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ov warning light
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nuckolls.bob(at)aeroelect
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PostPosted: Mon Apr 01, 2019 4:38 pm    Post subject: ov warning light Reply with quote

At 06:17 PM 4/1/2019, you wrote:
Quote:
Bob said "Breaking the b-lead per Z-24 will get 'er done but it's not preferred."
My question is WHY if opening the b-lead will work, it is "not preferred."

Z-24 was created to accommodate builders
wanting to install Van's favorite, internally
regulated alternator. Some time after the
drawing was published, an RV builder
reported having killed his alternator
by cycling the on/off switch with the engine
running.

RPM, loads, and numbers of cycles were
not known. But it was predictable that
doing a b-lead disconnect under load
produces a spectacular load-dump. A
transient that trashed the built-in
regulator.

Some time later I came to understand
that Van was selling remaned alternators
from sources unknown. Later still
I visited Motor Car Parts of America
facilities in Tijuana, Mexico followed
by a meeting with their chief engineer
in San Diego. I witnessed deliberate
full-load b-lead disconnects that
produced flashes of light that totally
swamped my video camera. Suffice it
to say that event after 6 or 7 such events
in a row, the regulators were undamaged.

This led me to suppose that the
load-dump damage to the RV builder's
alternator was not something that
should be expected. Nonetheless,
Z-24 got 'black listed'.

In fact, Z-24 WILL perform as advertised
with minimal or zero risk to an
alternator assembled with the same
skills demonstrated by MCPA (See chapter
on alternators in the 'Connection).

There's a down-side to
Z-24 (interim). When a runaway
alternator b-lead is disconnected from
the airplane, it STILL drives its
own field to destruction. But
you would have to tear it down
just to replace the regulator . . .
the smoked field winding is a
feature offered at no extra charge.

Some time later, I conceived the crowbar
disconnect scheme that would not only
unhook the runaway alternator, it would
bring it to heel and protect the
field windings.

BOTH b-lead disconnect techniques
are rather in-elegant compared to
legacy field supply disconnect methods.



Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Mon Apr 01, 2019 4:40 pm    Post subject: ov warning light Reply with quote

At 06:44 PM 4/1/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com>

Shorting the B-lead through a FET is also going to pull the main bus to zero, as well as the battery, no?

No . . . you FIRST disconnect it
through the contactor followed by
crowbar to ground LATER.



Bob . . .


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kenryan



Joined: 20 Oct 2009
Posts: 423

PostPosted: Mon Apr 01, 2019 5:14 pm    Post subject: ov warning light Reply with quote

Thanks.

Sent from my Android. Sorry Steve.
On Mon, Apr 1, 2019, 16:43 Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
At 06:17 PM 4/1/2019, you wrote:
Quote:
Bob said "Breaking the b-lead per Z-24 will get 'er done but it's not preferred."
My question is WHY if opening the b-lead will work, it is "not preferred."

 Z-24 was created to accommodate builders
 wanting to install Van's favorite, internally
 regulated alternator. Some time after the
 drawing was published, an RV builder
 reported having killed his alternator
 by cycling the on/off switch with the engine
 running.

 RPM, loads, and numbers of cycles were
 not known. But it was predictable that
 doing a b-lead disconnect under load
 produces a spectacular load-dump. A
 transient that trashed the built-in
 regulator.

 Some time later I came to understand
 that Van was selling remaned alternators
 from sources unknown. Later still
 I visited Motor Car Parts of America
 facilities in Tijuana, Mexico followed
 by a meeting with their chief engineer
 in San Diego. I witnessed deliberate
 full-load b-lead disconnects that
 produced flashes of light that totally
 swamped my video camera. Suffice it
 to say that event after 6 or 7 such events
 in a row, the regulators were undamaged.

 This led me to suppose that the
 load-dump damage to the RV builder's
 alternator was not something that
 should be expected. Nonetheless,
 Z-24 got 'black listed'.

 In fact, Z-24 WILL perform as advertised
 with minimal or zero risk to an
 alternator assembled with the same
 skills demonstrated by MCPA (See chapter
 on alternators in the 'Connection).

