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jdubner
Joined: 17 Jul 2012
Posts: 35
Location: Independence, OR
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 Posted: Sun Jul 07, 2019 7:26 am Post subject: Overvoltage protection |
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A friend is working on a Grumman Tiger in which the alternator field circuit
breaker was found tripped. Upon digging in the manual, he found the overvoltage
protection was simply a Zener diode wired from the output of the field breaker
to ground. The diode was found to be shorted, which would easily trip the
breaker.
I can only find a "house number" on the Zener. The diode was removed, the old
regulator was replaced with a Zeftronics with integral overvoltage protection,
the split rocker switch was replaced with a new one, and all seems well --
except that one electrical instrument is inoperative (possibly due to an
overvoltage event).
My questions are as follows: can a physically small Zener diode (similar in size
to a 1N5401 diode) handle the amount of energy required to trip a 5A breaker,
even one time? Can the Zener always be counted upon to fail shorted and not open?
Thanks,
Joe
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jul 07, 2019 8:48 am Post subject: Overvoltage protection |
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At 10:25 AM 7/7/2019, you wrote:
| Quote: | --> AeroElectric-List message posted by: Joe Dubner <jdubner(at)yahoo.com>
A friend is working on a Grumman Tiger in which the alternator field circuit breaker was found tripped. Upon digging in the manual, he found the overvoltage protection was simply a Zener diode wired from the output of the field breaker to ground. The diode was found to be shorted, which would easily trip the breaker. |
Yup. A stone simple ov protection scheme
that made it onto a TC aircraft. Wrote about
this for SA back in '93 . . .
https://tinyurl.com/y38og7he
Discovered later that the idea was not
'bad' as originally implemented. The
design called for a GLASS, 1N4745, 1W zener
tied to ground downstream of a 5A
FUSE.
[img]cid:.0[/img]
I did some testing on various
zeners and found that only GLASS enclosed
could be depended upon to fail shorted . . .
plastics would occasionally split
and fail to burn the fuse.
[img]cid:.1[/img]
This is why the zener could only be
'legally' replaced with the Grumman house
part number to make sure that the part
was GLASS encased.
Some airplanes were modified to replace
cartridge fuses with breakers but left
the zener in place . . . risky because
the I(squared)t operation numbers
for a breaker are larger than the fuse.
| Quote: | | I can only find a "house number" on the Zener. The diode was removed, the old regulator was replaced with a Zeftronics with integral overvoltage protection, the split rocker switch was replaced with a new one, and all seems well -- except that one electrical instrument is inoperative (possibly due to an overvoltage event). |
Once the regulator is replaced with one
that INCLUDES ov protection, the zener
should be removed.
| Quote: | | My questions are as follows: can a physically small Zener diode (similar in size to a 1N5401 diode) handle the amount of energy required to trip a 5A breaker, even one time? Can the Zener always be counted upon to fail shorted and not open? |
Good question but moot after the
regulator is replaced.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jul 07, 2019 10:04 am Post subject: Overvoltage protection |
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At 10:25 AM 7/7/2019, you wrote:
| Quote: | --> AeroElectric-List message posted by: Joe Dubner <jdubner(at)yahoo.com>
A friend is working on a Grumman Tiger in which the alternator field circuit breaker was found tripped. Upon digging in the manual, he found the overvoltage protection was simply a Zener diode wired from the output of the field breaker to ground. The diode was found to be shorted, which would easily trip the breaker. |
Yup. A stone simple ov protection scheme
that made it onto a TC aircraft. Wrote about
this for SA back in '93 . . .
https://tinyurl.com/y38og7he
Discovered later that the idea was not
'bad' as originally implemented. The
design called for a GLASS, 1N4745, 1W zener
tied to ground downstream of a 5A
FUSE. The thing was designed to be a single
event operator . . . IF you experienced
an ov condition, the zener was expected to
short, the fuse was expected to open.
You would have to investigate and fix
root cause of the ov condtion, then replace the
zener and fuse before flying upward and onward.
[img]cid:.0[/img]
I did some testing on various
zeners and found that only GLASS enclosed
could be depended upon to fail shorted . . .
plastics would occasionally split apart
and fail to burn the fuse.
[img]cid:.1[/img]
This is why the zener could only be
'legally' replaced with the Grumman house
part number to make sure that the part
was GLASS encased.
Some airplanes were modified to replace
cartridge fuses with breakers but left
the zener in place . . . risky because
the I(squared)t operation numbers
for the breaker are larger than a fuse.
| Quote: | | I can only find a "house number" on the Zener. The diode was removed, the old regulator was replaced with a Zeftronics with integral overvoltage protection, the split rocker switch was replaced with a new one, and all seems well -- except that one electrical instrument is inoperative (possibly due to an overvoltage event). |
Once the regulator is replaced with one
that INCLUDES ov protection, the zener
should be removed.
| Quote: | | My questions are as follows: can a physically small Zener diode (similar in size to a 1N5401 diode) handle the amount of energy required to trip a 5A breaker, even one time? Can the Zener always be counted upon to fail shorted and not open? |
Good question but moot after the
regulator is replaced.
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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|
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| Viewed: |
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jdubner
Joined: 17 Jul 2012
Posts: 35
Location: Independence, OR
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| Posted: Sun Jul 07, 2019 12:46 pm Post subject: Overvoltage protection |
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Thank you, Bob. Mystery solved! You nailed it with this information and in the
article you wrote for S.A. in 1993. But it's the first time I've heard of such
a thing and was somewhat bewildered at a design depending on an unspecified
parameter in this way. Thanks for the history and explanation.
BTW, the diode we removed appeared to be plastic (like the one in your second
attached image), not glass.
But as you conclude (and we do too): it's moot after the regulator is replaced
with one containing over-voltage regulation.
Thanks again,
Joe
Robert L. Nuckolls, III wrote, On 7/7/2019 09:45:
| Quote: | At 10:25 AM 7/7/2019, you wrote:
>
>
> A friend is working on a Grumman Tiger in which the alternator field
> circuit breaker was found tripped. Upon digging in the manual, he
> found the overvoltage protection was simply a Zener diode wired from
> the output of the field breaker to ground. The diode was found to be
> shorted, which would easily trip the breaker.
Yup. A stone simple ov protection scheme
that made it onto a TC aircraft. Wrote about
this for SA back in '93 . . .
https://tinyurl.com/y38og7he
Discovered later that the idea was not
'bad' as originally implemented. The
design called for a GLASS, 1N4745, 1W zener
tied to ground downstream of a 5A
FUSE.
Emacs!
I did some testing on various
zeners and found that only GLASS enclosed
could be depended upon to fail shorted . . .
plastics would occasionally split
and fail to burn the fuse.
Emacs!
This is why the zener could only be
'legally' replaced with the Grumman house
part number to make sure that the part
was GLASS encased.
Some airplanes were modified to replace
cartridge fuses with breakers but left
the zener in place . . . risky because
the I(squared)t operation numbers
for a breaker are larger than the fuse.
> I can only find a "house number" on the Zener. The diode was removed,
> the old regulator was replaced with a Zeftronics with integral
> overvoltage protection, the split rocker switch was replaced with a
> new one, and all seems well -- except that one electrical instrument
> is inoperative (possibly due to an overvoltage event).
Once the regulator is replaced with one
that INCLUDES ov protection, the zener
should be removed.
> My questions are as follows: can a physically small Zener diode
> (similar in size to a 1N5401 diode) handle the amount of energy
> required to trip a 5A breaker, even one time? Can the Zener always be
> counted upon to fail shorted and not open?
Good question but moot after the
regulator is replaced.
Bob . . .
|
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