nuckolls.bob(at)aeroelect
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 Posted: Sun Jan 25, 2015 12:41 pm Post subject: Dual Alternator, Dual Battery, Single Bus |
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At 09:58 2015-01-25, you wrote:
| Quote: | Hello Bob,
My project will have a dual electronic ignition and an all-electric
panel. I intend to have the two battery and individual battery buses
per your Figure Z-30. I will have a single power bus that is
supplied by a 60 amp main alternator (Plane Power AL12-C60) with a
30 amp backup alternator (Plane Power FS1-14). The B-leads from both
alternators are connected through a Maxi fuse block to the hot side
of the starter contactor which then goes through the firewall to the bus.
I have some questions:
1) The 6 AGW B-leads from the alternators can easily carry 80
amps. Can I protect the both leads with 80 amp Maxi fuses? I believe
I might have read that this is okay in the List FAQs.
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Yes . . . as long as your bus feeder protection is much more
robust than the downstream protection . . . you can choose
about anything.
Consider the chain of protection for some device you might
plug in the wall . . .
Protection within the device needs to be much faster than
the breaker that feeds that outlet considering that it
too may be loaded to the maximum continuous rating of
the device. In other words, the failure inside the appliance
needs to have a small fraction of total effects on the
breaker in the panel. As you move upstream in the distribution
system, each branch is protected with careful attention
to dynamics such that a small event in somebody's house
doesn't trigger a 'blackout' in the neighborhood.
It might be better to use the miniature current limiters
like . . .
http://tinyurl.com/qj4vojb
In holders with vertical studs upon which you stack
the current limiter tabs and any/all ring terminals
with good force.
| Quote: | 2) According to Hartzell Engine Technologies (new owners of
Plane Power alternators) the main alternator puts out 14.2 v and the
backup puts out 13.6 v so if the main drops below 13.6 v the backup takes over.
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Yes . . . B&C pioneered that philosophy 20+ years
ago when we introduced the first pad-driven, wound-
field alternators into OBAM aviation.
| Quote: | Their wiring diagram does not show a diode in the circuit to
stop the flow of electricity from the bus to the B-terminal of the
backup alternator. I
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Doesn't need it. Alternators, unlike generators, are
incapable of taking power INTO their b-terminal. They
have diodes built in. See:
http://tinyurl.com/okegwfd
| Quote: | thought that this may affect the backup alternators life but the
technician at HET said not to worry about it.
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. . . now, if he had only explained why you wouldn't
have been left with a dangling question . . .
| Quote: | If I was really concerned I could turn the field off on the backup
under normal operation and turn it on in the event of a low voltage
indication. I prefer the automatic takeover of the backup so my
question is this, do I need to have a diode in the circuit to block
the reverse flow to the backup alternator or is the 0.6 v potential
no big deal? If it is prudent to add the diode what type of diode do
you recommend?
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Absolutely not. Wire with guidance from Figure Z-12 which
describes the ancestral configuration . . .
http://tinyurl.com/ag46m2f
| Quote: | 3) I also think I remember reading in the List FAQs (but can't
seem to find it) that in the event of the battery contactor opening
and disconnecting the battery from the bus, a load on the bus could
cause precipitous failure of the alternator. It would be nice to
have a battery contactor open indicator light. What is the best way
to add such a device to your dual battery circuit?
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As long as you don't have 250w incanescant landing lights
or an electro-hydraulic pump system, transient loads
capable of stalling a self-excited alternator don't
exist. Further, since you're running dual batteries,
you'd have to crap two contactors to set that scenario
up.
What does your power distribution look like. What electro-whizzies
from which which busses?
Bob . . .
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