Today's Message Index:
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1. 09:19 AM - Re: Bob's Email Outage - Missed Threads? (Robert L. Nuckolls, III)
2. 01:33 PM - Re: Bob's Email Outage - Missed Threads? (Finn Lassen)
3. 05:29 PM - Next generation Crowbar OVM (Robert L. Nuckolls, III)
4. 10:12 PM - Re: Next generation Crowbar OVM (Eric Page)
5. 10:14 PM - Re: Bob's Email Outage - Missed Threads? (Eric Page)
Message 1
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| Subject: | Re: Bob's Email Outage - Missed Threads? |
>Hi Bob -- sorry to hear that you've been incommunicado lately. I
>posted a couple of threads recently on which I was hoping to get
>your feedback. Perhaps they appeared during your comms
>outage? Links to those threads follow.
>
>Overvoltage Protection for Rotax 9-Series Engines
>http://forum.matronics.com/viewtopic.php?t=16780921
----------
In a forum thread that I started in October 2021 about using a Rotax
912iS on my Kitfox, there was some discussion about my use of crowbar
overvoltage protection (OVP). In that thread, Joe Gores asked, "Can
it be designed to just open the relay without blowing a 1 amp fuse?"
It turns out that, yes, it can. After several prototypes, I have a
non-crowbar OVP Module for Rotax 9-series engines. See the attached
PDF document.
Good work Eric!
Of course, this becomes a classic ov protection relay that simply
latches off in response to an ov event and needs to be reset
by action of the pilot.
My very first task at Electro-Mech back
in the dark ages was for just such a device.
If memory serves, the trip response for that first effort was
sd in the Cessna procurement specification was:
A step response from nominal bus voltage of 14.2 to
20.0 would produce a shutdown in 60 +/- 10 milliseconds.
As a matter of fact, this was an unnecessarily short-
coupled requirement.
DO-160/Mil-STD-704 dictates even back then called for
a certifiable appliance to withstand a 20V excursion
for 1 Second; a 40V excursion for 100 milliseconds.
The 60Ms requirement led to some 'twitchy' designs.
Nonetheless, design goals for ov protection were
pretty similar across the industry. Tens of thousands
of such devices were manufactured and successfully
operated in the GA fleet.
I don't recall the exact time-frame but
around 1980, while crafting a response to a
request for proposal from Beech, I suggested that
their response profile be adjusted to 500+/-50
Milliseconds for a 16V setpoint. With trip
time being independent of magnitude of ov
event. Further, if bus voltage dropped below
16v at any time before the 500 Ms trip target,
the timer resets to zero.
That produced a vociferous barrage of 'incoming'
from various factions at Beech. While all the
electron-herders agreed that the change would
produce a perfectly adequate and less twitchy
design, making such a change would generate
a boat load of re-certification efforts across
several venues.
A classic example of "Once certified: carved
in stone" mentality. I can cite a goodly number
of similar incidents in my GA career when a
marginal (if not poor) condition was allowed
to persist due to cost of running the re-cert
guantlet.
Just for grins, I've sketched up a somewhat
modernized version of that proposal and attached
it to this posting. Input to the voltage sense
comparator need not be filtered for short
transients/noise due to the auto reset feature.
The two comparators are 'open collector' devices
so voltage sense need only pull down on the RC
timing capacitor. If the voltage sense comparator
stays 'open' for the requisite time, the second
comparator will trip and turn on a beefy FET
to supply the crowbar effect. Replacing the
SCR with the FET eliminates one of the 'problem
children' of the legacy design.
With a little shuffling of the schematic,
this might be convertable to a relay driver
that would control the AC side of a PM
Dynamo system. I'll pray over that idea
a bit.
Did a quick pass at a board layout and I think
all the parts fit on the same size board as
our original 9003 CBOV module; about 1.1 x
0.5 inches. Out here in Podunk Kansas I think
I might find some kids who would like to learn
how to assemble the critters. We may just resurrect
the 9003 program with a modernized version of
the design I proposed 40+ years ago.
Bob . . .
////
(o o)
===========o00o=(_)=o00o========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
Message 2
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| Subject: | Re: Bob's Email Outage - Missed Threads? |
On 8/14/2023 12:18 PM, Robert L. Nuckolls, III wrote:
>> Hi Bob -- sorry to hear that you've been incommunicado lately. I
>> posted a couple of threads recently on which I was hoping to get your
>> feedback. Perhaps they appeared during your comms outage? Links to
>> those threads follow.
