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johnbright
Joined: 14 Dec 2011
Posts: 165
Location: Newport News, VA
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 Posted: Wed Feb 22, 2023 5:35 pm Post subject: fuses in series |
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I have to wonder what Bob and others think about this test Dan Horton of VAF did re ATO “regular size” blade fuses in series.
The relevant text is below the photo.
https://vansairforce.net/community/showpost.php?p=1668674&postcount=55
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_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links |
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user9253
Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan
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| Posted: Thu Feb 23, 2023 7:18 pm Post subject: Re: fuses in series |
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Theories need to be proven by experimenting and testing.
Dan's testing shows that it is OK to have fuses in series.
On the other hand, why take a chance on the main fuse blowing when there are are alternatives?
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Joe Gores |
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nuckolls.bob(at)aeroelect
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| Posted: Fri Feb 24, 2023 5:48 am Post subject: fuses in series |
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At 09:18 PM 2/23/2023, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
Theories need to be proven by experimenting and testing.
Dan's testing shows that it is OK to have fuses in series.
On the other hand, why take a chance on the main fuse blowing when there are are alternatives? |
What FMEA conditions ever suggest that fuses
in series are a good and necessary thing?
I've read several narratives where the writer
talks about a "main" breaker . . . and I cannot
imagine what they're talking about or just how
such a device became a part of his/her
airplane.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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Voyager
Joined: 30 Jun 2020
Posts: 77
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| Posted: Fri Feb 24, 2023 6:01 am Post subject: fuses in series |
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I could see someone following the architecture used in home and building electrical distribution systems where series fuses/breakers are very common. Electric utilities have fuses on their distribution lines. Most buildings have a main breaker on the incoming service. And then each circuit has a breaker. And finally many end devices have their own internal fuses or breakers. So, fuses/breakers in series are common in many applications.
I don’t recall seeing that in a vehicle though, although I think my new Equinox does have a fuse on the main positive battery lead, which is a first.
Why would one not want to have a fuse on the main battery lead to protect a short of the battery cable? I know this isn’t common, but I also have seen battery cables contact ground a few times and the results are generally fairly impressive. Is the issue just one of not wanting an additional point of failure? Or the cost of a large fuse and fuse holder?
Regards,
Matt
| Quote: | On Feb 24, 2023, at 8:47 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:
At 09:18 PM 2/23/2023, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
Theories need to be proven by experimenting and testing.
Dan's testing shows that it is OK to have fuses in series.
On the other hand, why take a chance on the main fuse blowing when there are are alternatives? |
What FMEA conditions ever suggest that fuses
in series are a good and necessary thing?
I've read several narratives where the writer
talks about a "main" breaker . . . and I cannot
imagine what they're talking about or just how
such a device became a part of his/her
airplane.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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nuckolls.bob(at)aeroelect
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| Posted: Sat Feb 25, 2023 7:05 am Post subject: fuses in series |
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At 08:00 AM 2/24/2023, you wrote:
I could see someone following the architecture used in home and building electrical distribution systems where series fuses/breakers are very common. Electric utilities have fuses on their distribution lines. Most buildings have a main breaker on the incoming service. And then each circuit has a breaker. And finally many end devices have their own internal fuses or breakers. So, fuses/breakers in series are common in many applications.
In large scale distribution systems, failure mode effects
analysis will define the risks to conductors and equipment
based on known and anticipated failures.
Needless to say, the power grid is LARGE scale and
fraught with risks for faults. So indeed, from power
plant down to your wall outlet, there will be
many protective devices.
Our airplanes are very small scale systems. Fault
risks are pretty well understood by virtue of a
century of experience that gives rise to a
volumes of standard practices.
I don't recall seeing that in a vehicle though, although
I think my new Equinox does have a fuse on the main positive
battery lead, which is a first.
Yeah, my Sedona has a cluster of current limiters
built into a rather busy battery(+) terminal.
Why would one not want to have a fuse on the main battery lead to
protect a short of the battery cable? I know this isn't common,
but I also have seen battery cables contact ground a few
times and the results are generally fairly impressive.
Is the issue just one of not wanting an additional point of
failure? Or the cost of a large fuse and fuse holder?
