Today's Message Index:
----------------------
1. 08:20 AM - Re: Re: Three Questions on Z-07 (Robert L. Nuckolls, III)
2. 08:37 AM - Re: Starters (Steve Kelly)
3. 08:41 AM - Battery BMS failures? (Ken Ryan)
4. 10:19 AM - Re: Starters (Paul Millner)
5. 10:31 AM - Re: Starters (Robert L. Nuckolls, III)
6. 10:48 AM - Re: Battery BMS failures? (Robert L. Nuckolls, III)
7. 02:51 PM - Re: Starters (Steve Kelly)
8. 05:47 PM - Re: Battery BMS failures? (Ernest Christley)
9. 07:03 PM - Re: Starters (Kelly McMullen)
Message 1
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| Subject: | Re: Three Questions on Z-07 |
At 03:43 PM 3/17/2019, you wrote:
>
>Bob,
>
>I have assumed that I would use two batteries for 4 reasons:
>
>1. I believed that there was a requirement to have a working battery
>to (magically to me) "cushion" delicate avionics from the alternator current;
not true
>2. I assumed that I could parallel the LiFePO4 batteries to aid in starting
sure . . . would one larger battery do it too?
>3. I was trying to guard against a battery failure "from bringing
>down the whole system".
battery failures don't bring down the whole system.
The alternator will run self excited and you
probably wouldn't know that the battery was
gone until you shut the alternator off.
>4. It is easier for me to mount two smaller batteries in parallel
>than one large one given my alternator-out mission requirements.
available space can drive battery
configuration . . .
>It seems that reason #1 is bogus, since your discussion of "one
>large battery" assumes that the alternator alone can run everything
>required without a problem. I don't know where I got this idea.
>
>Reason #2 turns out to (maybe) be bogus as well. Two manufacturers
>who supply a BMS with their LiFePo4 batteries recommend AGAINST
>running their batteries in parallel. Apparently, low resistance in a
>single cell of these multi-cell LiFePO4 batteries can greatly reduce
>capacity and longevity. The manufacturers take great care to match
>the resistance of the battery cells when they build them, and their
>BMS's spend a lot of time "optimizing" the batteries during charge
>and discharge. This is not possible between paralleled batteries and
>a Resistance mismatch between the batteries of (for example) 20% can
>reduce performance by 40%.
I don't see how this is possible. How does one
battery with a BMS know that there's another
battery on line with it? The bus voltage is
a function of regulator set point. Bus voltage
is the sole determinant for optimal charging
of the battery. The fact that a second battery
shares the bus is totally transparent to the
first battery.
>On the other hand another manufacturer who does not supply a BMS
>with their batteries says nothing about this. A friend of mine has
>used their product in parallel for 3 years without problem.
Exactly. This is what battery charge
balancing is all about. If any single
cell (or cell group) is lagging behind
the rest in achieving full charge (due
perhaps to slightly lower impedance)
then the balancing system places an
artificial load on the remaining cells
in the string until the lagging cell
catches up.
>So, your Z-07 diagram without parallel batteries may still be useful
>for people who believe this is a problem for them.
Believing is subordinate to knowing . . .
knowing is subordinate to understanding.
>Reason #3 was actually a quote from your 1998 paper "What's all this
>Battery Isolator Stuff Anyhow?". I have also heard it mentioned in
>various discussions of dual battery installations. As you point out
>in your 2008 paper "Myths of Multiple Battery Installation" a
>shorted cell is exceedingly rare. However, in an electrically
>dependent airplane, "rare" is in the eye of the beholder. Is there
>any data on this? Given the cell resistance issue LiFePO4 batteries
>might that chemistry be more susceptible to this problem?
If it worries you, you'd better find out.
Just suppose you have two batteries
with their own contactors? How would you become
aware that you had a shorted cell? How would
you know which battery to take off line?
If a cell were shorted in one battery, how
do you know that taking the battery off
line will markedly reduce risk? Each
failure has it's own fingerprint (or
failureprint) in how it manifests,
progresses, propagates and terminates.
Hence, each failure has an optimal
response that drives toward a probable outcome.
>Finally, reason #4 is a problem that you mention and is certainly
>not unique to my situation. My current theory is to use the TCW
>backup battery solution. It is automatic, does not parallel the
>batteries and is a lightweight LiFePO4 solution. The disadvantage is
>that (currently) it is limited to a 6 amp/hr capacity, which is 30
>minutes for me throttled back if I lost BOTH my alternator and
>primary battery.
