NIMH Cells Zero Volts Shorts Whiskers

[Wild_Bill]

For years, I've read that nicad cells develop shorts from crystalline(?)
whisker growth penetrating the insulating layer. I've encountered many of
'em.

Do NIMH cells develop the same faults? I realize the Ni represents nickel.

I acquired a used 14.4V NIMH battery pack and the voltage is maybe 35mV for
the entire pack. It's relatively difficult to open the pack case (have
already done an identical pack), but I suppose I'll end up doing that.

There's no indication of the pack's age, although it was military surplus,
and could be as old as about ten years.
The battery pack is for a Xenonics NightHunter II short arc long range
flashlight, as mentioned in some of my earlier posts.

Still haven't found a source for the 4/3-A NIMH 4000mAh cells with a length
of only 63mm (normal consumer cells are about 67mm in length).

--
Cheers,
WB
..............

 

[Jeff Liebermann]

On Thu, 4 Jul 2013 15:33:50 -0400, "Wild_Bill"
<wb_wildbill@XSPAMyahoo.com> wrote:

For years, I've read that nicad cells develop shorts from crystalline(?)
whisker growth penetrating the insulating layer. I've encountered many of
'em.

Mee Too. However, I usually see them with one shorted cell in the
pack, not an entire pack of shorted cells as you seem to have found.

Do NIMH cells develop the same faults? I realize the Ni represents nickel.

I don't think so. Here's my logic.

The positive electrodes are identical in NiCd and NiMH. The whiskers
come from the cadmium in the negative side of the NiCd cell. The NiMH
negative electrode is an alloy of various rare earths known as AB2 and
AB5 alloys. AB5 is LaNi5 and AB2 is TiN2. Neither alloy is known to
produce whiskers. For example, I could find no mention of whiskers in
the military study of NiMH batteries, which seems cover everything
else:
<http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA320764>

I acquired a used 14.4V NIMH battery pack and the voltage is maybe 35mV for
the entire pack. It's relatively difficult to open the pack case (have
already done an identical pack), but I suppose I'll end up doing that.

Don't you find it odd that the entire battery pack would
simultaneously develope whiskers at the same time?

There's no indication of the pack's age, although it was military surplus,
and could be as old as about ten years.
The battery pack is for a Xenonics NightHunter II short arc long range
flashlight, as mentioned in some of my earlier posts.

Still haven't found a source for the 4/3-A NIMH 4000mAh cells with a length
of only 63mm (normal consumer cells are about 67mm in length).

Sorry... I don't have a source. Also, are you SURE that they're NiMH
and not NiZn? Count the cells:
<http://en.wikipedia.org/wiki/Nizn>
With 0.4V per cell more than NiCd, no toxic substances, high peak
current, and the ability to run them down to zero, there are
advantages to using NiZn.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[William Sommerwerck]

For years, I've read that nicad cells develop shorts from
crystalline (?) whisker growth penetrating the insulating layer.
I've encountered many of 'em.

A recommended repair at one time was to open the cell, pull out the center
electrode, then re-insert.

As I write that, I'm aware of just how stupid it sounds. But I remember
reading it. (Of course, that doesn't prove it actually worked.)

 

[Wild_Bill]

Thanks, Jeff.. the packs are marked NIMH and 4.1Ah. There are 12 cells in
each pack. The size of the 4/3-A cells is about 18mm dia x 63.
NICD cells are limited to lower capacities.

The Wiki write-up states the NiZN are only available as sub-C and common AA,
AAA etc.
I dunno what the NiZN capacities are, but it would be interesting to see
greater energy density than NIMH.
And then there would be the need for different chargers.

I've seen NICD packs which had all cells shorted, typically a flea market
item that had probably been sitting around unused for years.

This is my first discovery of DTADN deader-than-a-door-nail NIMH cells.

--
Cheers,
WB
..............


"Jeff Liebermann" <jeffl@cruzio.com> wrote in message
news:67obt8109i4vha9pjggaj4clrhoedb13gg@4ax.com...

