Today's Message Index:
----------------------
1. 08:16 AM - Re: Re: One battery/two alternators IFR z-diagram (Robert L. Nuckolls, III)
2. 08:35 AM - Lithium BMS and 'load-dump' worries (Robert L. Nuckolls, III)
3. 09:33 AM - Re: Lithium BMS and 'load-dump' worries (Charlie England)
4. 10:54 AM - Re: Not receiving e-mail (Eric Page)
5. 01:30 PM - Re: Lithium BMS and 'load-dump' worries (Robert L. Nuckolls, III)
6. 04:15 PM - Re: Lithium BMS and 'load-dump' worries (C&K)
Message 1
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| Subject: | Re: One battery/two alternators IFR z-diagram |
>
>Hi Bob... question... need there be a load on a wound field
>alternator for it to continue working in case of battery disconnect?
No . . . you can 'stall' a free-running
alternator by hitting it with a big load,
generally larger than it's nameplate rating.
If you have and electro-hydraulic gear, then
inrush on the PM pump motor may well cause
a self-excited alternator to go down . . .
but if you remove most if not all loads, they'll
generally self excite and come back on line
whereupon you can turn some things back on.
Folks used to be fond of dual, 150 watt landing
lights . . . turning both of these puppies on at
the same time might take down an alternator that's
not supported by a battery.
With the advent of led lighting and the relative
rarity of retractable gear airplanes, those
antagonists are mostly ghosts of yesteryear.
Depending on the regulator design, most
alternators will come on line in an orderly
fashion with small or no loads . . . they
will run in a civilized manner as long as
you don't hammer them with a 'start up
transient' that exceeds nameplate rating.
Bob . . .
Message 2
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| Subject: | Lithium BMS and 'load-dump' worries |
>
>
>=C2 The recently referenced thread on the Vans Air
>Force forum proves that it's still the case. The
>original poster of that thread has been building
>electronic ignition and electronic injection
>systems for aircraft for at least a couple of
>decades, and he stumbled upon the knowledge
>while doing periodic load testing (that he
>obviously didn't do before putting the lithium
>tech battery of choice into service). This was
>not an EarthX aviation battery; it was one of
>the offerings from a motorsports company.
This underscores the value of 'getting the
numbers' . . .
Here is an excerpt from an Enersys-Hawker engineering
data publication.
Emacs!
No 'hat dancing' no undefined or vague terms. This chart
says that an off the shelf PC680 should deliver hard
values of stored energy depending on (1) discharge
rate or load and (2) condition of the battery [cap check].
In the course of our conversations, I sent a copy of this chart
to EarthX suggesting that until the aviation consumer
had this kind of data they were not serving their customer
well. CRANKING is one thing, ENDURANCE is quite another.
>=C2 To their credit, EarthX seems to have
>modified their aviation offerings and increased
>the cell size (count?) so that total energy does
>compare with the various SLAs they are marketing
>against. It did take some rather pointed, public
>comments on aviation forums for that to happen.
Good for them . . .and I suspect others but I've
not surveyed the market offerings.
>On the 'load dump' issue: The BMS in the EarthX
>(according to EX's own literature, and their rep
>who posts frequently on VAF) will disconnect the
>battery under what it considers an overvoltage charge condition . . .
I've never understood this feature if the
target market is either (1) TC aircraft or
(2) artfully crafted OBAM aircraft. The
ONLY source for an overvoltage condition is
a failed regulator. A fact that has been
recognized and addressed for 70 years by
the application of over voltage detection
and mitigation. They only reason to include it
in the battery's BMS is to cover the instances
where ov protection is NOT provided by the
owner/operator . . . and were I to offer
a lithium product to the non-TC community,
there would be a big sticker on the side of
the battery, "Warranty and Performance claims
are void unless the system is fitted with
ov protection".
> . . . also when it thinks the battery is in
> danger of being excessively depleted,
Yup, EVERY lithium product supplier says
don't discharge below x.x volts per cell . . .
2.8 being a popular number. Again, a condition
very easily addressed at the airframe system
level . . . to include this inside every
battery seems wasteful . . .
>or too high a current demand is being placed on it.
