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bobbarrow
Joined: 04 Sep 2011
Posts: 9
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 Posted: Wed Jan 28, 2015 6:53 pm Post subject: Z14 with different bus voltages ? |
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I have a Vans RV7A (finished but not yet flying) with the Z14 architecture (dual buses with crossfeed contactor). The only deviation from Z14 is that the system does not automatically crossfeed between buses at engine start).
Bus 1 has a B&C LR3C voltage regulator, a B&C L40 alternator and an Odyssey PC680 AGM battery (17 Amphours). The aircraft starts on Bus 1 and all heavy current users are on this bus.
Bus 2 has a B&C LR3C voltage regulator, a B&C SD20 alternator and an Odyssey PC310 AGM battery (8 Amphours). This bus supports only the primary EFIS and one LightSpeed EI (magneto on the other ignition side).
The LR3C regulators are both factory set to approx 14.4 volts but there is likely to be a very small difference in the settings. In practical terms this means that when the crossfeed contactor is activated one alternator will tend to hog the load but the other alternator will tend to flicker on and off. I think that this cannot be desirable.
Odyssey Batteries have advised me that the optimum bus voltage for charging either the PC310 or PC680 is 14.4 volts but that the recommended min/max is 13.6 to 14.8 volts. The B&C installation manual for the LR3C regulator says that the voltage can be manually adjusted up and down. So here are my questions:
1. Should I create a voltage spread between the LR3C regulators such that when the crossfeed contactor is activated the L40 takes all the load and the SD20 justs sit idle in the background as a true standby alternator. In other words Bus 1 and Bus 2 would run at different voltages when the crossfeed is NOT activated.
2. If the answer to question 1 is YES then what would be the optimum differential voltages for the alternators to achieve a satisfactory outcome. Would say running the L40 at 14.6 volts and the SD20 at 14.1 volts (thus creating a spread of 0.5 volts) be desirable.
Bob Barrow
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user9253
Joined: 28 Mar 2008
Posts: 1944
Location: Riley TWP Michigan
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| Posted: Wed Jan 28, 2015 8:05 pm Post subject: Re: Z14 with different bus voltages ? |
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Yes, adjust the regulators to achieve a 1/2 volt difference. Adjust L40 to 14.2 volts and SD20 to 13.7 volts. That is just an educated guess on my part. Bob N is the expert. Since the small battery is not intended for starting, it will not be discharged very much. 13.7 volts will keep the small battery charged if the cross feed contactor is not energized. And 14.2 volts is optimum for the big battery.
Joe
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Joe Gores |
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yellowduckduo(at)gmail.co
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| Posted: Thu Jan 29, 2015 4:56 am Post subject: Z14 with different bus voltages ? |
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I do not close the crossfeed unless one alternator has quit and
therefore don't have any concern about running the same voltage on both
systems. Seems little point of having dual systems if a failure in one
can affect the other. My crossfeed does auto close during cranking but
again not an issue.
Ken
On 28/01/2015 9:53 PM, bobbarrow wrote:
| Quote: |
I have a Vans RV7A (finished but not yet flying) with the Z14 architecture (dual buses with crossfeed contactor). The only deviation from Z14 is that the system does not automatically crossfeed between buses at engine start).
Bus 1 has a B&C LR3C voltage regulator, a B&C L40 alternator and an Odyssey PC680 AGM battery (17 Amphours). The aircraft starts on Bus 1 and all heavy current users are on this bus.
Bus 2 has a B&C LR3C voltage regulator, a B&C SD20 alternator and an Odyssey PC310 AGM battery (8 Amphours). This bus supports only the primary EFIS and one LightSpeed EI (magneto on the other ignition side).
The LR3C regulators are both factory set to approx 14.4 volts but there is likely to be a very small difference in the settings. In practical terms this means that when the crossfeed contactor is activated one alternator will tend to hog the load but the other alternator will tend to flicker on and off. I think that this cannot be desirable.
Odyssey Batteries have advised me that the optimum bus voltage for charging either the PC310 or PC680 is 14.4 volts but that the recommended min/max is 13.6 to 14.8 volts. The B&C installation manual for the LR3C regulator says that the voltage can be manually adjusted up and down. So here are my questions:
1. Should I create a voltage spread between the LR3C regulators such that when the crossfeed contactor is activated the L40 takes all the load and the SD20 justs sit idle in the background as a true standby alternator. In other words Bus 1 and Bus 2 would run at different voltages when the crossfeed is NOT activated.
2. If the answer to question 1 is YES then what would be the optimum differential voltages for the alternators to achieve a satisfactory outcome. Would say running the L40 at 14.6 volts and the SD20 at 14.1 volts (thus creating a spread of 0.5 volts) be desirable.
Bob Barrow
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=437794#437794
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jan 29, 2015 5:39 am Post subject: Z14 with different bus voltages ? |
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At 06:55 2015-01-29, you wrote:
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I do not close the crossfeed unless one alternator has quit and
therefore don't have any concern about running the same voltage on
both systems. Seems little point of having dual systems if a failure
in one can affect the other. My crossfeed does auto close during
cranking but again not an issue.
Ken
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That was the spirit and intent of the Z-14 architecture.
Two batteries for cranking . . . if useful . . . but
if the failure gods smile on your airplane with benevolence,
the cross-feed contactor is never closed in flight.
They are intended to be separate, independent systems
with the capability to share if needed . . . but no
more.
If you DO operate with the contactor closed, then you
have Z-12 with two batteries. In that case the smaller
alternator should be regulated with an SB-1 regulator
set up to conduct operations as an always-on but
relaxed, stand-by alternator with active notification
of activation.
