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creightonious
Joined: 10 Mar 2007
Posts: 40
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 Posted: Mon May 17, 2010 11:32 am Post subject: Dual EFI circuit(s) questions |
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I have a Rotax with 2 completely independent, stand-alone EFI systems. There is no commonality except fuel tank (at the selector) and electrical source (Batteries and alternator)
Figure Z-19 is a great help, and I intend to base the system on it but In my system there is no alternate or stand-by EFI system. Each is primary and co-equal, and is to be used on alternate flights. Only one is used at any given time.
Therefore, each must be able to be powered by a main bus and by the endurance bus (in the event of alternator failure or the failure of 1 battery or the failure of an EFI system).
One scheme for powering these is from an EFI bus powered by the main or engine bus and by the endurance bus with each feed isolated by a schottky diode to prevent feeding a dead bus.
I really am at a conceptual dead end here and all assistance is appreciated.
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nuckolls.bob(at)aeroelect
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| Posted: Mon May 17, 2010 12:38 pm Post subject: Dual EFI circuit(s) questions |
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At 02:32 PM 5/17/2010, you wrote:
| Quote: |
I have a Rotax with 2 completely independent, stand-alone EFI
systems. There is no commonality except fuel tank (at the selector)
and electrical source (Batteries and alternator)
Figure Z-19 is a great help, and I intend to base the system on it
but In my system there is no alternate or stand-by EFI system. Each
is primary and co-equal, and is to be used on alternate
flights. Only one is used at any given time.
Therefore, each must be able to be powered by a main bus and by the
endurance bus (in the event of alternator failure or the failure of
1 battery or the failure of an EFI system).
One scheme for powering these is from an EFI bus powered by the main
or engine bus and by the endurance bus with each feed isolated by a
schottky diode to prevent feeding a dead bus.
I really am at a conceptual dead end here and all assistance is appreciated.
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Use Z-16. Put each EFI on its own switch. #1
from a battery bus (not shown but easily added)
and #2 from the main bus. If the engine
is in trouble if BOTH systems are ON, then
arrange some form of mechanical lockout for
TWO SEPARATE switches to prevent both being
ON at the same time.
Exercise due diligence in maintaining your
battery such that its capacity is KNOWN
before flight. You'll save weight, money,
system complexity, and gain better system
reliability.
Bob . . .
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creightonious
Joined: 10 Mar 2007
Posts: 40
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| Posted: Mon May 17, 2010 9:29 pm Post subject: Re: Dual EFI circuit(s) questions |
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Bob and all,
I should have added that my all-electric Rotax has an internally-regulated 50amp alternator, belt driven off the back of the engine. The intake plenum blocks access to the pad at the gearbox, so a standby alternator is not an option.
I don't know that Z-16 is applicable.
A design goal is to have a real 2.5 hours in the event of an alternator failure. Engine system and e-radio load (including contactor) should total 12 amps.
I don't believe the stock charging system would handle even that load on a continuous basis-to say nothing of adding non-e loads like lighting, gauges, other radios, etc.
Speaking of contactors, is a 40 amp Bosch style relay an alternative? Saving .8 amps is worth someting.
I've been thinking 2 batteries for so long I'm having trouble letting go of Z-19. But 1ea 35 amp battery is lighter than 2ea 18amp ones...
Creighton
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nuckolls.bob(at)aeroelect
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| Posted: Tue May 18, 2010 5:42 am Post subject: Dual EFI circuit(s) questions |
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At 12:29 AM 5/18/2010, you wrote:
| Quote: |
Bob and all,
I should have added that my all-electric Rotax has an
internally-regulated 50amp alternator, belt driven off the back of
the engine. The intake plenum blocks access to the pad at the
gearbox, so a standby alternator is not an option.
I don't know that Z-16 is applicable.
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Hmmmm . . .is the "stock" permanent magnet alternator
still in place on the flywheel?
| Quote: | A design goal is to have a real 2.5 hours in the event of an
alternator failure. Engine system and e-radio load (including
contactor) should total 12 amps.
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If you still have the PM alternator, then 13/8 looks
attractive. The PM alternator is good for 18 amps
or so.
| Quote: |
I don't believe the stock charging system would handle even that
load on a continuous basis-to say nothing of adding non-e loads like
lighting, gauges, other radios, etc.
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| Quote: | Speaking of contactors, is a 40 amp Bosch style relay an
alternative? Saving .8 amps is worth someting.
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As a battery contactor? No. How close is your battery
mounted to where you sit? Can you consider a manual
battery switch?
| Quote: | I've been thinking 2 batteries for so long I'm having trouble
letting go of Z-19. But 1ea 35 amp battery is lighter than 2ea 18amp ones...
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Hmmmm . . . 12A seems like a LOT of energy for
a system this size. Do you know anyone who is flying
or at least doing ground runs on this engine? It
would be VERY useful to do your deliberations with
REAL numbers.
Bob . . .
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creightonious
Joined: 10 Mar 2007
Posts: 40
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| Posted: Wed May 19, 2010 1:04 pm Post subject: Re: Dual EFI circuit(s) questions |
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Bob,
To answer your questions on the EFI Rotax 912:
1) The stock Permagnet alternator is no longer in place,having been replaced by a Hall effect pickoff and the alternator pulley.
2) I agree that 12 amps sounds like a lot, but the hp pump (walbro) seems to draw about 7.2 amps (at) 40psi (SDSEFI's figures) but I don't know what the flow through the regulator and the return to the tank will be and how that will affect the amperage.
The computer is supposed to draw 0.11amps and the injectors draw 2.2(at)80 percent duty cycle and the coil pack draws3.2amps (at)6000rpm. For a total of 12.71amps. Granted this is at (presumably) max sea level T.O. power but since cruise is 5200rpm not a lot of coil load decrease can be expected.
The greatest load shed (at) cruise is maybe an amp from the injectors. So maybe 11amps but in all cases we must add an amp for the battery contactor. Ergo 12amps. A manual switch appears possible.
I suspect the pump will be semi-stalled at any cruise flow and I saw a Walbro graph predicting 5amps (at) 5gph and 40psi.
So maybe 10 amps?
But...GIGO applies since no hard data.
I wish I had some.
Regards,
Creighton Smith
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Wed May 19, 2010 5:12 pm Post subject: Dual EFI circuit(s) questions |
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At 04:04 PM 5/19/2010, you wrote:
| Quote: |
Bob,
To answer your questions on the EFI Rotax 912:
1) The stock Permagnet alternator is no longer in place,having been
replaced by a Hall effect pickoff and the alternator pulley.
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Does this mean that the original PM powered
ignition coils are gone too?
I've seen some rear pulley installations on
the 912 engines that still had their PM
alternators installed. Boy, given this engine's
special needs for electrons, it would REALLY
be nice if a main alternator failure wasn't
an emergency . . . or a condition that requires
dragging around 15# extra lead.
| Quote: | 2) I agree that 12 amps sounds like a lot, but the hp pump (walbro)
seems to draw about 7.2 amps (at) 40psi (SDSEFI's figures) but I don't
know what the flow through the regulator and the return to the tank
will be and how that will affect the amperage. A manual switch
appears possible.
|
Hmmmm . . . what do the guys who SELL this
engine recommend for system architecture
and operating philosophy?
Bob . . .
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