Power & Grounding Scheme

by Ramanathan SG in 912iS Technical Questions 6 years ago

References: Latest BRP Powertrain Installation manual & Operator Manual for Rotax Engine Type 912iS Series.

Our Understanding is as follows:

• Rectifier A (Gen A) connects to EMS ground
• Rectifier B ( Gen B ) connects to Airframe ground
• External Alternator connects to Engine ground (assumed as EMS Ground)
• On-Board Aircraft Battery connects to Airframe ground

Reference 1 : “While the engine is running, the generator B can be used for the aircraft instrumentation” as per Installation manual, Chapter 24-00-00, section Internal Generator, page 10.
Reference 2 :“If generator A fails, generator B takes over its functions. The airframe electrical components and the instruments will be supplied by the battery. The battery will no longer be charged!” as per Installation manual, Chapter 24-00-00, section Internal Generator, page 10.
Reference 3 : External alternator grounding details as follows: “Grounding Via engine block.” as per Installation manual, Chapter 24-00-00, section External Alternator (Optional Extra), page 17.
Reference 4 : “If necessary (e.g. in case of supply failure by the internal generator) the EMS system can be powered by the on-board battery by activating the Battery Backup Switch” as per Operator Manual, section 7.4 (Electric system, Control elements), page 7-9.

Questions with respect to above references:
1. With respect to Reference 2, on the normal operation of Gen A, what is the current we can use from Gen B for Aircraft/Avionics load as per Reference 1?
2. With respect to Reference 2, upon failure of Gen A, Can we use Gen B for Aircraft/Avionics load? If yes, how much Amps could be usable for Aircraft/Avionics load from Gen B as per Reference 1?
3. With respect to Reference 3, External Alternator is connected to EMS ground and battery is not connected to EMS ground, does it mean that, Aircraft/Avionics load limited to spare capacity of Gen B 14 Amp [30Amp – 16Amp (EMS requirements) = 14 Amp] and in case of, additional power requirement, should it be drawn from external alternator? In a way, Aircraft/Avionics Load connects partially to Gen B & partially to External Alternator, is it correct, Please comment on this statement.
4. With respect to Reference 4, should we accommodate EMS load (16Amp) on the on-board Battery while deciding to size of the on-board battery? Please confirm.

Request to clarify all above.

Re: Power & Grounding Scheme

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.98k

Q.1 All 30 Amps are available for your use. Limiting continuous use to 70% (21A) capacity is a good design principal.
The battery will initially present a high current draw that will diminish as it re-charges after starting.

Q.2 If Gen-A Fails, Gen -B is no longer connected to the battery so The answer is ZERO Power is available for the Panel Loads.
Unofficially, if you were to activate the Backup Switch, You can "Steal" some of the Gen-B capacity for the Panel loads.
It will be in your best interest to keep this Parasitic load to the absolute minimum. Less than 10Amps. Essential equipment Only.

Q.3 The Engine Block is connected to the Airframe/Battery ground via the Starter Motor and is Totally separate from the EMS Ground.
The EMS Ground only exists within the EMS, The A-Regulator Ground Plate, and within the Engine Wiring Harness connecter to the A-Regulator.
Panel loads with a 40A External Alternator could be 40Amps Plus The 30 Gen-B Amps ... 70 Amps Nominal.
I would Not recommend using more than 70% (50A) of the 70 Nominal amps for continuous use. Design conservatively.
Using all 70 Amps intermittently is acceptable. A couple of minutes of powering a "Midnight Sun" Search lamp would be doable.

Q.4 16Amp∙Hours is a reasonable capacity for a Battery to allow for ≈ 30 minutes of flight after a Dual/Tripple Generator failure.
This should give you enough time to land before the ignition circuits fail due to lack of electrical power.

A HAPPY NOTE:
The Installation Wiring Diagram in Section 24-00-00, Page 28 of the Current Edition 2, Revision 0 Installation Manual now show the "Aircraft Loads" CORRECTLY connected to the Airframe Ground. Edition 1 Manuals showed the Airframe Load INCORRECTLY connected to the EMS Ground.
This had been a long-standing mistake that has now been rectified.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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Re: Power & Grounding Scheme

by Ramanathan SG » 6 years ago

Ramanathan SG

10 14 17

Thank you for a quick response.

Brief about our Airplane program: We have certified 2 seater Airplane with Rotax 914 engine and now migrating to upgraded glass cockpit avionics & electrical systems with Rotax 912iSc engine in place. We are in the stage of defining the avionics & electrical load structural analysis.

Based on your response, the normal and failure scenarios are defined in the attached document for your review and feedback. Questions are also raised.

Kindly go through each scenario and comment on it.

Refer:

NormalFailureConditions.pdf (You do not have access to download this file.)

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Re: Power & Grounding Scheme

by Ramanathan SG » 6 years ago

Ramanathan SG

10 14 17

For your information, we have procured Rotax engine for integration from M/s Varmaan aerospace Bangalore.

If you could review & share your feedback on the various failure scenarios (above attachment), it will be useful for us to arrive a conclusion on the Electrical system architecture. Thanks in advance.

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Re: Power & Grounding Scheme

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.98k

The external alternator is Always available to power the panel loads.
In the event of a double Internal Gen Failure, the Ext-Alt could power the Panel and the ECU through the Backup-Power Switch.

You have a fundamental misunderstanding about the Battery.
The Battery is never to be considered a source of current in your power budget.
The Battery has a 20 Amp-Hour capacity.
It is not a 20 Amp source of current (Or even a 4 Amp source of current.)

By Analogy; if the generators were hoses capable of delivering 20-40 Gallons per hour;
The Battery would be a 20-gallon Barrel of water.
The Generator(Hose) can deliver 20-40 amps(Gallons) per hour indefinitely.
The Battery(Barrel) can deliver 20 Amps(Gallons) in an Hour or it could deliver 1 Amp(Gallon) for 20 Hours.
However, once it is empty, that is all you're going to get.
That is why the Battery is specified as 20Amp-Hour; NOT 20 Amp!

Unlike the Generators, The Battery is capable of delivering Hundreds of Amps for a short period.
1200 amps for 60 seconds is the same amount of power as 20 amps for an hour.
This is why it can power the starter motor for at least a few 10's of seconds.

The Battery's primary purpose is to start the engine and then get recharged but otherwise just be dead weight for the rest of the flight.
If needed in an emergency it can be used as a power source for a short period.
if fully charged, 20 Amp-Hours should give you 30-60 minutes of flight time before all power is depleted.

Do not include the battery in the Power budget.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

Thank you said by: RotaxOwner Admin

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Re: Power & Grounding Scheme

by Ken Ryan » 6 years ago

Ken Ryan

28 369 968

Bob Nuckolls (Aeroelectric) refers to the ship's battery as THE most reliable power source, providing it is properly inspected and maintained.

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Power & Grounding Scheme

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