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  #1  
Old 08-14-2022, 05:53 AM
Reflex Reflex is offline
 
Join Date: Jan 2015
Location: Kansas
Posts: 225
Default Yet another question on shunt location...

After reading enough material on where to put the shunt(s)to get me fully confused, I've decided that there is no agreed upon location. My aircraft configuration is:
  • Primary Alternator/external regulator
  • Back-up Alternator/external regulator
  • Manual switch over upon failure of alternator(s)
My thinking is to place the shunt on the battery rather than on the B-lead(s). Here's why:

Set Primary alternator to 14.2V
Set Back-up alternator to 13.8V

Won't the voltage will tell me if I have a failure? Ie: if below 14.2V the primary alt has failed, if below 13.8V back-up alt has failed. At that point I'd like to know what is being consumed from the battery.

Is this line of thinking sound?

One other question, why would I want to know the output of my alternator(s)? Seems if I have proper voltage, they are operational.

Thanks,

Fred
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  #2  
Old 08-14-2022, 05:56 AM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
Posts: 2,441
Default Yes but

Yes , if everything is going as expected, the voltage should tell you. But when the information will be the most important is when things are not going per plan. Then is not the time to be doing mental gymnastics to figure out what is wrong. JMHO

I have s simple system so in fact I have mine on the battery. Your system is a bit more complex, so It might warrant a different setup
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Last edited by PilotjohnS : 08-14-2022 at 05:58 AM.
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  #3  
Old 08-14-2022, 07:03 AM
DerekS DerekS is offline
 
Join Date: Apr 2013
Location: Ontario, Canada
Posts: 77
Default

Quote:
Originally Posted by Reflex View Post

One other question, why would I want to know the output of my alternator(s)? Seems if I have proper voltage, they are operational.

All valid approaches, no wrong choice in my mind.

I would also suggest thinking about it in the context of a pilot not as familar with the plane as they should be. Either clear annunciation or a placard. Alt1 amps / Alt2 amps makes it pretty clear, if relying on voltage a reminder placard of the voltages could make sense.

Derek
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  #4  
Old 08-14-2022, 07:31 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 7,487
Default

I see little value to knowing how much current is going to the battery. It only shows you how hungry the batteries are without giving a clear view on it's state of charge. Knowing how much current is coming out of the alternator will tell you how much current your ship is consuming. This is substantially more valuable information. Not going to list them all here - search.

Voltage will only tell you if an alternator stopped working or is sub optimal. Much better to know current AND voltage for in air diagnostics.
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Last edited by lr172 : 08-14-2022 at 07:34 AM.
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  #5  
Old 08-14-2022, 08:02 AM
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jcarne jcarne is offline
 
Join Date: Jul 2016
Location: Worland, Wyoming
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Default

I put mine to read current that is going into the busses. If alt. fails you will see it in voltage as you mention. In the air is a terrible time to trouble shoot just about anything electrical. I'm then getting on the ground to figure out the problem. The only purpose of the backup alt. is so that I can get get home instead of being stranded somewhere.
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  #6  
Old 08-14-2022, 09:53 AM
eric.the.blonde eric.the.blonde is offline
 
Join Date: Mar 2017
Location: Ann Arbor
Posts: 50
Default I Agree

Quote:
Originally Posted by Reflex View Post
After reading enough material on where to put the shunt(s)to get me fully confused, I've decided that there is no agreed upon location. My aircraft configuration is:
  • Primary Alternator/external regulator
  • Back-up Alternator/external regulator
  • Manual switch over upon failure of alternator(s)
My thinking is to place the shunt on the battery rather than on the B-lead(s). Here's why:

Set Primary alternator to 14.2V
Set Back-up alternator to 13.8V

Won't the voltage will tell me if I have a failure? Ie: if below 14.2V the primary alt has failed, if below 13.8V back-up alt has failed. At that point I'd like to know what is being consumed from the battery.

Is this line of thinking sound?

One other question, why would I want to know the output of my alternator(s)? Seems if I have proper voltage, they are operational.

Thanks,

Fred

I agree, the voltage reading tells you the source of your electrical power: primary alternator, standby alternator, or battery. This information gives shape to one aspect of your mission profile: fuel limited or battery limited.