 There's a down-side to
 Z-24 (interim). When a runaway
 alternator b-lead is disconnected from
 the airplane, it STILL drives its
 own field to destruction. But
 you would have to tear it down
 just to replace the regulator . . .
 the smoked field winding is a
 feature offered at no extra charge.

 Some time later, I conceived the crowbar
 disconnect scheme that would not only
 unhook the runaway alternator, it would
 bring it to heel and protect the
 field windings.

 BOTH b-lead disconnect techniques
 are rather in-elegant compared to
 legacy field supply disconnect methods.



  Bob . . .


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alec(at)alecmyers.com
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PostPosted: Mon Apr 01, 2019 5:22 pm    Post subject: ov warning light Reply with quote

In that case, why not put something across the contactor to sense the developing voltage difference when the contactor opens to trigger the FET (or how about an SCR?)
You cold develop the same circuit to wire across the B lead CB to dump the field coil current when the CB is manually pulled too, relieving any effects of a load dump.
On Apr 1, 2019, at 8:38 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:

At 06:44 PM 4/1/2019, you wrote:
Quote:


Shorting the B-lead through a FET is also going to pull the main bus to zero, as well as the battery, no?

No . . . you FIRST disconnect it
through the contactor followed by
crowbar to ground LATER.
Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Mon Apr 01, 2019 5:33 pm    Post subject: ov warning light Reply with quote

At 08:21 PM 4/1/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com>

In that case, why not put something across the contactor to sense the developing voltage difference when the contactor opens to trigger the FET

The proposed Z-24 ov control module
does monitor first opening of the
contactor to deduce when the FET
gets energized.

Quote:
(or how about an SCR?)

FET has lower on-resistance which takes
B-lead to level that won't excite the
field. A turned-on SCR has about 1.5
volts forward drop which WOULD seriously
excite the field . . . not good.
This would produce considerable heat
in the SCR. A power FET would suffer
no such abuse.

Quote:
You cold develop the same circuit to wire across the B
lead CB to dump the field coil current when the CB is
manually pulled too, relieving any effects of a load dump.

B-lead breakers should not be manually
pulled except for trouble shooting
on the ground and certainly not
while the alternator is under load.

In fact, there should not even BE a b-lead
breaker . . . b-lead protection has
been handled by current limiters under
the cowl for decades in TC aircraft.

Pulling the b-lead breaker on a loaded
alternator, whether internally or
externally regulated, is almost certain
to start a fire in the breaker . . . it
gets hot, smokes and smells really bad.


Bob . . .


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alec(at)alecmyers.com
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PostPosted: Mon Apr 01, 2019 5:44 pm    Post subject: ov warning light Reply with quote

Unfortunately for me I have a TC aircraft (it has at least three type certificates from EASA, the FAA and Transport Canada) with a Bosch 28V automotive alternator with built-in regulation. There is _no_ off-board OV regulation.

The Approved Flight Manual (I stress _approved_!) procedure for an “excessive charging" condition is “Alternator Circuit Breaker - PULL”

So, I’m looking for a mitigation strategy for me (and for my ab initial students!) who will be flying the aircraft. Smile

On Apr 1, 2019, at 9:32 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:

Pulling the b-lead breaker on a loaded
alternator, whether internally or
externally regulated, is almost certain
to start a fire in the breaker . . . it
gets hot, smokes and smells really bad.


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ceengland7(at)gmail.com
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PostPosted: Mon Apr 01, 2019 6:14 pm    Post subject: ov warning light Reply with quote

On 4/1/2019 7:37 PM, Robert L. Nuckolls, III wrote:

Quote:
At 06:17 PM 4/1/2019, you wrote:
Quote:
Bob said "Breaking the b-lead per Z-24 will get 'er done but it's not preferred."
My question is WHY if opening the b-lead will work, it is "not preferred."

Z-24 was created to accommodate builders
wanting to install Van's favorite, internally
regulated alternator. Some time after the
drawing was published, an RV builder
reported having killed his alternator
by cycling the on/off switch with the engine
running.