Gee, I thought that's what current limiters
were for . . .
>The very fact that the BMS *can* disconnect the
>battery (for whatever reason), should, it seems
>to me, require us to include that fact in
>failure mode analysis. If the BMS itself fails
>in a fashion that disconnects the battery,
>that's a new and different failure mode (which
>may come as a complete shock if one hasn't done
>his homework). If the BMS gets confused and
>thinks the alternator is in an OV condition, it
>may disconnect from the electrical system> load
>dump>potential alternator failure>dark airplane.
I have no doubts that the BMS offered by EarthX,
True Blue and perhaps others perform as advertised
with exceedingly low risk . . . but why all
the so much monkey motion built INSIDE each
delivered unit and repurchased every time
a battery is replaced is a mystery.
>While load dumps might not be an every day
>occurrence, they do happen. Many years ago, I
>killed an alternator with an ill-advised switch
>flip, so I know it can happen. An EarthX battery
>mixed with one of those old school IR
>alternators does up the odds of a dark airplane,
>if failure modes aren't accounted for.
Exemplar Load Dump Definition:
Load dump means the disconnection of a powered
load. It can cause 2 problems: failure of supply
to equipment or customers large voltage spikes
from the inductive generator In automotive
electronics, it refers to the disconnection of
the vehicle battery from the alternator while the
battery is being charged. Due to such a
disconnection of the battery, other loads
connected to the alternator see a surge in power
line. The peak voltage of this surge may be as
high as 120 V and the surge may take up to 400 ms
to decay. It it typically clamped to 40 V in 12 V
vehicles and about 60 V in 24 V systems.
A load dump event is simply an abrupt
disconnect of near max load from an
alternator. It doesn't need to be a
battery disconnect . . . but if there
is no battery, the dump transient can
be higher.
I've created many a 'load dump' on the test
bench with no battery on line. You load an
engine driven power source with a load equal
to nameplate rating at maximum expected operating
RPM. Then simply disconnect the load and measure
what happens.
The regulator/alternator dynamics determine
the severity of the recovery transient. But
as long as a battery is on line, the transient
is trivial. Further, DO160 qualification parameters
dictate that the righteous accessory is not
at risk for being subjected to such transients.
The likelihood that a deeply discharged battery
being recharged in a system otherwise lightly
loaded becomes disconnected from the bus is
exceedingly low . . .
A 'load dump' transient is short lived . . . a
few hundred milliseconds. It CAN be of significant
amplitude as I described in the last revision to the
chapter on alternators. But to see/measure one
of these critters takes some careful attention
to conditions that generate the event. The Van's
crowd got their nickers in a wad about 20 years
ago when a builder purposefully cycled the alternator
control switch in Figure Z24 into a less than
charged battery. Indeed it zorked his regulator.
The transient WAS NOT conducted onto the bus. It
affected only the alternator's build in regulator.
Van's alternator of choice was of unknown
pedigree and even then, failure of this particular
alternator may have been at the fringes of the
bell-curve. Nonetheless, the event triggered
a flurry of excited and under-informed assertions
and decisions by some members of the OBAM aviation
community.
The 'load dump' condition is poorly understood
and over-worried. Further, it's in a completely
separate basket from BMS considerations in
lithium batteries. The load-dump overshoot
will be greatly mitigated by the presence
of the battery and it's BMS will have no
reason to disconnect.
Bob . . .
Message 3
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| Subject: | Re: Lithium BMS and 'load-dump' worries |
On 1/10/2020 10:32 AM, Robert L. Nuckolls, III wrote:
>>
>>
>> The recently referenced thread on the Vans Air Force forum proves
>> that it's still the case. The original poster of that thread has been
>> building electronic ignition and electronic injection systems for
>> aircraft for at least a couple of decades, and he stumbled upon the
>> knowledge while doing periodic load testing (that he obviously didn't
>> do before putting the lithium tech battery of choice into service).
>> This was not an EarthX aviation battery; it was one of the offerings
>> from a motorsports company.
>
> This underscores the value of 'getting the
> numbers' . . .
>
> Here is an excerpt from an Enersys-Hawker engineering
> data publication.