On Thu, 4 Jul 2013 15:33:50 -0400, "Wild_Bill"
wb_wildbill@XSPAMyahoo.com> wrote:

For years, I've read that nicad cells develop shorts from crystalline(?)
whisker growth penetrating the insulating layer. I've encountered many of
'em.

Mee Too. However, I usually see them with one shorted cell in the
pack, not an entire pack of shorted cells as you seem to have found.

Do NIMH cells develop the same faults? I realize the Ni represents nickel.

I don't think so. Here's my logic.

The positive electrodes are identical in NiCd and NiMH. The whiskers
come from the cadmium in the negative side of the NiCd cell. The NiMH
negative electrode is an alloy of various rare earths known as AB2 and
AB5 alloys. AB5 is LaNi5 and AB2 is TiN2. Neither alloy is known to
produce whiskers. For example, I could find no mention of whiskers in
the military study of NiMH batteries, which seems cover everything
else:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA320764

I acquired a used 14.4V NIMH battery pack and the voltage is maybe 35mV
for
the entire pack. It's relatively difficult to open the pack case (have
already done an identical pack), but I suppose I'll end up doing that.

Don't you find it odd that the entire battery pack would
simultaneously develope whiskers at the same time?

There's no indication of the pack's age, although it was military surplus,
and could be as old as about ten years.
The battery pack is for a Xenonics NightHunter II short arc long range
flashlight, as mentioned in some of my earlier posts.

Still haven't found a source for the 4/3-A NIMH 4000mAh cells with a
length
of only 63mm (normal consumer cells are about 67mm in length).

Sorry... I don't have a source. Also, are you SURE that they're NiMH
and not NiZn? Count the cells:
http://en.wikipedia.org/wiki/Nizn
With 0.4V per cell more than NiCd, no toxic substances, high peak
current, and the ability to run them down to zero, there are
advantages to using NiZn.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Thu, 4 Jul 2013 22:29:23 -0400, "Wild_Bill"
<wb_wildbill@XSPAMyahoo.com> wrote:

Thanks, Jeff.. the packs are marked NIMH and 4.1Ah. There are 12 cells in
each pack. The size of the 4/3-A cells is about 18mm dia x 63.
NICD cells are limited to lower capacities.

That would be an 18630 cell.
I couldn't find anything in NiMH in size 18630 or nearby lengths.
The closest is an A battery at 17x50mm.
<https://en.wikipedia.org/wiki/List_of_battery_sizes#Round_single-cell>
Random source of NiMH in A battery size:
<http://www.batteryspace.com/nimhrechargeablecellasize12v2700mah1pc.aspx>
At least it will fit, although it's 13mm short and only 2.7A-hr
instead of 4.1A-hr.

I don't really believe the 4.1A-hr claim. Maybe at extremely low
discharge rates, but not a anything near 1C. For example, the size A
battery above is speced at 2.7A-hr at 1C discharge rate:
<http://www.batteryspace.com/prod-specs/SPEC_OF_NR50A2700P1%5B1%5D.2V.pdf.

The Wiki write-up states the NiZN are only available as sub-C and common AA,
AAA etc.

Looks like D cells are also available:
<http://image.made-in-china.com/2f0j00wBmTneYqGFol/Ni-Zn-Battery-1-6V2000mAh-SC-Battery-AA-AAA-SC-.jpg>
I've only seen a few of them and was rather surprised at the 1.6v
terminal voltage. I didn't believe that I could discharge these
batteries to zero, and not destroy them, so I tried it. No problem
(but I only tested one old cell). Shorting the terminals on a NiMH
cell is guaranteed destruction of the cell.

I dunno what the NiZN capacities are, but it would be interesting to see
greater energy density than NIMH.
And then there would be the need for different chargers.

Yep. Fortunately, they're are chargers for sale on eBay:
<http://www.ebay.com/itm/150890715550>
I'm tempted to buy some cells and a charger to see how they play.

