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  #1  
Old 06-15-2020, 07:41 AM
bkervaski's Avatar
bkervaski bkervaski is offline
 
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Default B&C Alternator + Backup

I went to watch a buddy of mine fire up his RV-10 for the first time and noticed that he didn't have a second field switch for his B&C backup alternator .. instead, there was a "hall sensor" in place to automatically switch to the backup.

I may swap my PP for this B&C+Backup alternator setup, any feedback on this type of install?

Can the regulators be installed on the hot side of the firewall?

Thanks for any advice
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Last edited by bkervaski : 06-15-2020 at 07:56 AM.
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  #2  
Old 06-15-2020, 08:05 AM
Lars Lars is offline
 
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Quote:
Originally Posted by bkervaski View Post
I went to watch a buddy of mine fire up his RV-10 for the first time and noticed that he didn't have a second field switch for his B&C backup alternator .. instead, there was a "hall sensor" in place to automatically switch to the backup.

I may swap my PP for this B&C+Backup alternator setup, any feedback on this type of install?

Does this take two regulators? If so, can the regulators be installed on the hot side of the firewall?
You don't need a field switch for the backup alternator, though their wiring diagram shows one. I installed the switch on my RV-7, my neighbor doesn't have one on his RV-14.

Installation instructions state that regulators (one for each alternator) must be installed on the cold side of the firewall.

The set voltage for the backup alternator is purposely adjusted lower (13 volts instead of 14-ish). The backup alternator coasts until the buss voltage reaches the lower value.

With the Hall sensor you get a fancy light warning light that glows steady once the backup alternator turns on, and starts blinking if the current draw is greater than what the backup alternator can put out. The sensor does not however turn on the backup regulator.

I've had mine come on once, when the B lead terminal on my primary alternator cable broke at the alternator due to a certain- ahem- error. Beings as my RV-7 has dual electronic ignitions, I was suddenly glad to have it.
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  #3  
Old 06-15-2020, 08:22 AM
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bkervaski bkervaski is offline
 
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Quote:
With the Hall sensor you get a fancy light warning light that glows steady once the backup alternator turns on, and starts blinking if the current draw is greater than what the backup alternator can put out. The sensor does not however turn on the backup regulator.
Hmm. So how are you enabling the backup regulator? With a switch?

I've built some regulators for RC so this might be an ignorant question as I'm sure the aviation regulators are far more advanced, but if the voltage goes low on the primary alternator, and the backup is enabled by the hall sensor, why would you need a separate regulator just for the backup?
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  #4  
Old 06-15-2020, 08:48 AM
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rwthompson67 rwthompson67 is offline
 
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https://bandc.com/product/standby-al...kit-homebuilt/

"If the primary alternator fails in flight, the SB1B-14 controller will sense the drop in system voltage and automatically activate the standby alternator."

I have this setup in my -14.BC460-H primary and BC410-H stby with LR3D-14 (primary) and SB1B-14 (stby) controllers. The controller/regulators should be mounted on the cool side of the firewall.

I have a single ALT field switch on the panel for the primary alternator, but have dedicated circuit breakers for both.

-Rick
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RV-8A N306R #82456 Bought/Sold
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Last edited by rwthompson67 : 06-15-2020 at 08:52 AM.
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  #5  
Old 06-15-2020, 09:05 AM
Lars Lars is offline
 
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Quote:
Originally Posted by bkervaski View Post
Hmm. So how are you enabling the backup regulator? With a switch?

I've built some regulators for RC so this might be an ignorant question as I'm sure the aviation regulators are far more advanced, but if the voltage goes low on the primary alternator, and the backup is enabled by the hall sensor, why would you need a separate regulator just for the backup?
Yes, I am enabling the backup field with a switch, but strictly speaking it's unnecessary. See also Rick's reply. That enables the regulator but doesn't turn on the alternator.

