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  #1  
Old 11-03-2020, 02:20 PM
Fenderbean Fenderbean is offline
 
Join Date: Jun 2018
Location: Huntsville AL
Posts: 78
Default Second alt

Is this accomplished be second belt drive or does everyone use the shaft version that seems to mount on the back?

I thought this was a cool way to go just incase the belt breaks?
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  #2  
Old 11-03-2020, 02:38 PM
airguy's Avatar
airguy airguy is offline
 
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Location: Garden City, Tx
Posts: 5,389
Default

A lot of folks use a vacuum-pad mounted standby alternator, after removing the vacuum pump.
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Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #3  
Old 11-03-2020, 03:05 PM
Fenderbean Fenderbean is offline
 
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Location: Huntsville AL
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Quote:
Originally Posted by airguy View Post
A lot of folks use a vacuum-pad mounted standby alternator, after removing the vacuum pump.
Ahhh maybe thats what this was I saw, had me scratching my head one two alts and the a/c compressors. Wish something made an a/c compressor that could mount the same way with a shear shaft.
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  #4  
Old 11-03-2020, 04:09 PM
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pierre smith pierre smith is offline
 
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Location: Louisville, Ga
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Default Plane power

I have the Plane power alternator driven by the gears in the accessory section and itís a 13.7 VOLT SYSTEM. You check it by running the engine up and shutting off the primary alternator. The voltage will drop until it reaches 13.7 volts and stabilizes, so you know itís working.

Regards,
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  #5  
Old 11-03-2020, 06:44 PM
Fenderbean Fenderbean is offline
 
Join Date: Jun 2018
Location: Huntsville AL
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Quote:
Originally Posted by pierre smith View Post
I have the Plane power alternator driven by the gears in the accessory section and itís a 13.7 VOLT SYSTEM. You check it by running the engine up and shutting off the primary alternator. The voltage will drop until it reaches 13.7 volts and stabilizes, so you know itís working.

Regards,
def on the list for the build, thanks for the information!
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  #6  
Old 11-04-2020, 10:49 AM
agent4573 agent4573 is offline
 
Join Date: Aug 2019
Location: Mountain view
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They also make that same pad mount alternator but regulated at full voltage as well. I believe you add a "B" to the end of the part number for the higher regulated version. It requires a switch since you can no longer leave both field wires powered at the same time. The full power backup is recommended if you're using a VP-X system since it controls the field wires of both alternators.
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  #7  
Old 11-04-2020, 12:00 PM
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Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
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I installed the very nice B&C 20 amp standby alternator on the vacuum pad, and recommend it and the associated B&C standby alternator regulator.

Note, the 20 amp unit - not the 30 amp. The 30 amp may not fit all application and 20 amps is more than you will need.

Setting this regulator to 13.5vdc or so means both alternator are always ďonĒ but the standby alternator does not produce power unless buss voltage drops to 13.5vdc (or whatever you set it to). This is what happens if the primary alternator fails.

No operator actions, no additional switches - the standby alternator just picks up the load.

You know this is going on as buss voltage drops to the 13.5vdc level from your normal ~14.1vdc, and the nice little yellow light that comes with the standby regulator comes on as well to tell you the primary alternator has failed.

Carl
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  #8  
Old 11-04-2020, 01:11 PM
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airguy airguy is offline
 
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Quote:
Originally Posted by agent4573 View Post
They also make that same pad mount alternator but regulated at full voltage as well. I believe you add a "B" to the end of the part number for the higher regulated version. It requires a switch since you can no longer leave both field wires powered at the same time. The full power backup is recommended if you're using a VP-X system since it controls the field wires of both alternators.
Why not? I have two alternators on my plane, and occasionally have them both powered up simultaneously.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2021 dues paid
N16GN flying 750 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, IFD440
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #9  
Old 11-04-2020, 01:53 PM
agent4573 agent4573 is offline
 
Join Date: Aug 2019
Location: Mountain view
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Quote:
Originally Posted by airguy View Post
Why not? I have two alternators on my plane, and occasionally have them both powered up simultaneously.
You can do it, its not recommended. The 2nd alternator is normally much smaller than the first, lets say 20 amps vs 60 amps as an example. If your backup alternator is regulated 0.05 volts higher than the primary and the plane is drawing 30 amps, you'll max out the backup alternator until its voltage starts to drop, only then will the primary start to produce power. This will likely lead to premature failure of the backup alternator. You'll never be able to regulate them identically to make sure they're sharing the load equally, so its better to only turn on one at a time, or to set your backup at a distinctly lower voltage than the primary. If you're running identical power ratings, say dual 60 amp then its even less likely to cause a problem if they're both on at once and set at similar voltages.
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Last edited by agent4573 : 11-04-2020 at 01:57 PM.
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  #10  
Old 11-05-2020, 09:35 AM
Fenderbean Fenderbean is offline
 
Join Date: Jun 2018
Location: Huntsville AL
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Dang it yet another place I enjoy coming to for information is making me feel like an idiot. You guys are smart lol
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