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Old 06-23-2020, 12:28 PM
Reflex Reflex is offline
Join Date: Jan 2015
Location: Kansas
Posts: 198
Default Nuckolls Z-12 Basic Question....

After pouring through a significant number of wiring diagrams on this site and looking though several others, I've decided that staying as close as possible to Bob Nuckolls Z-12 diagram would be best for me. Some of you have a real knack for seeing things in a diagram that I just don't. With this mind, I still have a question.

Below is the Z-12 wiring diagram from The AeroElectric Connection. I have a couple of questions:
  • Why is there a Hall Effect sensor AND an amp meter on the battery side of the secondary alternator?
  • If this is necessary, why isn't there both on the primary alternator?

See lower right side of the drawing below denoted by the red arrows.

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Old 06-23-2020, 02:33 PM
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MarkW MarkW is online now
Join Date: Sep 2011
Location: Edgewater, FL. X50
Posts: 1,183

The B & C standby alternator or Dynamo that is shown uses a SB1B-14 regulator and that is the way it is wired. Sensor not needed on a regular alternator.
RV9 - N14MW - Flying
G3X - ECI Titan I0-320
Catto three blade prop
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Old 06-23-2020, 04:17 PM
terrye terrye is offline
Join Date: Feb 2010
Location: Vancouver, BC, Canada
Posts: 970
Default Nuckolls Z-12 Basic Question....

The standby alternator voltage regulator is set lower than the primary. The sensor on the standby alternator alerts the standby voltage regulator that the voltage from the primary alternator is low (failed main alternator) and energizes the standby alternator to pick up the load. Each alternator has a current shunt (for the ammeter display) so you know what each alternator is putting out.

Pretty sure Bob Nuckolls explains this in the AeroElectric Connection
Terry Edwards
RV-9A (Fuselage)
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Old 06-23-2020, 04:34 PM
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mfleming mfleming is offline
Join Date: Sep 2016
Location: Joseph, Oregon
Posts: 817

You may be interested in Bob's latest dual alternator configuration Z101. He seems to be moving on from Z12. I think the latest thinking is with two reliable alternators an endurance bus is not needed.

Z101 shows an engine bus for an all electric ignition system. Just cut that part out if you using mags/Pmags or ShureFly.

I thought I wanted dual alternators when first planning my electrical system but realized with a TCW IBBS back up battery I didn't need the expense and complexity of two alternators. Here's my system which is a cut down version of Z101
Michael Fleming
Joseph, OR
sagriver at icloud dot com

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Last edited by mfleming : 06-23-2020 at 04:39 PM.
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Old 06-24-2020, 09:27 AM
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mburch mburch is offline
Join Date: Feb 2005
Location: Oregon
Posts: 1,322

According to the documentation for the SB1B-14 standby regulator, the Hall effect current sensor is optional. It is used to allow the regulator to flash the "STBY ALT ON" indicator lamp when the current being supplied by the standby alternator exceeds a threshold (which is I assume is around 20A). With any kind of modern electronic engine monitoring system, you can probably leave this out.
Matt Burch
RV-7 (last 90%)

Any opinions expressed in this message are my own and not those of my employer.

Last edited by mburch : 06-24-2020 at 09:52 AM.
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