Ed,
Congratulations on a fine piloting job!
I am also impressed in your willingness to lay yourself bare on the
Aeroelectric list. You seem to have created quite a stir there.
I think that Bob’s architectures are really good and well thought
out, but if you make any changes in them, all bets are off. Everything has
a consequence. In his Z-19, which I am hopefully using, you have to have
an externally controlled alternator. Anything else will cause a lot of
changes and most alternatives will not work as well. That is why I took
the standard alternator that Vans sells and removed the internal regulator.
It is not hard to do. Mark Steitle showed me how. That allows the
alternator switch to turn the alternator on or off. If the alternator is
working, it is always charging the entire system. The essential buss is
always hot thru the diode, albeit at a slightly lower voltage, and if you get
an alternator failure, you can turn the essential buss switch on, which effectively
removes the voltage drop thru the diode, and powers only what you need to keep
going.
Bill
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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