jmjones2000(at)mindspring
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 Posted: Sun Aug 31, 2014 5:05 pm Post subject: Fwd: AeroElectric-List: Re: Shunt - Location |
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Begin forwarded message:
[quote]From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
Date: August 31, 2014, 16:48:24 AKDT
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: AeroElectric-List: Re: Shunt - Location
Reply-To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
On Aug 30, 2014, at 6:47, Phillip Perry <philperry9(at)gmail.com (philperry9(at)gmail.com)> wrote:
Last night I was thinking about shunt locations and it seems like there are 3 different electrical locations for it.
1) Connected in the B-Lead (to measure the output of the ALT).
If you're going to measure current anywhere, this is the FIRST choice . . . I will elaborate later . . .
2) Connected to the battery (to measure the load on the battery; but it misses the contributions of electrons coming from the ALT to the main buss.)
This is how it was done on cars and some airplanes for decades. Useful ONLY to the individual who KNOWS about how a battery behaves with a lot of electro-whizzies wrapped around it. Good diagnostic tool but it requires attention, memory (monitoring of trends) and an understanding of battery physics. I don't recommend it.
3) Immediately before the main buss. So the ALT and Battery can be sending electrons to the buss and I'll be measuring them before they enter the buss as they're consumed. Then I'm getting a measurement of true load (minus the start).
But you KNOW what that number is . . . right? This is the FIRST task for crafting an electrical system is to list everything that needs power, separate to appropriate bus, tabulate the total bus energy needed under various flight configurations. It's called a Load Analysis and EVERY TC aircraft is blessed with one.
You won't find an ammeter in series with any bus structure on a biz jet . . . ammeters monitor generator loads.
The PRIMARY electrical system monitor is active notification of LOW VOLTS. When the light comes on, you look to see if the alternator is putting out ANYTHING . . . MAYBE it has popped a diode and is still putting out some energy but at a reduced rate. You have the option of reducing load until the light goes out.
Are we talking actual SHUNTS or Hall-Effect Current Sensors. If the latter, one sensor can be used to monitor the output of both alternators in a dual system like Z-12 or Z-13/8
http://tinyurl.com/kgg8nva
http://tinyurl.com/ag46m2f
Check out any of the architecture figures at
http://tinyurl.com/5wxzn7
You will not find an ammeter shunt anywhere except on the alternator B-leads . . .
Your NUMBER ONE tool for dealing with electrical system malfunction is active notification of low voltage. Your response to that event should be . . . at most . . . the repositioning of a couple of switches whereupon you assume Plan-B for getting comfortably on the ground.
If your Plan-B calls for reading displays, flipping switches, pushing/pulling breakers, fiddling with fuses and/or WONDERING how long the battery is going to last . . . then you blew it before your airplane's first flight.
For the most part, an ammeter is useful for figuring things out AFTER you get back on the ground. Not having one available in flight should NOT be a matter of concern.
Bob . . .
[b]
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