Today's Message Index:
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1. 07:15 AM - Re: TC wire and dsub (Robert L. Nuckolls, III)
2. 03:30 PM - Revmaster PM alternators (dj_theis)
3. 05:48 PM - Re: Flaky EGT Probe (fidot)
Message 1
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| Subject: | Re: TC wire and dsub |
At 08:36 AM 8/15/2019, you wrote:
>
>Theoretically, extending thermocouple wires using a dsub connector
>(with, say, gold over bronze contacts) should be ok provided any
>temperature gradient across the connector is ignored. The
>thermocouple voltages across the connector cancel out to 0.
>
>In practice there could be a problem with corrosion of a
>thermocouple wire where it meets gold.
Gold is electrolytically inert. I think
most thermocouple alloys are similarly
resistant to oxidation. I've run
TC wires though d-subs for decades with
good success . . . with one caveat:
My tasks were temporary instrumentation
installations so I've not personally
observed/demonstrated longevity in
field service. But given the low
reactivity of the alloys involved,
I'm pretty confident that they'll
last a long time.
Bob . . .
Message 2
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| Subject: | Revmaster PM alternators |
The subject of the Revmaster PM alternators has come up in the past, regarding
the regulators used and the nature of how best to wire them. In summary, I think
Professor Nuckolls declared there was not enough detail to offer significant,
specific advice.
I have a little more detail of a failure that was posted on the SonexBuilders forum
and would like to toss this to the AeroElectric group and see what wisdom
I might extract.
My interest is related to the fact that I have a Revmaster (R2300), the same design
as what is noted in the following story. The Revmaster has a dual PM alternator
setup as part of the flywheel assembly.
Two separate failures with very similar circumstances go as follows:
Dual PM alternators with the default, dual regulators. Both planes had both alternators
wired to charge full time. One engine did not have any method of shutoff
of either regulator (hardwired) and the other may have chosen to always
run with both (even though switches may have allowed for single PM operation)
One engine had 160 hours running with this configuration and the second had 450
hours. Both had Odyssey PC680 batteries.
The 160 hour plane experienced a difficult time starting the engine while exiting
KOSH a few weeks back and after wearing down the battery significantly (my
assumption, as it was reported that it took 30 minutes of cranking to finally
get started with no note of any ground recharging once is started). Once the
plane was started and after about 10 minutes in the air, the pilot noticed a
smell of smoke and promptly returned to KOSH. I think the plane was eventually
trailered back home (to TX) and upon disassembly, the stator(s) were/ was diagnosed
as "fried."
Please review the included drawing. I've added the relays and selection switches
but for the sake of this discussion, imagine the switches for PM selection
are both left in the "ON" state. I also have the patent of what I think the 2
wire regulator details include and will dig it out but I think it was posted in
the past. I've simplified the regulator in my sketch as an SCR controlled by
a black box.
An interesting note, the two (20 amp) auto fuses were not blown. I need to verify
if one or both of the stators were destroyed and likewise, if all 4 of the
PM regulator fuses were OK.
The second plane had 450 hours running both alternators full time during those
hours. As noted, same battery (PC680). I don't know if this failure had fuse
failures for the regulator, I don't believe so. I'll double check the report
but the pilot smelled smoke about 6 minutes after takeoff and once he landed
and had everything apart he identified that the stator was toast. Again, I'm
not sure if both sides had failed or just one. I'll follow up and check.
The manufacturer (Remaster) recommended not running both alternators at the same
time and pointed to this as a likely contributing factor. He also indicated
that the PC680 was partially to blame. His comment was that the RVLA batteries
draw too much current. Hmmm, why did the fuses not blow then.....
I think I know what the consensus will be regarding the PC680 (not likely a contributor
to the debacle). My sense, because the 20 amp inline fuses did not blow,
that the stators were not overloaded (else they have the wrong fuse selection)..I've
heard that each alternator is capable 18 amps but the detailed specifications
are very limited. I plan on checking my engine alternators for open
circuit voltage curves and short circuit current. I'm just a little ways away
from that...
The alternators are (as can be seen) single phase. I believe the two alternators
are in phase (I need to verify if it's possible to wire them so they charge
out of phase, i.e. the regulator is half wave so it might be that each alternator
could provide a half wave charge pulse, out of phase with the other.
My theory (aside from agreeing that only one system can run at a time) is that
running both on a heavily discharged battery allowed both regulators to operate.
At some point, the battery reached a "closer to" full voltage level and as
might be expected, one of the regulators started opening the charge circuit from
the alternator. If this occurred at the wrong time, with the other regulator
running, the inductive voltage spike(s) burned a hole in the stator winding
insulation at one or more spots. the result, a fried stator.
What do you guys think?
I look forward to hearing opinions.
Dan Theis
Sonex 1362R
--------
Scratch building Sonex #1362
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=490910#490910
Attachments:
http://forums.matronics.com//files/revmaster_regulators_111.pdf
http://forums.matronics.com//files/revmaster_regulators_880.pdf
Message 3
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| Subject: | Re: Flaky EGT Probe |
Art,
For what it's worth, when I had a similar problem on my EI Engine Monitor, it turned
out to be the bad input channel rather than probe. I'd start with trying
to move it to another channel (ie, swap two probes) and seeing what happens...
unless you've already done that...
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=490911#490911
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