I investigated this earlier and this is what I found:
1. No harm is done with both alternators online. The theory that there
is a problem stems from twin engine systems with elaborate schemes to
deal with 2 alternators.
I am using Z-13/8 and there are only 3 switches:
Main: (off)- (battery contactor)-(battery+main alternator)
Aux feed: (off)-(on)
Aux Alt: (off)-(on)
The endurance bus can be powered by:
Battery only
Battery + Main Alternator
Battery + Aux Alternator
Aux Alternator only
The Aux Feed provides a path that does not include the battery contactor.
Hope this helps,
John Morgensen
Grumman AA1B 150hp - For Sale
RV4 - Flying
RV9A - wiring
Matthew Schumacher wrote:
> List,
>
> I've been working on the wiring diagram for my airplane (electric panel,
> IFR, plane power internally regulated main alt and a SD-8 backup). So
> I've been reading though Bob's book and am familiar with the Z-13 wiring
> diagram, however there are a two things about it that I don't like:
>
> 1. It is possible to turn on both alternators at once. It is my
> understanding that you don't want to have both alternators online at
> once and I don't want the pilot to be able to cause damage by not using
> the correct switches.
>
> 2. Alternate feed switches. Feed switches seem cumbersome since it
> requires the pilot to know something about the electrical system.
>
> I think I have a new wiring diagram that addresses these things, but I
> want to run it past this list and perhaps Bob so that others can help me
> find the problems.
>
> Here is how it works:
>
> The avionics bus is treated like the endurance bus since the avionics
> are the only things I care about if my alternator fails (I have mags and
> a mechanical fuel pump.) When the master switch is on, the battery
> pulls the battery contactor which brings the main alternator and battery
> into the system. Should something happen to the main alternator the
> battery will continue to power the system unless I switch the ALT switch
> to AUX. When the alternator switch is on AUX it takes out the main alt
> and powers up the SD-8 wired up with the self exciting hack. This will
> allow my aux alternator to power the avionics bus (when the Avionics
> master is on AUX) but will keep my master contactor and battery separate
> from the rest of the system. In the event that I want to charge my main
> battery I can turn the master switch off which will then allow me to
> charge my battery should I desire to try and bring the main alternator
> back after a dead battery.
>
> In order to clear up any confusion here are the basic switches,
> settings, and mode of operation:
>
> Master: on, Alt: main, Avionics: main; Normal operation running on the
> main alternator and battery.
>
> Master on, Alt: Aux, Avionics: Main; Aux alternator is online and master
> alternator is offline, battery is powering everything.
>
> Master on, Alt: Aux, Avionics: Aux; Aux alternator is powering avionics,
> main alternator is offline, and battery is powering everything except
> avionics.
>
> Master off, Alt: Main, Avionics: main; Nothing is powered up.
>
> Master off, Alt: aux, Avionics: main; Avionics are off, Aux alternator
> is online and is charging the battery.
>
> Master Off, Alt: aux, Avoinics: aux; Avionics are on aux alternator, aux
> alternator is online and is charging the battery.
>
> Perhaps it would be more intuitive if I name the switches like this:
>
> Battery: On | Off (Aux Charge)
> Alternator : MAIN | AUX
> Avionics: MAIN | OFF | AUX
>
> This setup reduces the panel down to 3 switches and gives the operator
> good control over the system, allows for the battery to be isolated or
> charged from the aux alternator, and gives a way for non critical
> devices to run off the battery.
>
> If this doesn't look sane to you please post some feedback. Any help I
> can get is greatly appreciated.
>
> Thanks,
> schu
>
>
