From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: CofA
Date: Mon, 14 Jan 2019 08:00:51 +0800
References: <list-12098482@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-12098482@logan.com>
Message-Id: <4884F471-65A7-49D1-98AC-2C91E8DBE715@gmail.com>

Hi Charlie

Yes in relation to Aeroelectric, and I did a load analysis.
I was only going to rely on an over voltage alarm from the dynon, =
believing that OV wasn=E2=80=99t such a problem for modern automotive =
alternators, but given its electrically dependant perhaps the risk =
should be mitigated by a crowbar
What is the risk of over voltage from a modern automotive alternator and =
what happens next. Ive read various thoughts?
I thought the EC3, EM3, pumps, coils and injectors would survive 20v for =
time enough to put it on the ground.

Appreciate the feedback.

Steve


> On 14 Jan 2019, at 12:39 am, Charlie England ceengland7@gmail.com =
<flyrotary@lancaironline.net> wrote:
>=20
> On 1/13/2019 9:23 AM, Charlie England ceengland7@gmail.com wrote:
>>=20
>>=20
>> On Sun, Jan 13, 2019 at 9:00 AM Stephen Izett stephen.izett@gmail.com =
<flyrotary@lancaironline.net> wrote:
>> Hi there people
>>=20
>> We are in the process of getting the Certificate of Airworthiness for =
our Glasair powered by Renesis 4 port.
>>=20
>> Our AP is questioning the electrical system and wondering if we =
should have redundant supplies in case of electrical system failure.
>> Can any of you make comments on risk or preferred systems.
>>=20
>> Our setup has one automotive 40amp alternator and two HC20 (PC680 =
equivalent) paralleled (two batteries are used due to physical location) =
and mounted in tail for W&B and to keep cool.
>>=20
>> My planning was:
>> 1. Keep battery cool
>> 2. Replace every two years
>> 3. Battery Failure modes:
>>         Open circuit cell - Alternator and second battery do the job =
(No indication that one battery has failed)
>>         Short Circuit cell - Battery voltage drops and overcharges ??
>> 4. Alternator failure modes:
>>         Open Circuit - Low current and Low voltage alarm with 30min =
electrical reserve capacity
>>         Short Circuit - Charge circuit fuse blows then same as open =
circuit
>>=20
>> I understood that a shorted cell was very low risk in AGM=E2=80=99s =
if not overheated.
>> I thought creating redundancy may introduce other failure modes.
>>=20
>> Appreciate any feedback.
>> Steve
>>=20
>> Hi Steve,
>>=20
>> Are you signed up for the Matronics Aeroelectric List, and do you =
have a copy of the Aeroelectric Connection book? If not, then stop, do =
not pass go, and do both. Those issues are pretty well hashed out there.
>>=20
>> Now to specifics. Have you done a load analysis for your plane? If =
not, you might be a bit surprised at how much current can get sucked up =
by modern homebuilts, especially running automotive style injection. =
FWIW, 55-60 amp alternators are available for very little money (at =
least here in the USA) and likely will weigh no more than your 40A =
model. The higher output models will be running a lot farther from their =
max output (think heat).
>>=20
>> Failure modes: I'd agree that properly maintained, the battery is one =
of the least likely things to have a catastrophic failure. Alternators, =
not so much, though modern ones are pretty tough. You left out one =
failure mode: overvoltage due to regulator failure. That is the one that =
presents the biggest risk, because it can take out everything electrical =
in the a/c. There are simple protections for it, which result in the =
same plan B as your other failure modes: get on the ground within 30 =
minutes. Some have tested battery life in VFR a/c using Tracy's engine =
controller & minimal airframe electrical loads, & saw around 35-40 =
minutes life with a PC-680 size SLA battery.
>>=20
>> More later; time for breakfast.
>>=20
>> Charlie
>>=20
> Ok, refueled.
>=20
> The 'simple protections' mentioned earlier are an overvoltage =
detection module that monitors bus voltage and if it gets too high, has =
the power to shut down the alternator. B&C Specialty used to sell a =
little 'crowbar' module that did this job. It's fairly simple to =
fabricate your own, or you can buy something 'off the shelf' that can =
work in a similar manner. ex:
> https://www.tomtop.com/p-e1021.html
>=20
> Here in the USA, inspectors have accepted single alt, single battery, =
but most don't even question it; it's 'experimental'. But if you accept =
the premise that odds of multiple failures in a single flight =
*extremely* unlikely, and battery failures are almost always 'graceful' =
(meaning gradual and detectable), then the battery becomes the backup =
for the alternator. It's our job to decide how long we need that backup =
to last in operation, and to do our due diligence in maintaining the =
battery in good condition. That does mean doing capacity testing, =
because battery power and battery capacity are not the same thing. A =
very unhealthy battery can start an engine, but might have very reduced =
capacity to keep the electronics alive for the expected time. In my =
mind,  the biggest risk is the battery's variable capacity as it ages.
>=20
> I chose to add a 2nd identical alternator (~10 lb weight penalty), and =
my wiring architecture has my engine functions on one bus and the rest =
of the plane on a separate bus. Either bus can feed the other if there's =
a power feed issue to a bus (bad switch or contactor), and the engine =
will continue to run if the master must be turned off ('smoke in the =
cockpit' scenario).
>=20
> Charlie
>=20
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