Nobody looses BOTH unless they've done
something really dumb. What kind
of engine are we talking about?
>Yes, this is non-FEMA thinking to worry about two failures at the
>same time. I think that it depends on what the definition of
>"bringing down the whole system" is. If a shorted battery cell can
>somehow stop the alternator from functioning, isn't that actually one failure?
A shorted cell won't bring down the
alternator. It will probably proceed
to spectacular if not catastrophic
failure in the battery itself . . . recall
that a lithium cell contains a lot of
energy with respect to weight/volume.
That energy has to go somewhere . . . usually
toward warming things up and making really
bad smells. SVLA cells are not particularly
failure friendly either.
So the question before us is exactly what
are the probabilities for an LiFePO4 cell-
short? If it does short, what are the
electrical and physical consequences?
I used to have some friendly contacts at
the Navy's battery testing facilities
in Crane, Indiana. If any battery was
purchased by the Navy, they had put it
through rigorous tests including abuses
designed to produce the greatest risks.
TrueBlue has done extensive testing on
LiFePo4, cylindrical cells used in their
TSO/PMA offerings to TC aircraft. I've
witnessed some tests where a constant
42 volts was placed across the array
of cells in a 24v battery. The poor things
went into apoplectic self-destruction
with considerable out-gassing. Gasses
were vented overboard though the fitting
on top. Outside of the case never reached
temperatures hazardous to the aircraft's
environs.
Emacs!
I can also tell you that the volume of
electronics in these products is roughly
equal to the volume of batteries . . .
the BMS is specifically tasked with
preventing such a failure in the
first place.
It seems to be a choice of products. Just
how much BMS you want to buy ranging
from EarthX down to no BMS like Aerovoltz
. . . or you could pop for True Blue.
Aircraft Spruce covers the range . . .
https://tinyurl.com/y4o5xwuz
ACS has a world-wide market and
deep pockets at risk for very deep picking
should one of their offerings prove
dangerously unsuited to task.
Z07 as last published has lots of
bus structures which, in an electrically
dependent airplane could probably go
away. Wiring this up like a C150 but
with engine dependency serviced directly
from the battery bus is probably the
way to go.
You can go max-cold for smoke in the
cockpit while keeping that whirrly thing
up front turning. You can simply load-shed
in case of alternator failure. If you've
got enough chemical energy on board to
meet satisfactory endurance goals, splitting
that capacity between two, separately
controlled batteries doesn't seem to make
sense.
Bob . . .
Message 2
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Bob. Thanks for the help. I had a chance to do the voltage tests like you
suggested. They were fairly similar to your your're example. While
cranking the voltage at the battery was around 10.5 and at the starter it
was between 7.5 and 8.5 volts. I also acquired a load tester. At the end
of the 15 sec test current was about 330 amps. Battery voltage dropped to
11.3 volts. The starter is a Sky Tec 149xlt. It's about 3 years old and
has 170 hours on it. This is probably the smallest starter Sky Tec makes.
Not sure if it's the weakest one.
Other contributing factors are cooler weather, fresh engine overhaul, and
a lightweight prop. Still, the starter should spin it better than it is.
Do worn starters draw the battery down faster?
Also, just to be clear, replacing the battery at 75% refers to the time
it takes to drop to 10 volts, correct? In you're example above when the
PC680 gets to 10v in 2.25 hours it's time to consider replacement.
Steve
On Sat, Mar 16, 2019 at 10:13 AM Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 02:15 PM 3/15/2019, you wrote:
>
> That is a very common battery, any battery store will test it for you.
>
> On Fri, Mar 15, 2019, 13:31 Steve Kelly <amsk22@gmail.com> wrote:
>
> Bob,=C3=82 Thank you for the reply.=C3=82 I will try to get out to the
hanger
> early next week and check the voltage readings.=C3=82 The battery is a P
C680 at
> three months old.=C3=82 =C3=82 Do you have a method you would suggest to
do a
> load/capacity check on it.
> That's a pretty fresh battery . . . this suggests
> the problem is elsewhere. However, in answer to
> your testing questions, I'll suggest that
> every owner of an aircraft should also own
> something like this
>
> https://tinyurl.com/yag4529y
>
>
> This LOAD tester allows you to load the battery
> to an output of 9 volts while waiting for the
> 15 second timer light to go out. Note the current
> at the end of 15 seconds . . . it should be in
> excess of 200A for small engines, 300A for larger
> engines. This test confirms the battery's avbility
> to grunt the extra-ordinary demands for cranking
> the engine.
