The Murphy Builders Site

Hi everyone,

I just uploaded a drawing of the complete electrical system for my V8
powered SR to the SR-Systems folder. I sure would love to have some of you
people that know what you're doing look it over and tell me all the stuff
that's wrong. It includes the dual electronic ignition setup I am using.
Thanks in advance.

Mike Kimball
SR #044




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Mike

I've been subscribed to Bob Knuckoll's aeroelectric list for a few years
and I must admit that he has largely converted me to his thinking with
precise analysis and detailed data. That is really the place to hash out
your thoughts. I'd suggest you ponder the well thought out published
diagrams in his book and on his web site.

Post Message: aeroelectric-list@matronics.com
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My own wiring is still in my head but I have given it some thought.
The achievable goal is that no single failure should cause anything more
than a minor annoyance. As a preliminary starting point, your diagram is
reminiscent of old certified thinking. My immediate thoughts are:

What is the box labelled 'Bat Iso'? Fuses or an ANL might be a good idea
between the batteries but don't think you want anything in the way of
diodes there.

If your intent is that either battery can power your engine till you run
out of gas then the batteries must be replaced often to insure
sufficient reserve capacity. Weight wise, a small second alternator
becomes an interesting alternative. In fact though one RG battery and
one alternator gives you two sources of power. An RG battery is by far
the most reliable item in the electric system but capacity declines with
age of course. Your diagram implies two large batteries as the second
one does not appear dedicated to keeping the engine alive. With two
large batteries some guys use a crossfeed contactor so both can power
the starter (It looks like your system might be able to do that as well
depending on what your Bat Sel box is). With one alternator on an SR,
I'd lean in that direction with possibly two PC680 batteries and
rotating them with one new one every year to guarantee reserve capacity.
A crossfeed switch or relay might make more sense than your Bat Sel switch.

It is extremely important to incorporate a low voltage warning device as
the alternator lights are not reliable.

Some guys run both ignitions simultaneously for takeoff and landing.
However in any case I'd suggest two switches instead of one for
selecting. Why go to the trouble of dual ignition but wire them through
one switch such that one switch failure can kill both ignitions? And why
feed both from the same source of power? If you are going to carry two
batteries, use them as independant engine power sources. Wire at least
one ignition and fuel pump directly to a battery.

I am convinced that there is no technical need for an avionics master
switch. I'd also suggest that a split master is pointless as you'll want
a fuse or ANL current limiter between the battery and alternator anyway.
Ideally you'd also have an overvoltage device to kill the alternator.
All the damage will usually be done before you can manually turn off a
runaway alternator.

There are some practical reasons to consider using a fuse block for the
bus rather than c/b's. Compared to one wire into a fuse block, C/B's
are more hassle to wire and often take up significant panel space. With
a well though out system you won't have any need to reset circuit
breakers in flight. Mind you I picked up switch breakers cheaper than
switches would have cost so I'm not planning fuses either ;)

Ken



Mike Kimball wrote:

Hi everyone,

I just uploaded a drawing of the complete electrical system for my V8
powered SR to the SR-Systems folder. I sure would love to have some of you
people that know what you're doing look it over and tell me all the stuff
that's wrong. It includes the dual electronic ignition setup I am using.
Thanks in advance.

Mike Kimball
SR #044

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The "Bat Iso" my drawing refers to is the same device I use with my slide in
camper on my truck. It allows me to charge both batteries from the
alternator. It's also supposed to isolate the batteries such that loads on
the camper battery won't drain the truck battery and vice versa. My
intention was to run a large battery with the capability to start the engine
and a small motorcycle battery just to power the ignition if something goes
wrong with the main battery/alternator. Although, the odds that the
alternator and the main battery fails at the same time should be low. Of
course, the alternator could stop charging the battery and then the battery
gets drawn down from driving all the loads. I'd have to have a pretty poor
engine instrument scan to not notice. I am planning on an ampmeter and
voltmeter. A low voltage light would be nice too.

