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Deems Davis
Joined: 09 Jan 2006
Posts: 925
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 Posted: Tue Jun 19, 2007 9:13 am Post subject: Low Voltage plus Alt Loadmeter |
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THANK YOU sooo much for responding and for the additional information,
I've replied where appropriate below and asked an additional question
for some clarification.
Robert L. Nuckolls, III wrote:
| Quote: |
<nuckollsr(at)cox.net>
At 12:41 AM 6/19/2007 -0700, you wrote:
>
> <deemsdavis(at)cox.net>
>
> Warning this question is posed by an electron nerd....
>
> I'm planning the installation of probes & sensors for a Z14
> architecture. The Z-14 Figures in the 'Connection' seem to depict the
> shunts placed for use as 'loadmeters' i.e. they are placed on the
> Alternator B lead (which will measure Alt charging only). In
> reviewing Bob's notes. He favors a Battery Ammeter, the rationale
> seems to be that it measures both charging and discharging of the
> battery/s. This seems desirable to me.
The Z-figures represent the latest thinking with respect
to the optimal solutions. The chapter on electrical instrumentation
was written a long time ago and will be updated at revision 12. If
you have
only one electrical system monitor, it should be a low voltage
warning light.
I have the LR-3's from B&C which drive/include Low Voltage indicators.
|
| Quote: | If you add anything on top of that, I'd recommend
an expanded scale voltmeter on the e-bus and/or alternator
loadmeter(s) . . . but both of those are only small peeks at a variety
of test points you'll need to look at for diagnosis. Ammeters
and voltmeters are poor monitoring tools. And as diagnostic
tools, they are only a part of what's necessary for troubleshooting.
> However, I'm stumped as to where to locate the Shunts in the Z-14 so
> as to be able to connect Battery ammeters.
What kind of panel displays are you considering?
I have dual glass panels (EFIS) w a glass back-up. The Engine Interface
|
unit is a JPI product (black box) which captures information from probes
and sensors, it relies on Shunts for AMP meter input. The information
from the EIU black box is interpreted and displayed on graphic
indicators on a display page with the EFIS units.
| Quote: | If they're
steam-gages, then they'll likely use shunts but if they're
electronic displays, they'll most likely come with hall-effect
sensors. Hall sensors can be place ANYWHERE in the system that
you think is most useful to you for knowing how many electrons
per second are passing that point . . . however, adding shunts
in series with the battery as suggested in Chapter 7 is based
on wobbly logic and poor practice. However, a hall-sensor can
certainly be placed on a battery lead if you so choose.
A caveat on battery lead hall-sensors. When the starter hits the
battery with an inrush current of as much as 1000 amps, the magnetic
forces impressed upon the hall sensor are, shall we say, significant.
The hall sensor MUST (by certain pesky laws of physics) be fitted
with a core material that serves to restrain the field flux around
the wire and supply a proportional sample of that field to the
hall device. EVERY magnetic material has a retentivity value . . .
a measure of permanent "set" that the core material will take
on when excited by an extra-ordinary force.
Depending on the materials used in your hall sensor, the act
of starting the engine can cause a small but significant
semi-permanent "set" of the field flux in the core. This
will manifest itself as what is known as "offset" . . .
a fixed error value that shows up most strongly when
the stimulus to be measured is zero . . . the indicator
reads something other than zero due to the core's
retentivity and influence of the starter inrush current.
Based on this expanded thinking, recommendations for ammeter
locations were revised to what you have in your hands today.
OK, so I've got the low voltage indicators, and If I go ahead and
|
install the shunts per the Z-14 to supply Alternator loadmeters, I'm not
sure I understand how to interpret the information that I receive from
the Alternator loadmeters. What would this information be telling me? If
I understand it correctly (?) it would display the current that is being
output from the Alternator, correct? But if I understand correctly it
doesn't tell me that the battery is charging, (Is this what you mean
when you say that items 3 and higher have little or no significance in
Operations? can you illuminate?
| Quote: | Without knowing more about the specifics of any hall-sensor
that may be supplied to you, I cannot recommend that they
be used as battery ammeters EXCEPT where you avoid running
starter current through the conductors. This means backtracking
to the architecture common in 1965 C-172.
