temperature is "Temperature Range –– -40°F to 122°F"
|
The normal operating temperature for a device is given as the temperature range within which the given electrical specification is met. There's no expectation the the device can't or won't work, or shouldn't be used outside that temperature range, merely that you are somewhat on your own with respect to its characteristics.
On Jun 26, 2016, at 21:37, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: |
If the can is 120 deg F and the surrounding temperature is 0 degrees. What is the temperature inside the can? It depends on the rate of heat removal, but it's more than 120 deg F for sure, and a device rated for 122 deg F would be in trouble. |
Exactly . . .
If you take any 70 series device apart you
will find a collection of materials.
Threaded, copper terminal studs upon which
stationary contacts are formed.
A washer-like movable contact mounted to the
end of an iron armature that moves freely
within the cylindrical 'bore' of a coil
core.
The core has evolved a lot over the years.
But suffice it to say, that whether the
solenoid wires are (1) simply wound on a tube
and captured between disks of phenolic, (2)
embedded in a solidly potted assembly or (3)
wound on a complex molding that forms the
tube, end confines, terminals and mates with
contours of the shell . . . ALL materials used
must first hold components in their intended
positions while withstand expected internal
operating temperatures.
I used to work in a facility that specialized in
the design and manufacture of numerous electronic
and motor driven components . . . including the
actual motors.
I can tell you that ALL materials used in the
manufacture of a brushed DC motor including insulated
magnet wire, insulating varnishes, paper and molded
plastic insulators and components were RATED to
perform as advertised while enduring "Class H"
thermal conditions.
http://www.marathonelectric.com/generators/docs/manuals/thermal-life.pdf
Of course, these are INTERNAL conditions which
are expected to be hotter than external conditions.
122F is 50C . . . a rather benign condition for
many qualification levels in aircraft. 70C ambients
for black boxes are not uncommon. At the same time,
I can tell you that 100C ambients for most electronic
assemblies not dissipating a lot of power is no big
deal. An engineer I've worked with for years will often
throw his brass-board assemblies into the lab oven at
100C just to make sure he didn't overlook an unusually
vulnerable part in the design.
I trust this little dissertation goes to an understanding
that 'proper' temperatures for operation with limits
of design goals can be all over the map. Certainly
your cylinder heads will 'sizzle spit' under perfectly
normal conditions.
The contactor illustrated in
http://www.marathonelectric.com/generators/docs/manuals/thermal-life.pdf
demonstrates a temperature rise of ~50C with no air
flow over the device. Were we to operate this contactor
in its RATED 122F environment (70C) then we might expect the
contactor surface to go up to 120C . . . which will
sizzle-spit.
I can tell you that we didn't build a single motor
that could not be operated with surface temperatures in
sizzle-spit range . . . VERY much too hot to touch.
Hence I can assert confidently that while the observed
surface temperature for an operating 70 series contactor
is unfriendly the touch, the device is NOT being
unduly stressed internally. The 122F limit to operating
environment suggests something less than class-H ratings
for stuff inside . . . at the same time, it
poses no practical operating limits on how we use
the contactor.
Bob . . .
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Sun Jun 26, 2016 7:25 pm Post subject: Master contactor temp? |
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At 09:42 PM 6/26/2016, you wrote:
| Quote: | Is there any evidence it's actually a limiting temperature?
>>and the only reference I can find for temperature is "Temperature Range –– -40°F to 1o 122°F"
The normal operating temperature for a device is given as the temperature range within which the given electrical specification is met. There's no expectation the the device can't or won't work, or shouldn't be used outside that temperature range, merely that you are somewhat on your own with respect to its characteristics. |
Temperature ratings are a bit 'squishy' . . .
like contact ratings for current and voltage.
Most ratings are bounded by calculated or
laboratory demonstrations of service life.
The 70 series contactor isn't going to burst
into flames if operated in a 150F environment.
At the same time, it would probably not demonstrate
rated life limits either. Then again, we don't
even begin to stress the service life of any
switch or contactor in a GA single engine
airplane!
The 122F/50C recommended limit probably
assumes still air . . . sitting out on a
bench. Add a little moving air and internal
temperatures will fall like a stone . . .
which translates to a boost in recommended
limit to ambient air temperature.
I may have the data in my archives somewhere
that describes temperature conditions under
the cowl on a single engine airplane. We
were setting up a cooling test on a new alternator
installation and had 8 thermocouple channels
open on the DAS.
We scattered some extra thermocouples around and
discovered that in-flight temperatures are really
rather benign . . . the hottest spikes occurred
during cool-down after engine shutdown when
air flow dropped and heat stored on the engine
mass warmed things up under the cowl.
Of course, the thermocouples only gave us
total temperature of the air at various
locations. To assess cooling effects of air
movement, we would have to repeat the experiment
by mounting the thermocouples onto power resistors
and then plotting differences between static
air and in-flight conditions with stirred air
over components that were dissipating heat.
The constellation of variables can be all over
the map when it comes to in-situ thermal management
of components in the airplane . . . hence, making
a decision to buy brand X contactor rated at 50F
versus brand Y rated at 70C could very well be
a poor cost of ownership decision.
As our ol' buddy Lord Kelvin used to say, "Until you've
measured the thing . . . your knowledge of the
science is of a meager and unsatisfactory kind."
Bob . . .
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