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Alternator/shunt question
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user9253



Joined: 28 Mar 2008
Posts: 1396
Location: Riley TWP Michigan

PostPosted: Sat Jan 05, 2019 4:35 am    Post subject: Re: Alternator/shunt question Reply with quote

80 percent is a good rule of thumb for alternator output. But it is not written in
stone. Operating temperature is the real deciding factor. If an alternator is
kept cool, it can be operated at 100 percent continuously. Manufactures' ratings
are most likely conservative (unless made in China). So alternators could even
put out more than 100 percent as long as they are kept cool.


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supik



Joined: 22 Aug 2018
Posts: 45

PostPosted: Sat Jan 05, 2019 4:52 am    Post subject: Re: Alternator/shunt question Reply with quote

Kellym wrote:
No alternator should be run at greater than 80% of its rating for any length of time.


I will comply with that requirement. Typical draw on e-bus: 19Amps

Kellym wrote:
Not sure what the mission is calling for two alternators with one battery.


IFR capability without the need to declare emergency if only 1 alternator fails and continue to destination or conveniently divert to a better suitable (wx) airport. Limited by fuel, not by battery capacity remaining. I wouldn't like to perform a missed approach on battery only and cycle the flaps, lights, fuel pump for another approach..

Planing for one mag & one electronic ign.

Kellym wrote:
I don't know how high adjustable regulators will let you
go, but there really isn't much reason to have the primary operate above
14.5, and you probably want the standby to be at something more like
13.5-13.8.


Thanks, I made a mistake by aiming the set points too high. I will aim for 14.4 for the Main and 13.8 for the Stby Alt.

Kellym wrote:
Of course if battery fails where only certified
aircraft batteries are available, the Concorde will bolt right in.


You are right, I would prefer Odyssey but the Concorde is available of the shelf in Europe.

I was thinking about one more bkp battery, but with the dual Alternator setup I shall be fine for the mission without adding additional weight and complexity. Shall thinks go really bad, the bkp EFIS has its own battery.


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supik



Joined: 22 Aug 2018
Posts: 45

PostPosted: Sat Jan 05, 2019 4:55 am    Post subject: Re: Alternator/shunt question Reply with quote

user9253 wrote:
80 percent is a good rule of thumb for alternator output. But it is not written in
stone. Operating temperature is the real deciding factor. If an alternator is
kept cool, it can be operated at 100 percent continuously. Manufactures' ratings
are most likely conservative (unless made in China). So alternators could even
put out more than 100 percent as long as they are kept cool.


I think this is a figure (80) you have to comply with when calculating your load analysis.. Its continuous operation should not exceed 80%, intermittent loads might force it up to 100% for a short period of time.


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Kellym



Joined: 10 Jan 2006
Posts: 1598
Location: Sun Lakes AZ

PostPosted: Sat Jan 05, 2019 7:11 am    Post subject: Alternator/shunt question Reply with quote

I don't know what EFIS you plan on. The Dynon backup batteries are
definitely less wt than a backup alternator. I don't know European
guidance for emergency on electrical failure. I don't want to be
continuing on battery only more than 30 min in IMC if possible. I don't
know I would want to continue much more if I had backup alternator. I
will probably revisit, at least as a mental exercise, what I would gain
from a standby alternator and the cost/benefit, as well as complexity to
add one. Given my home flight area usually allows VFR 360 days a year,
IFR capability is mostly for out-of-state trips. Mechanically it is
simple, although may require reconfiguration of oil filter adapter.
Kelly

On 1/5/2019 5:52 AM, supik wrote:

Quote:
Kellym wrote:
> Not sure what the mission is calling for two alternators with one battery.


IFR capability without the need to declare emergency if only 1 alternator fails and continue to destination or conveniently divert to a better suitable (wx) airport. Limited by fuel, not by battery capacity remaining. I wouldn't like to perform a missed approach on battery only and cycle the flaps, lights, fuel pump for another approach..

Planing for one mag & one electronic ign.


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PostPosted: Sat Jan 05, 2019 8:07 am    Post subject: Alternator/shunt question Reply with quote

Don’t know if this has been covered before but an aircraft that needs those electrons for an electronic fuel injection as well as an electronic ignition system changes the backup storage or generation requirements considerably.

