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dan(at)syz.com
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 Posted: Thu Feb 12, 2015 2:06 pm Post subject: Question about monitoring output in two alternator configura |
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Hi everyone.
I have an electrical system with dual alternators (primary and backup) and have a question with regards to monitoring their output current. My EFIS has the capability of monitoring each output separately, but considering that the alternators are wired such that only one can be on at a time, I'm not a big fan of this, since I don't want to get used to the view of an alternator output always reading zero during normal operation - it desensitizes a person in noticing if there ever is a real problem. (I used to fly a Mooney that had a red gear warning light always on when the gear were up, by terrible design. You get really used to seeing a red light always on, and then completely ignore it).
Instead, I'd rather have the EFIS just provide a display showing a single output of either alternator - whichever is producing current. What seems to me to be a simple way of achieving this would be to just tie the output of each alternator to the same side of the shunt (the terminal opposite that going to the contactor). Then, it would seem to me as though the shunt would just measure the combined output of both alternators, which in effect would be just the output of the alternator that's currently active. But when I asked the EFIS manufacturer about this, they implied that this wouldn't be the "right way" to do it - instead, I should use a hall sensor and pass both wires through it.
But I can't understand why using the shunt in this manner wouldn't work (other than the shunt becoming a single point of failure if it should blow like a fuse).
Can anyone provide any advice on this? Thanks!
Dan
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Dan Charrois
President, Syzygy Research & Technology
Phone: 780-961-2213
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edpav8r(at)yahoo.com
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| Posted: Thu Feb 12, 2015 2:53 pm Post subject: Question about monitoring output in two alternator configura |
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Does the EFIS offer an adjustable millivolts-per-ampere setting for the alternator current display? If so, you should be able to use any shunt that suits your load with no problem -- just match the EFIS setting to the shunt's specification. If this setting is fixed in the EFIS software, you'd have to use a shunt that matched it exactly (or build a circuit to scale the shunt output to match what the EFIS expects).
Based on the EFIS manufacturer's comment, it almost sounds like the EFIS is designed to use a Hall effect sensor. Is a particular part specified in the installation manual, or did the guy you talked to suggest one? If you can use a Hall sensor, it would eliminate breaks in the heavy wires, save you four crimp operations, and eliminate a failure mode in those wires.
Eric
On Feb 12, 2015, at 2:05 PM, Dan Charrois <dan(at)syz.com> wrote:
| Quote: | ...I'd rather have the EFIS just provide a display showing a single output of either alternator - whichever is producing current. What seems to me to be a simple way of achieving this would be to just tie the output of each alternator to the same side of the shunt (the terminal opposite that going to the contactor). Then, it would seem to me as though the shunt would just measure the combined output of both alternators, which in effect would be just the output of the alternator that's currently active. But when I asked the EFIS manufacturer about this, they implied that this wouldn't be the "right way" to do it - instead, I should use a hall sensor and pass both wires through it.
But I can't understand why using the shunt in this manner wouldn't work (other than the shunt becoming a single point of failure if it should blow like a fuse).
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dan(at)syz.com
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| Posted: Thu Feb 12, 2015 3:40 pm Post subject: Question about monitoring output in two alternator configura |
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| Quote: | Does the EFIS offer an adjustable millivolts-per-ampere setting for the alternator current display? If so, you should be able to use any shunt that suits your load with no problem -- just match the EFIS setting to the shunt's specification. If this setting is fixed in the EFIS software, you'd have to use a shunt that matched it exactly (or build a circuit to scale the shunt output to match what the EFIS expects).
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Good question - I'm not sure if it's adjustable (Advanced Flight Systems) - their manual talks about setting the zero point, but not if the mV/A is adjustable. I was just planning on using the shunt that came with the EFIS, since I have it already... and it should already be appropriately sized.
| Quote: |
Based on the EFIS manufacturer's comment, it almost sounds like the EFIS is designed to use a Hall effect sensor. Is a particular part specified in the installation manual, or did the guy you talked to suggest one? If you can use a Hall sensor, it would eliminate breaks in the heavy wires, save you four crimp operations, and eliminate a failure mode in those wires.
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It can use either (or both) a Hall effect or a shunt. The shunt came with it, but the Hall effect sensor is an additional cost, which is why I was figuring on just using the shunt it came with. Though minimizing breaks in the heavy wires, as well as a potential failure mode, is certainly worth considering. Of course, the next question I'd have for them is whether their hall effect sensor is big enough to accommodate both alternator B-leads..
Thanks for your response!
Dan
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Dan Charrois
President, Syzygy Research & Technology
Phone: 780-961-2213
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edpav8r(at)yahoo.com
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| Posted: Thu Feb 12, 2015 4:22 pm Post subject: Question about monitoring output in two alternator configura |
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On Feb 12, 2015, at 3:38 PM, Dan Charrois <dan(at)syz.com> wrote:
| Quote: | Good question - I'm not sure if it's adjustable (Advanced Flight Systems) - their manual talks about setting the zero point, but not if the mV/A is adjustable. I was just planning on using the shunt that came with the EFIS, since I have it already... and it should already be appropriately sized.
