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nuckolls.bob(at)aeroelect
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 Posted: Thu Jun 11, 2020 5:14 am Post subject: Shorted cell risk? |
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At 06:05 PM 6/10/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
Bob, if two batteries are connected in parallel and one of the batteries
develops a shorted cell, will the good battery discharge into the bad battery?
If yes, would the rate of discharge be significant enough to quickly reduce
the good battery voltage to that of the bad battery?
Thanks
--------
Joe Gores |
A maintained battery doesn't get shorted cells.
This was true back in the days of flooded
batteries and especially true of RG devices
today.
'Shorting' requires motion . . . in the heyday
of flooded batteries, active material 'pasted'
into the cell grids was subject to degradation
with age/abuse. Chunks would fall out of the
plate and migrate into the wet space between
plates. Most of the stuff would fall to a
'sediment space' under the array of plates.
Plates were EXPECTED to shed chunks of expended
material so there was a 'basement' for storing
the dead stuff.
But a battery left in service past its prime
was subject to so much flaking of active
material that adjacent plates could become
electrically connected . . . i.e. 'shorted
cell'
An RG battery is a different breed of cat
all together. Separators between cells
is a pretty tough but thin, porous
plastic or fiber. The plates are compacted
with significant force before being
inserted into the battery case.
For 'motion' to occur in these devices,
requires severe degradation of the
cell's active materials. This happens
when the battery has been allowed to
self-destruct with age or when subjected
to sustained over charging. Then you
get swelling of the active material
and risk of separator compromise.
But even in extreme cases of AGM
battery abuse, shorted cells are not
a given. I've seen some pretty badly
'puffed up' AGM batteries that were essentially
destroyed but had presented no shorted
cells.
A battery removed from service in an aircraft
at the appointed time in its life cycle is not
going to exhibit effects of severe ageing or
abuse.
Bob . . .
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kenryan
Joined: 20 Oct 2009
Posts: 424
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| Posted: Thu Jun 11, 2020 5:30 am Post subject: Shorted cell risk? |
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What is an RG battery? Without trying to continue mudding the waters, I would venture to say that most builders these days who are using an auto conversion engine not only have a single, internally regulated alternator, they are also probably running LiPo batteries. Does this apply to LiPo batteries as well? All of the experimentals that I am personally familiar (eight or ten) are now using LiPo batteries.
On Thu, Jun 11, 2020 at 5:20 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 06:05 PM 6/10/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>
Bob, if two batteries are connected in parallel and one of the batteries
develops a shorted cell, will the good battery discharge into the bad battery?
If yes, would the rate of discharge be significant enough to quickly reduce
the good battery voltage to that of the bad battery?
Thanks
--------
Joe Gores |
 A maintained battery doesn't get shorted cells.
 This was true back in the days of flooded
 batteries and especially true of RG devices
 today.
 'Shorting' requires motion . . . in the heyday
 of flooded batteries, active material 'pasted'
 into the cell grids was subject to degradation
 with age/abuse. Chunks would fall out of the
 plate and migrate into the wet space between
 plates. Most of the stuff would fall to a
 'sediment space' under the array of plates.
 Plates were EXPECTED to shed chunks of expended
 material so there was a 'basement' for storing
 the dead stuff.
Â
 But a battery left in service past its prime
 was subject to so much flaking of active
 material that adjacent plates could become
 electrically connected . . . i.e. 'shorted
 cell'
 An RG battery is a different breed of cat
 all together. Separators between cells
 is a pretty tough but thin, porous
 plastic or fiber. The plates are compacted
 with significant force before being
 inserted into the battery case.
 For 'motion' to occur in these devices,
 requires severe degradation of the
 cell's active materials. This happens
 when the battery has been allowed to
 self-destruct with age or when subjected
 to sustained over charging. Then you
 get swelling of the active material
 and risk of separator compromise.
 But even in extreme cases of AGM
 battery abuse, shorted cells are not
 a given. I've seen some pretty badly
 'puffed up' AGM batteries that were essentially
 destroyed but had presented no shorted
 cells.
 A battery removed from service in an aircraft
 at the appointed time in its life cycle is not
 going to exhibit effects of severe ageing or
 abuse.
 Bob . . .
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Tim Olson
Joined: 25 Jan 2007
Posts: 2870
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| Posted: Thu Jun 11, 2020 5:48 am Post subject: Shorted cell risk? |
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I wouldn't make that assumption to "most". There are plenty of people using
both AGM and LiPo batteries. I know many of both, and many of both types
of alternators as well. So blanket statements don't really apply, but I do
agree that it would be nice to see architecture that covers both types of
alternators.
Tim
On 6/11/2020 8:27 AM, Ken Ryan wrote:
| Quote: | What is an RG battery? Without trying to continue mudding the waters, I would venture to say that most builders these days who are using an auto conversion engine not only have a single, internally regulated alternator, they are also probably running LiPo batteries. Does this apply to LiPo batteries as well? All of the experimentals that I am personally familiar (eight or ten) are now using LiPo batteries.