I've seen NICD packs which had all cells shorted, typically a flea market
item that had probably been sitting around unused for years.

This is my first discovery of DTADN deader-than-a-door-nail NIMH cells.

That agrees with my observations. I think (not sure) that I can make
an NiMH pack hit zero if I short the terminals and leave them shorted.
If I can find some old cells, I'll give it a try. Destroying
batteries is so much fun.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Wild_Bill]

I've spent more time than I'd like to admit, looking for the high capacity
4/3-A NIMH cells, and the too-long 67mm length was all I could find.

Yep, battery specs are a bit mystic (intentionally it seems) as there can be
a rated capacity and then a slightly higher average or nominal capacity.

The cells in the pack I opened previously were marked with a somewhat
standard number on the metal shell, NT410LAH.. no brand or other info on the
skins which is typical for commercial/industrial cells, but you knew that.
That number is similar to a GC industrial cell number.

This dead NIMH pack may have had the terminals shorted at one time, it's
used so anything's possible.

I recall seeing a couple of components in images of rechargeable cells
(Duracell, maybe) that are built-in to prevent destruction by shorting
and/or charging at an excessive rate, (although they may not provide
protection on a cells which were aleady partially discharged from normal
use).
I'm thinking those components are a thermistor and a poly-fuse (possibly a
3rd component), and had suspected that these military cells are shorter
because those items were left out, since they absolutely wouldn't be used in
consumer applications, thus liability protection not being needed.. just
speculation.

--
Cheers,
WB
..............


"Jeff Liebermann" <jeffl@cruzio.com> wrote in message
news6ict81jsf3c5ibt6e3s642s40f63ugdhm@4ax.com...

On Thu, 4 Jul 2013 22:29:23 -0400, "Wild_Bill"
wb_wildbill@XSPAMyahoo.com> wrote:

Thanks, Jeff.. the packs are marked NIMH and 4.1Ah. There are 12 cells in
each pack. The size of the 4/3-A cells is about 18mm dia x 63.
NICD cells are limited to lower capacities.

That would be an 18630 cell.
I couldn't find anything in NiMH in size 18630 or nearby lengths.
The closest is an A battery at 17x50mm.
https://en.wikipedia.org/wiki/List_of_battery_sizes#Round_single-cell
Random source of NiMH in A battery size:
http://www.batteryspace.com/nimhrechargeablecellasize12v2700mah1pc.aspx
At least it will fit, although it's 13mm short and only 2.7A-hr
instead of 4.1A-hr.

I don't really believe the 4.1A-hr claim. Maybe at extremely low
discharge rates, but not a anything near 1C. For example, the size A
battery above is speced at 2.7A-hr at 1C discharge rate:
http://www.batteryspace.com/prod-specs/SPEC_OF_NR50A2700P1%5B1%5D.2V.pdf.

The Wiki write-up states the NiZN are only available as sub-C and common
AA,
AAA etc.

Looks like D cells are also available:
http://image.made-in-china.com/2f0j00wBmTneYqGFol/Ni-Zn-Battery-1-6V2000mAh-SC-Battery-AA-AAA-SC-.jpg
I've only seen a few of them and was rather surprised at the 1.6v
terminal voltage. I didn't believe that I could discharge these
batteries to zero, and not destroy them, so I tried it. No problem
(but I only tested one old cell). Shorting the terminals on a NiMH
cell is guaranteed destruction of the cell.

I dunno what the NiZN capacities are, but it would be interesting to see
greater energy density than NIMH.
And then there would be the need for different chargers.

Yep. Fortunately, they're are chargers for sale on eBay:
http://www.ebay.com/itm/150890715550
I'm tempted to buy some cells and a charger to see how they play.

I've seen NICD packs which had all cells shorted, typically a flea market
item that had probably been sitting around unused for years.

This is my first discovery of DTADN deader-than-a-door-nail NIMH cells.

That agrees with my observations. I think (not sure) that I can make
an NiMH pack hit zero if I short the terminals and leave them shorted.
If I can find some old cells, I'll give it a try. Destroying
batteries is so much fun.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Wild_Bill]

Yep, Matt.. there are some strange testing procedures for rechargeable
cells.