Experience has demonstrated that such faults
are exceedingly rare and generally limited to
accidents of human origin. Hence the admonition
to unhook the battery (-) terminal before
swinging a wrench on your car. Airplanes
uniquely enjoy battery master switches . . .
very convenient for making the system 'cold'.
They are demonstrably immune to hard faults
that might be expected to trip active protection.
A robust wire's inadvertent connection with
ground is more likely to be a soft fault that
burns structure rather than the wire itself.
I've cited an example incident waaayyy back when
where a Beech C90 on short final to New Mexico airport
suddenly found the elevator mechanically disconnected
from the control column. They managed to land the
aircraft using pitch trim.
Subsequent investigation found the elevator
cables completely slack.
It seems that during maintenance activity
some time ago, some wire bundles under the floorboard
were mis-positioned for access but not properly
returned to as-manufactured.
One of the wires was feeder to the copilot's
windshield electric de-ice inverter . . . a relatively
fat wire protected at 75A or so. This wire was
being rubbed against the elevator control cables
until insulation was penetrated.
The intermittent arcing was so subtle that the
breaker never opened . . . and nothing untoward
was noticed by crew. Over a period of time
the steel control cable was eroded to failure
while copper wire strands were barely marked.
A similar thing would happen if a rear mounted
battery feeder were to become inappropriately
involved with the edge of a bulkhead lightening
hole under the floorboard . . . A little
insulation might smell bad but subsequent electrical
effects are more likely to burn away the aluminum
as opposed to over-stressing the wire.
Battery cable protection in cars goes to crash
safety. Batteries are generally mounted right
up front and exceedingly vulnerable to major
munching of sheet metal. Those protective
devices will be of the current-limiter/fusible-link
variety.
In airplanes, experience has demonstrated that
the lest destructive of unplanned arrivals with
the earth are controlled . . . i.e. pilot shuts
off fuel and master before striving to minimize
violence of the following events. The other
side of the coin is a completely unanticipated
termination of flight at high speed . . . wherein
condition of the electrical and fuel systems is
probably not relevant to the outcome.
Many moons ago I did some analysis of the bits-n-
pieces left of a King Air that hit a mountain in the Swiss
Alps at cruise. There were few chunks of
debris that would not fit into a 1-square foot
box. The thing they asked me to look at was
an Avionics Master switch that was missing some
wires . . . disconnected causing loss of nav aids
or ripped off as result of crash? The wires had
been 'tack soldered' as opposed to standard
practice of wrapping through the terminal's
wiring hole. Microscopic examination of exposed solder
surfaces showed that the wires were pulled off
and did not fall off due to joint failure.
The short answer is a study of power distribution
systems in hundreds of thousands of type
certified aircraft will reveal a minimalist
philosophy for power distribution current
limiting.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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fly4grins(at)gmail.com
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| Posted: Sat Feb 25, 2023 7:21 am Post subject: fuses in series |
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| Quote: |
Re: fuses in series
I could see someone following the architecture used in home and building
electrical distribution systems ...
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A couple more data points:
My 1970's VW Rabbit had a fusible link in the battery cable, and I guess I wouldn't be shocked to learn many cars were so equipped without it being general knowledge.
There are transport category aircraft with current limiters geographically distributed around the system to prevent hard faults from taking out the whole system.
No clue if that strategy is based upon crashworthiness considerations, maintenance considerations, corporate history, or some combination.
In my aft-battery RV-8, the fat wire runs through the crushable structure under the cabin floor, making it susceptible to pinching and a hard fault in a crash, especially given the model's tendency to shed its main gear. Not sure the practicality of trying to size a current limiter that would not open under cranking loads but still open with a hard fault. The guestimated risk for me centers on the probability of hitting the planet without knowing it's coming and thereby not getting the master off in time. Given how I operate, I judge that to be a low very order threat and one I can live with.
YMMV-
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Voyager
Joined: 30 Jun 2020
Posts: 77
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| Posted: Sat Feb 25, 2023 8:34 am Post subject: fuses in series |
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I agree that the likelihood of a direct short of a main battery cable is small. However, it is not zero and the localized heating from such a short could ignite combustibles. As long as the cable is kept away from combustibles, this isn’t an issue.
