Dual Alternator Isolation Schematic

[LOCARRE]

Hi all,

On my airplane, i want to install standby alternator B&C on vaccum pad.

Because i'm using 2 shunts actually with my main alternator, i considered to use isolation relays to select proper alternator when needed.

Anyone installed Bosch 75 amp relays to control output of each alternators?

Attached my proposed installation schematic, if you see some improvements could be done, it's welcome..

Attached my schematic in pdf

View attachment CCF_000004.pdf

regards,

Louis Carre
CGGVX

 

[Carl Froehlich]

Not sure why you would want to do this. The beauty of this standby alternator is that it will automatically pick up the load if the primary alternator fails. You know it has the load as the nice yellow lamp that comes with the standby alternator regulator comes on. No pilot action.

Adding switches, relays and such just adds more failure modes, and increasing pilot actions on an electrical fault.

Carl

 

[BillL]

I just did what Carl said with the Monkworkz M30. I tied the alternator output into the shunt so the amperage readout would be the same. Only indication of backup active is the amber light and line buss voltage at 14.0.

 

[LOCARRE]

Not sure why you would want to do this. The beauty of this standby alternator is that it will automatically pick up the load if the primary alternator fails. You know it has the load as the nice yellow lamp that comes with the standby alternator regulator comes on. No pilot action.

Adding switches, relays and such just adds more failure modes, and increasing pilot actions on an electrical fault.

Carl

This way is to isolate broken alternator from aircraft and ability to manage loading on backup alternator via shunt... I already have Main alternator failure indication on my G3X, so a soon the red alarm is on, i can swith to backup...

I've seen comparable installation on Mooney... You can switch from 1 to 2...

regards,

Louis

 

[Carl Froehlich]

This way is to isolate broken alternator from aircraft and ability to manage loading on backup alternator via shunt... I already have Main alternator failure indication on my G3X, so a soon the red alarm is on, i can swith to backup...

I've seen comparable installation on Mooney... You can switch from 1 to 2...

regards,

Louis

Again - you can do this but it is not needed.

Shoot fire - I don’t even install a shunt on anything as one does not tell me anything that I don’t get from voltage. But build as you want. Just understand what gain you get for adding complexity.

Side note - total current draw on my plane (dual SkyView, GTN-650 and such) is ~10-15 amps. Assuming you have a similar panel your backup alternator can easily carry that. In other words your concern about loading it is not warranted assuming you turn off pitot heat and don’t have 747 landing lights blazing away.

Carl

 

[LOCARRE]

Again - you can do this but it is not needed.

Shoot fire - I don’t even install a shunt on anything as one does not tell me anything that I don’t get from voltage. But build as you want. Just understand what gain you get for adding complexity.

Side note - total current draw on my plane (dual SkyView, GTN-650 and such) is ~10-15 amps. Assuming you have a similar panel your backup alternator can easily carry that. In other words your concern about loading it is not warranted assuming you turn off pitot heat and don’t have 747 landing lights blazing away.

Carl

Thanks for advise, i will check options to keep it simple..

I'm more at 25 amps with tcas, stormscope, wheelen strobes....

regards,

 

[LOCARRE]

I just did what Carl said with the Monkworkz M30. I tied the alternator output into the shunt so the amperage readout would be the same. Only indication of backup active is the amber light and line buss voltage at 14.0.

Did you wire both alternators to same point on shunt?

thanks

 

[BillL]

The only potential mode of failure I see is the simultaneous switching of the field and load removal. If you have already verified it has no damaging spikes internally for the alternator when shut off, then you look OK.

Aeroelectric booklet says that sudden removal of alternator load is damaging. but nothing about field and load. Personally, I would validate that accidental or deliberate switching for test purposes is acceptable.

Did you wire both alternators to same point on shunt?

thanks

Schematically, yes, but not physically.

 

[LOCARRE]

The only potential mode of failure I see is the simultaneous switching of the field and load removal. If you have already verified it has no damaging spikes internally for the alternator when shut off, then you look OK.

Aeroelectric booklet says that sudden removal of alternator load is damaging. but nothing about field and load. Personally, I would validate that accidental or deliberate switching for test purposes is acceptable.



Schematically, yes, but not physically.

Thanks Bill for info well appreciated...

Question, in the event of your main alternator is going away, by having same point connection, how you can isolate the faulty alternator from the aircraft?

thanks

 

[Carl Froehlich]

Thanks Bill for info well appreciated...

Question, in the event of your main alternator is going away, by having same point connection, how you can isolate the faulty alternator from the aircraft?

thanks

Considering alternator failure modes, isolation is not required. It’s not like it turns into a load after failure.

Carl

 

[LOCARRE]

Considering alternator failure modes, isolation is not required. It’s not like it turns into a load after failure.

Carl

Even my main alternator regulator is internal? (already modified to prevent the runaway mode, ie, internal regulator power is isolated from main winding output( B+))

Would you consider to connect both alternator in parrallel on same circuit breaker or 1 breaker for each alternator?

thanks

 

[BillL]

Isolation

Failure to produce voltage of the primary- I would simply shut off the field of the primary alternator. I plead ignorance on a failure mode that could cause trouble leaving the B+ connected. A failure of a diode could potentially cause trouble but they usually just get hot and become an open circuit.

 

[LOCARRE]

Failure to produce voltage of the primary- I would simply shut off the field of the primary alternator. I plead ignorance on a failure mode that could cause trouble leaving the B+ connected. A failure of a diode could potentially cause trouble but they usually just get hot and become an open circuit.

So the best way could be 1 breaker for each alternator, so we can isolate the alternator by simply popping the breaker of the faulty alternator when confirmed that we are on backup alt...

Could be more simple circuit than the first try... ;-)

thanks

 

[rocketbob]

In your proposed design failure of the regulator or associated wiring would render both alternators inoperative. Most modern multi-engine aircraft electrical systems have separate buses, with a normally open bus-tie contactor for dealing with an inop engine or alternator.

 

[LOCARRE]

In your proposed design failure of the regulator or associated wiring would render both alternators inoperative. Most modern multi-engine aircraft electrical systems have separate buses, with a normally open bus-tie contactor for dealing with an inop engine or alternator.

Not sure, if you look at alt swith, you can only use 1 alternator at a time, or nothing when centered position ON-OFF-ON.

Please explain...

regards,