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Z101B Aux Alternator and Overvoltage protection

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Patrick Nelson

Joined: 22 Nov 2020
Posts: 4

Posted: Wed Jan 20, 2021 6:36 pm Post subject: Z101B Aux Alternator and Overvoltage protection

For those with Z101B, what is your procedure for using the aux alternator?  My initial thought was to turn on the aux alternator with the main alternator and use a lower voltage setpoint for the aux regulator.  This allows the aux alternator to take over without intervention if the main alternator fails.



This causes a different problem, however.  The main regulator could fail resulting in an overvoltage condition.  The crowbar overvoltage protection circuits would blow the aux alt fuse and trip the main field circuit breaker.  Z101B shows the aux alt fuse forward of the firewall so it can't be replaced in flight.  Essentially, an overvoltage event on the main regulator will take out both alternators.



The solutions I can think of are:

* Enable the aux alternator only in case of main alternator failure.

* Move the aux field breaker/fuse to the main bus so it can be in the cabin, but this removes some fault tolerance of the design.

* Come up with an arrangement for the aux regulator that allows a slightly longer period before the overvoltage protection activates.  This seems like a fragile solution though.



Note: My aux alternator is a BC410 with an LR3C regulator.



Interested in hearing people's procedures for the aux alt switch and/or if they've deviated from the Z101B wiring diagram to solve this problem

Thanks!

-Patrick

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johnbright

Joined: 14 Dec 2011
Posts: 165
Location: Newport News, VA

Posted: Wed Jan 20, 2021 7:35 pm Post subject: Re: Z101B Aux Alternator and Overvoltage protection

Here's a Bob quote from 5 Dec, 2019:



"If you're using B&C alternator controllers in Z-12, the ov control systems are 'selective trip' . . . when an ov condition is detected, each ov system looks to see if 'my alternator' has field voltage on it. If so, then the 'my regulator' is bad and I trip only 'my alternator'.



If the field voltage is low or zero, the ov condition is generated by failure of the 'other regulator' it is expected to manage it's own shutdown operation."

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_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

Patrick Nelson

Joined: 22 Nov 2020
Posts: 4

Posted: Wed Jan 20, 2021 9:41 pm Post subject: Re: Z101B Aux Alternator and Overvoltage protection

Ah, thanks!

That makes sense.  If the voltage is over the set point then the field should have no voltage.  Presumably LR-3 OV protection kicks in if voltage at pin 3 exceeds 16V and there is voltage present on pin 4 (field winding).  That's easy enough to test next time I'm working on wiring.



Thank you for the info.

-Patrick

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