Hi Ed,
Great job handling the emergency! Very nice write up. I do have to admit that you made some unusual decisions in the electrical system. None of that stuff is new, electric Bob's advice is pretty sound. I think that the "master" solenoid is often called the "battery" master for a reason - it only isolates the battery. If you want to have another battery, have another battery master that truly isolates that battery. In your system, if either battery becomes a dead short - you have just taken out your essential buss with no way to recover in flight! All your buses (essential or not) should be on the other side of the 'master' solenoids. If you want to be able to isolate the alternator, that is a separate system. (crow-bar/solenoid/field switch/fuse link/breaker/whatever). I have come to the opinion that sudden over-voltage that frys your avionics is exceedingly unlikely. I have decided to only "isolate" my alternator with a fusible link. - nice and simple that way. The alternator also connects to the buss side of the battery master solenoids. To make one of the buses 'essential' provide an alternate path around any perceived possible points of failure. Batteries fail. I have seen it in cars, I'm sure you have too. Sure, it's mostly the older type, but a good solid short across a SLA could fail it as well.
I also find it unusual that your voltmeter is not simply reading the main buss voltage - no fancy switch. That way, you know what you are getting, if you know what I mean. If you want to see how one or another power source is doing, isolate the other sources from the master buss. Lastly, what about you ammeter? Does it not measure current directly from either the battery or the alternator?
I'm not sure that a diode is the solution you are looking for. I think what you really need is to re-do the big wires in your system altogether. If you have settled on a one-battery system, get rid of all that extra weight and do it according to the book. From what I know, you would use a diode to 1) re-route field decay spikes back to the battery, or 2) provide alternate path from a battery to an essential (always hot) buss. (i.e. If you wanted to use a diodes, your essential buss would be connected to the other side of the master contactors via diodes, and you would use a diode from each battery to the essential buss.) So at a minimum you would want 2 diodes, one from the alternator and another from your single battery to the essential buss.
I know you are a WAY better gEEk than me (i cant even spell AC). So I suspect that you already know what I am saying and you just need a kick in the arse to bite the bullet and re-do the system.
Highest regards as always,
On Fri, Jun 5, 2009 at 4:47 AM, Ed Anderson <eanderson@carolina.rr.com> wrote:
Jim Maher was kind enough to convert the large DXF files of my electrical
system to JPG so perhaps more of you can examine it. Recall I have removed
the 2nd battery stuff - so ignore that on the diagrams. Also the diagram
does not show any of the detailed EC2/injector/ignition wiring - follow
Tracy's recommendations on that.
As you will note there is no "isolation" diode between alternator and
battery and also that the battery voltage holds the master relay closed.
That is another change I must make. I must have decided (10+ years ago)
that the battery would never fail - only the alternator. Clearly (now),
without battery voltage (in my design) to hold the master relay closed -
when the battery voltage fall to around 6-7 volts (in my case) the relay
opens and all that good electrical power being produced by the perfectly
good alternator - can not reach any part of the electrical system. Clearly
NOT good as I could have continued to fly perfectly well with just the
alternator juice.
Your design is not going to be any better than the accuracy of your
assumptions. Clearly some of my assumptions make 10 years ago definitely
need revising.
Ed
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