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Dan Fritz
Joined: 02 Apr 2020
Posts: 16
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 Posted: Sat Apr 18, 2020 10:15 am Post subject: OV B-lead Relay |
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Hi all,
I'm using an IR alternator as my primary source of electrons on my Velocity. I'd like to provide overvoltage protection to include a B-Lead disconnect relay. With a 34A continuous normal system load, will an automotive cube relay rated at 70A be satisfactory in lieu of the normally used "metal can" style battery contactor?
Having read tons of posts on the relative merits of internal and external regulation and pedigree in millions of automotive hours of service, I'm really just interested in the actual b-lead disconnect relay part of the architecture as shown in Z-24. 
Thanks for your help!
Dan
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Sun Apr 19, 2020 12:46 pm Post subject: OV B-lead Relay |
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| Quote: | I'm using an IR alternator as my primary source of electrons on my
Velocity. I'd like to provide overvoltage protection to include
a B-Lead disconnect relay. With a 34A continuous normal system
load, will an automotive cube relay rated at 70A be satisfactory
in lieu of the normally used "metal can" style battery contactor? |
Figure Z24 has been a burr under my intellectual saddle
for over 20 years. It was a rather crude band-aid for
adding ov protection to an internally regulated alternator
where we, as system integrators, had no absolute control
over field excitation voltage of the alternator. This
produces failure modes initiating an uncontrollable
alternator runaway.
B&C's offerings to the OBAM aviation market exploited
the fine craftsmanship of some automotive alternators
by modifying them to accept field excitation from
an external controller. Plane-Power took a slightly
different approach . . . their first offerings retained
the built in regulator but included modifications to
(1) bring field excitation lead out of the alternator
and (2) add crowbar ov protection to that field power
feeder. You can see the crowbar ovm module piggy-backed
onto a P-P alternator in the attached photo.
The common theme for these offerings is MODIFICATION
of an off-the-shelf alternator to effect smooth integration
of the alternator into legacy aircraft system architectures.
Many moons ago, we had some in-depth discussions about
'reliability' of stock automotive products. Admittedly,
modern alternators do demonstrate exceptionally long
service lives. If one is content to hang their hat
on perceived reliability, then putting a stock
automotive alternator on YOUR project meets design
goals.
As a system integrator with a few decades of
experience designing to FMEA protocols, I couldn't
recommend running the stock alternator 'bare footed'.
So how to gracefully unhook the stock automotive
alternator in a runaway condition from the ship's
electrical system?
Breaking the b-lead is the only option. But instead
nailing the tiger's tail to the ground, we're working
on the other end of this flame-throwing beast.
The physical realities for this condition are:
The alternator's field excitation is derived
directly from the b-lead.
So once the b-lead disconnect's from the system
in general and the battery in particular, b-lead
voltage rises exponentially.
That rise is exacerbated by the fact that in
milliseconds after onset of the ov condition,
the alternator will be in full current limited
output with the battery grunting the excess
energy.
When the b-lead is broken, the effect is
like a race horse shot out of the gate on
springs. Voltage goes up, field excitation
goes up, voltage takes off for the moon.
While breaking this pathway will isolate
the alternator from the ship's systems, it
cannot isolate the alternator from itself.
The voltage will rise very rapidly to perhaps
hundreds of volts. This puts alternator
rectifiers and field windings at risk for
failure. It is almost a certainty that
the failed alternator will not enjoy
a gentle outcome for the ov event.
Selection of the disconnect relay is a
bit more problematic than routine
control tasks in the rest of the system.
Our relay must survive a break of this
rapidly rising, robust current source.
Spectacular arcing will most certainly
establish in the gap of spreading contacts.
The relay of choice should have thermally
massive contacts . . . and preferably
be of the double make-break variety.
Further, it the fire doesn't go out,
it's a pretty good idea to pick an
enclosure likely to contain the effects.
