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nuckolls.bob(at)aeroelect
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 Posted: Sun Aug 31, 2014 4:50 pm Post subject: RV10-List: Shunt - Location |
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On Aug 30, 2014, at 6:47, Phillip Perry <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 . . . [quote][b]
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jluckey(at)pacbell.net
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| Posted: Mon Sep 01, 2014 10:19 pm Post subject: RV10-List: Shunt - Location |
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My comments are in orange (hope they are legible) & a few paragraphs at the bottom.
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. There may be a good reason for that...
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 think you need a BSEE to understand how to read a battery ammeter. Besides, if you are going to fly around in an electrically-dependent airplane, it probably wouldn't hurt to learn a little about batteries & ammeters. As pilots we do a lot of "trend monitoring".You won't find an ammeter in series with any bus structure on a biz jet . . . ammeters monitor generator loads. Not sure the Biz Jet analogy is apt here. There are lots of differences between a biz jet & our OBAMs. Biz jets have 2 of lots of things, engines, generators (maybe 3 w/ APU), pilots, etc. They have more complicated feed/source switching. The pilots go to recurrent training which includes systems training, etc. Very little of that applies to OBAMs.
In other words, just 'cause they do it in Gulfstreams doesn't mean we should do it in our little airplanes.
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. You can do load reduction with the Battery Ammeter...
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. Absolutely. I don't have any of the Z figures in front of me but I have a question. In the most complicated Z design, how many switches does the pilot have to flip in a worst case scenario?
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. Maybe... but, I didn't hear anyone suggest pushing, pulling, or fiddling, (especially w/ fuses)... (are those checklist items? 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.OK
Here's what I like about Battery Ammeters:
1. Using a zero-center ammeter provides info on the health of the battery charging system when everything is working properly. By learning to watch the charge taper after start-up you can glean info about the health of your battery & charging system. Learning to watch trends: "hey, that looked different than it did last time I started-up. What's up with that?" 2. When the alternator fails, the ammeter automatically becomes a load meter to aid the pilot in load-shedding, if necessary. Exactly the info you want, exactly when you need it (without flipping any switches). What I don't like about Alternator Load Ammeters:1. Alternator load is not a very useful piece of informationDo you really care what the alternator is putting out? Will you take any action if the alternator load is 25 amps or if it is 40 amps - as long as the alternator is working properly, it's replacing the necessary volume of electrons to handle the load... automatically. It is either working properly or it isn't.
2. Alternator Load is kind of a muddled number. It is neither buss load nor is it battery charge current. Those are 2 numbers I care something about but Alternator Load gives me neither.
I'm unaware of a scenario where I would see some value on the Alternator Ammeter and say "I better do something about that!" If it is too high, indicating a full-field condition then I presume the my over-voltage protection system will kick-in (probably before I even have time to look at the ammeter) and shut-down the regulator. If the alternator stops making power, my low-volts alarm will go off and my Alternator Load Ammeter is useless.
-Jeff
On Sunday, August 31, 2014 6:01 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:
On Aug 30, 2014, at 6:47, Phillip Perry <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 . . .
[quote][b]
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JOHN TIPTON
Joined: 17 Sep 2006
Posts: 239
Location: Torquay - England
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| Posted: Mon Sep 01, 2014 11:50 pm Post subject: RV10-List: Shunt - Location |
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An answer I understand: thank you Jeff
Sent from my iPad
----x--O--x----
On 2 Sep 2014, at 07:18 am, Jeff Luckey <jluckey(at)pacbell.net (jluckey(at)pacbell.net)> wrote:
[quote]My comments are in orange (hope they are legible) & a few paragraphs at the bottom.
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. There may be a good reason for that...
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 think you need a BSEE to understand how to read a battery ammeter. Besides, if you are going to fly around in an electrically-dependent airplane, it probably wouldn't hurt to learn a little about batteries & ammeters. As pilots we do a lot of "trend monitoring".You won't find an ammeter in series with any bus structure on a biz jet . . . ammeters monitor generator loads. Not sure the Biz Jet analogy is apt here. There are lots of differences between a biz jet & our OBAMs. Biz jets have 2 of lots of things, engines, generators (maybe 3 w/ APU), pilots, etc. They have more complicated feed/source switching. The pilots go to recurrent training which includes systems training, etc. Very little of that applies to OBAMs.
In other words, just 'cause they do it in Gulfstreams doesn't mean we should do it in our little airplanes.
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. You can do load reduction with the Battery Ammeter...
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. Absolutely. I don't have any of the Z figures in front of me but I have a question. In the most complicated Z design, how many switches does the pilot have to flip in a worst case scenario?
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. Maybe... but, I didn't hear anyone suggest pushing, pulling, or fiddling, (especially w/ fuses)... (are those checklist items? 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.OK
Here's what I like about Battery Ammeters:
1. Using a zero-center ammeter provides info on the health of the battery charging system when everything is working properly. By learning to watch the charge taper after start-up you can glean info about the health of your battery & charging system. Learning to watch trends: "hey, that looked different than it did last time I started-up. What's up with that?" 2. When the alternator fails, the ammeter automatically becomes a load meter to aid the pilot in load-shedding, if necessary. Exactly the info you want, exactly when you need it (without flipping any switches). What I don't like about Alternator Load Ammeters:1. Alternator load is not a very useful piece of informationDo you really care what the alternator is putting out? Will you take any action if the alternator load is 25 amps or if it is 40 amps - as long as the alternator is working properly, it's replacing the necessary volume of electrons to handle the load... automatically. It is either working properly or it isn't.