The difference in current between starting and a significant short is pretty large so viable overcurrent protection is feasible. For example, most engines in EA-B aircraft probably draw 100 amps or less during starting. It takes a fairly large engine to draw 200 amps (think diesel pickup truck or larger). Yes, the initial current when the starter is not turning can be twice or more the normal cranking current, but that is very short duration and is not likely to blow/trip a 200 A fuse or breaker. A short circuit of a battery can easily draw 1000 amps or more which would blow a 200 A fuse fairly quickly.
[img]cid:E2577D00-CEE6-44B3-963B-7FE9316010E4[/img]VRLAshortCurrentsStorageBatterySystems
PDF Document · 163 KB
[img]cid:22B0F079-6A61-4D4A-B632-9F909E2D9767[/img]Cessna Flyer Association - Save your Starter
cessnaflyer.org
youtu.be
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I believe overcurrent protection on a battery is easily accomplished, but I tend to agree with Bob that the likelihood of needing this is small. Then again, you can make a similar argument for the battery contactor. You don’t see these in the automobile world as they are deemed unnecessary and for good reason. One could argue the same for aircraft.
Matt
Sent from my iPad
| Quote: | On Feb 25, 2023, at 10:23 AM, GLEN MATEJCEK <fly4grins(at)gmail.com> wrote:
| Quote: |
Re: fuses in series
I could see someone following the architecture used in home and building
electrical distribution systems ...
|
A couple more data points:
My 1970's VW Rabbit had a fusible link in the battery cable, and I guess I wouldn't be shocked to learn many cars were so equipped without it being general knowledge.
There are transport category aircraft with current limiters geographically distributed around the system to prevent hard faults from taking out the whole system.
No clue if that strategy is based upon crashworthiness considerations, maintenance considerations, corporate history, or some combination.
In my aft-battery RV-8, the fat wire runs through the crushable structure under the cabin floor, making it susceptible to pinching and a hard fault in a crash, especially given the model's tendency to shed its main gear. Not sure the practicality of trying to size a current limiter that would not open under cranking loads but still open with a hard fault. The guestimated risk for me centers on the probability of hitting the planet without knowing it's coming and thereby not getting the master off in time. Given how I operate, I judge that to be a low very order threat and one I can live with.
YMMV-
|
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cluros(at)gmail.com
Guest
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| Posted: Sat Feb 25, 2023 10:36 am Post subject: fuses in series |
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We definitely need SOME way to cut electrical power to the aircraft for several different emergency situations. A battery contactor solves this for all but the most sudden and catastrophic situations. A friend of mine crashed his F1 rocket at during a go-around at full throttle and ended up trapped upside down. He could smell the fuel from the damaged wing tank but couldn't reach the master switch. Fortunately the electrical system stayed intact and the fuel never ignited. I don't know of a single crash where a battery fuse could have changed the outcome.
As for current limiters rated for short starting loads, I flew King Airs for years with current limiters. We carried spares because they blew on engine start more than once. Beech eventually replaced them with bus ties.
When Cessna starts producing single engine aircraft with battery fuses, I think it will be worth another look. In the meantime I don't see a benefit to adding odds and ends to a proven system.
On Sat, 25 Feb 2023, 08:38 Matthew S. Whiting, <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:
| Quote: | I agree that the likelihood of a direct short of a main battery cable is small. However, it is not zero and the localized heating from such a short could ignite combustibles. As long as the cable is kept away from combustibles, this isn’t an issue.
The difference in current between starting and a significant short is pretty large so viable overcurrent protection is feasible. For example, most engines in EA-B aircraft probably draw 100 amps or less during starting. It takes a fairly large engine to draw 200 amps (think diesel pickup truck or larger). Yes, the initial current when the starter is not turning can be twice or more the normal cranking current, but that is very short duration and is not likely to blow/trip a 200 A fuse or breaker. A short circuit of a battery can easily draw 1000 amps or more which would blow a 200 A fuse fairly quickly.
[img]cid:E2577D00-CEE6-44B3-963B-7FE9316010E4[/img]VRLAshortCurrentsStorageBatterySystems
PDF Document · 163 KB
[img]cid:22B0F079-6A61-4D4A-B632-9F909E2D9767[/img]Cessna Flyer Association - Save your Starter
cessnaflyer.org
youtu.be
[url=https://youtu.be/d2nPHWNoDSA][/url]
I believe overcurrent protection on a battery is easily accomplished, but I tend to agree with Bob that the likelihood of needing this is small. Then again, you can make a similar argument for the battery contactor. You don’t see these in the automobile world as they are deemed unnecessary and for good reason. One could argue the same for aircraft.