Rich

Sent from my iPhone

Quote:
On Jan 5, 2019, at 9:09 AM, Kelly McMullen <kellym(at)aviating.com> wrote:



I don't know what EFIS you plan on. The Dynon backup batteries are definitely less wt than a backup alternator. I don't know European guidance for emergency on electrical failure. I don't want to be continuing on battery only more than 30 min in IMC if possible. I don't know I would want to continue much more if I had backup alternator. I will probably revisit, at least as a mental exercise, what I would gain from a standby alternator and the cost/benefit, as well as complexity to add one. Given my home flight area usually allows VFR 360 days a year, IFR capability is mostly for out-of-state trips. Mechanically it is simple, although may require reconfiguration of oil filter adapter.
Kelly

> On 1/5/2019 5:52 AM, supik wrote:
>
> Kellym wrote:
>> Not sure what the mission is calling for two alternators with one battery.
> IFR capability without the need to declare emergency if only 1 alternator fails and continue to destination or conveniently divert to a better suitable (wx) airport. Limited by fuel, not by battery capacity remaining. I wouldn't like to perform a missed approach on battery only and cycle the flaps, lights, fuel pump for another approach..
> Planing for one mag & one electronic ign.






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PostPosted: Sat Jan 05, 2019 8:36 am    Post subject: Alternator/shunt question Reply with quote

At 10:05 AM 1/5/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: A R Goldman <argoldman(at)aol.com>

Don’t know if this has been covered before but an aircraft that needs those electrons for an electronic fuel injection as well as an electronic ignition system changes the backup storage or generation requirements considerably.

Absolutely! That's what the load analysis
and FMEA are all about. Detailed discussions
about any one feature of the system will
be incomplete until that feature's duties,
limitations and effect on FMEA are thoroughly
understood.



Bob . . .


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supik



Joined: 22 Aug 2018
Posts: 45

PostPosted: Sat Jan 05, 2019 8:37 am    Post subject: Re: Alternator/shunt question Reply with quote

Kellym wrote:
I don't know what EFIS you plan on. The Dynon backup batteries are
definitely less wt than a backup alternator. I don't know European
guidance for emergency on electrical failure. I don't want to be
continuing on battery only more than 30 min in IMC if possible. I don't
know I would want to continue much more if I had backup alternator. I
will probably revisit, at least as a mental exercise, what I would gain
from a standby alternator and the cost/benefit, as well as complexity to
add one. Given my home flight area usually allows VFR 360 days a year,
IFR capability is mostly for out-of-state trips. Mechanically it is
simple, although may require reconfiguration of oil filter adapter.
Kelly

On 1/5/2019 5:52 AM, supik wrote:

Quote:
Kellym wrote:
> Not sure what the mission is calling for two alternators with one battery.


IFR capability without the need to declare emergency if only 1 alternator fails and continue to destination or conveniently divert to a better suitable (wx) airport. Limited by fuel, not by battery capacity remaining. I wouldn't like to perform a missed approach on battery only and cycle the flaps, lights, fuel pump for another approach..

Planing for one mag & one electronic ign.



The plan with Main Alternator failure:

IMC or NIGHT: Shed loads (1 switch) Land at nearest suitable airport. Then continue back home DAY only and VMC. The remaining configuration allows for a safe VFR day flight.

VFR & DAY: Shed loads (1 switch) Continue to destination, divert or fly back home with stopovers to refuel.

Europe's regulation is to be able to maintain ships critical items on battery for a minimum of 30min. My load analysis gives me an estimate of around 50min on battery only (calculated with 75% battery's capacity & very conservative max draw).


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Last edited by supik on Sat Jan 05, 2019 8:56 am; edited 1 time in total
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supik



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PostPosted: Sat Jan 05, 2019 8:48 am    Post subject: Re: Alternator/shunt question Reply with quote

nuckolls.bob(at)aeroelect wrote:
At 10:05 AM 1/5/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: A R Goldman <argoldman>

Don’t know if this has been covered before but an aircraft that needs those electrons for an electronic fuel injection as well as an electronic ignition system changes the backup storage or generation requirements considerably.