>
> Emacs!
>
> No 'hat dancing' no undefined or vague terms. This chart
> says that an off the shelf PC680 should deliver hard
> values of stored energy depending on (1) discharge
> rate or load and (2) condition of the battery [cap check].
>
> In the course of our conversations, I sent a copy of this chart
> to EarthX suggesting that until the aviation consumer
> had this kind of data they were not serving their customer
> well. CRANKING is one thing, ENDURANCE is quite another.
>
>> To their credit, EarthX seems to have modified their aviation
>> offerings and increased the cell size (count?) so that total energy
>> does compare with the various SLAs they are marketing against. It did
>> take some rather pointed, public comments on aviation forums for that
>> to happen.
>
> Good for them . . .and I suspect others but I've
> not surveyed the market offerings.
>
>
>> On the 'load dump' issue: The BMS in the EarthX (according to EX's
>> own literature, and their rep who posts frequently on VAF) will
>> disconnect the battery under what it considers an overvoltage charge
>> condition . . .
>
>
> I've never understood this feature if the
> target market is either (1) TC aircraft or
> (2) artfully crafted OBAM aircraft. The
> ONLY source for an overvoltage condition is
> a failed regulator. A fact that has been
> recognized and addressed for 70 years by
> the application of over voltage detection
> and mitigation. They only reason to include it
> in the battery's BMS is to cover the instances
> where ov protection is NOT provided by the
> owner/operator . . . and were I to offer
> a lithium product to the non-TC community,
> there would be a big sticker on the side of
> the battery, "Warranty and Performance claims
> are void unless the system is fitted with
> ov protection".
>
>> . . . also when it thinks the battery is in danger of being
>> excessively depleted,
>
> Yup, EVERY lithium product supplier says
> don't discharge below x.x volts per cell . . .
> 2.8 being a popular number. Again, a condition
> very easily addressed at the airframe system
> level . . . to include this inside every
> battery seems wasteful . . .
>
>> or too high a current demand is being placed on it.
>
> Gee, I thought that's what current limiters
> were for . . .
>
>> The very fact that the BMS *can* disconnect the battery (for whatever
>> reason), should, it seems to me, require us to include that fact in
>> failure mode analysis. If the BMS itself fails in a fashion that
>> disconnects the battery, that's a new and different failure mode
>> (which may come as a complete shock if one hasn't done his homework).
>> If the BMS gets confused and thinks the alternator is in an OV
>> condition, it may disconnect from the electrical system> load
>> dump>potential alternator failure>dark airplane.
>
> I have no doubts that the BMS offered by EarthX,
> True Blue and perhaps others perform as advertised
> with exceedingly low risk . . . but why all
> the so much monkey motion built INSIDE each
> delivered unit and repurchased every time
> a battery is replaced is a mystery.
>
>
>> While load dumps might not be an every day occurrence, they do
>> happen. Many years ago, I killed an alternator with an ill-advised
>> switch flip, so I know it can happen. An EarthX battery mixed with
>> one of those old school IR alternators does up the odds of a dark
>> airplane, if failure modes aren't accounted for.
>
> Exemplar Load Dump Definition:
>
> */Load dump means the disconnection of a powered load. It can cause 2
> problems: failure of supply to equipment or customers large voltage
> spikes from the inductive generator In automotive electronics, it
> refers to the disconnection of the vehicle battery from the alternator
> while the battery is being charged. Due to such a disconnection of the
> battery, other loads connected to the alternator see a surge in power
> line. The peak voltage of this surge may be as high as 120 V and the
> surge may take up to 400 ms to decay. It it typically clamped to 40 V
> in 12 V vehicles and about 60 V in 24 V systems.
>
>
> /* A load dump event is simply an abrupt
> disconnect of near max load from an
> alternator. It doesn't need to be a
> battery disconnect . . . but if there
> is no battery, the dump transient can
> be higher.
>
> I've created many a 'load dump' on the test
> bench with no battery on line. You load an
> engine driven power source with a load equal
> to nameplate rating at maximum expected operating
> RPM. Then simply disconnect the load and measure
> what happens.