Matt
Sent from my iPad
| Quote: | On Feb 25, 2023, at 10:23 AM, GLEN MATEJCEK <fly4grins(at)gmail.com (fly4grins(at)gmail.com)> wrote:
| Quote: |
Re: fuses in series
I could see someone following the architecture used in home and building
electrical distribution systems ...
|
A couple more data points:
My 1970's VW Rabbit had a fusible link in the battery cable, and I guess I wouldn't be shocked to learn many cars were so equipped without it being general knowledge.
There are transport category aircraft with current limiters geographically distributed around the system to prevent hard faults from taking out the whole system.
No clue if that strategy is based upon crashworthiness considerations, maintenance considerations, corporate history, or some combination.
In my aft-battery RV-8, the fat wire runs through the crushable structure under the cabin floor, making it susceptible to pinching and a hard fault in a crash, especially given the model's tendency to shed its main gear. Not sure the practicality of trying to size a current limiter that would not open under cranking loads but still open with a hard fault. The guestimated risk for me centers on the probability of hitting the planet without knowing it's coming and thereby not getting the master off in time. Given how I operate, I judge that to be a low very order threat and one I can live with.
YMMV-
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Voyager
Joined: 30 Jun 2020
Posts: 77
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| Posted: Sat Feb 25, 2023 12:40 pm Post subject: fuses in series |
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That is the beauty of EA-B. We can evaluate the risks and rewards and make our own decision. I am still on the fence, but leaning against overcurrent protection at the battery. Mainly since I am hoping to fit both batteries on the firewall. A battery under the baggage compartment or in the cockpit would most likely get an overcurrent protection device at the battery as I’d rather not have a 1,000 amp hot spot in the cabin area should a cable wear through the insulation.
Matt
Sent from my iPad
| Quote: | On Feb 25, 2023, at 1:39 PM, Sebastien <cluros(at)gmail.com> wrote:
We definitely need SOME way to cut electrical power to the aircraft for several different emergency situations. A battery contactor solves this for all but the most sudden and catastrophic situations. A friend of mine crashed his F1 rocket at during a go-around at full throttle and ended up trapped upside down. He could smell the fuel from the damaged wing tank but couldn't reach the master switch. Fortunately the electrical system stayed intact and the fuel never ignited. I don't know of a single crash where a battery fuse could have changed the outcome.
As for current limiters rated for short starting loads, I flew King Airs for years with current limiters. We carried spares because they blew on engine start more than once. Beech eventually replaced them with bus ties.
When Cessna starts producing single engine aircraft with battery fuses, I think it will be worth another look. In the meantime I don't see a benefit to adding odds and ends to a proven system.
On Sat, 25 Feb 2023, 08:38 Matthew S. Whiting, <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:
| Quote: | I agree that the likelihood of a direct short of a main battery cable is small. However, it is not zero and the localized heating from such a short could ignite combustibles. As long as the cable is kept away from combustibles, this isn’t an issue.
The difference in current between starting and a significant short is pretty large so viable overcurrent protection is feasible. For example, most engines in EA-B aircraft probably draw 100 amps or less during starting. It takes a fairly large engine to draw 200 amps (think diesel pickup truck or larger). Yes, the initial current when the starter is not turning can be twice or more the normal cranking current, but that is very short duration and is not likely to blow/trip a 200 A fuse or breaker. A short circuit of a battery can easily draw 1000 amps or more which would blow a 200 A fuse fairly quickly.
[img]cid:E2577D00-CEE6-44B3-963B-7FE9316010E4[/img]VRLAshortCurrentsStorageBatterySystems
PDF Document · 163 KB
[img]cid:22B0F079-6A61-4D4A-B632-9F909E2D9767[/img]Cessna Flyer Association - Save your Starter
cessnaflyer.org
youtu.be
[url=https://youtu.be/d2nPHWNoDSA][/url]
I believe overcurrent protection on a battery is easily accomplished, but I tend to agree with Bob that the likelihood of needing this is small. Then again, you can make a similar argument for the battery contactor. You don’t see these in the automobile world as they are deemed unnecessary and for good reason. One could argue the same for aircraft.
