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fvalarm(at)rapidnet.net
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 Posted: Tue Nov 20, 2007 1:07 am Post subject: SD-8/SD20 question |
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Bob,
The SD8/SD20 alternators are vacuum pad mounted. The output chart shows the
alt output at various RPMs. Obviously there is a "gear-ratio" between the
engine and the vacuum pump pad. Do you know what this ratio is and does it
vary? In other words, what RPM can I expect the alt to turn at a cruise RPM
of say 2000-2300 RPM? My engine will be IO-360 ECI or Superior, all
electric. This is needed to know what to expect for amp output.
Also, How much does a battery contactor weigh?
Thanks for your excellent resource and discussion list.
Bevan
RV7A All electric
Trying to decide between SD8 as backup Alt or SD20 for a few pounds more
including second contactor.
--
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nuckolls.bob(at)cox.net
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| Posted: Tue Nov 20, 2007 8:33 am Post subject: SD-8/SD20 question |
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At 01:01 AM 11/20/2007 -0800, you wrote:
| Quote: |
Bob,
The SD8/SD20 alternators are vacuum pad mounted. The output chart shows the
alt output at various RPMs. Obviously there is a "gear-ratio" between the
engine and the vacuum pump pad. Do you know what this ratio is and does it
vary? In other words, what RPM can I expect the alt to turn at a cruise RPM
of say 2000-2300 RPM? My engine will be IO-360 ECI or Superior, all
electric. This is needed to know what to expect for amp output.
|
You need to check with an engine guru. Call B&C. The
pad gear ratio is either 1:1.5 or 1:1.3 depending on
whether it's a Lycoming or Continental product and
the details escape me at the moment.
| Quote: | Also, How much does a battery contactor weigh?
|
The S701 series are 0.8 pounds.
| Quote: | Thanks for your excellent resource and discussion list.
|
Your most welcome.
| Quote: | Trying to decide between SD8 as backup Alt or SD20 for a few pounds more
including second contactor.
|
The SD20 is really intended for those unfortunate
individuals who are locked into the ever-safer,
ever-more-expensive, ever-less-efficient, ever-
less-useful world of TC aircraft. These airplanes
benefit greatly from an SD-20 installed like Z-12.
In the OBAM aircraft world, you're first free
to architecture, craft and understand a system that
will get you to airport of intended destination
BATTERY-ONLY if that is your design goal. Adding
the SD-8 on top of an artfully crafted system
increases your endurance capacity to 8A while
holding a battery completely in reserve for
approach to landing.
Given the demonstrated reliability of modern
alternators teamed with the capability offered
by a properly maintained RG battery, there is
no practical reason to burden your airplane and
your budget with an SD-20. I illustrate it in
the 'Connection because it's out there, it's a
good product and it satisfies a rarely encountered
suite of design goals which I humbly suggest
applies to an exceedingly small number of OBAM aircraft.
I keep reminding folks that the vast majority
of light aircraft flown in IMC environments
are architectured like a 1968 C-172. Yet in
all the years of crappy alternators, generally
ignored, flooded-batteries, and woefully ignorant
pilots, a very small number of unhappy arrivals
with the earth have root cause in electrical system
failure. Let's not jack up the worry-pressure by
praying over Z-11, Z-12, Z-13/8 and Z-14 hoping
for a life-preserving epiphany.
If you're planning an all-electric airplane
then Z-13/8 combined with a modern alternator
and dutifully maintained battery gives you
system reliability exceeding that which costs
$tens of thousands$ and $hundreds of pounds$
in the heavy-iron birds.
Bob . . .
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