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nuckolls.bob(at)aeroelect
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 Posted: Tue Jul 05, 2022 9:52 am Post subject: Thermocouples: grounded or ungrounded |
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At 11:13 AM 7/5/2022, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Paul Eckenroth" <jeckenroth(at)nbn.net>
Thanks for the reply Bob. Unfortunately my GRT EFIS cannot read Thermocouples except as used for EGT and CHT. Therefore I am using small inexpensive readers off Amazon. I seriously doubt if they have any specialized circuitry other than that require to give a basic reading of the thermocouple. Does the ground loop have the potential of rendering the reading totally unusable or is it more like a 5% loss of accuracy. The ungrounded probes are around twice as expensive as the grounded probes. I would certainly be willing to consider a better reader if it can be had in a small format. The Onex is a single seat very small plane with limited panel space. Thanks for your help. |
Okay, best bet is go grounded thermocouples PLUS
take your power ground wire for the instrument(s)
out to some handy spot on engine.
Got a link for these probes?
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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nuckolls.bob(at)aeroelect
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| Posted: Tue Jul 05, 2022 4:17 pm Post subject: Thermocouples: grounded or ungrounded |
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At 03:53 PM 7/5/2022, you wrote:
Okay, how do you plan to attach the probes to the
stator . . . bolts? We used to weasel small t/c
wires under the stator windings of a motor.
How many total points to you plan to monitor?
Have you considered a single instrument and rotary
selector switch to manually scan through the
array of thermocouples?
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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chaskuss(at)yahoo.com
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| Posted: Tue Jul 05, 2022 4:31 pm Post subject: Thermocouples: grounded or ungrounded |
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Paul, do you have a GRT EIS to go with your EFIS? If so, the EIS has the capability to have auxiliary inputs added. You can hook additional thermocouples to take temperature of other items on the aircraft using those auxiliary inputs.
Sent from Yahoo Mail on Android
| Quote: | On Tue, Jul 5, 2022 at 6:11 PM, Robert L. Nuckolls, III
<nuckolls.bob(at)aeroelectric.com> wrote:
At 11:13 AM 7/5/2022, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Paul Eckenroth" <jeckenroth(at)nbn.net>
Thanks for the reply Bob. Unfortunately my GRT EFIS cannot read Thermocouples except as used for EGT and CHT. Therefore I am using small inexpensive readers off Amazon. I seriously doubt if they have any specialized circuitry other than that require to give a basic reading of the thermocouple. Does the ground loop have the potential of rendering the reading totally unusable or is it more like a 5% loss of accuracy. The ungrounded probes are around twice as expensive as the grounded probes. I would certainly be willing to consider a better reader if it can be had in a small format. The Onex is a single seat very small plane with limited panel space. Thanks for your help. |
Okay, best bet is go grounded thermocouples PLUS
take your power ground wire for the instrument(s)
out to some handy spot on engine.
Got a link for these probes?
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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nuckolls.bob(at)aeroelect
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| Posted: Wed Jul 06, 2022 6:14 pm Post subject: Thermocouples: grounded or ungrounded |
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At 05:30 PM 7/6/2022, you wrote:
| Quote: | | Plan to attach two thermocouples to the stator with the stator attachment bolts. There is also a thermocouple imbedded in one of the generator coils by Revmaster, but the lead wires are solid and extremely thin so I'm not anticipating a long life. I will also attach a thermocouple to the voltage regulator. The most important temperature readings will be of the stator. Unfortunately since I can't run the readings through the EFIS, I will not have an alarm.I will look into a rotary switch. The grounds on my plane are all connected to 2 forest of tabs fore and aft on the firewall with a #4 wire to the engine, so I think that connecting the reader ground to this grounding point would be the same as connecting directly to the engine.  |
Suggestion attached . . .
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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9814_Thermocouple_Switch_R0.pdf |
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jul 07, 2022 11:20 am Post subject: Thermocouples: grounded or ungrounded |
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| Quote: | | The most important temperature readings will be of the stator. |
yeaaahhh . . . sort of. Temperature numbers of the stator
stack adjacent to mounting bolts will be greatly
influenced by heat transfer to the crankcase.
We know that the stator failures are generally limited
to one pole. How do the wires look on remaining poles?
To precipitate this 'isolated' failure suggests a thermal
runaway event where the resistance of copper rises with
temperature which in turn, increases energy dissipated in
the wires. I.e. a positive feedback for temperature
excursion.
To catch a pending failure suggest a need to monitor
each winding . . . unless field experience shows that
failures are concentrated.
In any case, other temperatures around the system's
components may be interesting data but I'm skeptical
as to their ability to flag impending failure any
one coil.
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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nuckolls.bob(at)aeroelect
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| Posted: Sun Jul 10, 2022 9:17 am Post subject: Thermocouples: grounded or ungrounded |
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At 04:04 PM 7/8/2022, you wrote:
| Quote: | Bob
I agree with what you are saying concerning the ideal method of monitoring the coils.
However I need to work with what I have and I don't think I can monitor 12 individual
coils with the tools at my disposal. |
Previous examples of failure involved but a single coil of the
5. Correct me if I'm wrong, but I seem to recall that Revmaster
presently splits the TEN alternator stator poles into two groups . . .
rated at 18A each.
Okay, this is the first photo I recall seeing of a total-toasting
of all 5 coils on the Revmaster alternator. This suggest a different
failure mode. Bad R/R? Too much system loads? Probably
something different than conditions the precipitates
a single pole conflagration.
The difference in coil failures suggests at least two,
different operational stresses.
It would be interesting to know the rational behind the
'dual alternator' decision. History shows us that capability
of the individual half-alternators is marginal.
Has anyone considered a single winding spread over all
ten pole pieces wound with fewer turns of heavier wire
to produce a single alternator of say 20, 25A . . .
or more?
If the two existing windings are reasonably matched,
they could be operated in parallel as a single winding.
Watts dissipated is proportional to I(squared) x R. So
dropping current in each winding by one half reduces
heat generated in that winding by 75%.
That offers greater value in stress reduction than
adding cooling air.
I do plan on using your idea of the rotary switch and I appreciate the schematic. I thought all might be interested in a picture of the stator after removal. The one coil suffered catastrophic damage with the phenolic spacer completely destroyed by the heat. I have machined the case to allow more ventilation and will add two blast tubes directly at the coils. And hope for the best.
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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