The "Bat Selector" in the drawing refers to exactly that. A switch to
select one battery or the other for use. I have one on my boat. It's a
huge thing that would have to go on the side panel down by my lower leg or
something. Wish it could be smaller but I guess it has to be large due to
the cables and current capacity.

I set my dual electronic ignition up exactly as specified by MSD for use in
circle track racers. There is no mention in MSD documentation of being able
to run both ignitions at the same time. I'd have to call them and ask if
that can be done.

I don't know what an "RG" battery is or what "ANL" stands for.

I do have a current limiter between the batter and the alternator: a 60 amp
circuit breaker. I did overlook overvoltage though.

I agree that there's no technical need for an avionics master. I just like
to set my radio volume and squelchs up once and then I don't have to do it
again. I just turn the avionics master on. I can also get clearances
without spinning up my gyros.

Too late on fuse blocks versus CBs. The CBs are all installed in a two inch
channel that runs along the bottom of the main panel. Turned out pretty
nice actually. I also used circuit breakers that can all be pulled. So I
have a bunch of switches to power stuff off individually if I want. I heard
a story about a guy whose turn coordinator started smoking and he had to run
with the entire electrical off just due to one device. Don't know if it's a
true story, but it's a good story.

Thanks for your advice and to the others that responded.

Mike Kimball

P.S. I've been all over the aeroelectric website and downloaded just about
everything.

-------Original Message-------

From: murphy-rebel@dcsol.com
Date: Monday, December 08, 2003 6:43:11 AM
To: murphy-rebel@dcsol.com
Subject: Re: SR electrical with V8

Mike

I've been subscribed to Bob Knuckoll's aeroelectric list for a few years
and I must admit that he has largely converted me to his thinking with
precise analysis and detailed data. That is really the place to hash out
your thoughts. I'd suggest you ponder the well thought out published
diagrams in his book and on his web site.

Post Message: aeroelectric-list@matronics.com
UN/SUBSCRIBE: http://www.matronics.com/subscription
List FAQ: http://www.matronics.com/FAQ/AeroElectric-List.htm
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7-Day Browse: http://www.matronics.com/browse/aeroelectric-list
Browse Digests: http://www.matronics.com/digest/aeroelectric-list

My own wiring is still in my head but I have given it some thought.
The achievable goal is that no single failure should cause anything more
than a minor annoyance. As a preliminary starting point, your diagram is
reminiscent of old certified thinking. My immediate thoughts are:

What is the box labelled 'Bat Iso'? Fuses or an ANL might be a good idea
between the batteries but don't think you want anything in the way of
diodes there.

If your intent is that either battery can power your engine till you run
out of gas then the batteries must be replaced often to insure
sufficient reserve capacity. Weight wise, a small second alternator
becomes an interesting alternative. In fact though one RG battery and
one alternator gives you two sources of power. An RG battery is by far
the most reliable item in the electric system but capacity declines with
age of course. Your diagram implies two large batteries as the second
one does not appear dedicated to keeping the engine alive. With two
large batteries some guys use a crossfeed contactor so both can power
the starter (It looks like your system might be able to do that as well
depending on what your Bat Sel box is). With one alternator on an SR,
I'd lean in that direction with possibly two PC680 batteries and
rotating them with one new one every year to guarantee reserve capacity.
A crossfeed switch or relay might make more sense than your Bat Sel switch.

It is extremely important to incorporate a low voltage warning device as
the alternator lights are not reliable.

Some guys run both ignitions simultaneously for takeoff and landing.
However in any case I'd suggest two switches instead of one for
selecting. Why go to the trouble of dual ignition but wire them through
one switch such that one switch failure can kill both ignitions? And why
feed both from the same source of power? If you are going to carry two
batteries, use them as independant engine power sources. Wire at least
one ignition and fuel pump directly to a battery.

I am convinced that there is no technical need for an avionics master
switch. I'd also suggest that a split master is pointless as you'll want
a fuse or ANL current limiter between the battery and alternator anyway.
Ideally you'd also have an overvoltage device to kill the alternator.
All the damage will usually be done before you can manually turn off a
runaway alternator.