The other attached figure speaks to features
in the legacy 'whisky barrel' contactors.
There are two contacts in series for
2x the spreading velocity of a 'relay'.
The contacts are thermally massive
to help conduct heat out of the arc as
the contacts spread. The enclosure is
likely to contain any electrical conflagration
that fails to extinguish.
The short answer to your question is: That
contactor was selected for reasons beyond
the device's ratings. Substitutions are
not recommended.
The elegant answer suggests you modify
your alternator to ground one brush and
bring the other one out to a generic
'ford' regulator as depicted in Z101.
It's not a difficult mod. Best yet, it
reduces energy release in an ov event
to a tiny fraction of that produced by
a b-lead disconnect. No arcs, no flame,
just a little 'click' as the field
breaker opens. No hardware in the alternator
b-lead.
Bob . . .
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Dan Fritz
Joined: 02 Apr 2020
Posts: 16
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| Posted: Sun Apr 19, 2020 8:17 pm Post subject: Re: OV B-lead Relay |
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Thanks for the explanation, Bob! Looks like it's the metal can or alternator surgery. I'll do a little research on my alternator and the best surgery option.
Dan
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Mon Apr 20, 2020 1:07 am Post subject: OV B-lead Relay |
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At 11:17 PM 4/19/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Dan Fritz" <Dfritzj(at)yahoo.com>
Thanks for the explanation, Bob! Looks like it's the metal can or alternator surgery. I'll do a little research on my alternator and the best surgery option.
Dan |
if you run across anything useful on the 'net,
be sure to let us know about it.
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:
http://www.matronics.com/Navigator?AeroElectric-List |
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bobnoffs
Joined: 04 Jul 2012
Posts: 132
Location: northern wi.
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| Posted: Mon Apr 20, 2020 3:47 am Post subject: OV B-lead Relay |
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there is a thread in the past 2 yrs. about ov disconnecting the b lead. bob posted a link to a 200 amp relay that i did use to wire an ov disconnect into my b lead. is it being said now that that is a bad idea? i always expected i would fry the alternator, i only need the disconnect once. bob noffs
On Sun, Apr 19, 2020 at 3:53 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | | Quote: | I'm using an IR alternator as my primary source of electrons on my
Velocity. I'd like to provide overvoltage protection to include
a B-Lead disconnect relay. With a 34A continuous normal system
load, will an automotive cube relay rated at 70A be satisfactory
in lieu of the normally used "metal can" style battery contactor? |
Figure Z24 has been a burr under my intellectual saddle
for over 20 years. It was a rather crude band-aid for
adding ov protection to an internally regulated alternator
where we, as system integrators, had no absolute control
over field excitation voltage of the alternator. This
produces failure modes initiating an uncontrollable
alternator runaway.
B&C's offerings to the OBAM aviation market exploited
the fine craftsmanship of some automotive alternators
by modifying them to accept field excitation from
an external controller. Plane-Power took a slightly
different approach . . . their first offerings retained
the built in regulator but included modifications to
(1) bring field excitation lead out of the alternator
and (2) add crowbar ov protection to that field power
feeder. You can see the crowbar ovm module piggy-backed
onto a P-P alternator in the attached photo.
The common theme for these offerings is MODIFICATION
of an off-the-shelf alternator to effect smooth integration
of the alternator into legacy aircraft system architectures.
Many moons ago, we had some in-depth discussions about
'reliability' of stock automotive products. Admittedly,
modern alternators do demonstrate exceptionally long
service lives. If one is content to hang their hat
on perceived reliability, then putting a stock
automotive alternator on YOUR project meets design
goals.
As a system integrator with a few decades of
experience designing to FMEA protocols, I couldn't
recommend running the stock alternator 'bare footed'.
So how to gracefully unhook the stock automotive
alternator in a runaway condition from the ship's
electrical system?
Breaking the b-lead is the only option. But instead
nailing the tiger's tail to the ground, we're working
on the other end of this flame-throwing beast.
