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velletazjp
Joined: 08 Oct 2019
Posts: 10
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 Posted: Wed Apr 01, 2026 12:37 am Post subject: Z12 Review for my Experimental Robin DR250 |
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Hello all,
I would greatly appreciate a review of my electrical wiring diagram, and I would be especially grateful for any feedback.
This is a 4-seat, wood & fabric, amateur-built, tailwheel aircraft. It's a clone of the famous Robin DR250.
The primary mission is day VFR, with a strong focus on mountain flying. The aircraft will also be used for cross-country flights, with occasional night VFR and light IFR operations (no icing - no precipitations) (supported by a certified GPS).
The engine is a Lycoming IO-360 (parallel valve) equipped with a Bendix-style mechanical fuel injection system. Ignition is currently provided by dual Slick magnetos, with provisions for a future upgrade to an electronic ignition system (PMAG).
The electrical generation system consists of:
- A PlanePower alternator (12V, 60A – ALY-8520LS) regulated by a B&C LR3E
- Backup alternator: B&C 410H with LS1B standby regulator
The avionics suite is based on Garmin G3X, including:
GAD27, GEA24
Dual-screen setup (PFD + MFD)
2-axis autopilot (GSA 28 servos)
The aircraft is equipped with:
Electric roll trim (Ray Allen T3-12A)
Electric pitch trim (Thomson Linear MD12)
Both trims are controlled through the Garmin autopilot servos.
The electrical distribution is organized around three buses:
MAIN BUS (20 positions)
E-BUS (10 positions)
BATT BUS (6 positions)
All using fuse blocks.
The architecture is based on the Z12 (dual alternator, single battery) design, with minimal modifications:
Replacement of fuselinks with ANL current limiters, as seen in more recent architectures
Replacement of shunt fuselinks with 1A breakers, per Garmin G3X installation manual recommendations
I am also intentionally trying to keep the number of circuit breakers to a strict minimum. At this stage, only two breakers are used, both dedicated to alternator field activation.
You will find the wiring diagram below.
Any comments, critiques, or suggestions are more than welcome.
Thank you very much for your time and expertise.
Best regards,
JP
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user9253
Joined: 28 Mar 2008
Posts: 1969
Location: Riley TWP Michigan
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| Posted: Sat Apr 04, 2026 1:21 pm Post subject: Re: Z12 Review for my Experimental Robin DR250 |
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Using one of Bob Nuckolls' diagrams with minimal modifications is a good way to go. You might consider using hall effect sensors instead of shunts.
Amploc has issued an END OF LIFE announcement for their KEY100 Hall Effect Sensor (and several others) effective June 1, 2026.
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wsimpso1
Joined: 04 Nov 2018
Posts: 39
Location: Saline MI
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| Posted: Fri Apr 10, 2026 5:49 am Post subject: Re: Z12 Review for my Experimental Robin DR250 |
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Using Z-12 is a great base.
I question having most of your Garmin suite on th essential bus. When do you need to turn off the main bus? Smoke in the cockpit is a big one. You don't 't know which wire orbox is smoking, so you kill the whole main bus. The more things you put on the Essential Bus, the more likely you are to not shut off the smoking stuff... We usually only want REALLY Essential stuff on the Essential Bus.
Then, after your smoking elements have gone to sleep, if you need something on the main bus, you can shut off everything on the main bus, turn on the Master, smell for smoke, try that item you need, smell for smoke, and get on the ground.
Now comes the nightmare. The smoke was being let out of something you really need. From my quick review, you have two EFIS, so gyro and altimetry functions are still available even if one EFIS is down, but you only have one GPS/NAV/COM. Good reason to have fully charged and engaged EFB and know how to engage it's backup display and Nav functions....
Billski
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wsimpso1
Joined: 04 Nov 2018
Posts: 39
Location: Saline MI
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| Posted: Fri Apr 10, 2026 5:49 am Post subject: Re: Z12 Review for my Experimental Robin DR250 |
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Using Z-12 is a great base.
I question having most of your Garmin suite on th essential bus. When do you need to turn off the main bus? Smoke in the cockpit is a big one. You don't 't know which wire orbox is smoking, so you kill the whole main bus. The more things you put on the Essential Bus, the more likely you are to not shut off the smoking stuff... We usually only want REALLY Essential stuff on the Essential Bus.
Then, after your smoking elements have gone to sleep, if you need something on the main bus, you can shut off everything on the main bus, turn on the Master, smell for smoke, try that item you need, smell for smoke, and get on the ground.
Now comes the nightmare. The smoke was being let out of something you really need. From my quick review, you have two EFIS, so gyro and altimetry functions are still available even if one EFIS is down, but you only have one GPS/NAV/COM. Good reason to have fully charged and engaged EFB and know how to engage it's backup display and Nav functions....
Billski
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velletazjp
Joined: 08 Oct 2019
Posts: 10
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| Posted: Mon Apr 13, 2026 7:31 am Post subject: Re: Z12 Review for my Experimental Robin DR250 |
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Thank you all for the very useful feedback.
I have updated the wiring accordingly and I am trying to stay as close as possible to Bob Nuckolls’ Z-12 philosophy.
My design intent for the endurance bus is the following:
in normal operation, all equipment is powered from the main bus
in case of loss of the main alternator, I want to be able to continue the flight on the endurance bus with the standby alternator
in case I need to shed the main bus, I want the endurance bus to keep only the truly necessary loads for safe continuation and landing
So I understand the concern about having too much Garmin equipment on the endurance bus, especially in a smoke-in-cockpit scenario. That is a very fair point. My goal is not to make the E-Bus a “second main bus”, but to preserve the minimum capability needed to keep control, navigate, communicate, and get on the ground.
Regarding the suggestion to use Hall effect sensors instead of shunts, I may have misunderstood the intent of that comment. My hesitation is that the AMPLOC KEY100 have an official end-of-life notice with no recommended replacement listed by the manufacturer. Since the G3X can also work with a conventional shunt, I am not sure a Hall sensor is the best path for a new installation at this point.
I also have a regulator/alternator integration question:
My main alternator is a Plane Power ALY-8520LS, and I plan to use a B&C LR3E regulator.
From what I understand:
the LR3 field output should go to the alternator F1 lead
F2 on some Plane Power/Hartzell units is either internally grounded or intended to be grounded externally, depending on configuration
I do not see a clear need for the AUX terminal when using the LR3E as a basic external regulator
Am I understanding this correctly?
More specifically:
Is the Plane Power ALY-8520LS considered fully compatible with the B&C LR3E?
Should I connect only F1 to the LR3E field output?
Should F2 be grounded, or is it already internally grounded on this alternator?
Should the AUX terminal remain unused in this installation?
My objective is to keep the architecture simple, robust, and as faithful as practical to the Z-12 concept, while still matching the Garmin/G3X installation requirements.
Thank you again for your time and for reviewing the updated diagram.
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