There are some practical reasons to consider using a fuse block for the
bus rather than c/b's. Compared to one wire into a fuse block, C/B's
are more hassle to wire and often take up significant panel space. With
a well though out system you won't have any need to reset circuit
breakers in flight. Mind you I picked up switch breakers cheaper than
switches would have cost so I'm not planning fuses either ;)

Ken



Mike Kimball wrote:

Hi everyone,

I just uploaded a drawing of the complete electrical system for my V8
powered SR to the SR-Systems folder. I sure would love to have some of you
people that know what you're doing look it over and tell me all the stuff
that's wrong. It includes the dual electronic ignition setup I am using.
Thanks in advance.

Mike Kimball
SR #044

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Mike,
I also followed Bob Knuckoll's and recommend you check out his stuff. I took
a quick look at your drawing and did not notice if you had engine
instruments. If you are, I would connect those on the avionics buss. I'm not
familiar with an auto conversion, but it looks like a single set of spark
plugs and a switch for 1 or 2 electronic ignition. I would add a relay in
the starter circuit to drop the avionics buss off line when the starter is
engaged. I would use one large battery for the full system and a small
battery to be the backup and not expect that battery to crank the engine but
to get you to a landing so things can be fixed. Knuckoll's preaches that no
in-flight electrical problem should be any more that a inconvenience. Save
your trouble shooting and repairs when your on the ground, so design
accordingly. Sounds simple, eh.
Al
Moose, N526AP
----- Original Message -----
From: <klehman@albedo.net>
To: <murphy-rebel@dcsol.com>
Sent: Monday, December 08, 2003 7:45 AM
Subject: Re: SR electrical with V8

Mike

I've been subscribed to Bob Knuckoll's aeroelectric list for a few years
and I must admit that he has largely converted me to his thinking with
precise analysis and detailed data. That is really the place to hash out
your thoughts. I'd suggest you ponder the well thought out published
diagrams in his book and on his web site.

Post Message: aeroelectric-list@matronics.com
UN/SUBSCRIBE: http://www.matronics.com/subscription
List FAQ: http://www.matronics.com/FAQ/AeroElectric-List.htm
Search Engine: http://www.matronics.com/search
7-Day Browse: http://www.matronics.com/browse/aeroelectric-list
Browse Digests: http://www.matronics.com/digest/aeroelectric-list

My own wiring is still in my head but I have given it some thought.
The achievable goal is that no single failure should cause anything more
than a minor annoyance. As a preliminary starting point, your diagram is
reminiscent of old certified thinking. My immediate thoughts are:

What is the box labelled 'Bat Iso'? Fuses or an ANL might be a good idea
between the batteries but don't think you want anything in the way of
diodes there.

If your intent is that either battery can power your engine till you run
out of gas then the batteries must be replaced often to insure
sufficient reserve capacity. Weight wise, a small second alternator
becomes an interesting alternative. In fact though one RG battery and
one alternator gives you two sources of power. An RG battery is by far
the most reliable item in the electric system but capacity declines with
age of course. Your diagram implies two large batteries as the second
one does not appear dedicated to keeping the engine alive. With two
large batteries some guys use a crossfeed contactor so both can power
the starter (It looks like your system might be able to do that as well
depending on what your Bat Sel box is). With one alternator on an SR,
I'd lean in that direction with possibly two PC680 batteries and
rotating them with one new one every year to guarantee reserve capacity.
A crossfeed switch or relay might make more sense than your Bat Sel

switch.

It is extremely important to incorporate a low voltage warning device as
the alternator lights are not reliable.

Some guys run both ignitions simultaneously for takeoff and landing.
However in any case I'd suggest two switches instead of one for
selecting. Why go to the trouble of dual ignition but wire them through
one switch such that one switch failure can kill both ignitions? And why
feed both from the same source of power? If you are going to carry two
batteries, use them as independant engine power sources. Wire at least
one ignition and fuel pump directly to a battery.