>>
>> Overvoltage Protection for Rotax 9-Series Engines
>> http://forum.matronics.com/viewtopic.php?t=16780921
>> <http://forum.matronics.com/viewtopic.php?t=16780921>
>
> ------------------------------------------------------------------------
> *
> In a forum thread that I started in October 2021 about using a Rotax
> 912iS on my Kitfox, there was some discussion about my use of crowbar
> overvoltage protection (OVP). In that thread, Joe Gores asked, "Can it
> be designed to just open the relay without blowing a 1 amp fuse?" It
> turns out that, yes, it can. After several prototypes, I have a
> non-crowbar OVP Module for Rotax 9-series engines. See the attached
> PDF document.
>
> *Good work Eric!
>
> * Of course, this becomes a classic ov protection relay that simply
> latches off in response to an ov event and needs to be reset
> by action of the pilot.
>
> My very first task at Electro-Mech back
> in the dark ages was for just such a device.
> * If memory serves, the trip response for that first effort was
> sd in the Cessna procurement specification was:
>
> A step response from nominal bus voltage of 14.2 to
> 20.0 would produce a shutdown in 60 +/- 10 milliseconds.
> As a matter of fact, this was an unnecessarily short-
> coupled requirement.
>
> DO-160/Mil-STD-704 dictates even back then called for
> a certifiable appliance to withstand a 20V excursion
> for 1 Second; a 40V excursion for 100 milliseconds.
>
> The 60Ms requirement led to some 'twitchy' designs.
> Nonetheless, design goals for ov protection were
> pretty similar across the industry. Tens of thousands
> of such devices were manufactured and successfully
> operated in the GA fleet.
>
> I don't recall the exact time-frame but
> around 1980, while crafting a response to a
> request for proposal from Beech, I suggested that
> their response profile be adjusted to 500+/-50
> Milliseconds for a 16V setpoint. With trip
> time being independent of magnitude of ov
> event. Further, if bus voltage dropped below
> 16v at any time before the 500 Ms trip target,
> the timer resets to zero.
>
> That produced a vociferous barrage of 'incoming'
> from various factions at Beech. While all the
> electron-herders agreed that the change would
> produce a perfectly adequate and less twitchy
> design, making such a change would generate
> a boat load of re-certification efforts across
> several venues.
>
> A classic example of "Once certified: carved
> in stone" mentality. I can cite a goodly number
> of similar incidents in my GA career when a
> marginal (if not poor) condition was allowed
> to persist due to cost of running the re-cert
> guantlet.
>
> Just for grins, I've sketched up a somewhat
> modernized version of that proposal and attached
> it to this posting. Input to the voltage sense
> comparator need not be filtered for short
> transients/noise due to the auto reset feature.
>
> The two comparators are 'open collector' devices
> so voltage sense need only pull down on the RC
> timing capacitor. If the voltage sense comparator
> stays 'open' for the requisite time, the second
> comparator will trip and turn on a beefy FET
> to supply the crowbar effect. Replacing the
> SCR with the FET eliminates one of the 'problem
> children' of the legacy design.
>
> With a little shuffling of the schematic,
> this might be convertable to a relay driver
> that would control the AC side of a PM
> Dynamo system. I'll pray over that idea
> a bit.
>
> Did a quick pass at a board layout and I think
> all the parts fit on the same size board as
> our original 9003 CBOV module; about 1.1 x
> 0.5 inches. Out here in Podunk Kansas I think
> I might find some kids who would like to learn
> how to assemble the critters. We may just resurrect
> the 9003 program with a modernized version of
> the design I proposed 40+ years ago.
>
>
> Bob . . .
>
> ////
> (o o)
> ===========o00o=(_)=o00o========
> < Go ahead, make my day . . . >
> < show me where I'm wrong. >
> ================================
>
> In the interest of creative evolution
> of the-best-we-know-how-to-do based
> on physics and good practice.
>
Looks promising. Do you have a schematic with part numbers? I'm not
familiar with the zener diode symbol with a third pin (input) which
appear to stabilize the 10V reference.
Finn
Message 3
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| Subject: | Next generation Crowbar OVM |
>Looks promising. Do you have a schematic with part numbers? I'm not
>familiar with the zener diode symbol with a third pin (input) which
>appear to stabilize the 10V reference.
That's an LM431 'adjustable zener' . . . a
big player in many of my contemporary projects.
I'm reluctant to publish values and part numbers
until the concept is, at least, bench tested
for conformance to design goals.