In that case, the standby regulator is set for 13.5
volts and never intended to charge batteries.
Bob . . .
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Mauledriver(at)nc.rr.com
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| Posted: Thu Jan 29, 2015 8:46 am Post subject: Z14 with different bus voltages ? |
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On 1/29/2015 8:38 AM, Robert L. Nuckolls, III wrote:
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<nuckolls.bob(at)aeroelectric.com>
At 06:55 2015-01-29, you wrote:
>
>
> I do not close the crossfeed unless one alternator has quit and
> therefore don't have any concern about running the same voltage on
> both systems. Seems little point of having dual systems if a failure
> in one can affect the other. My crossfeed does auto close during
> cranking but again not an issue.
> Ken
That was the spirit and intent of the Z-14 architecture.
Two batteries for cranking . . . if useful . . . but
if the failure gods smile on your airplane with benevolence,
the cross-feed contactor is never closed in flight.
It took me awhile to fully understand the spirit and intent of a
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straight up Z-14 but I have been operating that way for over year now
and am very satisfied. The (2) 960s give me what I need to reliably
turnover my cold IO540 with the lightweight starter....
| Quote: |
They are intended to be separate, independent systems
with the capability to share if needed . . . but no
more.
..and the peace of mind of having 2 separate electrical systems that
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can be linked if ever needed.
Given the (3) EFISs and the rest of the 'kitchen sink' panel I have, I
can turn the key parts on, do all my flight plan entry and clearance
work, and know that I still have at least 1 fresh battery to cross feed
with the somewhat discharged 2nd battery for a reliable start. This
capability was very important to me and my flying based on previous
experience with my Maule.
FWIW, I don't have any auto cross feed function during the start. That
would have been undesirable based on early experiences with the EFISs
re-booting due to low voltage during some cross feed starts. I learned
to do single battery starts in certain situations to avoid the (longish)
reboots - the same situations where a 2 battery start would otherwise be
most desirable. I eliminated that situation by adding a power
stabilizer to maintain adequate voltage levels during the start for the
EFISs. Now, an auto cross feed during the start would be nice but not
necessary.
| Quote: |
Bill "the happy RV10 driver" Watson
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bobbarrow
Joined: 04 Sep 2011
Posts: 9
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| Posted: Sun Feb 01, 2015 1:52 am Post subject: Re: Z14 with different bus voltages ? |
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| nuckolls.bob(at)aeroelect wrote: | That was the spirit and intent of the Z-14 architecture.
Two batteries for cranking . . . if useful . . . but
if the failure gods smile on your airplane with benevolence,
the cross-feed contactor is never closed in flight.
They are intended to be separate, independent systems
with the capability to share if needed . . . but no
more.
If you DO operate with the contactor closed, then you
have Z-12 with two batteries. In that case the smaller
alternator should be regulated with an SB-1 regulator
set up to conduct operations as an always-on but
relaxed, stand-by alternator with active notification
of activation.
In that case, the standby regulator is set for 13.5
volts and never intended to charge batteries.
Bob . . . |
It is not my intent to fly around with the crossfeed contactor closed for normal operations. However there might be circumstances where it is closed, such as for testing, or if inadvertently left on after a 2 battery start.
In that case one alternator is going to hog the load. Therefore wouldn't it make sense to ensure that a preferred alternator (in my case the bigger L40) simply takes all the load and the second alternator is not rapidly flickering on and off incessantly (which can't be good for it).
Is there a perceived problem with setting the SD20 to a slightly lower voltage? If there is no problem then what would be an ideal voltage spread.
Cheers Bob
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nuckolls.bob(at)aeroelect
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| Posted: Sun Feb 01, 2015 8:21 am Post subject: Z14 with different bus voltages ? |
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| Quote: |
Is there a perceived problem with setting the SD20 to a slightly
lower voltage? If there is no problem then what would be an ideal
voltage spread.
No, that IS the way it's done in Z-12.
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The 'standby' alternator is set lower such
that it relaxes but high enough to prevent
discharge of the second battery . . . which
guarantees that the second battery doesn't
get fully charged unless the cross-feed is
closed.
Two alternators set to the same voltage generally
don't 'argue' with each other but when we do that
on purpose, it's usually done with regulators
designed to effect load-sharing between paralleled
alternators. If the SD-20 is 'higher' . . . it would
pick up loads to the limit of its capacity whereupon
bus voltage sags and the other alternator starts
picking up the difference . . . no spectacular
or annoying events.
"Left on after a two-battery start"? I really
dislike that word "inadvertently". It's like
"I inadvertently let IAS decay and spun the
sucker in" . . . we're pilots. We are encouraged . . .
indeed expected to pay attention to critical things
and either automate potentially distracting
conditions . . . or design them out of the system.
If that's a real concern, perhaps "X_FEED CLOSED"
should be an item on your annunciator panel.
If you want single-battery start for the purpose
of avoiding brown-out resets . . . then your
airplane is a dual-battery/dual-alternator
split bus system for all but the most pressing
circumstances with rarified probabilities.
Given the disparity of battery sizes, two-battery
starts are probably in that rarified category
managed best by better management of the main
battery's condition.
I suggest that the two systems be treated as
completely independent. Both set to 14.4v and
the cross-feed switch ignored until you encounter
a situation where remembering that it's there
may be useful to you. With prudent preventative
maintenance and given the demonstrated reliability
of modern electrics, it seems likely that you'll
never need to close that switch.
Bob . . .
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