I am convinced that there is no technical need for an avionics master
switch. I'd also suggest that a split master is pointless as you'll want
a fuse or ANL current limiter between the battery and alternator anyway.
Ideally you'd also have an overvoltage device to kill the alternator.
All the damage will usually be done before you can manually turn off a
runaway alternator.

There are some practical reasons to consider using a fuse block for the
bus rather than c/b's. Compared to one wire into a fuse block, C/B's
are more hassle to wire and often take up significant panel space. With
a well though out system you won't have any need to reset circuit
breakers in flight. Mind you I picked up switch breakers cheaper than
switches would have cost so I'm not planning fuses either ;)

Ken



Mike Kimball wrote:

Hi everyone,

I just uploaded a drawing of the complete electrical system for my V8
powered SR to the SR-Systems folder. I sure would love to have some of

you

people that know what you're doing look it over and tell me all the

stuff

that's wrong. It includes the dual electronic ignition setup I am

using.

Thanks in advance.

Mike Kimball
SR #044

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Mike Kimball wrote:

The "Bat Iso" my drawing refers to is the same device I use with my slide in
camper on my truck. It allows me to charge both batteries from the
alternator. It's also supposed to isolate the batteries such that loads on
the camper battery won't drain the truck battery and vice versa. My
intention was to run a large battery with the capability to start the engine
and a small motorcycle battery just to power the ignition if something goes
wrong with the main battery/alternator. Although, the odds that the
alternator and the main battery fails at the same time should be low. Of
course, the alternator could stop charging the battery and then the battery
gets drawn down from driving all the loads. I'd have to have a pretty poor
engine instrument scan to not notice. I am planning on an ampmeter and
voltmeter. A low voltage light would be nice too.

Actually with such a system I think immediate reliable notice of low
voltage is critical. Think its only $20 or $30. from BCC.

OK so the bat iso must have diodes in it. I think it serves no useful
purpose in this case, adds something to fail, and will possibly increase
alternator noise. One battery really can not charge another even if one
is dead because even a fully charged battery is too low voltage to
charge another. Two batteries can and should be simply paralleled to
charge off the same source especially with an internally regulated (non
adjustable) alternator. In an RV such a device can certainly prevent
draining both batteries overnight but don't think it is appropriate here.

The "Bat Selector" in the drawing refers to exactly that. A switch to
select one battery or the other for use. I have one on my boat. It's a
huge thing that would have to go on the side panel down by my lower leg or
something. Wish it could be smaller but I guess it has to be large due to
the cables and current capacity.

Why? Take a look at the concept of an essential bus in Bob's stuff.
There the second battery will automatically power the essential bus
through a diode to keep your engine running without manual intervention.
I think you'll find that an automatic or semi-automatic crossfeed relay
or even a manual crossfeed switch will work out better.

I set my dual electronic ignition up exactly as specified by MSD for use in
circle track racers. There is no mention in MSD documentation of being able
to run both ignitions at the same time. I'd have to call them and ask if
that can be done.

Don't know about the MSD ignitions but it is not an issue for the coil
joiner. And the purpose of the joiner is to prevent one ignition from
knowing about the other. Guys do it both ways but I plan to run mine
simultaneously for takeoff and landing.

I don't know what an "RG" battery is or what "ANL" stands for.

RG is recombinant gas also known by other names. THese are modern
reliable spill proof batteries with long shelf lives etc. They are not
the older Gell cells, flooded cell, or vented batteries.

ANL is just a current limiter. A kind of slow acting fuse designed
specifically to handle high currents while tolerating short term
overcurrent (like a circuit breaker will). Considerably more reliable
than in line fuses for 30 amps and up. Sounds like you have that covered
with your 60 amp breaker.

I do have a current limiter between the batter and the alternator: a 60 amp
circuit breaker. I did overlook overvoltage though.

I agree that there's no technical need for an avionics master. I just like
to set my radio volume and squelchs up once and then I don't have to do it
again. I just turn the avionics master on. I can also get clearances
without spinning up my gyros.

