AeroElectric-List Digest Archive

Sat 09/22/18


Total Messages Posted: 5



Today's Message Index:
----------------------
 
     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)
 
 
 


Message 1


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    Time: 06:56:08 AM PST US
    Subject: Re: Alternator/shunt question
    From: "user9253" <fransew@gmail.com>
    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


    Message 2


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    Time: 09:51:23 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    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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    Time: 12:05:37 PM PST US
    Subject: Re: Alternator/shunt question
    From: "woxofswa" <woxof@aol.com>
    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


    Message 4


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    Time: 03:22:46 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    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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    Time: 07:22:46 PM PST US
    Subject: Re: Alternator/shunt question
    From: "user9253" <fransew@gmail.com>
    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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