Matt
Sent from my iPad
| Quote: | On Feb 25, 2023, at 10:23 AM, GLEN MATEJCEK <fly4grins(at)gmail.com (fly4grins(at)gmail.com)> wrote:
| Quote: |
Re: fuses in series
I could see someone following the architecture used in home and building
electrical distribution systems ...
|
A couple more data points:
My 1970's VW Rabbit had a fusible link in the battery cable, and I guess I wouldn't be shocked to learn many cars were so equipped without it being general knowledge.
There are transport category aircraft with current limiters geographically distributed around the system to prevent hard faults from taking out the whole system.
No clue if that strategy is based upon crashworthiness considerations, maintenance considerations, corporate history, or some combination.
In my aft-battery RV-8, the fat wire runs through the crushable structure under the cabin floor, making it susceptible to pinching and a hard fault in a crash, especially given the model's tendencyto shed its main gear. Not sure the practicality of trying to size a current limiter that would not open under cranking loads but still open with a hard fault. The guestimated risk for me centers on the probability of hitting the planet without knowing it's coming and thereby not getting the master off in time. Given how I operate, I judge that to be a low very order threat and one I can live with.
YMMV-
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<03224d1fcb0108937e9b07deb18cf473_M.jpg>
<preview.png>
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alec(at)alecmyers.com
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| Posted: Sat Feb 25, 2023 1:37 pm Post subject: fuses in series |
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You can start a very healthy fire with a 10 or 20 amp short circuit, as evidenced by the old fashioned cigarette lighters, as it will apply sustained heat for long enough to ignite nearby materiel.
A short circuit that takes out a 200A fusible link is more like a small fast explosion and as Bob points out, the structure to which the short circuit is made will evaporate, acting as it’s own fusible device
A 200 amp breaker won’t stop a cabin fire.
Sent from my iPhone
| Quote: | On Feb 25, 2023, at 15:41, Matthew S. Whiting <m.whiting(at)frontier.com> wrote:
That is the beauty of EA-B. We can evaluate the risks and rewards and make our own decision. I am still on the fence, but leaning against overcurrent protection at the battery. Mainly since I am hoping to fit both batteries on the firewall. A battery under the baggage compartment or in the cockpit would most likely get an overcurrent protection device at the battery as I’d rather not have a 1,000 amp hot spot in the cabin area should a cable wear through the insulation.
Matt
Sent from my iPad
| Quote: | On Feb 25, 2023, at 1:39 PM, Sebastien <cluros(at)gmail.com> wrote:
We definitely need SOME way to cut electrical power to the aircraft for several different emergency situations. A battery contactor solves this for all but the most sudden and catastrophic situations. A friend of mine crashed his F1 rocket at during a go-around at full throttle and ended up trapped upside down. He could smell the fuel from the damaged wing tank but couldn't reach the master switch. Fortunately the electrical system stayed intact and the fuel never ignited. I don't know of a single crash where a battery fuse could have changed the outcome.
As for current limiters rated for short starting loads, I flew King Airs for years with current limiters. We carried spares because they blew on engine start more than once. Beech eventually replaced them with bus ties.
When Cessna starts producing single engine aircraft with battery fuses, I think it will be worth another look. In the meantime I don't see a benefit to adding odds and ends to a proven system.
On Sat, 25 Feb 2023, 08:38 Matthew S. Whiting, <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:
| Quote: | I agree that the likelihood of a direct short of a main battery cable is small. However, it is not zero and the localized heating from such a short could ignite combustibles. As long as the cable is kept away from combustibles, this isn’t an issue.
The difference in current between starting and a significant short is pretty large so viable overcurrent protection is feasible. For example, most engines in EA-B aircraft probably draw 100 amps or less during starting. It takes a fairly large engine to draw 200 amps (think diesel pickup truck or larger). Yes, the initial current when the starter is not turning can be twice or more the normal cranking current, but that is very short duration and is not likely to blow/trip a 200 A fuse or breaker. A short circuit of a battery can easily draw 1000 amps or more which would blow a 200 A fuse fairly quickly.