Absolutely! That's what the load analysis
and FMEA are all about. Detailed discussions
about any one feature of the system will
be incomplete until that feature's duties,
limitations and effect on FMEA are thoroughly
understood.



Bob . . .


I haven't found any special backup storage or generation requirements if running a combination of 1 Mag and 1 Electronic Ignition.

Maybe I miss something??


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PostPosted: Sat Jan 05, 2019 9:53 am    Post subject: Alternator/shunt question Reply with quote

Quote:

I haven't found any special backup storage or generation requirements if running a combination of 1 Mag and 1 Electronic Ignition.

Maybe I miss something??

Are we talking one or two alernators?
How much power is required by the
electronic ignition?



Bob . . .


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supik



Joined: 22 Aug 2018
Posts: 45

PostPosted: Sat Jan 05, 2019 11:30 am    Post subject: Re: Alternator/shunt question Reply with quote

nuckolls.bob(at)aeroelect wrote:
Quote:

I haven't found any special backup storage or generation requirements if running a combination of 1 Mag and 1 Electronic Ignition.

Maybe I miss something??

Are we talking one or two alernators?
How much power is required by the
electronic ignition?



Bob . . .


Two alternators
Surefly Electronic Ign 1.2 Amps


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PostPosted: Sat Jan 05, 2019 1:54 pm    Post subject: Alternator/shunt question Reply with quote

Quote:

Two alternators
Surefly Electronic Ign 1.2 Amps

Okay. If your design goals for operations
with aux alternator only are gasping for
amps, consider turning off the electronic
ignition for alt-out ops.

The engine will run fine and improve your
energy head-room for continued flight. Should
your mag become recalcitrant too (exceedingly
unlikely) . . . the electronic ignition will
be ready to pick up the slack. I suggest that
a lower, non-charging bus voltage for main alternator
out ops makes a lot of sense. You want to
tap 100% of aux alternator capability before
you worry about the battery . . . which in
all likelihood contains a lot of snort.


Bob . . .


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supik



Joined: 22 Aug 2018
Posts: 45

PostPosted: Sat Jan 05, 2019 2:08 pm    Post subject: Re: Alternator/shunt question Reply with quote

nuckolls.bob(at)aeroelect wrote:
Quote:

Two alternators
Surefly Electronic Ign 1.2 Amps

Okay. If your design goals for operations
with aux alternator only are gasping for
amps, consider turning off the electronic
ignition for alt-out ops.

The engine will run fine and improve your
energy head-room for continued flight. Should
your mag become recalcitrant too (exceedingly
unlikely) . . . the electronic ignition will
be ready to pick up the slack. I suggest that
a lower, non-charging bus voltage for main alternator
out ops makes a lot of sense. You want to
tap 100% of aux alternator capability before
you worry about the battery . . . which in
all likelihood contains a lot of snort.


Bob . . .


As mentioned before, I expect to be at 19Amps with Main Alt out ops (load shed), that calculation includes the electr ignition. With a 30Amps Stby Alt online what sense would that make to turn off the electr. ignition?


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PostPosted: Sat Jan 05, 2019 3:55 pm    Post subject: Alternator/shunt question Reply with quote

At 04:08 PM 1/5/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: "supik" <bionicad(at)hotmail.com>


nuckolls.bob(at)aeroelect wrote:
>
> >
> > Two alternators
> > Surefly Electronic Ign 1.2 Amps
>
> Okay. If your design goals for operations
> with aux alternator only are gasping for
> amps, consider turning off the electronic
> ignition for alt-out ops.
>
> The engine will run fine and improve your
> energy head-room for continued flight. Should
> your mag become recalcitrant too (exceedingly
> unlikely) . . . the electronic ignition will
> be ready to pick up the slack. I suggest that
> a lower, non-charging bus voltage for main alternator
> out ops makes a lot of sense. You want to
> tap 100% of aux alternator capability before
> you worry about the battery . . . which in
> all likelihood contains a lot of snort.
>
>
> Bob . . .


As mentioned before, I expect to be at 19Amps with Main Alt out ops (load shed), that calculation includes the electr ignition. With a 30Amps Stby Alt online what sense would make it to turn off the electr. ignition?

if you're not gasping for amps . . . then
nothing . . .

If you've accomplished a righteous load analysis
then you're golden.



Bob . . .


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