Today's Message Index:
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1. 05:12 AM - Still noisy voltmeter (Achille)
2. 06:14 AM - Re: Still noisy voltmeter (user9253)
3. 08:15 AM - Re: Battery BMS failures? (Robert L. Nuckolls, III)
4. 11:38 AM - Re: Battery BMS failures? (Eric Page)
Message 1
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| Subject: | Still noisy voltmeter |
Hi all,
I send a message because I have since months a noisy voltmeter after the total
change of my electrical system. And I tried to resolved it without good evolution.
I have used the book of bob, and it's the Z19 electrical diagram or very close
to.
I have 2 votmeters, one for main batterie and the other one for the aux bat 7amp/h
bat. Set with one 2 way switch.
The both voltmeters are on the same place and the wire of each other are a wire
harness. This wire harness pass below my VHF. And just the voltmeter 1 (Main
system) is noisy. The other not. (pictures below)
My voltmeter 1 was set on the ESS bus bar after the diode. I tried to connect it
before the diode. And in this case it's a bit (but still noisy) less noisy.
I have the noise a low level when I set voltmeter in ON and intercom ON, and when
I set radio in ON the noise is higher.
In all case if I set my voltmeters in OFF no more noise.
Voltmeters switch ON but voltmeter 1 disconnected no noise... [Rolling Eyes]
Any idea ? Thank you
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=488163#488163
Attachments:
http://forums.matronics.com//files/voltmeter_246.jpg
http://forums.matronics.com//files/voltmeter_2_173.pdf
Message 2
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| Subject: | Re: Still noisy voltmeter |
How is voltmeter 1 grounded? I suggest to NOT ground the voltmeter to the
airframe. Instead, twist the positive and negative wires together all of the way
from the voltmeter to the battery. At the switch, loop the ground wire around
the switch, then continue the twisted pair to the battery.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=488164#488164
Message 3
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| Subject: | Re: Battery BMS failures? |
>Bob,
>
>Speaking of BMS, perhaps you can explain (since EarthX seems
>unable) why EarthX batteries, with their 'full BMS', have a limit on
>alternator current capability based on their battery capacity. I am
>unable to see why a BMS that can manage individual cell charging,
>and protect individual cells plus the entire battery, is unable to
>limit overall charge current to the battery to a safe level. I've
>repeatedly asked that question of their spokesperson on the VAF (RV)
>forum, and gotten words without answers.
>
>Charlie
Interesting question . . .
I've oft asserted that batteries are
like houseplants. Given the right treatment
in proper proportions and protected from
deleterious stress, they will 'bloom'
and thrive.
But the term 'battery' is not quantified
and the selection of a battery is to
craft a kind of marriage between a host
of players not the least of which are
the engine driven power source(s) and
design goals for normal and abnormal
operations.
Lithium cells are the orchids of the
battery family . . . capable of extra-
ordinary performance in some respects
but exceedingly sensitive to
stress largely tolerated or
shrugged off by the likes of
Flooded, SVLA, gell and NiCad
technologies.
Lithium is extra-ordinarily vulnerable
to over and under voltage conditions.
Hence the 'real' BMS will strive to
operate the array of cells between
about 20 and 90 percent of charge.
This is a goal stated by the electric
and hybrid car folks. No doubt, EarthX
has their own numbers but what ever
the numbers, ignoring them risks
premature battery failure.
Then there's temperature . . . stuffing
energy back into a lithium array
MUST raise the chemistry's temperature
as does prolonged heavy rate discharge.
So the agile BMS watches temperatures
and strives to limit those effects
on the cells irrespective of system
demands from the outside.
External hard faults cause spectacular
current flows with a new constellation
of risks for catastrophic failures.
A BMS tailored for engine cranking
expects to see some really high
current flows for short periods of
time . . . but it must differentiate
between starter inrush/engine spin-up
and a hard fault.
I've mentioned that the enclosure
for a True Blue, TC/TSO battery
is filled with electronics . . .
electronics with agility and robustness
to accomplish all these things to
prevent premature failure while packaged
to keep the rare catastrophic failure
from migrating to the rest of the
aircraft.
True Blue batteries are used on twin
turbine aircraft with starter generators
up to and including 400A per side or
800A of recharge capability. Starter
inrush is typically 1500-2000 amps
followed by spin-up currents on the
order of 500-700A lasting 20-30
seconds. My hat is off to the folks
who crafted an array of silicon that
can operate in series with those loads
yet meet design goals for safety and
battery life.
AeroVoltz seems to be moving toward
offering an EXTERNAL BMS for their
product line . . . methinks a fine
idea. That way you don't trash a
bunch of perfectly good transistors
along with a shot battery.