>
> The regulator/alternator dynamics determine
> the severity of the recovery transient. But
> as long as a battery is on line, the transient
> is trivial. Further, DO160 qualification parameters
> dictate that the righteous accessory is not
> at risk for being subjected to such transients.
> The likelihood that a deeply discharged battery
> being recharged in a system otherwise lightly
> loaded becomes disconnected from the bus is
> exceedingly low . . .
>
> A 'load dump' transient is short lived . . . a
> few hundred milliseconds. It CAN be of significant
> amplitude as I described in the last revision to the
> chapter on alternators. But to see/measure one
> of these critters takes some careful attention
> to conditions that generate the event. The Van's
> crowd got their nickers in a wad about 20 years
> ago when a builder purposefully cycled the alternator
> control switch in Figure Z24 into a less than
> charged battery. Indeed it zorked his regulator.
> The transient WAS NOT conducted onto the bus. It
> affected only the alternator's build in regulator.
>
> Van's alternator of choice was of unknown
> pedigree and even then, failure of this particular
> alternator may have been at the fringes of the
> bell-curve. Nonetheless, the event triggered
> a flurry of excited and under-informed assertions
> and decisions by some members of the OBAM aviation
> community.
>
> The 'load dump' condition is poorly understood
> and over-worried. Further, it's in a completely
> separate basket from BMS considerations in
> lithium batteries. The load-dump overshoot
> will be greatly mitigated by the presence
> of the battery and it's BMS will have no
> reason to disconnect.
>
> Bob . . .
>
No argument with any of the above, *except* this: Saying that there's no
reason to have avoidable issues if we do our research, doesn't mean that
we'll actually *do* our research. (ex: the recent VAF thread on battery
capacity.) I promise you that until Ross (on VAF) posted his endurance
report, virtually every person on VAF that's replaced an SLA with
lithium tech has *assumed* that because the CCA numbers are equal, the
capacity is equal. The RVx guys, as a group, are incredibly resistant to
looking at any info source other than VAF. And after years of reading
VAF posts giving electrical advice, I can tell you that a lot of it is
quite bad. On a related point, SLA capacity numbers are available from a
number of different vendors, but for lithium tech, it's much more
difficult to find and/or interpret, for a more 'typical' aviator.
My point about 'load dump' is that many of us are still using
alternators from that 2 decade old era you reference, and many (likely
almost all) of those in that subset have no idea about the research
documented here on this list.
I agree that the likelihood of BMS failure in a brand EX battery is
unlikely. BUT: IIRC, it's already been documented by someone flying an
RVx. Wouldn't you agree that when doing a failure mode analysis of our
wiring architecture, we should include that failure mode? I know that
the B&C products are immune to 'load dump' issues, but for those of us
running alternators of 'unknown pedigree', don't we need to consider the
risk of a BMS disconnect also taking out our regulator?
Charlie
Message 4
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| Subject: | Re: Not receiving e-mail |
Here=99s a perfect example of the problem. The message below, which B
ob sent on the 8th, arrived to my inbox twice on that day. This morning
=94 two days later =94 it arrived again.
I don=99t know how this could be anything but a Matronics server probl
em. It happens only with messages from the Aero-Electric List and no others
.
Eric
=94=94=94=94=94
Re: AeroElectric-List: Re: One battery/two alternators IFR z-diagram
>> On Jan 8, 2020, at 13:05, Robert L. Nuckolls, III <nuckolls.bob@aeroelect
ric.com> wrote:
>> Hi Bob... question... need there be a load on a wound field alternator fo
r it to continue working in case of battery disconnect?
>
> No . . . you can 'stall' a free-running alternator by hitting it with a b
ig load, generally larger than it's nameplate rating.
> [SNIP]
Message 5
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| Subject: | Re: Lithium BMS and 'load-dump' worries |
>The RVx guys, as a group, are incredibly resistant to looking at any
>info source other than VAF. And after years of reading VAF posts
>giving electrical advice, I can tell you that a lot of it is quite bad.
That's one of the reasons that the AE-List
came into existence.