RPM, loads, and numbers of cycles were
not known. But it was predictable that
doing a b-lead disconnect under load
produces a spectacular load-dump. A
transient that trashed the built-in
regulator.

Some time later I came to understand
that Van was selling remaned alternators
from sources unknown. Later still
I visited Motor Car Parts of America
facilities in Tijuana, Mexico followed
by a meeting with their chief engineer
in San Diego. I witnessed deliberate
full-load b-lead disconnects that
produced flashes of light that totally
swamped my video camera. Suffice it
to say that event after 6 or 7 such events
in a row, the regulators were undamaged.

This led me to suppose that the
load-dump damage to the RV builder's
alternator was not something that
should be expected. Nonetheless,
Z-24 got 'black listed'.

In fact, Z-24 WILL perform as advertised
with minimal or zero risk to an
alternator assembled with the same
skills demonstrated by MCPA (See chapter
on alternators in the 'Connection).

There's a down-side to
Z-24 (interim). When a runaway
alternator b-lead is disconnected from
the airplane, it STILL drives its
own field to destruction. But
you would have to tear it down
just to replace the regulator . . .
the smoked field winding is a
feature offered at no extra charge.

Some time later, I conceived the crowbar
disconnect scheme that would not only
unhook the runaway alternator, it would
bring it to heel and protect the
field windings.

BOTH b-lead disconnect techniques
are rather in-elegant compared to
legacy field supply disconnect methods.



Bob . . .
That's the logic I used when accepting my 'compromise'. I figure that if my IR alternator goes OV and triggers the crowbar, and then the rest of the alt goes to toast, I don't care, because I'll be buying an entire new $70 alternator, anyway. And I'll avoid the old Van's load dump issue by following the advice of the He Haw Doctor: If it hurts when you do that, DON'T DO THAT.

And the $70 alternator cost explains my $600 inelegant compromise. Smile

Charlie
Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Apr 02, 2019 4:46 am    Post subject: ov warning light Reply with quote

At 08:42 PM 4/1/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com>

Unfortunately for me I have a TC aircraft (it has at least three type certificates from EASA, the FAA and Transport Canada) with a Bosch 28V automotive alternator with built-in regulation. There is _no_ off-board OV regulation.

The Approved Flight Manual (I stress _approved_!) procedure for an “excessive charging" condition is “Alternator Circuit Breaker - PULL”

So, I’m looking for a mitigation strategy for me (and for my ab initial students!) who will be flying the aircraft.

I'm astounded . . . . what can I say?



Bob . . .


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alec(at)alecmyers.com
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PostPosted: Tue Apr 02, 2019 5:22 am    Post subject: ov warning light Reply with quote

I don’t know!

But I’m keeping my ear open for an easy retro-fit (and easily approved) mitigation. Replacing the B-lead breaker with one that has built-in OV protection seemed an easy half-win.

On Apr 2, 2019, at 8:45 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:

At 08:42 PM 4/1/2019, you wrote:
Quote:


Unfortunately for me I have a TC aircraft (it has at least three type certificates from EASA, the FAA and Transport Canada) with a Bosch 28V automotive alternator with built-in regulation. There is _no_ off-board OV regulation.

The Approved Flight Manual (I stress _approved_!) procedure for an “excessive charging" condition is “Alternator Circuit Breaker - PULL”

So, I’m looking for a mitigation strategy for me (and for my ab initial students!) who will be flying the aircraft.

I'm astounded . . . . what can I say?
Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Apr 02, 2019 10:22 am    Post subject: ov warning light Reply with quote

At 08:22 AM 4/2/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com>

I don’t know!

But I’m keeping my ear open for an easy retro-fit (and easily approved) mitigation. Replacing the B-lead breaker with one that has built-in OV protection seemed an easy half-win.


You're not going to find a
light-footed breaker that will
fit into the same slot. There
are remote-trip breakers that
can be triggered by an external
ov sensor . . . but that's
not going to be any less
complicated than Z-14 (interim).

What kind of airplane are we
talking about? How tightly
is it bound to the TC/STC/
Field Approval processes?



Bob . . .


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