The most difficult thing for a BMS
to do is throttle currents . . . in
either a charge or discharge mode.
The series connected control devices
are either switched on hard (saturated)
or totally open (off). This offers
the smallest form factor of electronics
to manage such current levels.
Battery recharge limits are largely
a thermal management issue. The
very low internal impedance of the
lithium cell COMBINED with its
low mass raises concerns for overheating
during prolonged high rates of charge.
True Blue isn't immune to these
forces either but they're designed to
work in a world of currents a magnitude
greater than piston driven light aircraft.
EarthX and contemporaries are not immune
from the need to make compromises in design
goals. They are marketing good cranking
performance and light weight. Light
weight generally brings extra-ordinary
requirements in thermal management.
Light weight and small size puts limits
on capacity . . . largely independent
of short term cranking ability.
Given the fact that a BMS cannot 'throttle'
current into or out of the battery,
they must be cognizant of the risks for
marrying their 'orchid' to a system
recently divorced from a 'bromeliad'
that may not easily bloom but it doesn't
lay down and die when insulted.
So what's the responsible supplier of
light cranking batteries to do when
marketing to relative technical
novices about the care and feeding
of their products. To be sure, lots
of their batteries are being married
to systems that already have alternators
that are too big.
If the engine starts easily when
smartly cranked time needed to recharge
is limited even if too fast. If the
operator NEVER allows the battery to
be deeply discharged followed by
an in-situ recharge by the ship's
too-big alternator . . . then risks
to the battery are low.
At the same time, the operator purchased
"light" and "whippy-starting" and made
no demands for electrical and thermal
robustness. So it makes sense that
EarthX would recommend limiting the
size of the alternator depending
on size of battery . . . not a very
realistic expectation but a good
CYA move nonetheless.
This raises a recollection of experiences
with another shotgun wedding between
poorly matched components. Waayyy
back when we got all exercised about
what was then a big quantum leap
in light weight, robust cranking
batteries with flooded NiCads.
After setting a few airplanes on fire
with a marriage of nicad and twin
turbines, powers-that=be decided
that the BEST thing to do was add
a remote reading battery temperature
meter paired with yellow warning
and red danger lights designed
to assist crews in managing their
'orchids' to prevent overheat
and thermal runaway.
I argued then that we could craft
an accessory to the starter-generator
controllers that would automatically
adjust bus voltage in response to
battery overheat. That wasn't well
received so we added another thing
on the panel that was harder to
install and drove up pilot work
loads.
The same thing could be done here.
The BMS for the alternator/lithium
marriage could easily include an
regulator that would prevent an
alternator of ANY SIZE from abusing
the battery . . . maybe AeroVoltz
will do it.
Bob . . .
Message 4
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| Subject: | Re: Battery BMS failures? |
Charlie England wrote:
> Speaking of BMS, perhaps you can explain (since EarthX seems unable) why EarthX
batteries, with their 'full BMS', have a limit on alternator current capability
based on their battery capacity. I am unable to see why a BMS that can manage
individual cell charging, and protect individual cells plus the entire battery,
is unable to limit overall charge current to the battery to a safe level.
I've repeatedly asked that question of their spokesperson on the VAF (RV) forum,
and gotten words without answers.
My guess is that it's a limitation of the cell balancing circuitry in the BMS.
As a cell within the battery reaches full charge, the BMS puts a resistance across
it (either a fixed resistor hard-switched across the cell or a linear-mode
transistor) to burn the current that would otherwise overcharge the cell while
the others continue to charge. There must be a limit to the power that this
system can dissipate, which may explain the alternator output limitation.
Robert L. Nuckolls, III wrote:
> After setting a few airplanes on fire with a marriage of nicad and twin turbines,
powers-that=be decided that the BEST thing to do was add a remote reading
battery temperature meter paired with yellow warning and red danger lights designed
to assist crews in managing their 'orchids' to prevent overheat and thermal
runaway.
Indeed, the deHavilland DHC-8-202 that I flew in a previous life was fitted with
battery temperature gauges on the overhead panel (just below the left fire t-handle
in the linked image).
https://bitly.com/2uj9V9F+
The airline I worked for operated them in the desert southwest, where ambient temps
routinely exceed 100F. Given the short-hop, quick-turn nature of the flying
we did, and the eye-watering current required to start a >2,000shp engine,
we kept a close eye on those gauges.
Eric
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=488170#488170
Attachments:
http://forums.matronics.com//files/dhc_8_batt_temp_855.jpg
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