On Thu, Jun 11, 2020 at 5:20 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 06:05 PM 6/10/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>
Bob, if two batteries are connected in parallel and one of the batteries
develops a shorted cell, will the good battery discharge into the bad battery?
If yes, would the rate of discharge be significant enough to quickly reduce
the good battery voltage to that of the bad battery?
Thanks
--------
Joe Gores |
 A maintained battery doesn't get shorted cells.
 This was true back in the days of flooded
 batteries and especially true of RG devices
 today.
 'Shorting' requires motion . . . in the heyday
 of flooded batteries, active material 'pasted'
 into the cell grids was subject to degradation
 with age/abuse. Chunks would fall out of the
 plate and migrate into the wet space between
 plates. Most of the stuff would fall to a
 'sediment space' under the array of plates.
 Plates were EXPECTED to shed chunks of expended
 material so there was a 'basement' for storing
 the dead stuff.
Â
 But a battery left in service past its prime
 was subject to so much flaking of active
 material that adjacent plates could become
 electrically connected . . . i.e. 'shorted
 cell'
 An RG battery is a different breed of cat
 all together. Separators between cells
 is a pretty tough but thin, porous
 plastic or fiber. The plates are compacted
 with significant force before being
 inserted into the battery case.
 For 'motion' to occur in these devices,
 requires severe degradation of the
 cell's active materials. This happens
 when the battery has been allowed to
 self-destruct with age or when subjected
 to sustained over charging. Then you
 get swelling of the active material
 and risk of separator compromise.
 But even in extreme cases of AGM
 battery abuse, shorted cells are not
 a given. I've seen some pretty badly
 'puffed up' AGM batteries that were essentially
 destroyed but had presented no shorted
 cells.
 A battery removed from service in an aircraft
 at the appointed time in its life cycle is not
 going to exhibit effects of severe ageing or
 abuse.
 Bob . . .
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Thu Jun 11, 2020 11:45 am Post subject: Shorted cell risk? |
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At 08:27 AM 6/11/2020, you wrote:
| Quote: | | What is an RG battery? |
Sorry . . . recombinant gas (RG) also known as absorbed glass mat (AGM)
and valve regulated sealed lead acid (VRLA) and starved electrolyte
cells. Lots of ways to describe the same technology.
| Quote: | Without trying to continue mudding the waters, I would venture to say that most
builders these days who are using an auto conversion engine not only have a
single, internally regulated alternator, they are also probably running LiPo
batteries. |
Hmmm . . . 'most'?
| Quote: | Does this apply to LiPo batteries as well? All of the experimentals
that I am personally familiar (eight or ten) are now using LiPo batteries. |
As to cell shorting . . . we're told that
lithium related fires are initiated by short
circuiting the cell. In the 787 batteries,
the shorts were internal. Given their energy
density, the aftermath of a cell-short is
almost guaranteed to be spectacular.
The LiPoFe technology seems most sensitive
to electrical abuse . . . a condition that
gave impetus to rather elaborate battery
management systems being folded into
'holy watered' products.
I've been playing with my new West Mountain Radio
battery analyzer. Did a constellation of deep
discharge tests on some 18650 cells. I'll take
a few of them down to zero . . . let them set
for a day or so and then see what happens to
their demonstrated capacity.
Bob . . .
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kenryan
Joined: 20 Oct 2009
Posts: 424
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| Posted: Thu Jun 11, 2020 12:58 pm Post subject: Shorted cell risk? |
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| Quote: |
 Hmmm . . . 'most'?Â
|
I can only speak to my experience. I am personally familiar with 5 SuperSTOLs, 1 Highlander, 2 Zeniths and 1 Rans. Every one has ditched lead acid for LiPo. Of course these are all Light Sport Aircraft and weight is a big concern when max gross is 1320. I would guess LiPo has not been as widely adopted in larger aircraft with more weight to play with.
Ken
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jan_de_jong(at)casema.nl
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| Posted: Thu Jun 11, 2020 1:37 pm Post subject: Shorted cell risk? |
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Dear all,
Better not confuse LiPo with LiFePO4 (also called LFP). Important
differences.
A search with both terms will lead to some clarity I expect.
Cheers,
Jan de Jong
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yellowduckduo(at)gmail.co
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| Posted: Thu Jun 11, 2020 2:28 pm Post subject: Shorted cell risk? |
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Opposite experience for me with only one out of six familiar local
aircraft using Lithium. With the relatively economical older aircraft
in my neighborhood that I'm not familiar with I'd be very surprised if
even one out of 10 has converted.
Ken L
On 11/06/2020 4:43 PM, Ken Ryan wrote:
| Quote: |
 Hmmm . . . 'most'?
I can only speak to my experience. I am personally familiar with 5
SuperSTOLs, 1 Highlander, 2 Zeniths and 1 Rans. Every one has ditched
lead acid for LiPo. Of course these are all Light Sport Aircraft and
weight is a big concern when max gross is 1320. I would guess LiPo has
not been as widely adopted in larger aircraft with more weight to play
with.
Ken
|
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