Thanks,
Bill
Well, no doubt
pot-shots will be taken by some, but for the most part, folks are appreciative
to have the facts (as best I know them) as it could possibly happen to them –
or some variation. Back when I first got started (1992), I really did
not know Bob K and his deserved
reputation. In fact, because of his view about fuses vs Circuit breakers
– which I disagreed with him about at least for crucial systems - may have
influence my assessment of his excellent wiring
diagrams.
You are correct about
the alternator; I was somewhat surprised when I discovered that once my
alternator (auto) starts producing voltage, pulling the field coil circuit
breaker does not shut down the alternator. So your suggestion to use a
modified one makes good sense.
I always say you
“..Live and learn – provided you live!..” I am always prepared to learn
from my mistakes. So far I haven’t committed the same one
twice.
In any case, if my
“full disclosure” reporting precludes even one person from experiencing such
excitement and leaves me with my “glider time” record intact – that is payback
enough {:>).
Ed
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Friday, June 05, 2009 2:04
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Ed's Electrical
System was Incident 5119
Hi
David,
You ever hear that
old saying “…it seemed like a good idea at the time…” ? {:>) I
agree that Bob’s stuff is a good place to start. I also realized exactly
what you point out. While I could isolate my battery from a failed (or
good for that matter {:>)) alternator – with my design, I could do nothing
to isolate my essential bus from a bad battery. The only reason I can
give you (10+ years later) is that I apparently viewed the alternator as the
likely cause of a problem, since I swap my batteries out every two years.
But, clearly a new battery short – an open circuit would not likely pose
a real problem – an no essential bus power.
Along those same
lines of thinking, is probably why I had the battery voltage holding the
master relay closed.
Clearly pilot played
major role in this incident from one 10 year point to the next 10 year
point.
Regarding the “fancy”
voltmeter switch, at the time since I had two batteries and an alternator, it
seemed like a good idea to be able to know the state of the three power
devices. Having it just to the main circuit did not seem to provide any
information on the voltage state of each battery. I like, it did not
case the problem, so I’ll leave it in there. No amp
meter.
I agree there is some
rewiring in the very near future. I do find it sort of Ironic that the
very thing I put in to permit me to have sufficient time (battery time) to get
to an airfield – showed that it could do just that {:>). The two year
old 17AH battery showed it could easily provide 30 minutes of quality
voltage. It did not start to get really nasty until approx 50 minutes
after launch (with two EFI and boost pumps running – I turn one EFI and boost
pump off at cruise altitude).
Past 50
minutes, things were clearly going to Hades in a hand basket, my EFISM showed
the EC2 was still sending the correct pulse duration to injectors (based on my
fuel flow reading), however, there was simply not enough voltage/power to pull
the injectors completely open or for long enough. All in all I was
pleased how long things did stay functional. Based on the measured
voltage later on the ground (where it might have a chance to recovery some)
the battery was reading six volts. So things probably continue to
work/more or less down to around 7-8 volts.
Some good suggestions
David. One of the reasons for providing these incidents is so that folks
can learn from them (self included).
Ed
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of David Leonard
Sent: Friday, June 05, 2009 1:03
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Ed's Electrical
System was Incident 5119
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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