>
> A CAPACITY test seeks to quantify the battery's
> ENERGY content . . . which is entirely separate
> from the capability to grunt a cranking load.
> There are some rather small batteries that have
> demonstrated the ability to crank a turbine
> engine
>
> https://tinyurl.com/yye6znqp
>
> But this product wouldn't run the aircraft's
> critical systems for very long after the
> alternator quits. There are dozens of 'tiny'
> products that offer a similar utility
>
> https://tinyurl.com/y2hzkq9l
>
> The way to cap check your battery is to set
> up your panel to operate your Plan-B (alternator
> out) electrical loads and monitor battery voltage
> with a voltmeter. The time it takes to reduce
> battery voltage to 10V (the lower limit for
> your avionics to operate).
>
> For example, a NEW PC680 has the following
> ENERGY delivery capability.
>
> [image: Emacs!]
> Assume a 4A endurance load. The curves say you're
> good to 3 hours. Here you have to tailor the question
> to match your own endurance requirements. If one hour
> meets your own Plan-B design goals, then according
> to the chart, the new battery is good for about 10A.
> Actually, you would want to rate the battery for about
> 8A given that maintenance protocols suggest replacing
> the battery at 75% of new capacity.
>
> Then there's the real-life test . . . turn on the
> goodies, start the clock, watch the voltage, measure
> the time then recharge the battery. If that time
> is equal to or greater than your design goals, then
> you're good to fly.
>
> How old is your starter? It MIGHT be that brushes
> and/or commutator are worn to the point of producing
> degraded performance.
>
>
> Bob . . .
>
Message 3
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| Subject: | Battery BMS failures? |
On the Aircraft Spruce page for the Aerovoltz battery, under the "Overview"
tab, the following text appears:
"An Aerovoltz external BMS is in a prototype stage and will be made
available to all Lithium Battery owners in the near future. Putting the
unit internally dramatically drives up the battery cost and all batteries
will wear out eventually so making it external will keep the cost of
ownership lower down the road when it comes time to replace.
*The current BMS systems on the market are very sensitive to damage* and it
can disable a perfectly good battery that will then need replacing. We
don=99t feel that=99s fair to our customers."
Has anyone heard about a rash of BMS failures?
Message 4
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2-3 volts is a huge voltage drop. You need to determine where that=99s
happening... SkyTec has a troubleshooting chart to help you find the bad ac
tor
Sent from my iPhone
> On Mar 18, 2019, at 8:35 AM, Steve Kelly <amsk22@gmail.com> wrote:
>
> Bob. Thanks for the help. I had a chance to do the voltage tests like yo
u suggested. They were fairly similar to your your're example. While crank
ing the voltage at the battery was around 10.5 and at the starter it was bet
ween 7.5 and 8.5 volts. I also acquired a load tester. At the end of the 1
5 sec test current was about 330 amps. Battery voltage dropped to 11.3 volt
s. The starter is a Sky Tec 149xlt. It's about 3 years old and has 170 hou
rs on it. This is probably the smallest starter Sky Tec makes. Not sure if
it's the weakest one.
> Other contributing factors are cooler weather, fresh engine overhaul, an
d a lightweight prop. Still, the starter should spin it better than it is.
Do worn starters draw the battery down faster?
> Also, just to be clear, replacing the battery at 75% refers to the time i
t takes to drop to 10 volts, correct? In you're example above when the PC68
0 gets to 10v in 2.25 hours it's time to consider replacement.
> Steve
>
>
>
>> On Sat, Mar 16, 2019 at 10:13 AM Robert L. Nuckolls, III <nuckolls.bob@ae
roelectric.com> wrote:
>> At 02:15 PM 3/15/2019, you wrote:
>>> That is a very common battery, any battery store will test it for you.
>>>
>>> On Fri, Mar 15, 2019, 13:31 Steve Kelly <amsk22@gmail.com> wrote:
>>
>> Bob,=C3=82 Thank you for the reply.=C3=82 I will try to get out to the h
anger early next week and check the voltage readings.=C3=82 The battery is a
PC680 at three months old.=C3=82 =C3=82 Do you have a method you would sug
gest to do a load/capacity check on it.