I've read numerous datasheets, and they may do a specific test for the first
50 recharges, then change the parameters for later test cycles. I guess that
means something to someone who specs cells.

The 4/3-A cells aren't popular like the other sizes used in the RC hobby,
and there aren't many suppliers that sell the high capacity cells.

I could modify the flashlight battery space although it's not just a matter
of trimming away some plastic, as it generally would be in a consumer grade
device.
The 67mm length cells are about 1/4" too long to fit in the original battery
pack plastic case, so I'd need to fabricate cases too.. still, not extremely
difficult, but quite a bit of trouble for a light that uses a $450 lamp.

Alternatively, these lights have a power cord connector on them, so using a
corded battery pack which hooks onto a waistband or pocket would be an
option.

--
Cheers,
WB
..............


<mroberds@att.net> wrote in message news:kr6ao2$q62$1@dont-email.me...

Jeff Liebermann <jeffl@cruzio.com> wrote:
On Thu, 4 Jul 2013 22:29:23 -0400, "Wild_Bill"
wb_wildbill@XSPAMyahoo.com> wrote:

Thanks, Jeff.. the packs are marked NIMH and 4.1Ah. There are 12
cells in each pack. The size of the 4/3-A cells is about 18mm dia
x 63.

You might have already been pointed at powerstream.com , but the 4/3-A
batteries they have are all 67 mm. They seem to have some kind of
relationship with a manufacturer in China, so if you want to order a
bunch of the 60 mm cells, they may be able to have them made.

I think (not sure) that I can make an NiMH pack hit zero if I short
the terminals and leave them shorted. If I can find some old cells,
I'll give it a try.

One manufacturer of sealed lead-acid batteries refers to a "DIN
overdischarge recovery test". They don't mention the DIN standard
number, but the procedure is apparently:

1. Discharge at 20 hour rate to 1.70 volts per cell.
2. Connect 5 ohm resistor across battery and leave it there for 28 days.
3. Remove resistor, recharge at a constant 2.25 volts per cell for 48
hours.
4. Capacity test.

(See page 12 of
http://www.odysseybattery.com/documents/US-GPL-AM-003_0906.pdf ).
Obviously some of the numbers would be different for NiMH, NiCD, or
other chemistries.

A hit from another battery manufacturer suggests that the relevant
standard might be DIN 43539. This has apparently been superseded by
both DIN EN 60896-1 and DIN EN 60896-2. All of these standards are
secrets.

Standard disclaimers apply; I don't get money or other consideration
from any companies mentioned.

Matt Roberds

 

Jeff Liebermann <jeffl@cruzio.com> wrote:

On Thu, 4 Jul 2013 22:29:23 -0400, "Wild_Bill"
wb_wildbill@XSPAMyahoo.com> wrote:

Thanks, Jeff.. the packs are marked NIMH and 4.1Ah. There are 12
cells in each pack. The size of the 4/3-A cells is about 18mm dia
x 63.

You might have already been pointed at powerstream.com , but the 4/3-A
batteries they have are all 67 mm. They seem to have some kind of
relationship with a manufacturer in China, so if you want to order a
bunch of the 60 mm cells, they may be able to have them made.

I think (not sure) that I can make an NiMH pack hit zero if I short
the terminals and leave them shorted. If I can find some old cells,
I'll give it a try.

One manufacturer of sealed lead-acid batteries refers to a "DIN
overdischarge recovery test". They don't mention the DIN standard
number, but the procedure is apparently:

1. Discharge at 20 hour rate to 1.70 volts per cell.
2. Connect 5 ohm resistor across battery and leave it there for 28 days.
3. Remove resistor, recharge at a constant 2.25 volts per cell for 48
hours.
4. Capacity test.

(See page 12 of
http://www.odysseybattery.com/documents/US-GPL-AM-003_0906.pdf ).
Obviously some of the numbers would be different for NiMH, NiCD, or
other chemistries.