2. Alternator Load is kind of a muddled number. It is neither buss load nor is it battery charge current. Those are 2 numbers I care something about but Alternator Load gives me neither.
I'm unaware of a scenario where I would see some value on the Alternator Ammeter and say "I better do something about that!" If it is too high, indicating a full-field condition then I presume the my over-voltage protection system will kick-in (probably before I even have time to look at the ammeter) and shut-down the regulator. If the alternator stops making power, my low-volts alarm will go off and my Alternator Load Ammeter is useless.
-Jeff
On Sunday, August 31, 2014 6:01 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
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 . . .
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nuckolls.bob(at)aeroelect
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| Posted: Tue Sep 02, 2014 4:49 pm Post subject: RV10-List: Shunt - Location |
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Here's what I like about Battery Ammeters:
1. Using a zero-center ammeter provides info on the health of the battery charging system when everything is
working properly. By learning to watch the charge taper after start-up you can glean info about the health of your battery & charging system. Learning to watch trends: "hey, that looked different than it did last time I started-up. What's up with that?"
Yes, it has that functionality . . . my first car ('41 Pontiac) had one and it took a bit to figure out the nuances of behavior. But is THIS a useful way to track battery condition. If you're a day-vfr airplane and you don't care about battery capacity, then you run the battery until it doesn't crank the engine any more. You're more likely to replace the battery because it is given you soggy starts than if 'the needle is returning to zero just a tad too soon'.
If you have specific endurance goals then unless those goals allow you to run a battery down to 80% of new capacity, then you're not likely to see much of an accelerated recharge rate on the battery ammeter when in fact, it IS time to replace the battery.
2. When the alternator fails, the ammeter automatically becomes a load meter to aid the pilot in load-shedding, if necessary. Exactly the info you want, exactly when you need it (without flipping any switches).
Say what? Your Plan-B is "flip switches until you see what you like"? This presumes, of course, that what-you-like is consistent with prior knowledge of battery capacity and you KNOW that the what-you-like-reading is going to get you on the ground.
Plan-B is best crafted by (1) maintaining a battery at some level consistent with design goals and (2) knowing exactly what loads are to be shed after alternator failure - BEFORE TAKEOFF.
What I don't like about Alternator Load Ammeters:
1. Alternator load is not a very useful piece of information
Do you really care what the alternator is putting out?
Nope, that's what I've said. Ammeters are of little use as an in-flight, system management tool. Of course, you get the same behavior from the alternator load meter after engine start as you do with the -0+ battery ammeter . . . a peaking of demand while the battery is being recharged that tapers as the battery recovers. Same date.
Will you take any action if the alternator load is 25 amps or if it is 40 amps - as long as the alternator is working properly, it's replacing the necessary volume of electrons to handle the load... automatically. It is either working properly or it isn't.
Actually, I've had an instance for loosing one phase in an alternator on a car that I had bought. The a/c was out so I didn't run blower loads until months later during heating season. Only then did I discover that the battery would not get recharged during night ops with both head-lights and blower.
When diagnosing the system I discovered that the alternator was de-graded to about a 15-20A machine . . . adequate to all ops when the blower was off.
The factory stock alt warning light never did come on. In any case, you're correct that if a low-volts warning light is dark, then alternator output, what ever its limits are, is adequate for the current task.
2. Alternator Load is kind of a muddled number. It is neither buss load nor is it battery charge current. Those are 2 numbers I care something about but Alternator Load gives me neither.
Which is precisely why it's not a flight ops display . . .
I'm unaware of a scenario where I would see some value on the Alternator Ammeter and say "I better do something about that!" If it is too high, indicating a full-field condition then I presume the my over-voltage protection system will kick-in (probably before I even have time to look at the ammeter) and shut-down the regulator. If the alternator stops making power, my low-volts alarm will go off and my Alternator Load Ammeter is useless.
Absolutely . . . and so is the battery ammeter.
Lord Kelvin once opined:
“When you can measure what you are speaking about, and express it in numbers, you know something about it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts advanced to the stage of science.”
A load analysis is comprised of measurable values. Capacity checks produce measurable values. Endurance based on known capacity divided by verifiable load is a number base on measured values.
Look through the POH for any TC aircraft having a battery ammeter and see if the manufacturer offers a narrative on its use as a in-flight tool beyond an obvious failure of engine driven power source.
[img]cid:.0[/img]
Most are no more carefully calibrated than the stock ammeters on cars of the era . . . doing the battery ammeter was easy, doing a low volts warning light not so much. But it DID satisfy the FARs for offering the pilot a means of monitoring health of the GENERATOR . . . not the battery.
Nowadays, the low volts warning is child's play.
Bob . . .
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