>On a related point, SLA capacity numbers are available from a number
>of different vendors, but for lithium tech, it's much more difficult
>to find and/or interpret, for a more 'typical' aviator.
But it's easy to acquire . . . call the
manufacturer. Alternatively, go measure
it . . . or get somebody to do it for you.
Then publish the findings.
If there are any concerns, worries,
uncertainties about system performance
or reliability . . . there is a process
by which they can be resolved. Recorded
measurements under documented test
conditions are pretty solid foundations
for design descisions.
>My point about 'load dump' is that many of us are still using
>alternators from that
>2 decade old era you reference, and many (likely almost all) of those in that
>subset have no idea about the research documented here on this list.
Has there been more than the one
load-dump failure event that planted the
seeds of concerns, worries, uncertainties?
We know that the triggering circumstance
for the original failure was the builder's
repetitive operation of the alternator
ON-OFF control with a Z-24 ov management
system.
In this case, the battery wasn't disconnected
from the system . . . rather the alternator
b-lead connection was broken. We're not privy
to the state of the battery. For the sake
of argument, let's assume the battery was in
a low state of charge. It's not likely that
there was a large load on the bus.
The alternator has no way of knowing what
is loading the output. All it knows is
total load. So when the b-lead was repeatedly
made and broken, what ever total load was
present contributed to excitation of dump
transient.
No investigation was made for assessing
first failure in the regulator. Nobody knows
if it was an OEM regulator or an after market
device. No failure analysis of consequence was conducted
or even possible. I suggest that factoring this single
event into a couple decades of 'advice' INCREASES
rather than REDUCES risk.
>I agree that the likelihood of BMS failure in a brand EX battery is
>unlikely. BUT: IIRC, it's already been documented by someone flying
>an RVx. Wouldn't you agree that when doing a failure mode analysis
>of our wiring architecture, we should include that failure mode?
Sure. So from time of master switch ON to
master switch OFF on any given flight cycle,
what sequence of conditions have to stack up
for a BMS battery disconnect failure to initiate
a potentially risky load dump event?
(1) Engine rpm would have to be high
(2) battery in poor state of charge
(3) BMS (or battery contactor) has to suffer
sudden open circuit. The potential for
battery contactor, wiring and switch
to trigger the event is no different
than BMS failure.
Do we think the failure rate on a solid state BMS
is greater than failure rate on the contactor/wiring/
switch combination? And what is the outcome we're
trying to mitigate? Loss of alternator, runaway
alternator. Are there circumstances other than
loss of contactor/BMS that might trigger the
same condition? How about failure within the
sketchy regulator's components?
>I know that the B&C products are immune to 'load dump' issues, but
>for those of us running alternators of 'unknown pedigree',
>don't we need to consider the risk of a BMS disconnect also
>taking out our regulator?
Sure. If it were my airplane and I was flying
an internally regulated alternator of unknown
pedigree, I'd install Z-24 and refrain from
operating the alternator ON/OFF switch at
high rpm and high alternator loads. In this
case, loss of BMS (or contactor) under optimally
unhappy conditions MIGHT take out the regulator.
(a) If the alternator just QUITS, your in-flight decision
making process is no different than if you'd
broken a belt.
(b) If the alternator goes into
RUNAWAY, the OV protection system will
bring it under control.
The alternator switch is ONLY operated at
idle rpm after start up and before shut down.
With this design philosophy and operating
protocol, it doesn't matter what kind of
battery or alternator you've installed.
The lithium battery BMS is of no more
concern than your battery contactor.
Bob . . .
Message 6
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| Subject: | Re: Lithium BMS and 'load-dump' worries |
There are also a lot of us running PM alternators and there are a lot of
them on rotax engines. Most of those regulators are not terribly robust.
I permanently failed a 20 amp oem John Deere Rectifier/Regulator just by
idling the engine with a flat battery. Yes I knew better but... Anyway
the voltage immediately went high enough to trip the crowbar OVM. With
an EFI engine I will be staying with VRLA batteries and no BMS for the
time being despite the extra weight.