Too late on fuse blocks versus CBs. The CBs are all installed in a two inch
channel that runs along the bottom of the main panel. Turned out pretty
nice actually. I also used circuit breakers that can all be pulled. So I
have a bunch of switches to power stuff off individually if I want. I heard
a story about a guy whose turn coordinator started smoking and he had to run
with the entire electrical off just due to one device. Don't know if it's a
true story, but it's a good story.

Thanks for your advice and to the others that responded.

Mike Kimball

P.S. I've been all over the aeroelectric website and downloaded just about
everything.

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Mike Kimball wrote:

The "Bat Iso" my drawing refers to is the same device I use with my slide in
camper on my truck. It allows me to charge both batteries from the
alternator. It's also supposed to isolate the batteries such that loads on
the camper battery won't drain the truck battery and vice versa. My
intention was to run a large battery with the capability to start the engine
and a small motorcycle battery just to power the ignition if something goes
wrong with the main battery/alternator. Although, the odds that the
alternator and the main battery fails at the same time should be low. Of
course, the alternator could stop charging the battery and then the battery
gets drawn down from driving all the loads. I'd have to have a pretty poor
engine instrument scan to not notice. I am planning on an ampmeter and
voltmeter. A low voltage light would be nice too.

Actually with any electrical dependant engine I think immediate reliable
notice of low voltage is critical. Think its only $20 or $30. from BCC.
You don't want to wondering how long the alternator has been dead and
how much time you have left in the batteries.

OK so the bat iso must have diodes in it. Make sure it only has a diode
to the small battery. You don't want a diode in series with the main
battery as it would serve no useful purpose, adds something to fail, and
will possibly increase alternator noise. One battery really can not
charge another even if one is dead because even a fully charged battery
is too low voltage to charge another. Two batteries can and should be
simply paralleled to charge off the same source especially with an
internally regulated (non adjustable) alternator. However a block
mounted diode for the small battery only is only about $3. and
recommended for a setup like this where the small battery immediately
starts backing up the main battery after an alternator failure. It adds
no additional connections in the line to the main battery.

The "Bat Selector" in the drawing refers to exactly that. A switch to
select one battery or the other for use. I have one on my boat. It's a
huge thing that would have to go on the side panel down by my lower leg or
something. Wish it could be smaller but I guess it has to be large due to
the cables and current capacity.

Why? Take a look at the concept of an essential bus in Bob's stuff.
There the second battery will automatically power the essential bus
through a diode to keep your engine running without manual intervention
and annunciate that it is doing it. If you don't like that for some
reason I think you'll find that an automatic or semi-automatic crossfeed
relay or even a manual crossfeed switch will work out better than a
battery selector. I'd suggest that there are quite a few reasons why
your battery selector is a bad idea. More connections, more ways to fail
the system, more resistance and electrical noise, weight, voltage
spikes, workload, mismanagement possibilites, etc.

I set my dual electronic ignition up exactly as specified by MSD for use in
circle track racers. There is no mention in MSD documentation of being able
to run both ignitions at the same time. I'd have to call them and ask if
that can be done.

Don't know what MSD says but it is not an issue for the coil joiner. And
the purpose of the joiner is to prevent one ignition from knowing about
the other. Guys do it both ways but I plan to run mine simultaneously
for takeoff and landing. Spark plug wear is accelerated a bit with both
on. Make sure the two ignitions don't share the same power path and
wiring in any case.

I don't know what an "RG" battery is or what "ANL" stands for.

I do have a current limiter between the batter and the alternator: a 60 amp
circuit breaker. I did overlook overvoltage though.

RG is recombinant gas also known by other names such as SLA. These are
modern reliable batteries with long shelf lives that won't spill acid
even if cracked or punctured. A battery box is not required. They are
not the older Gell cells, flooded cell, or vented batteries.

ANL is just a current limiter. A kind of slow acting fuse designed
specifically to handle high currents while tolerating short term
overcurrent (like a circuit breaker will). Considerably more reliable
than in line fuses for 30 amps and up. Sounds like you have that covered
with your 60 amp breaker.