The motivation for publishing the 'cartoon' was
to plant seeds of an alternative idea based on
a couple decades of experience, allegiance to
the legacy design rules and just perhaps, a
bit of irritation at decisions driven more
by economics and bureaucratic intransigence
than a quest for the best we know how to
do.
The two ic's are lm311 style comparators.
You can probably dope out a workable
constellation of values based on the
stated design goals.
While the FET may indeed be suited to the
'crowbaring' of a circuit breaker, how
do we insure that it maintains a saturated,
on condition from the time it switches ON
until the breaker opens?
The gate voltage cannot fall below the minimum
value for necessary conduction while the
breaker is deciding to toss in the towel . . .
probably 15 to 50 milliseconds.
Thid critical performance question demands
more prayer over the drawing board.
Thank you so much for your interest . . .
Bob . . .
////
(o o)
===========o00o=(_)=o00o========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
Message 4
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| Subject: | Re: Next generation Crowbar OVM |
Thanks for including all of the history on your OVP efforts in your first reply,
Bob. It's fascinating to hear how these things developed over time, and to
see how the regulatory and corporate bureaucracies stand in the way of progress.
Quoting from your replies in my thread and this one, in no particular order...
> DO-160/Mil-STD-704 dictates even back then called for a certifiable appliance
to withstand a 20V excursion for 1 Second; a 40V excursion for 100 milliseconds.
So, if I understand this correctly, and read between the lines a little bit, the
~3mS delay in your legacy OVP circuit...
http://www.aeroelectric.com/DIY/DIY_Crowbar_OVP_F.pdf
...is shorter than ideal, and the relevant standards allow a much longer response
time. If we adopt a longer delay, we get a system that's significantly more
tolerant of bus transients but still protects our avionics when things truly
go sideways. Does that sound right?
> While the FET may indeed be suited to the 'crowbarring' of a circuit breaker,
how do we insure that it maintains a saturated, on condition from the time it
switches ON until the breaker opens?
>
> The gate voltage cannot fall below the minimum value for necessary conduction
while the breaker is deciding to toss in the towel... probably 15 to 50 milliseconds.
Yeah, good point. When the FET turns on, the supply is pulled HARD toward 0V,
which kills the FET's gate drive.
Perhaps the following might work (see "Crowbar FET.pdf" below): Isolate the pullup
resistor from the rest of the 10V circuit using a diode with low reverse leakage
(i.e. BAS33: 1nA@15V), use a modestly low value pullup resistor (1k?) and
a logic-level FET so the minimum Rds-on occurs at a low drive voltage.
Something like the IRLZ44 (TO-220 through-hole) or BUK962 (TO-263-3 surface mount)
might work. Both are limited to a Vgs of +/-10V, but that's protected by
the forward voltage of the isolating diode. I couldn't find any high current,
logic level FETs with higher Vgs.
FET datasheets:
IRLZ44: https://www.vishay.com/docs/91328/irlz44.pdf
BUK962: https://assets.nexperia.com/documents/data-sheet/BUK962R5-60E.pdf
> You can probably dope out a workable constellation of values based on the stated
design goals.
Indeed, I took a stab at it with an eye toward using it as a relay driver for a
PM stator (see "2-Comp OVP Relay Driver.pdf" below).
- Used an LM393 (vs the LM311, the LM393 has two comparators in one package and
it's cheaper).
- P-FET on the output to drive relay coil(s).
- N-FET to latch timer comparator's reference input to ground.
- Separate reference divider for timer comparator so latching FET can't pull 431's
REF pin to ground.
- 7.5V Zener on both comparators to protect non-inverting inputs from exceeding
Vsupply minus 2V (LM393's input voltage range).
- N-FET to ensure timing capacitor is fully discharged during reset so comparator
can't restart in latched state.
- Timing: 10V charging 10uF through 10k should take ~69mS to reach the 5V reference.
What do you think? Is a 69mS delay OK, or would you aim for something shorter
or longer?
-Eric
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511269#511269
Attachments:
http://forums.matronics.com//files/crowbar_fet_589.pdf
http://forums.matronics.com//files/2_comp_ovp_relay_driver_995.pdf
Message 5
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| Subject: | Re: Bob's Email Outage - Missed Threads? |
Thank you, Bob. Much appreciated!
Did you have a second to look at the other thread too?
Starter Circuit: Verner 7U Radial
http://forum.matronics.com/viewtopic.php?t=16780986
Cheers,
Eric
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511270#511270
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