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nuckolls.bob(at)aeroelect
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 Posted: Thu Oct 10, 2019 1:49 pm Post subject: fusible link downstream of circuit breaker |
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At 12:40 PM 10/10/2019, you wrote:
| Quote: | --> AeroElectric-List message posted by: "johnbright" <john_s_bright(at)yahoo.com>
One of the electronic fuel injection systems marketed to EAB delivers a harness with fusible links inside a firewall passthru connector. I sketched what they recommend and attached it here.
I see:
* The unprotected wire between the essential bus and the circuit breaker.
* The possibility of the wire between the breaker and the firewall connector opening or shorting to ground taking out all four injectors.
But I'm wondering if the fusible links do anything at all. I don't know the awg of the links but suppose they were 24 awg which has a fusing current of 29 A. If an injector wire shorted to ground between the firewall connector and an individual injector would the circuit breaker trip taking out all four injectors?
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I would power each injector from its
own fuse off the battery bus. The
injectors are powered down any time
power is off the ECU . . . no need
to make battery power crew controlled.
The fusible links serve no purpose.
Bob . . .
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johnbright
Joined: 14 Dec 2011
Posts: 166
Location: Newport News, VA
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| Posted: Thu Oct 10, 2019 4:25 pm Post subject: Re: fusible link downstream of circuit breaker |
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Thanks Bob,
My plan is to fuse the injectors individually at the bus as you suggest. I'm using two batteries and I have two battery buses with an injector bus connected to both with diodes. I show the diodes in parallel pairs because they come two to a case and I don't know whether or not there is a failure mode that could open both at the same time.
To explain what the injector relays are... they switch the injectors to the backup ECU by means of a toggle switch on the panel in case of primary ECU failure.
Schematic attached.
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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
Last edited by johnbright on Fri Oct 11, 2019 6:35 am; edited 3 times in total |
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user9253
Joined: 28 Mar 2008
Posts: 1944
Location: Riley TWP Michigan
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| Posted: Thu Oct 10, 2019 5:25 pm Post subject: Re: fusible link downstream of circuit breaker |
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Whenever fuses are connected in series, there is a chance that both could blow. Consider increasing the 15 amp fuses to 20 or 30 amps.
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Joe Gores |
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johnbright
Joined: 14 Dec 2011
Posts: 166
Location: Newport News, VA
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| Posted: Fri Oct 11, 2019 6:27 am Post subject: Re: fusible link downstream of circuit breaker |
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Schematic edited to delete fuses and relays between injector bus and battery buses.
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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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nuckolls.bob(at)aeroelect
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| Posted: Fri Oct 11, 2019 7:14 am Post subject: fusible link downstream of circuit breaker |
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At 08:25 PM 10/10/2019, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
Whenever fuses are connected in series, there is a chance that both could blow. Consider increasing the 15 amp fuses to 20 or 30 amps.
--------
Joe Gores |
better yet . . . one protective device
per feeder with that protection located
as close as practical to the source.
Fusible links are baby brothers to
'current limiters' . . .
[img]cid:.0[/img]
These are for protection of power distribution
feeders and their stated ratings are exceedingly
conservative . . . they will generally continuous
carry several times their "nameplate" rating
as do fusible links.
http://aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ANL_Specs.pdf
Note spec sheet cited above says an ANL35
trip curve goes parallel to infinite trip-time at
about 95 amps! A 22AWG fusible link has a "nameplate"
rating on the order of 7A with a continuous
carry of more than 20A.
http://aeroelectric.com/Pictures/Wire/22AWG_20A.pdf
They stand off hazards for hard faults against
upstream batteries. You will rarely
find these used on small aircraft but
they can be useful . . . like extending
the feeder from a fused bus to the
breaker in a crowbar ov protection
system. But they are NOT substitutes
for fuses. They do have good and useful
applications where the physics of the
risk so indicates.
Bob . . .
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