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nuckolls.bob(at)aeroelect
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 Posted: Wed May 06, 2020 7:43 am Post subject: OV push to test button, is there a hack for SB1B |
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At 08:07 PM 5/5/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "johnbright" <john_s_bright(at)yahoo.com>
Hi Bob,
Seems like a nice feature that SB1B has an annunciatior light that it has
come online but unlike LR3C there is not an OV PTT... is there a way to
hack into SB1B for an OV PTT button? |
That feature was included in the first iterations
of the LR series regulators but never 'implemented'
in the installation instructions. I seem to recall
the recommendation was that it be manually checked
at intervals . . . like oil changes or annuals.
The ov protection system in all B&C (and AEC)
products are 'passive monitors'. They experience
miniscul operational stresses. Hence, under mil-hndbk-217
reliability studies, the device suffers no practical
service life limits.
It was decided that periodic ptt or 'live'
verification of functionality was more than
sufficient for continued airworthiness. If
you never tested the thing, you risk for
failure to perform is exceedingly low.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Wed May 06, 2020 3:42 pm Post subject: OV push to test button, is there a hack for SB1B |
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At 05:00 PM 5/6/2020, you wrote:
| Quote: | | Bob, you say "they worked good and lasted a long time." What was the eventual failure mode? How did one know when they did fail? |
Good question. I know there were spares
stocked and shipped over the years but
I'm not privy to the failure modes.
I do know that they were vulnerable
to shorts on the output lead which
would cause them to open up.
Did a quick search on
cessna single engine over voltage
Didn't find any postings on failures
Did find this service bulletin from
1972 that added an external capacitor
to preclude nuisance trips.
https://tinyurl.com/ybojxucx
That was the first ov protection system
ever installed on the Pawnee Plant
Cessnas. The term "over voltage"
was not a well quantified event
in terms of cause, effect and timing.
The protocol then was to shut down
'quickly' i.e. in 50 to 100 mS after
detection of a condition. The
circuitry was a bit sensitive to
otherwise normal transients on the bus.
Nowadays, the static trip points are
generally lower (16v) which must
sustain for 500 milliseconds or so.
If the transient ends before time-out,
the timer resets.
This protocol is still well inside
qualification test limits (20v for 1
second; 40v for 100 mS) and virtually
trip-free.
I was well out of the loop on that
line of aircraft after about 1975
so I have no first-hand knowledge
of any failure modes.
Installation instructions for the CBOVM
module I used to sell describes
a recommended yearly test for functionality.
https://tinyurl.com/ybojxucx
Bob . . .
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