A hit from another battery manufacturer suggests that the relevant
standard might be DIN 43539. This has apparently been superseded by
both DIN EN 60896-1 and DIN EN 60896-2. All of these standards are
secrets.

Standard disclaimers apply; I don't get money or other consideration
from any companies mentioned.

Matt Roberds

 

[Jeff Liebermann]

On Fri, 5 Jul 2013 08:21:45 -0400, "Wild_Bill"
<wb_wildbill@XSPAMyahoo.com> wrote:

I've spent more time than I'd like to admit, looking for the high capacity
4/3-A NIMH cells, and the too-long 67mm length was all I could find.

Well, there's nothing wrong (in my opinion) using the too short A
battery size cells.

Yep, battery specs are a bit mystic (intentionally it seems) as there can be
a rated capacity and then a slightly higher average or nominal capacity.

The specs seem to have been written by battery manufacturers looking
for very high numbers to make their products look better. I normally
use high discharge rate cells at ummm.... high discharge rates. Yet
many of the capacity tests are done at C/20 or less, resulting in
highly inflated numbers. All I can suggest is try to find the data
sheet and determine how a cell was tested before accepting the number
printed on the garish shrink-wrap coverings.

The cells in the pack I opened previously were marked with a somewhat
standard number on the metal shell, NT410LAH.. no brand or other info on the
skins which is typical for commercial/industrial cells, but you knew that.
That number is similar to a GC industrial cell number.

This dead NIMH pack may have had the terminals shorted at one time, it's
used so anything's possible.

I recall seeing a couple of components in images of rechargeable cells
(Duracell, maybe) that are built-in to prevent destruction by shorting
and/or charging at an excessive rate, (although they may not provide
protection on a cells which were aleady partially discharged from normal
use).

You may be thinking of the common LiIon 18650 cell, which has a disk
shaped PCB on the negative terminal end to protect the cell.
<https://www.google.com/search?tbm=isch&q=18650+protection+circuit>

Diversion: I just love the names given to the various 18650 batteries
such as Trustfire, Truefire, Ultrafire, Fireworm, Marsfire, etc.
Somehow, such names fail to inspire confidence in the safety of their
products.

I'm thinking those components are a thermistor and a poly-fuse (possibly a
3rd component), and had suspected that these military cells are shorter
because those items were left out, since they absolutely wouldn't be used in
consumer applications, thus liability protection not being needed.. just
speculation.

I've never seen any per-cell protection on a NiCd or NiMH battery or
pack. There are some PCB's found in radio battery packs that are
coulomb counters, but I don't think there are any that offer short
circuit protection for the individual cells.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Robert Roland]

On Thu, 4 Jul 2013 15:33:50 -0400, "Wild_Bill"
<wb_wildbill@XSPAMyahoo.com> wrote:

a used 14.4V NIMH battery pack

That voltage is perfect for lithium conversion. 3S LiPo is 14.8V
nominal.

Even if you can't effectively make use of the space, you might still
get close to the original capacity, but at much less weight.
--
RoRo

 

[Phoena]

On 07/04/2013 09:15 PM, Jeff Liebermann wrote:

On Thu, 4 Jul 2013 15:33:50 -0400, "Wild_Bill"
wb_wildbill@XSPAMyahoo.com> wrote:

For years, I've read that nicad cells develop shorts from crystalline(?)
whisker growth penetrating the insulating layer. I've encountered many of
'em.

Mee Too. However, I usually see them with one shorted cell in the
pack, not an entire pack of shorted cells as you seem to have found.

Do NIMH cells develop the same faults? I realize the Ni represents nickel.

I don't think so. Here's my logic.