The physical realities for this condition are:
The alternator's field excitation is derived
directly from the b-lead.
So once the b-lead disconnect's from the system
in general and the battery in particular, b-lead
voltage rises exponentially.
That rise is exacerbated by the fact that in
milliseconds after onset of the ov condition,
the alternator will be in full current limited
output with the battery grunting the excess
energy.
When the b-lead is broken, the effect is
like a race horse shot out of the gate on
springs. Voltage goes up, field excitation
goes up, voltage takes off for the moon.
While breaking this pathway will isolate
the alternator from the ship's systems, it
cannot isolate the alternator from itself.
The voltage will rise very rapidly to perhaps
hundreds of volts. This puts alternator
rectifiers and field windings at risk for
failure. It is almost a certainty that
the failed alternator will not enjoy
a gentle outcome for the ov event.
Selection of the disconnect relay is a
bit more problematic than routine
control tasks in the rest of the system.
Our relay must survive a break of this
rapidly rising, robust current source.
Spectacular arcing will most certainly
establish in the gap of spreading contacts.
The relay of choice should have thermally
massive contacts . . . and preferably
be of the double make-break variety.
Further, it the fire doesn't go out,
it's a pretty good idea to pick an
enclosure likely to contain the effects.
The other attached figure speaks to features
in the legacy 'whisky barrel' contactors.
There are two contacts in series for
2x the spreading velocity of a 'relay'.
The contacts are thermally massive
to help conduct heat out of the arc as
the contacts spread. The enclosure is
likely to contain any electrical conflagration
that fails to extinguish.
The short answer to your question is: That
contactor was selected for reasons beyond
the device's ratings. Substitutions are
not recommended.
The elegant answer suggests you modify
your alternator to ground one brush and
bring the other one out to a generic
'ford' regulator as depicted in Z101.
It's not a difficult mod. Best yet, it
reduces energy release in an ov event
to a tiny fraction of that produced by
a b-lead disconnect. No arcs, no flame,
just a little 'click' as the field
breaker opens. No hardware in the alternator
b-lead.
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:
http://www.matronics.com/Navigator?AeroElectric-List |
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jluckey(at)pacbell.net
Guest
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| Posted: Mon Apr 20, 2020 9:02 am Post subject: OV B-lead Relay |
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I am currently bench testing a Motorcraft alternator from a 84 Bronco. It's a re-build from the local NAPA auto parts store. About $60. It's rated at 60A and weighs about 10 pounds.
I selected it because:
1. It's setup for/requires an external regulator
2. It is a 'B' circuit alternator
3. It was used in all kinds of Fords in the 80s and therefore should be easy to get replacement when "on the road"
4. It comes with a single-groove pulley. (more modern alternators have pulleys for serpentine belts)
5. It's inexpensive
I'm curious what other people are using...
-Jeff
On Monday, April 20, 2020, 02:15:04 AM PDT, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:
At 11:17 PM 4/19/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Dan Fritz" <Dfritzj(at)yahoo.com>
Thanks for the explanation, Bob! Looks like it's the metal can or alternator surgery. I'll do a little research on my alternator and the best surgery option.
Dan |
if you run across anything useful on the 'net,
be sure to let us know about it.
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:
http://www.matronics.com/Navigator?AeroElectric-List |
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art(at)zemon.name
Guest
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| Posted: Mon Apr 20, 2020 9:52 am Post subject: OV B-lead Relay |
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Jeff,
I have two alternators, a B&C Aero BC460-H (60 amps, 7.1 pounds) and a backup alternator the BC410-H (20-40 amps, 5.75 pounds)
-- Art Z.
On Mon, Apr 20, 2020 at 12:29 PM Jeff Luckey <jluckey(at)pacbell.net (jluckey(at)pacbell.net)> wrote:
| Quote: |
I am currently bench testing a Motorcraft alternator from a 84 Bronco. It's a re-build from the local NAPA auto parts store. About $60. It's rated at 60A and weighs about 10 pounds.