[img]cid:E2577D00-CEE6-44B3-963B-7FE9316010E4[/img]VRLAshortCurrentsStorageBatterySystems
PDF Document · 163 KB
[img]cid:22B0F079-6A61-4D4A-B632-9F909E2D9767[/img]Cessna Flyer Association - Save your Starter
cessnaflyer.org
youtu.be
[url=https://youtu.be/d2nPHWNoDSA][/url]
I believe overcurrent protection on a battery is easily accomplished, but I tend to agree with Bob that the likelihood of needing this is small. Then again, you can make a similar argument for the battery contactor. You don’t see these in the automobile world as they are deemed unnecessary and for good reason. One could argue the same for aircraft.
Matt
Sent from my iPad
| Quote: | On Feb 25, 2023, at 10:23 AM, GLEN MATEJCEK <fly4grins(at)gmail.com (fly4grins(at)gmail.com)> wrote:
| Quote: |
Re: fuses in series
I could see someone following the architecture used in home and building
electrical distribution systems ...
|
A couple more data points:
My 1970's VW Rabbit had a fusible link in the battery cable, and I guess I wouldn't be shocked to learn many cars were so equipped without it being general knowledge.
There are transport category aircraft with current limiters geographically distributed around the system to prevent hard faults from taking out the whole system.
No clue if that strategy is based upon crashworthiness considerations, maintenance considerations, corporate history, or some combination.
In my aft-battery RV-8, the fat wire runs through the crushable structure under the cabin floor, making it susceptible to pinching and a hard fault in a crash, especially given the model's tendency to shed its main gear. Not sure the practicality of trying to size a current limiter that would not open under cranking loads but still open with a hard fault. The guestimated risk for me centers on the probability of hitting the planet without knowing it's coming and thereby not getting the master off in time. Given how I operate, I judge that to be a low very order threat and one I can live with.
YMMV-
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<03224d1fcb0108937e9b07deb18cf473_M.jpg>
<preview.png>
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ashleysc(at)broadstripe.n
Guest
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| Posted: Sat Feb 25, 2023 5:36 pm Post subject: fuses in series |
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Hi All;
I suppose it's a matter of opinion, but I think two fuses in series confuses diagnosis and increases the time for replacement, when that time sometimes may not be available.
Cheers! Stu.
From: "Matthew S. Whiting" <m.whiting(at)frontier.com>
To: aeroelectric-list(at)matronics.com
Sent: Saturday, February 25, 2023 12:40:02 PM
Subject: Re: Re: fuses in series
That is the beauty of EA-B. We can evaluate the risks and rewards and make our own decision. I am still on the fence, but leaning against overcurrent protection at the battery. Mainly since I am hoping to fit both batteries on the firewall. A battery under the baggage compartment or in the cockpit would most likely get an overcurrent protection device at the battery as I’d rather not have a 1,000 amp hot spot in the cabin area should a cable wear through the insulation.
Matt
Sent from my iPad
| Quote: | On Feb 25, 2023, at 1:39 PM, Sebastien <cluros(at)gmail.com> wrote:
We definitely need SOME way to cut electrical power to the aircraft for several different emergency situations. A battery contactor solves this for all but the most sudden and catastrophic situations. A friend of mine crashed his F1 rocket at during a go-around at full throttle and ended up trapped upside down. He could smell the fuel from the damaged wing tank but couldn't reach the master switch. Fortunately the electrical system stayed intact and the fuel never ignited. I don't know of a single crash where a battery fuse could have changed the outcome.
As for current limiters rated for short starting loads, I flew King Airs for years with current limiters. We carried spares because they blew on engine start more than once. Beech eventually replaced them with bus ties.
When Cessna starts producing single engine aircraft with battery fuses, I think it will be worth another look. In the meantime I don't see a benefit to adding odds and ends to a proven system.
On Sat, 25 Feb 2023, 08:38 Matthew S. Whiting, <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:
| Quote: | I agree that the likelihood of a direct short of a main battery cable is small. However, it is not zero and the localized heating from such a short could ignite combustibles. As long as the cable is kept away from combustibles, this isn’t an issue.
