Today's Message Index:
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1. 06:54 AM - Re: OVM-14 question (racerjerry)
2. 09:04 AM - Re: Re: OVM-14 question (Robert L. Nuckolls, III)
3. 09:12 AM - Re: Re: OVM-14 question (Robert L. Nuckolls, III)
4. 10:40 AM - Re: OVM-14 question (jdpnm)
5. 12:36 PM - Re: OVM-14 question (jonlaury)
Message 1
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| Subject: | Re: OVM-14 question |
> Reason I have circuit breakers on some items is because with a momentary switch,
I can short to ground items to lighten load, which will trip the breakers
reducing loads. Then if appropriate I can return function to selected items as
the situation permits, By resetting the individual CB.
>
PURPOSELY shorting out circuit breakers is generally not a good idea and will cause
them to degrade. Shorting, for rare over-voltage events is acceptable, but
repeated high current events could cause a circuit breaker to malfunction;
even possibly welding contacts closed.
A shorting switch is even more susceptible to arc damage and welding of contacts.
This reminds me of an Underwriter's Laboratory report describing a homeowner that
"tested" his circuit breakers yearly using a screwdriver. His house burned
down as a direct result.
--------
Jerry King
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=493726#493726
Message 2
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| Subject: | Re: OVM-14 question |
>
>PURPOSELY shorting out circuit breakers is generally not a good idea
>and will cause them to degrade. Shorting, for rare over-voltage
>events is acceptable, but repeated high current events could cause a
>circuit breaker to malfunction; even possibly welding contacts closed.
An urban technomyth completely unsupported by
the physics and over a century of practice.
A quality circuit breaker will find its
way onto Qualified Products Lists (QPL) for
government/military purchase by DEMONSTRATING
anh ability to OPEN a faulted line supplied by
a source current hundreds of times greater
than the breaker's trip-rating. An exemplar
table of qualifications for the Klixon 7274
series breakers reads as follows:
Emacs!
A 5A breaker upstream of a crowbar OV protection
system is qualified in systems capable of up to 800
Amps of fault current. A typical ov trip current
in a GA aircraft with crowbar OV management is
on the order of 150 amps.
Beech did crowbar OV management in a regulator I
proposed for the single-engine, turbine prototype
back about 1980. Of ALL the contemporary OV management
systems on hand at the time, my prototype was the only
one to manage a series of 50 OV events at the rate
of one event every two minutes. After the test, the
'abused' breaker still tested to design specs.
>A shorting switch is even more susceptible to arc damage and welding
>of contacts.
Do you mean a switch that closes a fault against
a high current source source, or a switch used to open a
a high current condition?
Contacts used to 'break' a faulted circuit, such
as those used in a breaker, may indeed suffer arc
damage if used to open a condition beyond the device's
ratings (see Endurance and Interrupt ratings above).
The crowbar OVM system that flies now in thousands
of OBAM and TC aircraft were designed and tested to
stay will within those limits.
>This reminds me of an Underwriter's Laboratory report describing a
>homeowner that "tested" his circuit breakers yearly using a
>screwdriver. His house burned down as a direct result.
I've heard several such stories over the years . . . all
of which argue with contemporary design and qualification
practices for modern breakers, switches and relays.
I'd need to see the published failure analysis on
this . . . sounds like an urban myth
to me.
Bob . . .
Message 3
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| Subject: | Re: OVM-14 question |
Graybeards here on the List will recall some
animated discussions about 14 years ago on the
topic of 'abused breakers' in crowbar ov
protection systems.
Here's a white paper I generated as a contribution
to those discussions:
http://www.aeroelectric.com/articles/Crowbar_OV_Protection/DC_Power_System_Dynamics_C.pdf
Bob . . .
Message 4
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| Subject: | Re: OVM-14 question |
thanks Bob.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=493730#493730
Message 5
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| Subject: | Re: OVM-14 question |
nuckolls.bob(at)aeroelect wrote:
> At 10:47 AM 12/4/2019, you wrote:
>
>
... You need one and
only one low volts warning light on the main
bus. If you have an LR3 regulator on your main
alternator, that light is built in.
Bob . . .[/quote]
At the time of my installation, I thought that alternator 1 needed LVW through
the LR3 reg.
Didn't think that the LR3 was monitoring the main bus so installed AEC 9005 LVW
for Alt 2/Ford reg.
Now I have redundant LVW [Embarassed]
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=493732#493732
Attachments:
http://forums.matronics.com//files/redundant_lvw_969.jpg
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