Today's Message Index:
----------------------
1. 03:38 PM - Lithium Webinar (Ken Ryan)
2. 10:35 PM - old B and C SD-8 Dynamo failure (Mark Todd)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
Because there is interest on this list I thought it might be appropriate to
post that there is an upcoming EAA Webinar on the subject of lithium
batteries:
http://pages.eaa.org/WBN2017-05-31LithiumBatteriesExplained_LP-Registration.html
Ken
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | 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
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|