>>
>> That's a pretty fresh battery . . . this suggests
>> the problem is elsewhere. However, in answer to
>> your testing questions, I'll suggest that
>> every owner of an aircraft should also own
>> something like this
>>
>> https://tinyurl.com/yag4529y
>>
>>
>> This LOAD tester allows you to load the battery
>> to an output of 9 volts while waiting for the
>> 15 second timer light to go out. Note the current
>> at the end of 15 seconds . . . it should be in
>> excess of 200A for small engines, 300A for larger
>> engines. This test confirms the battery's avbility
>> to grunt the extra-ordinary demands for cranking
>> the engine.
>>
>> A CAPACITY test seeks to quantify the battery's
>> ENERGY content . . . which is entirely separate
>> from the capability to grunt a cranking load.
>> There are some rather small batteries that have
>> demonstrated the ability to crank a turbine
>> engine
>>
>> https://tinyurl.com/yye6znqp
>>
>> But this product wouldn't run the aircraft's
>> critical systems for very long after the
>> alternator quits. There are dozens of 'tiny'
>> products that offer a similar utility
>>
>> https://tinyurl.com/y2hzkq9l
>>
>> The way to cap check your battery is to set
>> up your panel to operate your Plan-B (alternator
>> out) electrical loads and monitor battery voltage
>> with a voltmeter. The time it takes to reduce
>> battery voltage to 10V (the lower limit for
>> your avionics to operate).
>>
>> For example, a NEW PC680 has the following
>> ENERGY delivery capability.
>>
>> <10a704b8.jpg>
>> Assume a 4A endurance load. The curves say you're
>> good to 3 hours. Here you have to tailor the question
>> to match your own endurance requirements. If one hour
>> meets your own Plan-B design goals, then according
>> to the chart, the new battery is good for about 10A.
>> Actually, you would want to rate the battery for about
>> 8A given that maintenance protocols suggest replacing
>> the battery at 75% of new capacity.
>>
>> Then there's the real-life test . . . turn on the
>> goodies, start the clock, watch the voltage, measure
>> the time then recharge the battery. If that time
>> is equal to or greater than your design goals, then
>> you're good to fly.
>>
>> How old is your starter? It MIGHT be that brushes
>> and/or commutator are worn to the point of producing
>> degraded performance.
>>
>>
>> Bob . . .
Message 5
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At 12:09 PM 3/18/2019, you wrote:
>2-3 volts is a huge voltage drop. You need to
>determine where that=99s happening... SkyTec has
>a troubleshooting chart to help you find the bad actor
Agreed. Use a voltmeter between
(1) battery(+) and starter power terminal
while cranking.
(2) battery(-) and crankcase.
Where is your battery located with respect
to starter i.e. how long are the wires
and what gage are they?
This is a NEW condition . . . used to crank
right smartly and only now sluggish?
Bob . . .
Message 6
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| Subject: | Re: Battery BMS failures? |
>
>Has anyone heard about a rash of BMS failures?
Good catch Ken. I'd be interested
(as would we all) in knowing what
kind of BMS failures have occurred.
Unfortunately, every battery failure
I've tried to follow up with the
manufacture was greeted with a stone
wall . . . take that back . . . used
to get great data dumps from Skip
Koss on Concorde product issues.
I've asked to be the recipient of any
failed batteries (or other devices)
so that I might disassemble for close
examination in a quest for answers . . .
but those opportunities are rare
to non-existent.
The outcome of non-communication is
ignorant assumption which gets traded
around the various venues . . . with
demonstrable data creep.
The first difficulty we have is defining
"Battery Management System". Many
lithium cylindrical cells are fitted
with dead short mitigation and are
advertised to be fitted with a "BMS".
Batteries and array of series-parallel
cells might include a cell balancing
module and advertised to include
a built-in "BMS".
Then there are full-up BMS like EarthX
and True Blue that will manage overheat,
over volts, charge balance/limiting,
fault mitigation and, in True Blue
case, comfortable management of vented
gasses in case the unthinkable does
happen.
Unless we're favored with a published
product performance specification for
the failure being studied, any assertions
about 'BMS failure' are exceedingly short
on useful data.
Keep your ears to the ground guys . . .
we might get lucky . . .
Bob . . .
Message 7
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Bob,
The slow prop became more noticeable after rebuilding the engine last
summer. Fresh cylinders along with upping the compression ratio from 7 to
8.5.