I selected it because:
1. It's setup for/requires an external regulator
2. It is a 'B' circuit alternator
3. It was used in all kinds of Fords in the 80s and therefore should be easy to get replacement when "on the road"
4. It comes with a single-groove pulley. (more modern alternators have pulleys for serpentine belts)
5. It's inexpensive
I'm curious what other people are using...
-Jeff
On Monday, April 20, 2020, 02:15:04 AM PDT, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
At 11:17 PM 4/19/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Dan Fritz" <Dfritzj(at)yahoo.com (Dfritzj(at)yahoo.com)>
Thanks for the explanation, Bob! Looks like it's the metal can or alternator surgery. I'll do a little research on my alternator and the best surgery option.
Dan |
if you run across anything useful on the 'net,
be sure to let us know about it.
Bob . . .
|
--
https://CheerfulCurmudgeon.com/Sooner meet a bereaved she-bear than a fool with his nonsense. Proverbs 17:12
| | - 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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skywagon185(at)GMAIL.COM
Guest
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| Posted: Mon Apr 20, 2020 10:12 am Post subject: OV B-lead Relay |
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Jeff,
Ford Alternator...
Good choice, besides your list of benefits, add these
* can use Ford regulators, even the heavy duty ones are in the $20+ range
* If you ever have to have the alt. serviced, checked, etc., any electrical shop will do it and you won't have to fib that it is out of an airplane. (mention airplane and the shop may hand it back to you...). But, clearly a Ford product that they have serviced 100's of ; no questions.
On Mon, Apr 20, 2020 at 10:57 AM Art Zemon <art(at)zemon.name (art(at)zemon.name)> wrote:
| Quote: | Jeff,
I have two alternators, a B&C Aero BC460-H (60 amps, 7.1 pounds) and a backup alternator the BC410-H (20-40 amps, 5.75 pounds)
-- Art Z.
On Mon, Apr 20, 2020 at 12:29 PM Jeff Luckey <jluckey(at)pacbell.net (jluckey(at)pacbell.net)> wrote:
| Quote: |
I am currently bench testing a Motorcraft alternator from a 84 Bronco. It's a re-build from the local NAPA auto parts store. About $60. It's rated at 60A and weighs about 10 pounds.
I selected it because:
1. It's setup for/requires an external regulator
2. It is a 'B' circuit alternator
3. It was used in all kinds of Fords in the 80s and therefore should be easy to get replacement when "on the road"
4. It comes with a single-groove pulley. (more modern alternators have pulleys for serpentine belts)
5. It's inexpensive
I'm curious what other people are using...
-Jeff
On Monday, April 20, 2020, 02:15:04 AM PDT, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
At 11:17 PM 4/19/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Dan Fritz" <Dfritzj(at)yahoo.com (Dfritzj(at)yahoo.com)>
Thanks for the explanation, Bob! Looks like it's the metal can or alternator surgery. I'll do a little research on my alternator and the best surgery option.
Dan |
if you run across anything useful on the 'net,
be sure to let us know about it.
Bob . . .
|
--
https://CheerfulCurmudgeon.com/Sooner meet a bereaved she-bear than a fool with his nonsense. Proverbs 17:12
|
| | - 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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nuckolls.bob(at)aeroelect
Guest
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| Posted: Mon Apr 20, 2020 10:28 am Post subject: OV B-lead Relay |
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At 06:44 AM 4/20/2020, you wrote:
| Quote: | there is a thread in the past 2 yrs. about ov disconnecting the b lead. bob posted a link to a 200 amp relay that i did use to wire an ov disconnect into my b lead. is it being said now that that is a bad idea? i always expected i would fry the alternator, i only need the disconnect once.
bob noffs |
Refresh my memory . . . what kind of relay
made it into your system? Can you give
me a date on the thread?
