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nuckolls.bob(at)aeroelect Guest
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Posted: Sun Sep 23, 2012 12:38 pm Post subject: Misprint in Z-16, v.12/ OV with Rotax generators? |
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At 11:18 PM 9/22/2012, you wrote:
Thanks Bob,
I almost didn't mention it as I thought it was
"obviously wrongh but now I'm glad I did as I
learnt something! (Is there a detailed
discussion of how each Z figure works somewhere
that beginners can read?). Still wondering about
the diff between the Z16 and Z17 alternator disconnect wiring.
Just variations on a theme. Primary design
goal is to achieve absolute control over energy
from the alternator as seen by the rest of the
airplane. Opening the DC pathway out of the
rectifier-regulator does that. Opening the AC
power into the regulator does too.
AC is generally easier to control than DC for
considerations of contact arcing. But given
the low duty cycle of stressful events in these
systems, either will do fine and last a long
time.
As Ken noted, the RR can be placed at risk for
high rpm ops without having the battery connected.
So while the control schemes presented in Z-16/17
are golden for the rest of the airplane, Z-17
carries the protection further back toward the
alternator and would perhaps have saved Ken's
RR from untimely demise due to the unloaded
condition.
I've not taken the time to really thrash through
the physics of a PM regulator. Seems it SHOULD
be designed to handle worst case failures including
unloaded operations. It can probably be done but
Z-17 is a work-around until the golden PM rectifier
regulator comes along.
Bob . . .
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uuccio(at)gmail.com Guest
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Posted: Mon Sep 24, 2012 7:02 am Post subject: Misprint in Z-16, v.12/ OV with Rotax generators? |
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Bob/Ken/Bob,
Thanks a lot for your replies.
BobMc> what about the case of the one in a million "abnormal" failure
where an OV occurs?
You're right... I have to keep reminding myself it's not how unlikely the
event is that counts, it's how bad the consequences could be (vs how easy it
is to design a redundant system to avoid those bad consequences... In this
case it's easy so should be done).
Ken> The regulator failed even though the overvoltage disconnect relay was
between the
Ken> alternator and the regulator so the voltage must have risen faster than
the relay
Ken> could open when the engine started. I credit Bob's crowbar ovm for
keeping the buss
Ken> voltage clamped though and preventing any further damage.
I'm not clear to me how the OVM could have achieved that. I thought the way
the OVM module works is that it grounds the number 4 pole in the S1 switch
in Z16/Z17 and therefore causes the breaker to open and disconnects the OV
relay.
BobN> I've not taken the time to really thrash through
BobN> the physics of a PM regulator. Seems it SHOULD
BobN> be designed to handle worst case failures including
BobN> unloaded operations. It can probably be done but
BobN> Z-17 is a work-around until the golden PM rectifier
BobN> regulator comes along.
I think you mean Z-16 is golden... Z-17 is the simplified version.
I would also be interested in how the RR as well as the permanent magnet
generator in the Rotax works. I'll dig around... Thanks again!
Sacha
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klehman(at)albedo.net Guest
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Posted: Mon Sep 24, 2012 9:29 am Post subject: Misprint in Z-16, v.12/ OV with Rotax generators? |
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Hi Sacha
I might be a bit optimistic with that comment. My thoughts are that when
my OVM activates it immediately shorts out the relay but it is still
connected to the buss and is clamping the buss voltage until the circuit
breaker pops. So you are correct that with a slow opening relay and a
fast acting CB there could be a few milliseconds delay during which time
the voltage will be rising again.
Probably shouldn't mention it since I can't claim they are significant
but I also have a few TVS diodes on the buss. Since they are fast acting
and cheap they seemed like a good idea (several years ago) with an
electrically dependent engine.
Ken
On 24/09/2012 11:01 AM, s wrote:
[quote]
Bob/Ken/Bob,
Thanks a lot for your replies.
BobMc> what about the case of the one in a million "abnormal" failure
where an OV occurs?
You're right... I have to keep reminding myself it's not how unlikely the
event is that counts, it's how bad the consequences could be (vs how easy it
is to design a redundant system to avoid those bad consequences... In this
case it's easy so should be done).
Ken> The regulator failed even though the overvoltage disconnect relay was
between the
Ken> alternator and the regulator so the voltage must have risen faster than
the relay
Ken> could open when the engine started. I credit Bob's crowbar ovm for
keeping the buss
Ken> voltage clamped though and preventing any further damage.
I'm not clear to me how the OVM could have achieved that. I thought the way
the OVM module works is that it grounds the number 4 pole in the S1 switch
in Z16/Z17 and therefore causes the breaker to open and disconnects the OV
relay.
BobN> I've not taken the time to really thrash through
BobN> the physics of a PM regulator. Seems it SHOULD
BobN> be designed to handle worst case failures including
BobN> unloaded operations. It can probably be done but
BobN> Z-17 is a work-around until the golden PM rectifier
BobN> regulator comes along.
I think you mean Z-16 is golden... Z-17 is the simplified version.
I would also be interested in how the RR as well as the permanent magnet
generator in the Rotax works. I'll dig around... Thanks again!
Sacha
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