The positive electrodes are identical in NiCd and NiMH. The whiskers
come from the cadmium in the negative side of the NiCd cell. The NiMH
negative electrode is an alloy of various rare earths known as AB2 and
AB5 alloys. AB5 is LaNi5 and AB2 is TiN2. Neither alloy is known to
produce whiskers. For example, I could find no mention of whiskers in
the military study of NiMH batteries, which seems cover everything
else:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA320764

I acquired a used 14.4V NIMH battery pack and the voltage is maybe 35mV for
the entire pack. It's relatively difficult to open the pack case (have
already done an identical pack), but I suppose I'll end up doing that.

Don't you find it odd that the entire battery pack would
simultaneously develope whiskers at the same time?

There's no indication of the pack's age, although it was military surplus,
and could be as old as about ten years.
The battery pack is for a Xenonics NightHunter II short arc long range
flashlight, as mentioned in some of my earlier posts.

Still haven't found a source for the 4/3-A NIMH 4000mAh cells with a length
of only 63mm (normal consumer cells are about 67mm in length).

Sorry... I don't have a source. Also, are you SURE that they're NiMH
and not NiZn? Count the cells:
http://en.wikipedia.org/wiki/Nizn
With 0.4V per cell more than NiCd, no toxic substances, high peak
current, and the ability to run them down to zero, there are
advantages to using NiZn.

HEY DIPSHIT LIEBERMANN

HOW WOULD YOU LIKE TO BE A PROUD OWNER OF A STYROFOAM MCDONALDS
FILET-O-FISH CONTAINER?

http://www.ebay.com/itm/McDonalds-Filet-O-Fish-Styrofoam-Container-/231010730591?pt=LH_DefaultDomain_0&hash=item35c950025f

 

[hrhofmann@sbcglobal.net]

On Thursday, July 4, 2013 2:33:50 PM UTC-5, Wild_Bill wrote:

For years, I've read that nicad cells develop shorts from crystalline(?) whisker growth penetrating the insulating layer. I've encountered many of 'em. Do NIMH cells develop the same faults? I realize the Ni represents nickel. I acquired a used 14.4V NIMH battery pack and the voltage is maybe 35mV for the entire pack. It's relatively difficult to open the pack case (have already done an identical pack), but I suppose I'll end up doing that. There's no indication of the pack's age, although it was military surplus, and could be as old as about ten years. The battery pack is for a Xenonics NightHunter II short arc long range flashlight, as mentioned in some of my earlier posts. Still haven't found a source for the 4/3-A NIMH 4000mAh cells with a length of only 63mm (normal consumer cells are about 67mm in length). -- Cheers, WB .............

I would try to burn the apparent shorts open by putting the power pack across a 12V battery, being carefule to avoid melting wires burning something up. Nothing really to lose, as long as the 12V source battery can take a momentary high-short-circuit load. I would sort of brush one lead across the source battery a few times while monitoring the powerpack voltage, and see if it comes up at all as you brush the clip lead onto the 12V source battery. Really do exactly the same as you would for a NiCad battery pack short..

 

[William Sommerwerck]

I recently suggested opening the cell, pulling out the anode, then reinserting
it.

No one has commented on this, possibly because it seems absurd. But I remember
reading it in the PPC calculator journal over 30 years ago.

 

[Rich Webb]

On Wed, 10 Jul 2013 06:28:36 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net> wrote:

I recently suggested opening the cell, pulling out the anode, then reinserting
it.

No one has commented on this, possibly because it seems absurd. But I remember
reading it in the PPC calculator journal over 30 years ago.

For mechanical palliation of the whiskers, what about a small paint
shaker, such as
<http://www.micromark.com/paint-shaker-120v-ac,6781.html>

I've never tried it (for batteries) but maybe it would work. Beats
prying open the cell casing.

 

[Wild_Bill]

Thanks.. that seems to be a fairly popular although fairly desperate easy
fix-it method for nicad cells.
If I were to try this method, I'd use a safety barrier of some sort between
the batteries and myself, as the results could be unpredictable.

I might try this after I open the pack case to see if there are other
issues, leaking, etc.

I was more curious about anyone's knowledge of the whisker/short failure
mode in NIMH cells, because I didn't remember hearing about it, and thought
that I'd read that this would not be a failure mode in NIMH cells.