The best I know how to do at the moment suggests that active
notification of low volts is #1. A voltmeter on the e-bus
(gas gage for battery during alternator out operations) is
#2. Items 3 and higher have little or no significance in
the OPERATION of your airplane . . . so sprinkle sample
and display items about your electrical system as you see
fit and you budget allows. Just understand that items 3
and higher offer no useful functions in flight and there
won't be enough of them to do a detailed troubleshooting
study on the ground.
|
Trying to become less of an electron nerd
Deems Davis
RV-10
http://deemsrv10.com/
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nuckollsr(at)cox.net
Guest
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| Posted: Wed Jun 20, 2007 10:19 am Post subject: Low Voltage plus Alt Loadmeter |
|
|
At 10:12 AM 6/19/2007 -0700, you wrote:
| Quote: |
THANK YOU sooo much for responding and for the additional information,
I've replied where appropriate below and asked an additional question for
some clarification.
>
I have the LR-3's from B&C which drive/include Low Voltage indicators.
|
That covers the "essentials" . . .
| Quote: | >If you add anything on top of that, I'd recommend
> an expanded scale voltmeter on the e-bus and/or alternator
> loadmeter(s) . . . but both of those are only small peeks at a variety
> of test points you'll need to look at for diagnosis. Ammeters
> and voltmeters are poor monitoring tools. And as diagnostic
> tools, they are only a part of what's necessary for troubleshooting.
>
>>However, I'm stumped as to where to locate the Shunts in the Z-14 so as
>>to be able to connect Battery ammeters.
>
> What kind of panel displays are you considering?
I have dual glass panels (EFIS) w a glass back-up. The Engine Interface
unit is a JPI product (black box) which captures information from probes
and sensors, it relies on Shunts for AMP meter input. The information
from the EIU black box is interpreted and displayed on graphic indicators
on a display page with the EFIS units.
|
You use the plural version of shunt. Does the system
have more than one input for monitoring a current? Or
is there one input that can be switched to one of mulitple
shunts?
| Quote: | OK, so I've got the low voltage indicators, and If I go ahead and install
the shunts per the Z-14 to supply Alternator loadmeters, I'm not sure I
understand how to interpret the information that I receive from the
Alternator loadmeters. What would this information be telling me? If I
understand it correctly (?) it would display the current that is being
output from the Alternator, correct? But if I understand correctly it
doesn't tell me that the battery is charging, (Is this what you mean when
you say that items 3 and higher have little or no significance in
Operations? can you illuminate?
|
IF the bus is being supported at the design set point (i.e.
13.8 to 14.6 volts with 14.2 being nominal) AND assuming
further that the battery is in good shape and capable of
accepting a charge, then it IS being charged. There is no
value in having a minus-zero-plus indicator (battery ammeter)
to confirm this.
I'm presuming that you intend to MAINTAIN the battery with
respect to KNOWING that its capacity is sufficient to your
endurance needs, then knowing that the bus voltage is where
it should be is sufficient.
Alternator loadmeters are generally set up to display percent
of full load. See:
https://matronics.com/aeroelectric/Catalog/9007-120-1_Loadmeter.jpg
The instrument is then paired with shunt(s) that are sized
for the capability of the device being monitored. E.g. a
55A alternator should get a 55A shunt, a 20A alternator is
fitted with a 20A shunt. This allows one to switch a single
instrument to as many devices as you wish and know what
PERCENTAGE of that device's capabilities are in demand
at any given time.
As to operations . . . if the low volts warning light is
OUT (and the engine monitor confirms the bus at an acceptable
voltage) of what value is it as a pilot to know what ANY
current is? You have designed your system to carry all the
loads required for operation. Knowing what those loads are
at any given moment are incidental to piloting the airplane.
If the low voltage warning light is ON, of what value is
it to know what any current is? You have designed your
Plan-B operations and KNOW that the battery will support
Plan-B for x number of hours with loads you've already
decided to support.
My assertion is that every load situation for both normal
and alternator-out operations are known in advance and
knowing a reading only validates your Plan-B design
. . . it adds no value for comfortable completion of flight.
Once you're on the ground, you're going to find that
you need a LOT more data to interpret the failure and
deduce needs for repair. So unless you're going to install
a LOT of shunts and voltage sample points for the purpose
of diagnosing the failure from the pilot's seat, the
classic choices for instrumentation beyond a low-volts
warning and an e-bus voltmeter are a toss up.
Bob . . .