The battery and solenoids are located on the firewall. So the cables are
not very long. Maybe 5' total and 2' for ground. They are B&Cs 4 ga. weld
cable.
Looking at the measurements I made yesterday, the drop on the negative
was small, maybe .3 volts. The biggest drop was somewhere between the
battery and in side of the starter solenoid. 10.5 volts down to around
8. Didn't check either side of the battery contactor as the battery was
getting low. I have a brass strap that connects between the two
contactors. 1/2' wide by about 4" long. Do you think this may not be
adequate. Either that or the battery contactor. I will check the voltages
there when I get back out to the hanger.
Thanks, Steve
On Mon, Mar 18, 2019 at 1:37 PM Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 12:09 PM 3/18/2019, you wrote:
>
> 2-3 volts is a huge voltage drop. You need to determine where that=C3=A2
=82=AC=84=A2s
> happening... SkyTec has a troubleshooting chart to help you find the bad
> actor
>
>
> Agreed. Use a voltmeter between
>
> (1) battery(+) and starter power terminal
> while cranking.
>
> (2) battery(-) and crankcase.
>
> Where is your battery located with respect
> to starter i.e. how long are the wires
> and what gage are they?
>
> This is a NEW condition . . . used to crank
> right smartly and only now sluggish?
>
>
> Bob . . .
>
Message 8
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| Subject: | Re: Battery BMS failures? |
I have heard about the desulfater (sp?) charges killing the electronics du
e to their large voltage spikes.=C2- The battery manufacturers themselves
warn about those.
Otherwise....nada.
On Monday, March 18, 2019, 11:42:05 AM EDT, Ken Ryan <keninalaska@gmail
.com> wrote:
On the Aircraft Spruce page for the Aerovoltz battery, under the "Overview
" tab, the following text appears:
"An Aerovoltz external BMS is in a prototype stage and will be made availab
le to all Lithium Battery owners in the near future. Putting the unit inter
nally dramatically drives up the battery cost and all batteries will wear o
ut eventually so making it external will keep the cost of ownership lower d
own the road when it comes time to replace.
The current BMS systems on the market are very sensitive to damage and it c
an disable a perfectly good battery that will then need replacing. We don
=99t feel that=99s fair to our customers."
Has anyone heard about a rash of BMS failures?
Message 9
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Your compression change is not significant in terms of starter cranking.
A PC680 easily cranks an 0-360 with 8.5 compression.
Check to see that each connection is at proper torque at the max end of
scale for bolt size. Check the drop across the solenoid.
Now that you have run the battery down a fair amount, charge it at
around 3 amps until full charge. Should have a resting voltage of 12.9
to 13.0 four or more hours after off charger. If less, may need
rejuvenation through several discharge, charge cycles.
On 3/18/2019 2:49 PM, Steve Kelly wrote:
> Bob,
> The slow prop became more noticeable after rebuilding the engine last
> summer. Fresh cylinders along with upping the compression ratio from 7
> to 8.5.
> The battery and solenoids are located on the firewall. So the cables
> are not very long. Maybe 5' total and 2' for ground. They are B&Cs 4
> ga. weld cable.
> Looking at the measurements I made yesterday, the drop on the
> negative was small, maybe .3 volts. The biggest drop was somewhere
> between the battery and in side of the starter solenoid. 10.5 volts
> down to around 8. Didn't check either side of the battery contactor as
> the battery was getting low. I have a brass strap that connects between
> the two contactors. 1/2' wide by about 4" long. Do you think this may
> not be adequate. Either that or the battery contactor. I will check
> the voltages there when I get back out to the hanger.
> Thanks, Steve
>
> On Mon, Mar 18, 2019 at 1:37 PM Robert L. Nuckolls, III
> <nuckolls.bob@aeroelectric.com <mailto:nuckolls.bob@aeroelectric.com>>
> wrote:
>
> At 12:09 PM 3/18/2019, you wrote:
>> 2-3 volts is a huge voltage drop. You need to determine where
>> thats happening... SkyTec has a troubleshooting chart to help
>> you find the bad actor
>>
>
> Agreed. Use a voltmeter between
>
> (1) battery(+) and starter power terminal
> while cranking.
>
> (2) battery(-) and crankcase.
>
> Where is your battery located with respect
> to starter i.e. how long are the wires
> and what gage are they?
>
> This is a NEW condition . . . used to crank
> right smartly and only now sluggish?
>
>
> __
>
> __ Bob . . .
>
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