Today's Message Index:
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1. 06:56 AM - Re: Alternator/shunt question (user9253)
2. 09:51 AM - Re: Alternator/shunt question (Robert L. Nuckolls, III)
3. 12:05 PM - Re: Alternator/shunt question (woxofswa)
4. 03:22 PM - Re: Re: Alternator/shunt question (Robert L. Nuckolls, III)
5. 07:22 PM - Re: Alternator/shunt question (user9253)
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Subject: | Re: Alternator/shunt question |
Yes, the ammeter will display reasonably correct. Look at it this way:
Even though the main alternator is rated for 60 amps, most of the time it is only
putting out about half of its capacity. The shunt will not know which alternator
is sending 30 amps through it. The load determines the current, not the
alternator.
Shunts have been known to fail, usually because of a loose connection that makes
heat.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=483311#483311
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Subject: | Re: Alternator/shunt question |
At 04:22 PM 9/21/2018, you wrote:
>
>Question. If I run a 30amp backup alternator
>through the same shunt (Dynon) as the primary 60
>amp alternator., mating at the shunt entry and
>sharing the single cable at the shunt exit (wired as a battery load meter)
...
You can run as many wires as you like
through a current sensor. The instrument
reading the current sensor will display
the SUM of the currents in all wires.
So, if two alternator b-leads share the
same sensor, then the instrument displays
only the operative alternator -OR- the
sum of their efforts depending if they
are both ON.
However, b-lead monitoring of the alternators
is NOT a battery load meter.
Know that an ammeter is NOT generally considered
a systems management tool for flight ops. It's
a diagnostic tool that will sometime yield useful
information . . . ON THE GROUND for chasing and
subduing electro-gremlins.
But it's important to know the significance of
the displayed current reading. If only b-leads
traverse the sensor, then you will never see
the minus-zero-plus readings reminiscent of
the legacy automotive ammeters popularized by
Henry Ford and contemporaries.
Battery ammeter readings are not definitive
indicators of system performance and not recommended
for new construction.
>When the primary is offline, would the amp draw
>shown for the backup alternator be reasonably
>correct or would it show artificially
>low? Would it=99s own distinct shunt be
>required give an accurate measurement of alternator output?
The Dynon display for current will be as accurate
as the instrument's designed capability irrespective of
how many signal sources are being impressed on the
sensor.
The most useful indicator of system
performance is the voltmeter . . . which is
easily augmented by ACTIVE NOTIFICATION OF
LOW VOLTAGE . . . your first lines of defense
against the dark-panel syndrome.
Bob . . .
Message 3
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Subject: | Re: Alternator/shunt question |
Thanks for the responses. Let me break the scenario down further.
I recently installed the B&C 30 amp backup alternator.
On my first longish flight to test the system I flew with basic essentials running
at 2500 rpm. Turning off both alternators, my ammeter read minus (-9) Amps
at 12.5 volts. Turning on the standby alternator, the ammeter showed minus
(-2) amps at 12.9 volts which stayed more or less constant for several minutes.
Obviously the backup is producing power, it just doesnt seem to be producing as
much as I was expecting at what looks to me to be about 7 Amps. What I am trying
to determine is if it is a low production issue, false indication issue, or
a misinterpretation of correct indications.
--------
Myron Nelson
Mesa, AZ
Flew May 10 2014
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=483316#483316
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Subject: | Re: Alternator/shunt question |
At 02:04 PM 9/22/2018, you wrote:
>
>Thanks for the responses. Let me break the scenario down further.
>
>I recently installed the B&C 30 amp backup alternator.
>
>On my first longish flight to test the system I
>flew with basic essentials running at 2500
>rpm. Turning off both alternators, my ammeter
>read minus (-9) Amps at 12.5 volts. Turning on
>the standby alternator, the ammeter showed minus
>(-2) amps at 12.9 volts which stayed more or
>less constant for several minutes.
>Obviously the backup is producing power, it just
>doesn=99t seem to be producing as much as I was
>expecting at what looks to me to be about 7
>Amps. What I am trying to determine is if it is
>a low production issue, false indication issue,
>or a misinterpretation of correct indications.
If your ammeter does indeed produce minus readings
with the alternator(s) OFF, then it is indeed
wired as a battery ammeter and should have NO
b-lead wires running through it.
If the standby alternator boosts the bus voltage
to something greater than 13.5 volts, then it
is carrying ALL system loads and perhaps adding
a bit to recharging the battery.
If this condition is true, then the alternator
is just fine irrespective of what the b-lead
current might be.
An alternator under regulation will deliver
no more current than the system demands of it.
B-lead current will be electro-whizzie demands
added to battery demands . . . and could
be quite low. If your bus voltage is correct,
then the alternator is fine.
Can you publish a schematic of how the current
sensor is installed in your system?
Bob . . .
Message 5
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Subject: | Re: Alternator/shunt question |
Myron, based on your description, I agree that the aux alternator is putting out
7 amps. Perhaps the alternator is not spinning fast enough to generate its
rated capacity.
Looking at the attached picture from a Dynon manual, confirm that the shunt is
in location A, and not B or C.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=483322#483322
Attachments:
http://forums.matronics.com//files/shunt_location_867.jpg
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