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Deems Davis
Joined: 09 Jan 2006
Posts: 925
|
| Posted: Thu Jun 21, 2007 12:39 am Post subject: Low Voltage plus Alt Loadmeter |
|
|
Thank you, The fog is beginning to lift
Deems
Robert L. Nuckolls, III wrote:
| Quote: |
<nuckollsr(at)cox.net>
At 10:12 AM 6/19/2007 -0700, you wrote:
>
> <deemsdavis(at)cox.net>
>
> THANK YOU sooo much for responding and for the additional
> information, I've replied where appropriate below and asked an
> additional question for some clarification.
>>
> I have the LR-3's from B&C which drive/include Low Voltage indicators.
That covers the "essentials" . . .
>> If you add anything on top of that, I'd recommend
>> an expanded scale voltmeter on the e-bus and/or alternator
>> loadmeter(s) . . . but both of those are only small peeks at a
>> variety
>> of test points you'll need to look at for diagnosis. Ammeters
>> and voltmeters are poor monitoring tools. And as diagnostic
>> tools, they are only a part of what's necessary for troubleshooting.
>>
>>> However, I'm stumped as to where to locate the Shunts in the Z-14
>>> so as to be able to connect Battery ammeters.
>>
>> What kind of panel displays are you considering?
> I have dual glass panels (EFIS) w a glass back-up. The Engine
> Interface unit is a JPI product (black box) which captures
> information from probes and sensors, it relies on Shunts for AMP
> meter input. The information from the EIU black box is interpreted
> and displayed on graphic indicators on a display page with the EFIS
> units.
You use the plural version of shunt. Does the system
have more than one input for monitoring a current? Or
is there one input that can be switched to one of mulitple
shunts?
> OK, so I've got the low voltage indicators, and If I go ahead and
> install the shunts per the Z-14 to supply Alternator loadmeters, I'm
> not sure I understand how to interpret the information that I receive
> from the Alternator loadmeters. What would this information be
> telling me? If I understand it correctly (?) it would display the
> current that is being output from the Alternator, correct? But if I
> understand correctly it doesn't tell me that the battery is charging,
> (Is this what you mean when you say that items 3 and higher have
> little or no significance in Operations? can you illuminate?
IF the bus is being supported at the design set point (i.e.
13.8 to 14.6 volts with 14.2 being nominal) AND assuming
further that the battery is in good shape and capable of
accepting a charge, then it IS being charged. There is no
value in having a minus-zero-plus indicator (battery ammeter)
to confirm this.
I'm presuming that you intend to MAINTAIN the battery with
respect to KNOWING that its capacity is sufficient to your
endurance needs, then knowing that the bus voltage is where
it should be is sufficient.
Alternator loadmeters are generally set up to display percent
of full load. See:
https://matronics.com/aeroelectric/Catalog/9007-120-1_Loadmeter.jpg
The instrument is then paired with shunt(s) that are sized
for the capability of the device being monitored. E.g. a
55A alternator should get a 55A shunt, a 20A alternator is
fitted with a 20A shunt. This allows one to switch a single
instrument to as many devices as you wish and know what
PERCENTAGE of that device's capabilities are in demand
at any given time.
As to operations . . . if the low volts warning light is
OUT (and the engine monitor confirms the bus at an acceptable
voltage) of what value is it as a pilot to know what ANY
current is? You have designed your system to carry all the
loads required for operation. Knowing what those loads are
at any given moment are incidental to piloting the airplane.
If the low voltage warning light is ON, of what value is
it to know what any current is? You have designed your
Plan-B operations and KNOW that the battery will support
Plan-B for x number of hours with loads you've already
decided to support.
My assertion is that every load situation for both normal
and alternator-out operations are known in advance and
knowing a reading only validates your Plan-B design
. . . it adds no value for comfortable completion of flight.
Once you're on the ground, you're going to find that
you need a LOT more data to interpret the failure and
deduce needs for repair. So unless you're going to install
a LOT of shunts and voltage sample points for the purpose
of diagnosing the failure from the pilot's seat, the
classic choices for instrumentation beyond a low-volts
warning and an e-bus voltmeter are a toss up.
Bob . . .
|
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nuckollsr(at)cox.net
Guest
|
| Posted: Thu Jun 21, 2007 7:44 am Post subject: Low Voltage plus Alt Loadmeter |
|
|
At 01:31 AM 6/21/2007 -0700, you wrote:
| Quote: |
Thank you, The fog is beginning to lift
Deems
|
Very good . . . that's the mission here on the List. If you
need more clarification, don't hesitate to ask.
Bob . . .
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