Ken
On 10/01/2020 4:27 PM, Robert L. Nuckolls, III wrote:
>> The RVx guys, as a group, are incredibly resistant to looking at any
>> info source other than VAF. And after years of reading VAF posts
>> giving electrical advice, I can tell you that a lot of it is quite bad.
>
> That's one of the reasons that the AE-List
> came into existence.
>
>> On a related point, SLA capacity numbers are available from a number
>> of different vendors, but for lithium tech, it's much more difficult
>> to find and/or interpret, for a more 'typical' aviator.
>
> But it's easy to acquire . . . call the
> manufacturer. Alternatively, go measure
> it . . . or get somebody to do it for you.
> Then publish the findings.
>
> If there are any concerns, worries,
> uncertainties about system performance
> or reliability . . . there is a process
> by which they can be resolved. Recorded
> measurements under documented test
> conditions are pretty solid foundations
> for design descisions.
>
>
>> My point about 'load dump' is that many of us are still using
>> alternators from that
>> 2 decade old era you reference, and many (likely almost all) of those
>> in that
>> subset have no idea about the research documented here on this list.
>
> Has there been more than the one
> load-dump failure event that planted the
> seeds of concerns, worries, uncertainties?
>
> We know that the triggering circumstance
> for the original failure was the builder's
> repetitive operation of the alternator
> ON-OFF control with a Z-24 ov management
> system.
>
> In this case, the battery wasn't disconnected
> from the system . . . rather the alternator
> b-lead connection was broken. We're not privy
> to the state of the battery. For the sake
> of argument, let's assume the battery was in
> a low state of charge. It's not likely that
> there was a large load on the bus.
>
> The alternator has no way of knowing what
> is loading the output. All it knows is
> total load. So when the b-lead was repeatedly
> made and broken, what ever total load was
> present contributed to excitation of dump
> transient.
>
> No investigation was made for assessing
> first failure in the regulator. Nobody knows
> if it was an OEM regulator or an after market
> device. No failure analysis of consequence was conducted
> or even possible. I suggest that factoring this single
> event into a couple decades of 'advice' INCREASES
> rather than REDUCES risk.
>
>> I agree that the likelihood of BMS failure in a brand EX battery is
>> unlikely. BUT: IIRC, it's already been documented by someone flying
>> an RVx. Wouldn't you agree that when doing a failure mode analysis of
>> our wiring architecture, we should include that failure mode?
>
> Sure. So from time of master switch ON to
> master switch OFF on any given flight cycle,
> what sequence of conditions have to stack up
> for a BMS battery disconnect failure to initiate
> a potentially risky load dump event?
>
> (1) Engine rpm would have to be high
>
> (2) battery in poor state of charge
>
> (3) BMS (or battery contactor) has to suffer
> sudden open circuit. The potential for
> battery contactor, wiring and switch
> to trigger the event is no different
> than BMS failure.
>
> Do we think the failure rate on a solid state BMS
> is greater than failure rate on the contactor/wiring/
> switch combination? And what is the outcome we're
> trying to mitigate? Loss of alternator, runaway
> alternator. Are there circumstances other than
> loss of contactor/BMS that might trigger the
> same condition? How about failure within the
> sketchy regulator's components?
>
>> I know that the B&C products are immune to 'load dump' issues, but
>> for those of us running alternators of 'unknown pedigree',
>> don't we need to consider the risk of a BMS disconnect also
>> taking out our regulator?
>
> Sure. If it were my airplane and I was flying
> an internally regulated alternator of unknown
> pedigree, I'd install Z-24 and refrain from
> operating the alternator ON/OFF switch at
> high rpm and high alternator loads. In this
> case, loss of BMS (or contactor) under optimally
> unhappy conditions MIGHT take out the regulator.
>
> (a) If the alternator just QUITS, your in-flight decision
> making process is no different than if you'd
> broken a belt.
>
> (b) If the alternator goes into
> RUNAWAY, the OV protection system will
> bring it under control.
>
> The alternator switch is ONLY operated at
> idle rpm after start up and before shut down.
> With this design philosophy and operating
> protocol, it doesn't matter what kind of
> battery or alternator you've installed.
> The lithium battery BMS is of no more
> concern than your battery contactor.
>
>
> Bob . . .
>
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