Today's Message Index:
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1. 04:06 AM - Re: old B and C SD-8 Dynamo failure (user9253)
2. 04:50 AM - Re: old B and C SD-8 Dynamo failure (Robert L. Nuckolls, III)
3. 07:43 AM - Re: old B and C SD-8 Dynamo failure (ashleysc@broadstripe.net)
4. 08:45 PM - MGL CHT probe (Jeff Point)
5. 09:05 PM - K Type Thermocouple Wire Striping (William Hunter)
Message 1
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Subject: | Re: old B and C SD-8 Dynamo failure |
The saying, "Ring it out", when referring to electrical testing, got its beginnings
when troubleshooters used a doorbell for testing electrical motors. There
is not much difference in resistance between a good motor and one with a shorted
winding. But there is a difference in the inductance. An experienced electrician
could tell the difference in doorbell sound when connected in series
with a shorted motor winding compared to a good winding. Modern doorbells are
not suitable for this task. The doorbell must be of the old fashioned clanger
and bell type.
This information might be of use to you 27 years from now when your new SD-8
dynamo malfunctions. :-)
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=468022#468022
Message 2
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Subject: | Re: old B and C SD-8 Dynamo failure |
>
>I have no complaints about this SD-8 failure. I certainly got a
>reasonable service life out of this unit. I just thought I'd share my
>story as just one more data point, although I appreciate it's kinda
>ancient history. I'm planning on taking the dynamo apart (curiosity)
>and maybe salvaging the magnets.
Are the windings smoked? Do they smell bad?
The DC resistance of this product is less than
0.25 ohms. So if you had a shorted turn or two,
you could not resolve it with jelly-bean test
equipment. The magnets are ferrites . . . rather
brittle. You probably couldn't get them loose
without breaking them up.
>Bob, if you wanted to look at this dynamo for some reason, I'll be happy
>to mail it to you. I suspect you've got much better things to do than
>'paleo-forensics' on this dated item.
>
>Mark
Actually, I would like to see it. I have
a drive stand running that fits the SD8
and I'm equipped to test/inspect it in
detail. Getting a close up look at a sample
with this kind of service on it would be
illuminating.
Send the rectifier/regulator too. I'll
get them checked out and repaired/replaced
as needed.
Bob . . .
Message 3
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Subject: | Re: old B and C SD-8 Dynamo failure |
Hi Mark;
Hi All;
I read this as an endorsement, not a complaint. Who gets 27 years of operation
from a car, washing machine, or computer? It gives me great confidence in B &
C products.
Cheers! Stu.
----- Original Message -----
From: "Mark Todd" <motodd@frontier.com>
Sent: Monday, April 3, 2017 10:32:48 PM
Subject: AeroElectric-List: old B and C SD-8 Dynamo failure
Well, after 27 years and 2300+ hours, my good old SD-8 dynamo finally
gave me a problem. It was installed in my day/VFR RV4 in 1989 as the
only charging source. It could produce up to 8.6 amps at high RPM and
met my modest electrical load requirements (<4 amps in cruise) for all
these years. Of course, I could expect my low voltage light to come on
(at 12.5V) at low rpms depending on the loads. I didn't mind. It made
for a nice reminder to turn off my boost pump as I exited the runway on
landing.
On a recent flight, I noticed that the low voltage light came on a
little earlier than I expected on landing. At high RPM, the voltage
was only going to 13.9 instead of the usual 14.1V. A quick run through
my switchable loads showed they were pulling their expected currents.
I have a switchable volt/amp gauge on my panel so I can look at one or
the other but not both simultaneously. The amp readings are taken off
my B lead and it takes several seconds for the amp reading to stabilize
on my gauge after it's selected. I never saw an unexpectedly high amp
reading on the gauge. Back at the hangar, a brief look at my B lead
connections didn't reveal any problems. On the next flight, the low
voltage light came on even sooner and the voltage only got to 13.7V.