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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Dan Fritz
Joined: 02 Apr 2020
Posts: 16
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| Posted: Mon Apr 20, 2020 8:39 pm Post subject: Re: OV B-lead Relay |
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Hi Bob, I've been doing some searching and found a couple of tutorials on modifying an alternator to external regulation and am considering whether to attempt the mod. While searching, I also found an article of yours from Feb 2004 (“Load Dump” Damage to Alternators with Built-in Regulators). Were you ever able to get test results from your proposed Z-24 with a TVS diode installed?
Dan
| | - 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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bobnoffs
Joined: 04 Jul 2012
Posts: 132
Location: northern wi.
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| Posted: Tue Apr 21, 2020 4:46 am Post subject: OV B-lead Relay |
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hi bob, you posted on 8/23/18 on the subject of ''crowbars''. it looks like the link is a dead end now but maybe i have the receipt of a hx on ebay in my account.
bob noffs
On Mon, Apr 20, 2020 at 1:34 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 06:44 AM 4/20/2020, you wrote:
| Quote: | there is a thread in the past 2 yrs. about ov disconnecting the b lead. bob posted a link to a 200 amp relay that i did use to wire an ov disconnect into my b lead. is it being said now that that is a bad idea? i always expected i would fry the alternator, i only need the disconnect once.
 bob noffs |
Refresh my memory . . . what kind of relay
made it into your system? Can you give
me a date on the thread?
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:
http://www.matronics.com/Navigator?AeroElectric-List |
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bobnoffs
Joined: 04 Jul 2012
Posts: 132
Location: northern wi.
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| Posted: Tue Apr 21, 2020 4:59 am Post subject: OV B-lead Relay |
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bob, all i could find of it was a pic. it i black plastic. at the time of the post connector types was in question. yp180, yp-100-12 and 12v-200a are printed on the unit. it is for auto, continuous duty. it has 3/16 or 1/4'' lugs and is rated 200 amps. bob noffs
On Tue, Apr 21, 2020 at 7:43 AM bob noffs <icubob(at)gmail.com (icubob(at)gmail.com)> wrote:
| Quote: | hi bob, you posted on 8/23/18 on the subject of ''crowbars''. it looks like the link is a dead end now but maybe i have the receipt of a hx on ebay in my account.
bob noffs
On Mon, Apr 20, 2020 at 1:34 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 06:44 AM 4/20/2020, you wrote:
| Quote: | there is a thread in the past 2 yrs. about ov disconnecting the b lead. bob posted a link to a 200 amp relay that i did use to wire an ov disconnect into my b lead. is it being said now that that is a bad idea? i always expected i would fry the alternator, i only need the disconnect once.
 bob noffs |
Refresh my memory . . . what kind of relay
made it into your system? Can you give
me a date on the thread?
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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johnbright
Joined: 14 Dec 2011
Posts: 165
Location: Newport News, VA
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| Posted: Tue Apr 21, 2020 6:18 am Post subject: Re: OV B-lead Relay |
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| bobnoffs wrote: | | ... yp180, yp-100-12 and 12v-200a are printed on the unit... |
https://www.ebay.com/c/20012698760
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_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Tue Apr 21, 2020 8:01 am Post subject: OV B-lead Relay |
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At 09:18 AM 4/21/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "johnbright" <john_s_bright(at)yahoo.com>
bobnoffs wrote:
> ... yp180, yp-100-12 and 12v-200a are printed on the unit...
https://www.ebay.com/c/20012698760
|
Yeah, this is the one I did a tear-down on
but for the life of me, I can't find the
pictures in the archive. I'm skeptical of
the 200A rating and to be sure, the single
break contact gap is unsuitable for a
b-lead disconnect.
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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bobnoffs
Joined: 04 Jul 2012
Posts: 132
Location: northern wi.
