nuckollsr(at)cox.net
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 Posted: Fri Apr 13, 2007 5:54 am Post subject: 12V batteries in series - a few more followup questions |
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| Quote: | I might have missed it (I re-checked), but I never saw an answer/reply to
the questions below. As always, I appreciate any thoughts you offer. I'm
indebted to your efforts/experience.
Rick
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You done good. I sift through the e-mails and respond
from the bottom up. If I didn't, I'd be making replies
to stuff posted back in 2006.
So if someone's query doesn't make the cut for time and
inspiration several days in a row, it's not likely to
bubble to the top automatically and needs to be reposted.
| Quote: | BobN,
Thanks much (as usual)!!! I'm going to try the omega bend connector, it
should be pretty simple with the thin material - probably better than the
straight/flat connector, perhaps not as robust as the 4AWG cable - sort of a
compromise in my mind.
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Agreed.
| Quote: | Follow-up question#1: Let's say sometime in the future, one of the battery
terminals or the omega connector strap comes loose or breaks off in flight.
How would I know (during the flight)? My ignorant guesses below.
a) The ammeter (shunt on the battery lead) would move from perhaps a slight
charging state to zero, but that might not be noticeable.
b) I understand the alternator would not be happy without the battery. But,
how would I know? Voltage fluctuations? Potential overvoltage (crowbar)
scenario?
c) Other???
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I don't recommend battery ammeters and for the most part,
you wouldn't notice anything. Many a Bonanza pilot has landed
and during shutdown discovered that he mis-flipped a switch
somewhere along the way and the battery has been off line
for some time.
The risk for running sans battery with alternators is that
a high inrush current system (landing lights, hydraulic gear motors,
etc) will "stall" the alternator if the battery is not on line
to fill in for milliseconds of inrush time. For the most
part, voltage regulation sans battery is not seriously
affected except for highly dynamic situations and these
situations do not offer hazardous situations.
One of the studies I want to conduct after the drive stand
is running . . .
http://www.aeroelectric.com/Pictures/Alternator_Test_Stand/DSCN0961.JPG
http://www.aeroelectric.com/Pictures/Alternator_Test_Stand/DSCN0962.JPG
http://www.aeroelectric.com/Pictures/Alternator_Test_Stand/DSCN0963.JPG
. . . is to explore and quantify system operating conditions
sans battery along with an investigation of how well modern
alternators will self-excite. It's been a long standing assumption
based on 1960's alternator technologies that one should always
have a source of alternator excitation energy aboard to insure
availability of engine driven power. For the most part, the
battery fills this role but some worriers have gone to the
effort of providing little kick-starting systems that run
whether or not a battery is present. We stirred that stew
on the C-337 in the mid 60's.
Alternators on Bonanzas will self excite and run sans
battery. It's not real clear that we don't have a similar
situation with belt driven automotives which cruise at over
10,000 rpm on the front of a Lyc.
Another new idea coming over the hill calls for inclusion
of a super-capacitor (1 farad or more) across the main
bus. This device may have much better noise filtering
characteristics than any battery. We'll see . . .
| Quote: | Follow-up question #2: What type of nut should I use on the threaded
battery terminals? I'm assuming just a plain (AN345) nut (Cad plated,
Stainless, other)? However, it would be nice to safety it somehow (perhaps
overkill). Would it make sense to use two nuts (a jam nut)? Would it make
sense to use a nylon lock nut as the 2nd jam nut? Would it make most sense
to just use one all metal stop nut (AN363)
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The thing that's going to put these joints at risk
for loosening is vibration of a mass that imparts
ROTATIONAL forces. The light and flexible welding
cable leads and your thin brass omega jumper do not
present great risks. Any of the schemes you've described
are probably overkill. Go the easiest route if at all.
| Quote: | Follow-up question #3: Assuming a ground stud through the firewall, what
should the stud be made of (steel) (zink plated) ((brass) (other)? What
type of nut(s) should I use on it (same as the battery terminals)? What
type of nut should I use on the engine side of the engine ground braid?
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Please use brass hardware for this. 5/16" minimum and 3/8" preferred.
Ordinary brass nuts torqued to recommended values. After your
40 hour fly-off, consider disassembling the array of ground stud,
nuts and terminals. Do final cleaning. Re-assemble with Locktite
271 or similar on threads and torque to recommended values.
It's unlikely that this joint needs to be opened over the lifetime
of the airplane. Making it semi-permanent after you've completed
the development phase of construction is not an unreasonable thing
to consider.
Bob . . .
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