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  #11  
Old 04-05-2018, 06:33 PM
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hgerhardt hgerhardt is offline
 
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Quote:
Originally Posted by rocketbob View Post
...A few times over the years I've had car batteries fail dead short.
I've never had one fail dead short, but I have had several that failed OPEN, probably when a cell connector failed internally.

And you guys testing what happens when disconnecting the battery with a running engine, you need to turn on/off a heavy load (landing lights, etc) while you're doing this. The regulator often can't keep up with a changing load and causes the alternator to go offline.
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  #12  
Old 04-05-2018, 08:17 PM
krw5927 krw5927 is offline
 
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Originally Posted by hgerhardt View Post
I've never had one fail dead short, but I have had several that failed OPEN, probably when a cell connector failed internally.

And you guys testing what happens when disconnecting the battery with a running engine, you need to turn on/off a heavy load (landing lights, etc) while you're doing this. The regulator often can't keep up with a changing load and causes the alternator to go offline.
Mine did. After disconnecting the battery master I turned on all loads in my plane one at a time so that eventually they were all on. Landing lights, pitot heat, all the big loads. Then reversed the process. Noisy, dirty power. But the alternator adjusted. But I agree that just because mine did, that one time, doesn't mean it's a reliable result.
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  #13  
Old 04-05-2018, 09:29 PM
crabandy crabandy is offline
 
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Quote:
Originally Posted by hgerhardt View Post
I've never had one fail dead short, but I have had several that failed OPEN, probably when a cell connector failed internally.

And you guys testing what happens when disconnecting the battery with a running engine, you need to turn on/off a heavy load (landing lights, etc) while you're doing this. The regulator often can't keep up with a changing load and causes the alternator to go offline.
I did not test this, itís on my list next time I have the cowl off.
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  #14  
Old 04-06-2018, 06:26 AM
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I would not disconnect the battery with the engine-alternator running in fear of a voltage spike or other voltage regulator confusion and possibly damaging some onboard electronics or the regulator. I am electron dependent to turn the fan and went this route, two batteries, one alternator, (certified PP 70 A) one EarthX on the firewall and one behind me, if anything happened on the firewall I wanted another power source on the other side of the firewall to power the EFII stuff, Backup battery power test for me is, AUX battery on, field off, master off. Then if all is well, master on, field on, AUX off.
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  #15  
Old 04-07-2018, 06:15 AM
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Am I wrong -- I thought you shouldn't run an alternator without a battery online?

This is a timely discussion, because I'm working through analyzing various failure modes of my electrical system. I'm using a Nuckolls Z-13 architecture. My backup alternator is a SD-8 dynamo, which doesn't need an energized field to make power, so perhaps its output would be enough to keep the main alternator field energized? I assumed that if I lost the main battery I'd want to shut down both alternators and fly on the backup batteries in my EFISs, which are on a completely separate circuit (G3X) / internal (G5). Am I missing the obvious here?

Rob

BTW, I'm not sure what the plural of EFIS is: EFISs? EFII?
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  #16  
Old 04-07-2018, 07:48 AM
krw5927 krw5927 is offline
 
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Originally Posted by Nihon_Ni View Post
Am I wrong -- I thought you shouldn't run an alternator without a battery online?
Aside from the possibility of the field not remaining self-exciting which would result in the alternator ceasing to produce power anyway, and the fact that there will be more than ideal (but not harmful) AC ripple in the power supply without the battery to filter, what would be the reasoning that you shouldn't do it?

Asking out of genuine interest.
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  #17  
Old 04-07-2018, 08:04 AM
drdriddle drdriddle is offline
 
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Any thoughts about a pop-out Ram air turbine to supply back-up for he backups if they fail? Aircraft spruce sells one (its pricey) but its only five pounds and provides 6 amps at 85mph. Would this be enough to power enough systems to get the plane close to a runway? yes there would be a definite drag penalty and it would take some engineering but it seems this crowd would be the perfect group of people to come up with a solution to get this to work.
or is this a pipe dream thats overly complicated? http://www.aircraftspruce.com/catalo...clickkey=25762
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  #18  
Old 04-07-2018, 08:34 AM
rv7charlie rv7charlie is offline
 
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Quote:
Originally Posted by drdriddle View Post
Any thoughts about a pop-out Ram air turbine to supply back-up for he backups if they fail? Aircraft spruce sells one (its pricey) but its only five pounds and provides 6 amps at 85mph. Would this be enough to power enough systems to get the plane close to a runway? yes there would be a definite drag penalty and it would take some engineering but it seems this crowd would be the perfect group of people to come up with a solution to get this to work.
or is this a pipe dream thats overly complicated? http://www.aircraftspruce.com/catalo...clickkey=25762
Only your plane can answer that question. If you're running electronic injection (high pressure electric fuel pump), 6A is not-quite-enough to keep the engine running, so it'll push the site of the crash farther out.

Sure, it can be done, but it'll likely be a lot more complicated than a 2nd alternator on the engine. And you need to ask the mfgr if it will survive at roughly twice that 85mph speed.
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  #19  
Old 04-08-2018, 06:13 AM
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Quote:
Originally Posted by Nihon_Ni View Post
Am I wrong -- I thought you shouldn't run an alternator without a battery online?

This is a timely discussion, because I'm working through analyzing various failure modes of my electrical system. I'm using a Nuckolls Z-13 architecture. My backup alternator is a SD-8 dynamo, which doesn't need an energized field to make power, so perhaps its output would be enough to keep the main alternator field energized? I assumed that if I lost the main battery I'd want to shut down both alternators and fly on the backup batteries in my EFISs, which are on a completely separate circuit (G3X) / internal (G5). Am I missing the obvious here?

Rob

BTW, I'm not sure what the plural of EFIS is: EFISs? EFII?
Electronic Fuel Injection and Ignition...https://www.flyefii.com/
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  #20  
Old 04-16-2018, 06:31 PM
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Quote:
Originally Posted by krw5927 View Post
Aside from the possibility of the field not remaining self-exciting which would result in the alternator ceasing to produce power anyway, and the fact that there will be more than ideal (but not harmful) AC ripple in the power supply without the battery to filter, what would be the reasoning that you shouldn't do it?

Asking out of genuine interest.
I'm not sure and I was hoping someone smarter than me would chime in. I understand the battery acts as a capacitor for alternator surges, or something of that nature, so it's a safety rule not a capability analysis.

I was taught years ago that Cessna used the Bendix switch for the master, so you cannot have the alternator on without the battery on first, as a safety measure.

I asked the question because I'm working through my electrical malfunction list, and wondering what to do if I have to turn the battery off. My master/main alternator is also on a single switch, so the main alternator would be shut off along with the battery. But my aux alternator is an SD-8 on a separate switch, and I'm not sure if I could safely leave this on without a battery or not.
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