Here's some of my thought process about shunts (YMMV):

Since I was focused on schematic z-12 (dual alternator, single battery) which shows a shunt on each b-lead and subsequently realizing my intended EFIS has only 1 shunt input, forced me to think long and hard about where that shunt should go.

Obviously, measuring one of the b-leads (presumably primary) I'd lose amperage information just when I'm more intently interested. Since the b-leads tie together on a single post, putting a shunt next to that and before further distribution of current is like reading either b-lead.

In the micro-miniscule chance that both alternators have failed, measuring any b-lead deprives me of amperage information just when it is most important. I then realized that in this failed alternator configuration and by putting the shunt next to the battery (my preference is the negative side), I am effectively reading the overall current draw whether I'm on the main+e busses or just the e-bus.

In other words, I agree with your line of thinking.

In this configuration, a normal reading of 14.2V/0 amps is enough information for me. Most days, I couldn't care less whether the ship is consuming 22.8 or 47.3 amps. A table can be built of various voltage/amperage combinations and their meanings.

If more current measurement locations are desired, I believe an EFIS accepts Hall-effect sensors as inputs (details I've not worked out). While I have not settled on one, the most likely location for the first one of these is the main bus. Unfortunately, Hall-effect sensors cost several times more than a shunt.
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  #7  
Old 08-14-2022, 09:56 AM
BillL's Avatar
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,739
Default

Quote:
Originally Posted by Reflex View Post
After reading enough material on where to put the shunt(s)to get me fully confused, I've decided that there is no agreed upon location. My aircraft configuration is:
  • Primary Alternator/external regulator
  • Back-up Alternator/external regulator
  • Manual switch over upon failure of alternator(s)
My thinking is to place the shunt on the battery rather than on the B-lead(s). Here's why:

Set Primary alternator to 14.2V
Set Back-up alternator to 13.8V

Won't the voltage will tell me if I have a failure? Ie: if below 14.2V the primary alt has failed, if below 13.8V back-up alt has failed. At that point I'd like to know what is being consumed from the battery.

Is this line of thinking sound?

One other question, why would I want to know the output of my alternator(s)? Seems if I have proper voltage, they are operational.

Thanks,

Fred
Agree with your sound thinking.

I have shunt in the battery-to-system there for two reasons: 1. The amp shunt will tell me what all the system demands are. 2. When an alternator fails, then I can still monitor ampere demand to manage to a specific number.

And - yes- -you can determine the alternator health by its voltage. I use voltage to assess the alternator health, it is the primary indicator of health. One caveat though . . you could use a discrete input to capture the 2nd alternator voltage if needed, I use a discrete for monitoring a backup battery voltage for drain.

Not sure why you desire a manual switch for the alternator though, a simple alarm light can be used to indicate the failure/backup active condition.
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  #8  
Old 08-14-2022, 11:52 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,835
Default

Quote:
Originally Posted by BillL View Post
SNIP
Not sure why you desire a manual switch for the alternator though, a simple alarm light can be used to indicate the failure/backup active condition.
+1
Assuming you are using the B&C backup alternator, or the nice Monkworkz generator on your vacuum pad there is no reason to have a manual switch.

If the primary alternator fails:
- With the B&C the yellow light that comes with the backup alternator VR comes on telling you the primary alternator failed
- With the Monkworkz it sends a signal when it is on to an “Aux Alt” light I programmed on the SkyView EMS display.

Thoughts on shunts:
- Three RVs and never installed one, and do not find a need to have it. During testing I know exactly what power draw on the plane so having a constant measure of that adds no new information - that and I consider voltage a better indication of operation and early indication of problems. I have no problem with people who do but I just dislike the clunky thing on the firewall - along with the big terminals. If you must have a shunt I suggest getting a current sensor from Grand Rapids: https://grtavionics.com/product-cate...rrent-sensors/
- If you use the Monkworkx generator it has a built in current shunt. All you do is wire it to your EMS.

Carl
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  #9  
Old 08-15-2022, 08:38 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,425
Default

The shunt should NOT carry starter motor current. That rules out connecting the shunt to the negative battery terminal. Not only could the shunt be damaged by starter current, but the added resistance will slow down the engine cranking speed. Carl's advice is good about using a hall effect sensor which only costs $25 more than a shunt. The vast majority of electrical problems are due to bad connections. Eliminating the shunt eliminates 4 connections: 2 crimps and 2 bolted ring terminals that can corrode or loosen or short to ground.
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