Overvoltage is an alternator voltage regulator failure when the
alternator puts out max juice and I think much rarer than a low voltage
situation. I could debate the value of protection for it especially with
a large battery and smallish alternators. However Aeroelectric
recommends it and it will protect marginal electronics from voltage
excursions on a poorly designed electrical system or from a runaway
alternator. With an internally regulated alternator it requires again
about a $30. module and a relay. Much more reliable than mechanical
systems of days gone by and much more useful than the avionics switch
that some people claim protects their avionics.

I agree that there's no technical need for an avionics master. I just like
to set my radio volume and squelchs up once and then I don't have to do it
again. I just turn the avionics master on. I can also get clearances
without spinning up my gyros.

Too late on fuse blocks versus CBs. The CBs are all installed in a two inch
channel that runs along the bottom of the main panel. Turned out pretty
nice actually. I also used circuit breakers that can all be pulled. So I
have a bunch of switches to power stuff off individually if I want. I heard
a story about a guy whose turn coordinator started smoking and he had to run
with the entire electrical off just due to one device. Don't know if it's a
true story, but it's a good story.

Sounds reasonable to me.

Thanks for your advice and to the others that responded.
Mike Kimball
P.S. I've been all over the aeroelectric website and downloaded just about
everything.

I found his $30. book to be about the best homebuilding reference that I
have.

Ken






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Thanks. I figured that out on my own. Lots of stuff beyond my level of
knowledge, like OK, put a diode here or a diode there. I wouldn't have any
idea how to size the diodes. I certainly would not know how to put together
whatever it takes to have an automatic fail-over system from one battery to
the other. I better get the aeroelectric book and start studying.

A friend pointed out to me that the way I have my avionics master drawn in
it does allow me to get clearances without spinning up the gyros, but now I
have two switches I have to remember to turn off when I walk away from the
airplane or risk a dead battery when I return. Guess I'll think about
putting the avionics switch on the other side of the main bus switch and
accept spinning up the gyros. I was also thinking that I don't need an
alternator switch because the field circuit breaker is one that I can pull
if I want to disable the alternator. Too bad I already cut the hole in the
panel for the split master switch because I may end up not needing the
second half of that switch.

I was wondering if there would be any reason why I couldn't just run the two
batteries in parallel with the alternator. Thanks for answering that
question.

Thanks again to everyone for the great responses. The builder's list is
AWESOME!.

Mike Kimball
SR#044

-------Original Message-------

From: murphy-rebel@dcsol.com
Date: Tuesday, December 09, 2003 9:30:58 AM
To: murphy-rebel@dcsol.com
Subject: Re: SR electrical with V8

oops!

Mike I guess I sent two e-mails this morning by mistake. The one that
should have gone was the later dated one which was edited and corrected
on a couple of points.

Ken




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oops!

Mike I guess I sent two e-mails this morning by mistake. The one that
should have gone was the later dated one which was edited and corrected
on a couple of points.

Ken




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Bob uses cheap full wave rectifier diodes that are actually four diodes
in a one inch square metal case. Bolt it to a handy piece of aluminum
structure and only use one of the diodes (two of the four push on
connections). They are typically rated for something like 25 amps which
should be fine for small battery charging or to insure that any
available power source will keep your engine running or gyros spinning.
They come in larger or smaller ratings of course.

Diodes are typically silicon diodes with a 0.6 volt drop through them so
you don't want any extras in the circuitry but the book explains a lot
of things pretty well. I Don't have any electric gyros but I think if I
did I'd also arrange some way of removing power to them with a c/b or
switch like you guys are doing.

I'm leaning towards two small 4.4 lb 5 amp-hr ultra start red batteries
with an ignition and efi wired direct to each battery. Fine for engine
starting and I don't need much reserve capacity with my two small
alternators.

Ken

Mike Kimball wrote:

Thanks. I figured that out on my own. Lots of stuff beyond my level of
knowledge, like OK, put a diode here or a diode there. I wouldn't have any
idea how to size the diodes. I certainly would not know how to put together
whatever it takes to have an automatic fail-over system from one battery to
the other. I better get the aeroelectric book and start studying.
snip

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