The difference in current between starting and a significant short is pretty large so viable overcurrent protection is feasible. For example, most engines in EA-B aircraft probably draw 100 amps or less during starting. It takes a fairly large engine to draw 200 amps (think diesel pickup truck or larger). Yes, the initial current when the starter is not turning can be twice or more the normal cranking current, but that is very short duration and is not likely to blow/trip a 200 A fuse or breaker. A short circuit of a battery can easily draw 1000 amps or more which would blow a 200 A fuse fairly quickly.
[img]cid:E2577D00-CEE6-44B3-963B-7FE9316010E4[/img]
VRLAshortCurrentsStorageBatterySystems
PDF Document · 163 KB
|
[img]cid:22B0F079-6A61-4D4A-B632-9F909E2D9767[/img]
Cessna Flyer Association - Save your Starter
cessnaflyer.org
youtu.be
[url=https://youtu.be/d2nPHWNoDSA][/url]
|
I believe overcurrent protection on a battery is easily accomplished, but I tend to agree with Bob that the likelihood of needing this is small. Then again, you can make a similar argument for the battery contactor. You don’t see these in the automobile world as they are deemed unnecessary and for good reason. One could argue the same for aircraft.
Matt
Sent from my iPad
| Quote: | On Feb 25, 2023, at 10:23 AM, GLEN MATEJCEK <fly4grins(at)gmail.com (fly4grins(at)gmail.com)> wrote:
| Quote: |
Re: fuses in series
I could see someone following the architecture used in home and building
electrical distribution systems ...
|
A couple more data points:
My 1970's VW Rabbit had a fusible link in the battery cable, and I guess I wouldn't be shocked to learn many cars were so equipped without it being general knowledge.
There are transport category aircraft with current limiters geographically distributed around the system to prevent hard faults from taking out the whole system.
No clue if that strategy is based upon crashworthiness considerations, maintenance considerations, corporate history, or some combination.
In my aft-battery RV-8, the fat wire runs through the crushable structure under the cabin floor, making it susceptible to pinching and a hard fault in a crash, especially given the model's tendency to shed its main gear. Not sure the practicality of trying to size a current limiter that would not open under cranking loads but still open with a hard fault. The guestimated risk for me centers on the probability of hitting the planet without knowing it's coming and thereby not getting the master off in time. Given how I operate, I judge that to be a low very order threat and one I can live with.
YMMV-
|
<03224d1fcb0108937e9b07deb18cf473_M.jpg>
<preview.png>
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Ceengland
Joined: 11 Oct 2020
Posts: 391
Location: MS
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| Posted: Sat Feb 25, 2023 5:56 pm Post subject: fuses in series |
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So, you're pressed for time because you're flying IFR and about to fly an approach? Kinda violates the whole idea of saving troubleshooting until you're on the ground.
On 2/25/2023 7:36 PM, ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net) wrote:
| Quote: | Hi All;
I suppose it's a matter of opinion, but I think two fuses in series confuses diagnosis and increases the time for replacement, when that time sometimes may not be available.
Cheers! Stu.
From: "Matthew S. Whiting" <m.whiting(at)frontier.com> (m.whiting(at)frontier.com)
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Sent: Saturday, February 25, 2023 12:40:02 PM
Subject: Re: Re: fuses in series
That is the beauty of EA-B. We can evaluate the risks and rewards and make our own decision. I am still on the fence, but leaning against overcurrent protection at the battery. Mainly since I am hoping to fit both batteries on the firewall. A battery under the baggage compartment or in the cockpit would most likely get an overcurrent protection device at the battery as I’d rather not have a 1,000 amp hot spot in the cabin area should a cable wear through the insulation.
Matt
Sent from my iPad
| Quote: | On Feb 25, 2023, at 1:39 PM, Sebastien <cluros(at)gmail.com> (cluros(at)gmail.com) wrote:
We definitely need SOME way to cut electrical power to the aircraft for several different emergency situations. A battery contactor solves this for all but the most sudden and catastrophic situations. A friend of mine crashed his F1 rocket at during a go-around at full throttle and ended up trapped upside down. He could smell the fuel from the damaged wing tank but couldn't reach the master switch. Fortunately the electrical system stayed intact and the fuel never ignited. I don't know of a single crash where a battery fuse could have changed the outcome.