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| Posted: Tue Apr 21, 2020 8:50 am Post subject: OV B-lead Relay |
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|
bob, do you have a link or part # for something that would work for b lead disconnect? how unsuitable is this 200 amp relay? i mean, are the number of cycles that it will function be limited or will it be shot after its first cycle? if i use it once i am going to have an alternator to replace, why not the relay too? it is not likely this thing is ever likely to see even one use. your take on this would be appreciated.
bob noffs
On Tue, Apr 21, 2020 at 11:09 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 09:18 AM 4/21/2020, you wrote:
Yeah, this is the one I did a tear-down on
but for the life of me, I can't find the
pictures in the archive. I'm skeptical of
the 200A rating and to be sure, the single
break contact gap is unsuitable for a
b-lead disconnect.
Bob . . .
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Tue Apr 21, 2020 8:56 am Post subject: OV B-lead Relay |
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At 11:39 PM 4/20/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Dan Fritz" <Dfritzj(at)yahoo.com>
Hi Bob, I've been doing some searching and found a couple of tutorials on modifying an alternator to external regulation and am considering whether to attempt the mod. While searching, I also found an article of yours from Feb 2004 (“Load Dump” Damage to Alternators with Built-in Regulators). Were you ever able to get test results from your proposed Z-24 with a TVS diode installed?
Dan
|
That's been awhile back . . . I don't recall
that I ever got to explore that option on the
bench. There's a LOT of energy sourcing the
output of a runaway alternator. TVS are
transient suppressors: High current, rapidly
rising voltage but of limited duration hence
low energy.
The runaway alternator is suited to being
jury-rigged into a arc welder!
I do recall a visit to Motorcar Parts of
America facilities in Tijuana Mexico in 2004
where I witnessed the extreme load-dump being
impressed on an alternator under test.
The narrative of that trip can be found
on page 3-6 of this document
https://tinyurl.com/y7qzlfw6
We cannot know the source for alternators
popular with the Van's crowd back then
but common sense suggests that immunity
from load-dump effects are pretty much
the gold standard. It's not hard to do . . .
so why not do it? Your competition does.
I have a design proposal on the hard drive
that takes a little different approach
to b-lead management of an ov condition.
This approach drive the bus through a
diode capable of carrying full alternator
output. Instead of attempting to BREAK
the b-lead, I simply short it to ground
with a fat FET. In a mater of microseconds,
b-lead voltage is reduced to millivolts.
Since the field is sourced from the b-lead,
the runaway alternator is simultaneously
deprived of field excitation. The whole
thing simply relaxes. The cited diode
prevents reflection of the crowbar
on the rest of the airplane.
Intuitively, this has to work. Best
yet, it would prevent the alternator's
suicide attempt.
I didn't push this idea forward . . . it
seemed like a lot of monkey-motion to
avoid the simple mod to run the
alternator with an external regulator.
If anyone would like to explore the b-lead,
crowbar method for bringing an internally
regulated alternator to heel, I'll publish
the sketches.
Bob . . .
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ceengland7(at)gmail.com
Guest
|
| Posted: Tue Apr 21, 2020 10:16 am Post subject: OV B-lead Relay |
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|
On 4/21/2020 11:52 AM, Robert L. Nuckolls, III wrote:
| Quote: | At 11:39 PM 4/20/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Dan Fritz" <Dfritzj(at)yahoo.com> (Dfritzj(at)yahoo.com)
Hi Bob, I've been doing some searching and found a couple of tutorials on modifying an alternator to external regulation and am considering whether to attempt the mod. While searching, I also found an article of yours from Feb 2004 (“Load Dump” Damage to Alternators with Built-in Regulators). Were you ever able to get test results from your proposed Z-24 with a TVS diode installed?
Dan
|
That's been awhile back . . . I don't recall
that I ever got to explore that option on the
bench. There's a LOT of energy sourcing the
output of a runaway alternator. TVS are
transient suppressors: High current, rapidly
rising voltage but of limited duration hence
low energy.
