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What happens if OV trips?

 
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scott(at)randolphs.net
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PostPosted: Thu Feb 23, 2006 11:18 pm    Post subject: What happens if OV trips? Reply with quote

If the "crowbar" overvoltage protection trips, is it a permanent fault or
something that can be reset on the fly?

I'm interested in general in how it works, but specificly thinking now about
the possibility of one alternator tripping both OV circuits if both
alternators happen to be on (by design or switchology error). If that
happened, would both alternators be permanently disabled or would turning
off the faulty one allow the other to be brought back online?

Thanks!

Scott.


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klehman(at)albedo.net
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PostPosted: Fri Feb 24, 2006 6:47 am    Post subject: What happens if OV trips? Reply with quote

Hi Scott
I don't believe any of the Z architectures run two alternators in
parallel such that both would trip together.
However if a crowbar activates it becomes a momentary short until the CB
pops. Reset the CB and everything goes back to normal unless the voltage
goes high again in which case the breaker will immediately pop again.
Nuisance tripping seems to be quite rare and IMO one should not tolerate
any nuisance trips but rather find out why that is happening and fix it.
While I don't have much engine running time accumulated yet, I have not
been able to instigate a single nuisance trip with the latest homemade
version of Bob's crowbar circuit dated Jan 2006. I could instigate them
with earlier homemade versions.
Ken

Scott wrote:

Quote:


If the "crowbar" overvoltage protection trips, is it a permanent fault or
something that can be reset on the fly?

I'm interested in general in how it works, but specificly thinking now about
the possibility of one alternator tripping both OV circuits if both
alternators happen to be on (by design or switchology error). If that
happened, would both alternators be permanently disabled or would turning
off the faulty one allow the other to be brought back online?

Thanks!

Scott.




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nuckollsr(at)cox.net
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PostPosted: Fri Feb 24, 2006 9:17 am    Post subject: What happens if OV trips? Reply with quote

At 08:25 AM 2/24/2006 -0500, you wrote:

Quote:


Hi Scott
I don't believe any of the Z architectures run two alternators in
parallel such that both would trip together.

Z-12 does and the regulators specified are 'smart' enough to know
if an ov condition is caused by local failure or is coming from another
alternator.

Quote:
However if a crowbar activates it becomes a momentary short until the CB
pops. Reset the CB and everything goes back to normal unless the voltage
goes high again in which case the breaker will immediately pop again.
Nuisance tripping seems to be quite rare and IMO one should not tolerate
any nuisance trips but rather find out why that is happening and fix it.
While I don't have much engine running time accumulated yet, I have not
been able to instigate a single nuisance trip with the latest homemade
version of Bob's crowbar circuit dated Jan 2006. I could instigate them
with earlier homemade versions.
Ken

Absolutely. Nuisance trips are a fact of life in virtually every
design that stands as close as practical to the edge. You DESIRE
sensitivity to the failure but in some cases, there is overlap
between things that should and should not be reacted to.

Of all the OV systems I've worked in the past 30 years, I'll guess
that perhaps 1/3 of them needed some tweaking after first delivery.
This is the nature of the beast that is a quest for best response to
a hazard and ability to filter and ignore conditions that are not
hazardous.
Quote:
Scott wrote:

>
>
>If the "crowbar" overvoltage protection trips, is it a permanent fault or
>something that can be reset on the fly?
>
>I'm interested in general in how it works, but specificly thinking now about
>the possibility of one alternator tripping both OV circuits if both
>alternators happen to be on (by design or switchology error). If that
>happened, would both alternators be permanently disabled or would turning
>off the faulty one allow the other to be brought back online?

Virtually all ov systems for aircraft have allowed resetting by
the pilot with one notable exception. American/Grumman had a po' boy's
crowbar OV system using a zener and an upstream fuse. A trip event
took out a fuse and most often shorted the zener. However, while
crude in implementation, this system was immune to nuisance trips.
Cheap, effective and few downsides.

Bob . . .


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