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Hilarious. They ship the EFIS a with a shunt, then tell their customers that using the shunt isn't the right way to set it up. Customer support by Laurel & Hardy.
Eric
do not archive
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dan(at)syz.com
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| Posted: Thu Feb 12, 2015 5:31 pm Post subject: Question about monitoring output in two alternator configura |
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To clarify (especially for those who may be looking to this thread in the future), they ship the EFIS with a shunt, and for a single alternator setup, it's a perfectly good and reliable method of monitoring the current generated by it. Their system supports either/and/or. Where they suggested the hall effect sensor is only for cases like mine with a backup alternator where they suggest it's a better way of a single point measurement from two different sources. I've had a very good experience with their customer support - I'm just trying to see if I'm missing anything critical as to why a shunt wouldn't be equally effective.
Dan
| Quote: | On 2015-Feb-12, at 5:16 PM, Eric Page <edpav8r(at)yahoo.com> wrote:
On Feb 12, 2015, at 3:38 PM, Dan Charrois <dan(at)syz.com> wrote:
> Good question - I'm not sure if it's adjustable (Advanced Flight Systems) - their manual talks about setting the zero point, but not if the mV/A is adjustable. I was just planning on using the shunt that came with the EFIS, since I have it already... and it should already be appropriately sized.
Hilarious. They ship the EFIS a with a shunt, then tell their customers that using the shunt isn't the right way to set it up. Customer support by Laurel & Hardy.
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Dan Charrois
President, Syzygy Research & Technology
Phone: 780-961-2213
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user9253
Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan
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| Posted: Fri Feb 13, 2015 6:51 am Post subject: Re: Question about monitoring output in two alternator confi |
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Becoming used to seeing zero amps on the standby alternator is of no concern because an EFIS can be setup to alarm at user selected parameters. In other words, you would setup the EFIS to alarm when the standby alternator current is NOT zero. Also, many EFIS allow the user to choose what to display on the main page. So, display the standby alternator current on another page, not the main page.
The purpose of having two alternators is for redundancy in case one fails. If the two alternators share one shunt, redundancy is defeated. Would both alternators be disconnected if the main alternator current limiter blows?
An ammeter on the standby alternator is not a necessity. In the event of main alternator failure, the voltmeter can be just as useful to help the pilot shed non essential loads. Just shut off loads one at a time until system voltage rises up to 13 volts (like Bob suggested).
Joe
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jonlaury
Joined: 06 Nov 2006
Posts: 336
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| Posted: Fri Feb 13, 2015 8:41 am Post subject: Re: Question about monitoring output in two alternator confi |
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[/quote]
Of course, the next question I'd have for them is whether their hall effect sensor is big enough to accommodate both alternator B-leads..
Thanks for your response!
Dan
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Dan Charrois
President, Syzygy Research & Technology
Phone: 780-961-2213[/quote]
Dan,
I set up my 2 alt system for the AFS 4500 using their HE sensor. I was able to fit #8 & #10 tefzel covered wires through it. The short # 10 wire (Alt 2) can easily handle the 25 amps for keeping my ED (EFI, EI) ship afloat.
John
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dan(at)syz.com
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| Posted: Fri Feb 13, 2015 9:27 pm Post subject: Question about monitoring output in two alternator configura |
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| Quote: | I have an electrical system with dual alternators (primary and backup) and have a question with regards to monitoring their output current.
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Thanks, everyone, for your clarification and insight on this. I can definitely see how running both alternators through a single shunt for current monitoring, though it would work electrically, does introduce a single point of failure that really doesn't need to be there. A hall sensor does seem the more sensible choice if I were to want to monitor the output of both alternators with a single sensor, or like Bob and others suggested, perhaps current monitoring of the backup alternator isn't even necessary considering that voltage monitoring of the bus is the primary indicator of electrical health anyway.
Dan
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Dan Charrois
President, Syzygy Research & Technology
Phone: 780-961-2213
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user9253
Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan
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| Posted: Sat Feb 14, 2015 10:19 am Post subject: Re: Question about monitoring output in two alternator confi |
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I have a great idea (sometimes they turn out to be not so great). 
If only a single shunt is installed, put it in the standby alternator output circuit where it will be most useful. When the main alternator fails, that is when monitoring the current can help the pilot choose which loads to turn on or off. Of course if the electrical system includes an E-Bus, then the loads that are most important have been predetermined. During normal operations, if it is desired to know what the current is, the main alternator can be shut off and current from the standby alternator can be observed. Doing that could be part of a pre-flight check to be sure that the standby alternator is working.
Joe
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