The runaway alternator is suited to being
jury-rigged into a arc welder!
I do recall a visit to Motorcar Parts of
America facilities in Tijuana Mexico in 2004
where I witnessed the extreme load-dump being
impressed on an alternator under test.
The narrative of that trip can be found
on page 3-6 of this document
https://tinyurl.com/y7qzlfw6
We cannot know the source for alternators
popular with the Van's crowd back then
but common sense suggests that immunity
from load-dump effects are pretty much
the gold standard. It's not hard to do . . .
so why not do it? Your competition does.
I have a design proposal on the hard drive
that takes a little different approach
to b-lead management of an ov condition.
This approach drive the bus through a
diode capable of carrying full alternator
output. Instead of attempting to BREAK
the b-lead, I simply short it to ground
with a fat FET. In a mater of microseconds,
b-lead voltage is reduced to millivolts.
Since the field is sourced from the b-lead,
the runaway alternator is simultaneously
deprived of field excitation. The whole
thing simply relaxes. The cited diode
prevents reflection of the crowbar
on the rest of the airplane.
Intuitively, this has to work. Best
yet, it would prevent the alternator's
suicide attempt.
I didn't push this idea forward . . . it
seemed like a lot of monkey-motion to
avoid the simple mod to run the
alternator with an external regulator.
If anyone would like to explore the b-lead,
crowbar method for bringing an internally
regulated alternator to heel, I'll publish
the sketches.
Bob . . . |
My admittedly sometimes faulty memory of the whole 'load dump' situation two decades ago was that guys were flipping their alt switches/breakers (which controlled the B lead contactor) while the alt was under load, and killing the alt. IIRC, after multiple incidents like that, the OV module/contactor circuit became a lot harder to find in the AEC docs.
My solution is the He Haw Solution: 'If it hurts when you do that, DON'T DO THAT!'
Here's my take: If I operate the IR alternator just like it's operated in the car, I'll never have a load dump event. If I use an OV module that is relatively immune to 'false positives', along with a relatively robust B lead contactor, the only penalty I see is carrying a few ounces of extra weight for the contactor. The contactor will never operate unless the regulator has failed (in an OV mode), in which case the 'load dump' issue is already moot.
This lets me use an off the shelf, *very inexpensive*, available at any auto supply, alternator. It won't be as reliable as a B&C, but based on anecdotal evidence from RV-x owners, a *lot* more reliable than a Plane Power. And I'll have about $500 left over to buy fuel. (Replacement alts, if ever needed, will be free.) If I do have to replace the alt while away from home, no mod to the alt is needed, and replacement can happen on the ramp with only a couple of wrenches.
I have had several different 'lives' as an electronics tech, from home electronics to pro sound, to industrial gear. Even though I'd consider myself to be well above average in qualifications, I trust an 'as-built' alternator to be more reliable than one that I've modded.
My opinion is that if any update is made, it would be to redesign the OV module to reduce the risk of 'false positive' nuisance trips, and retain the B lead relay. Perhaps do a little testing on whether a single contact automotive cube relay can reliably open the B lead, *once*, as Bob Noffs mentioned, and treat the relay as if it's a fusible link. Realistically, if the OV module fires at ~16V, how much energy is really there? How much delay will there be from hitting the voltage threshold to the contacts opening? If we used a 100A cube relay (which *should*, by definition, be able to actively control a 100A load), will it really be stressed by 60-70 amps at ~20V? Or will the voltage (and energy) be much higher by the time the contacts actually start to open? I realize that voltage will spike upward as the contacts separate, but will it be bad enough in a 'one shot' environment to weld the contacts?