As for current limiters rated for short starting loads, I flew King Airs for years with current limiters. We carried spares because they blew on engine start more than once. Beech eventually replaced them with bus ties.
When Cessna starts producing single engine aircraft with battery fuses, I think it will be worth another look. In the meantime I don't see a benefit to adding odds and ends to a proven system.
On Sat, 25 Feb 2023, 08:38 Matthew S. Whiting, <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:
| Quote: | I agree that the likelihood of a direct short of a main battery cable is small. However, it is not zero and the localized heating from such a short could ignite combustibles. As long as the cable is kept away from combustibles, this isn’t an issue.
The difference in current between starting and a significant short is pretty large so viable overcurrent protection is feasible. For example, most engines in EA-B aircraft probably draw 100 amps or less during starting. It takes a fairly large engine to draw 200 amps (think diesel pickup truck or larger). Yes, the initial current when the starter is not turning can be twice or more the normal cranking current, but that is very short duration and is not likely to blow/trip a 200 A fuse or breaker. A short circuit of a battery can easily draw 1000 amps or more which would blow a 200 A fuse fairly quickly.
[img]cid:E2577D00-CEE6-44B3-963B-7FE9316010E4[/img]
VRLAshortCurrentsStorageBatterySystems
PDF Document · 163 KB
|
[img]cid:22B0F079-6A61-4D4A-B632-9F909E2D9767[/img]
Cessna Flyer Association - Save your Starter
cessnaflyer.org
youtu.be
[/url]
|
I believe overcurrent protection on a battery is easily accomplished, but I tend to agree with Bob that the likelihood of needing this is small. Then again, you can make a similar argument for the battery contactor. You don’t see these in the automobile world as they are deemed unnecessary and for good reason. One could argue the same for aircraft.
Matt
Sent from my iPad
| Quote: | On Feb 25, 2023, at 10:23 AM, GLEN MATEJCEK <fly4grins(at)gmail.com (fly4grins(at)gmail.com)> wrote:
| Quote: |
Re: fuses in series
I could see someone following the architecture used in home and building
electrical distribution systems ...
|
A couple more data points:
My 1970's VW Rabbit had a fusible link in the battery cable, and I guess I wouldn't be shocked to learn many cars were so equipped without it being general knowledge.
There are transport category aircraft with current limiters geographically distributed around the system to prevent hard faults from taking out the whole system.
No clue if that strategy is based upon crashworthiness considerations, maintenance considerations, corporate history, or some combination.
In my aft-battery RV-8, the fat wire runs through the crushable structure under the cabin floor, making it susceptible to pinching and a hard fault in a crash, especially given the model's tendency to shed its main gear. Not sure the practicality of trying to size a current limiter that would not open under cranking loads but still open with a hard fault. The guestimated risk for me centers on the probability of hitting the planet without knowing it's coming and thereby not getting the master off in time. Given how I operate, I judge that to be a low very order threat and one I can live with.
YMMV-
|
<03224d1fcb0108937e9b07deb18cf473_M.jpg>
<preview.png>
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Sun Feb 26, 2023 8:30 am Post subject: fuses in series |
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At 07:58 PM 2/25/2023, you wrote:
| Quote: | So, you're pressed for time because you're flying IFR and about to fly an approach? Kinda violates the whole idea of saving troubleshooting until you're on the ground.
|
Agreed. If failure of ANY component of your project
places you at operational risk then you need to
have a back-up for it. Back-up may be totally dependent
on your personal skills. Ever shoot an approach DG-needle-
ball-and-airspeed? I used to ride shotgun for an associate that
routinely practiced that. Never watched him shoot the
approaches with everything working, "That's easy sez
he . . . I need to be prepared for the hard ones"
For every failure that manifests with open circuit
protection there are dozens of conditions equally
deleterious to system operations that DO NOT open
circuit protection. Further, if circuit protection
does open in flight, what is the probability that
restoring power will gain use of that system? If
the fuse opens, something is BROKE. Time to switch
to plan-B.
FAT wire protection goes to crash safety . . . if
your airplane is so badly balled up that FAT wires
are likely to experience hard faults . . . it's
likely your bod is equally balled up. That's
what battery master contactors and current limited
battery busses are all about.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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