B&C's architecture for this requires two regulators, one for each. Again, the set voltage on the backup regulator is set lower than the primary, so the backup doesn't come on until the buss voltage drops to the backup regulator's set level. The Hall sensor does not turn on the backup. Its purpose is only for the (optional) warning light logic.
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  #6  
Old 06-15-2020, 09:39 AM
Bavafa Bavafa is offline
 
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The operation is just as described above.

However, the B&C alternators are so reliable that the backup alternator may never become in use unless "- ahem- error"

But in case if it happened, it is nice to have a backup that is just as reliable.
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  #7  
Old 06-15-2020, 09:52 AM
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rwthompson67 rwthompson67 is offline
 
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Quote:
Originally Posted by Bavafa View Post
The operation is just as described above.

However, the B&C alternators are so reliable that the backup alternator may never become in use unless "- ahem- error"

But in case if it happened, it is nice to have a backup that is just as reliable.
Primary alternator reliability is only half the equation...the belt being an equally critical component.
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RV-8A N306R #82456 Bought/Sold
RV-14 N327RT #140347 Slow Built/Flying
TBolt IO-390, Dual PMAGS, Hartzell composite, Dual HDX, GTN-650
Phase 1 Complete 4/17/2019
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  #8  
Old 06-15-2020, 11:12 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Lars View Post

The set voltage for the backup alternator is purposely adjusted lower (13 volts instead of 14-ish). The backup alternator coasts until the buss voltage reaches the lower value.
a permanent magnet alternator (e.g. SD-8) doesn't coast. It takes the same amount of energy to rotate the alt regardless of the amount of wattage it is supplying via that regulator (it just throws away excess energy below that required to reach the set voltage). The output will vary, depending upon the regulator request, but this doen't change the rotational load required to spin the alt. This is different than a std alternator, where the output, is determined by the current delivered to the alt's field circuit and driven load is proportional to the output wattage.

Letting the b/u alternator deliver full power and supplement via the main alternator would create less parasitic HP loss from your engine, as the HP required for the b/u is static and variable for the main.

Larry
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Last edited by lr172 : 06-15-2020 at 11:24 AM.
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  #9  
Old 06-15-2020, 12:19 PM
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N546RV N546RV is offline
 
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Quote:
Originally Posted by bkervaski View Post
Hmm. So how are you enabling the backup regulator? With a switch?

I've built some regulators for RC so this might be an ignorant question as I'm sure the aviation regulators are far more advanced, but if the voltage goes low on the primary alternator, and the backup is enabled by the hall sensor, why would you need a separate regulator just for the backup?
The hall sensor is a red herring in this discussion - the regulators do all the work. Both regulators are energized at all times. Since the primary regulator is set to a higher point than the secondary, it drives the primary alt to a high enough voltage that the standby regulator takes its alt offline.

Everything remains in this state unless the primary alt fails for whatever reason. At that point bus voltage begins to drop to what the battery can provide. When it falls below the set point of the standby regulator, it dutifully wakes up the standby alt.

This is the architecture I'm planning for my -8. I really like that there's no action required by the pilot to activate the standby in case of a failure. Fewer manual tasks to execute means fewer things to potentially screw up.
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  #10  
Old 06-15-2020, 03:40 PM
Lars Lars is offline
 
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Quote:
Originally Posted by lr172 View Post
a permanent magnet alternator (e.g. SD-8) doesn't coast. It takes the same amount of energy to rotate the alt regardless of the amount of wattage it is supplying via that regulator (it just throws away excess energy below that required to reach the set voltage). The output will vary, depending upon the regulator request, but this doen't change the rotational load required to spin the alt. This is different than a std alternator, where the output, is determined by the current delivered to the alt's field circuit and driven load is proportional to the output wattage.

Letting the b/u alternator deliver full power and supplement via the main alternator would create less parasitic HP loss from your engine, as the HP required for the b/u is static and variable for the main.

Larry
True enough. But the BC410-H alternator in question is not a permanent magnet alternator. Different animal.
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