Charlie
 Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]
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Dan Fritz
Joined: 02 Apr 2020
Posts: 16
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| Posted: Tue Apr 21, 2020 11:25 am Post subject: Re: OV B-lead Relay |
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|
One of the things I've always wondered about with Z-24 was the impact of the B-lead contactor opening when the field switch is opened. This appears to negate any positive influence of having a progressive switch for the master contactor and field power. What do you all think of the adjustment propose in the attached to Z-24 to re-introduce the goodness of the progressive switch while keeping the full protection offered by Z-24. One could also consider putting a TVS across the B-lead between the B-lead contactor and the alternator in an attempt to save the regulator if a nuisance trip of the Overvoltage protection were to take place.
thoughts? Dan
P.S. did this "old school" with whiteout and a pencil, excuse the messiness...
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finn.lassen(at)verizon.ne
Guest
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| Posted: Tue Apr 21, 2020 12:07 pm Post subject: OV B-lead Relay |
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|
On 4/21/2020 12:52 PM, Robert L. Nuckolls, III wrote:
| Quote: | � This approach drive the bus through a
� diode capable of carrying full alternator
� output. Instead of attempting to BREAK
� the b-lead, I simply short it to ground
� with a fat FET. In a mater of microseconds,
� b-lead voltage is reduced to millivolts.
� Since the field is sourced from the b-lead,
� the runaway alternator is simultaneously
� deprived of field excitation. The whole
� thing simply relaxes.
|
Is it possible that some car alternators have built-in filtering
(capacitor) in the internal regulator that would extend microseconds to
milliseconds or more?
Looking at the output windings as a coil, wouldn't shorting them result
in a huge spike destroying the rectifier diodes or would all the energy
stored in the coil be dissipated as heat?
Shorting B+ to ground would put the rectifier diodes in the shorted
path. Any chance that the rectifier diodes would be destroyed?
Finn
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Tue Apr 21, 2020 4:24 pm Post subject: OV B-lead Relay |
|
|
| Quote: |
Is it possible that some car alternators have built-in filtering (capacitor) in the internal regulator that would extend microseconds to milliseconds or more?
Looking at the output windings as a coil, wouldn't shorting them result in a huge spike destroying the rectifier diodes or would all the energy stored in the coil be dissipated as heat?
Shorting B+ to ground would put the rectifier diodes in the shorted path. Any chance that the rectifier diodes would be destroyed?
|
No, no and no. The alternator is simply modeled
as a current limited source of power the magnitude
of which can be controlled by adjustment to
input RPM and field current.
Whether you tax the alternator at nameplate ratings
in a normal energy production mode -OR- throw
a dead short across the b-lead . . . the current
that will flow in the alternator's output hardware
will be the same . . . at or slightly above nameplate
rating of the alternator.
Unlike a really fat capacitor or a battery, the
b-lead fault current is limited by the alternator's
magnetics.
Even if the field were continuously excited a
dead short on the b-lead would only produce a
STEADY current flow at or above nameplate ratings.
That condition WOULD continue to warm the diodes
and stator windings as if the machine were producing
useful power. Given that the field on an internally
regulated alternator is SUPPLIED from the b-lead,
hitting the b-lead with a short not only shunts
a nominal current source to ground, it deprives
the alternator of it's field excitation. The
current that flows would be very short and things
would settle down to what ever current is generated
by residual field flux. The whole thing is brought
gracefully to a low energy state.
That's an interesting bench experiment I'm
planning to conduct . . . I've attached
a sketch of what the system would look like.
The series diode would drop the alternator
output by a volt or so . . . no big deal.
Everything on the panel is lit up. This
'crowbar' needs to use a really low resistance
FET (easy to get). If you used an SCR to
effect the short, the SCR still drops about
a volt in the on-state. 1 volt on an ND
alternator at 10,000 rpm will generate a LOT
of snort.
Our short needs to take the b-lead down to
millivolt levels and hold it there.
But given the ease with which the alternator
can be modified into a real 'aircraft'
part, any notions of a Z24 update are not
so interesting.
Bob . . .
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