A more detailed inspection was made of the wiring, including
micro-ohming some connections (using Bob's 100mA current clamp
micro-ohmmeter design I've enjoyed using for several years). I thought
I detected a little bit of a burnt electrical smell near the dynamo
housing where the armature leads pass through a clip screwed into the
rim of the housing. Using a cheap digital multimeter, I checked the
resistance across the disconnected dynamo leads and got 5.6 ohms. Not
sure what it's suppose to be.
I flew the plane again and this time, I got a low voltage light in
cruise and zero B lead amps when checked. I checked the resistance
across the dynamo leads again with the same meter.. and got a reading of
zero. My micro-ohm meter said it was about 700 milliohms. I bought a
new SD-8 and am back in the air trouble free. Since removing the
problem unit, I removed the clip that held the leads at the rim of the
dynamo housing and slid the protective sheathing back. The lead wires
look fine, including the half-inch of wire I can see inside the
housing. The resistance across the leads remains 'zero' when checked
with another cheap digital mulitmeter.
I concluded that I had probably experienced a progressive short within
the dynamo, probably in the windings themselves. This dynamo was from
the 1980's and the exterior design has changed a lot since then. This
includes a protected routing of the leads out of the dynamo housing with
a better clamping system. The insides have probably changed as well.
Lord knows the new unit is easier to install with much better access to
the mounting nuts.
I have no complaints about this SD-8 failure. I certainly got a
reasonable service life out of this unit. I just thought I'd share my
story as just one more data point, although I appreciate it's kinda
ancient history. I'm planning on taking the dynamo apart (curiosity)
and maybe salvaging the magnets.
Bob, if you wanted to look at this dynamo for some reason, I'll be happy
to mail it to you. I suspect you've got much better things to do than
'paleo-forensics' on this dated item.
Mark
Message 4
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I recently purchased the MGL 18mm spark plug CHT probes from Aircraft
Spruce. The photo on both their website and MGL's shows a copper ring
soldered to a K-type thermocouple wire, a pretty standard setup. What
they sent me is pictured below. Since the bare wire ends connect
directly to the RDAC brain box, I deduced that the other end- a 1/4 PIDG
fast-on, crimped to the thermocouple wires- must just attach to the
copper ring. The tab end of the copper ring is exactly 1/4 inch, so
this makes sense.
This seems like a pretty cheeseball setup. From what I know of K-type
thermocouples (mostly from reading the 'Connection) that wires must be
silver soldered to the probe and to each other. Or, am I mistaken and
is this a reasonable setup?
I am also reaching out to MGL about this, but I thought I'd ping this
group for your thoughts as well.
Thanks
Jeff Point
Milwaukee
Message 5
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Subject: | K Type Thermocouple Wire Striping |
Hi All,
How does one (me) strip K Type Thermocouple Wires.
The wire I bought from eBay Aircraft Supply has a metal shield and two
wires inside that appear to be covered with some kind of a fabric type
insulator.
The metal shield can be stripped back with a pick, bandaids, and some bad
words. The two inner wires insulation do not strip back with a mechanical
wire stripper and if I use a razor blade the fabric insulation will simply
unravel like a sweater thread.
There has got to be a better way?!?!?
Thanks,
Bill Hunter
On Apr 4, 2017 8:55 PM, "Jeff Point" <jpoint@wi.rr.com> wrote:
I recently purchased the MGL 18mm spark plug CHT probes from Aircraft
Spruce. The photo on both their website and MGL's shows a copper ring
soldered to a K-type thermocouple wire, a pretty standard setup. What they
sent me is pictured below. Since the bare wire ends connect directly to
the RDAC brain box, I deduced that the other end- a 1/4 PIDG fast-on,
crimped to the thermocouple wires- must just attach to the copper ring.
The tab end of the copper ring is exactly 1/4 inch, so this makes sense.
This seems like a pretty cheeseball setup. From what I know of K-type
thermocouples (mostly from reading the 'Connection) that wires must be
silver soldered to the probe and to each other. Or, am I mistaken and is
this a reasonable setup?
I am also reaching out to MGL about this, but I thought I'd ping this group
for your thoughts as well.
Thanks
Jeff Point
Milwaukee
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