In this instance replacing the cells, which would be my usual choice, isn't
easily accomplished unless I can find a source for the 63mm length cells.

--
Cheers,
WB
..............


<hrhofmann@sbcglobal.net> wrote in message
news:3a2dce52-f779-4b26-90ea-6ea91eed3f44@googlegroups.com...
On Thursday, July 4, 2013 2:33:50 PM UTC-5, Wild_Bill wrote:

For years, I've read that nicad cells develop shorts from crystalline(?)
whisker >growth penetrating the insulating layer. I've encountered many of
'em. Do NIMH >cells develop the same faults?

I would try to burn the apparent shorts open by putting the power pack
across a 12V battery, being carefule to avoid melting wires burning
something up. Nothing really to lose, as long as the 12V source battery can
take a momentary high-short-circuit load. I would sort of brush one lead
across the source battery a few times while monitoring the powerpack
voltage, and see if it comes up at all as you brush the clip lead onto the
12V source battery. Really do exactly the same as you would for a NiCad
battery pack short.

 

[Wild_Bill]

Often, the battery pack cases include insulator material for mechanical
shock, so 'percussive maintenance' with the cells still inside the case
might be complicated.

These particular packs use silicone glue and the thin DST double sided tape
(the membrane type) to hold the cells in place within the packs.

I dunno how severe the G-forces are for a paint shaker, but probably low
compared to some other relatively common machines.
I have some lab agitator mixers, but they're fairly mild compared to a
commercial paint mixer.

Your suggestion caused me to remember a small pneumatic tool (inline scraper
of sorts, nothing as severe as an autobody panel cutter) I saw years ago,
and fast, repeated mechanical shock may be a worthwhile experiment at least,
and may produce positive results.
I'm visualizing a heavy duty housing for an individual cell which holds the
cell securely, but prevents any physical deformation/damage to the cell
while transferring the forces. If the holder were subjected to rapid-fast
rise time mechanical shock(s), I would imagine that salt whiskers could be
persuaded to break, although any holes/penetrations in an internal separator
layer would likely still exist.

Another device happened to occur to me.. the armature in one of those
transformer-type motors such as the vibrating motor used in Wagner paint
applicators, hair clippers and a variety of other common devices.
If the cell were firmly attached to the vibrating armature, a sustained
buzzing vibration may be a worthwhile exercise.

--
Cheers,
WB
..............


"Rich Webb" <webb.ra@example.net> wrote in message
news:nqpqt8t54l4hokr0og8124al3qp5bopflm@4ax.com...

On Wed, 10 Jul 2013 06:28:36 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net> wrote:

I recently suggested opening the cell, pulling out the anode, then
reinserting
it.

No one has commented on this, possibly because it seems absurd. But I
remember
reading it in the PPC calculator journal over 30 years ago.

For mechanical palliation of the whiskers, what about a small paint
shaker, such as
http://www.micromark.com/paint-shaker-120v-ac,6781.html

I've never tried it (for batteries) but maybe it would work. Beats
prying open the cell casing.

 

[Wild_Bill]

Thanks for the suggestion. I don't have many devices which use lithium
chemistry batteries, so I'd prefer to utilize NIMH, which I already have
numerous universal, multi-voltage chargers for.

NIMH seem to be less problematic than others, and have high capacities in
compact sizes.. simple to recharge, and AC or DC (mobile/field) chargers are
inexpensive.

--
Cheers,
WB
..............


"Robert Roland" <fake@ddress.no> wrote in message
news:af4et8l9b8d63qcqicdd5ecqrmeevaa8sk@4ax.com...

On Thu, 4 Jul 2013 15:33:50 -0400, "Wild_Bill"
wb_wildbill@XSPAMyahoo.com> wrote:

a used 14.4V NIMH battery pack

That voltage is perfect for lithium conversion. 3S LiPo is 14.8V
nominal.

Even if you can't effectively make use of the space, you might still
get close to the original capacity, but at much less weight.
--
RoRo