Any nicad experts out there? This is an interesting one. (I'm not looking for
a "solution", just an explanation, out of curiosity.)

Many years ago I bought the Sony TCD-D3 DAT Walkman, which fits a fat pocket.
I made a few live recordings, as it was a lot less bulky than a processor/VCR
system.

The other day I pulled it out to confirm it was still working. I'd bought two
extra batteries with the unit, and put all three on charge. They all charged
up, but the third battery wouldn't power the unit. Its end-of-charge voltage
was nearly 7V (though these batteries are nominally 6V), and the other two
charged to about 6.4V.

When I put the third battery on charge again, it rose to about 7.5V, even
before charge was terminated. I let it sit overnight, and it self-discharged
(?) to about 5.5V. (The others //did not// show significant self-discharge.)
It still wouldn't power the unit.

"Obviously" this battery pack is defective. I'm just wondering if anyone knows
what's going on.

It's no big deal, as I have two good packs (which are 20+ years old!), and the
AC adapter. Also, the packs are "external", so I could (if I wanted) saw open
the pack and replace the cells. Or simply throw together a homebrew pack to
fit the DC jack.

Just askin'.


"We already know the answers -- we just haven't asked the right questions."
-- Edwin Land

William Sommerwerck wrote:
Any nicad experts out there? This is an interesting one. (I'm not
looking for a "solution", just an explanation, out of curiosity.)

Many years ago I bought the Sony TCD-D3 DAT Walkman, which fits a fat
pocket. I made a few live recordings, as it was a lot less bulky than
a processor/VCR system.

The other day I pulled it out to confirm it was still working. I'd
bought two extra batteries with the unit, and put all three on
charge. They all charged up, but the third battery wouldn't power the
unit. Its end-of-charge voltage was nearly 7V (though these batteries
are nominally 6V), and the other two charged to about 6.4V.

When I put the third battery on charge again, it rose to about 7.5V,
even before charge was terminated. I let it sit overnight, and it
self-discharged (?) to about 5.5V. (The others //did not// show
significant self-discharge.) It still wouldn't power the unit.

"Obviously" this battery pack is defective. I'm just wondering if
anyone knows what's going on.

It's no big deal, as I have two good packs (which are 20+ years
old!), and the AC adapter. Also, the packs are "external", so I could
(if I wanted) saw open the pack and replace the cells. Or simply
throw together a homebrew pack to fit the DC jack.

Just askin'.


"We already know the answers -- we just haven't asked the right
questions." -- Edwin Land

--

Nicads have historically been plagued by "dendrites", or crystals of
conductive material (probably cadmium, but not sure) between the electrolyte
layers in the cells. This creates a low resistance leakage path inside the
cells, rendering them incapable of retaining a charge for any length of time
or putting out their rated voltage. Dendrites are responsible for the
so-called "memory effect" that nicads are famous for.

There have been several procedures published on the net as to how to remove
dendrites (search for "nicad dendrites"). One process involves charging a
large electrolytic capacitor (eg., 500uF) to a few hundred volts,
discharging it through the bad cell, then running the cell through a couple
of charge/discharge cycles. I built a little box for this process several
years ago, and it seems to work. It consists of a transformer, a voltage
doubler, and a large capacitor. A push-button switch triggers an SCR that
lets the capacitor discharge into the bad cell (sort of like a one-shot CD
ignition)

Dave M

On Thu, 9 Jan 2014 11:46:15 -0600, "Dave M"
wrote:

William Sommerwerck wrote:
Any nicad experts out there? This is an interesting one. (I'm not
looking for a "solution", just an explanation, out of curiosity.)

Many years ago I bought the Sony TCD-D3 DAT Walkman, which fits a fat
pocket. I made a few live recordings, as it was a lot less bulky than
a processor/VCR system.

The other day I pulled it out to confirm it was still working. I'd
bought two extra batteries with the unit, and put all three on
charge. They all charged up, but the third battery wouldn't power the
unit. Its end-of-charge voltage was nearly 7V (though these batteries
are nominally 6V), and the other two charged to about 6.4V.

When I put the third battery on charge again, it rose to about 7.5V,
even before charge was terminated. I let it sit overnight, and it
self-discharged (?) to about 5.5V. (The others //did not// show
significant self-discharge.) It still wouldn't power the unit.

"Obviously" this battery pack is defective. I'm just wondering if
anyone knows what's going on.

It's no big deal, as I have two good packs (which are 20+ years
old!), and the AC adapter. Also, the packs are "external", so I could
(if I wanted) saw open the pack and replace the cells. Or simply
throw together a homebrew pack to fit the DC jack.

Just askin'.


"We already know the answers -- we just haven't asked the right
questions." -- Edwin Land
My son just did this, running high voltage spikes through some bad
nicads he had. And he said they now charge prpperly and hold a charge.
He's happy.
Eric

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"Dave M" wrote in message
...

Nicads have historically been plagued by "dendrites", or crystals of
conductive material (probably cadmium, but not sure) between the
electrolyte layers in the cells. This creates a low resistance leakage
path inside the cells, rendering them incapable of retaining a charge
for any length of time or putting out their rated voltage. Dendrites are
responsible for the so-called "memory effect" that nicads are famous for.

There have been several procedures published on the net as to how to
remove dendrites (search for "nicad dendrites"). One process involves
charging a large electrolytic capacitor (eg, 500uF) to a few hundred volts,
discharging it through the bad cell, then running the cell through a couple
of charge/discharge cycles.

I assume the discharge is + to +.


I built a little box for this process several years ago, and it seems to
work.
It consists of a transformer, a voltage doubler, and a large capacitor.
A push-button switch triggers an SCR that lets the capacitor discharge into
the bad cell (sort of like a one-shot CD ignition).


I'll give this serious thought. The worst that can happen is that the battery
is ruined. (!!!) Thanks.

I'm still curious about the battery's unnaturally high voltage.

On 1/9/2014 4:47 PM, William Sommerwerck wrote:
"Dave M" wrote in message
...

Nicads have historically been plagued by "dendrites", or crystals of
conductive material (probably cadmium, but not sure) between the
electrolyte layers in the cells. This creates a low resistance leakage
path inside the cells, rendering them incapable of retaining a charge
for any length of time or putting out their rated voltage. Dendrites are
responsible for the so-called "memory effect" that nicads are famous for.

There have been several procedures published on the net as to how to
remove dendrites (search for "nicad dendrites"). One process involves
charging a large electrolytic capacitor (eg, 500uF) to a few hundred
volts, discharging it through the bad cell, then running the cell
through a couple of charge/discharge cycles.

I assume the discharge is + to +.

I'd be careful. Energy is proportional to the square of the voltage.
I use 12,000 uF and 10-20V, mostly because that's what was handy.
You want to hit the sweet spot where you instantly vaporize the dendrite,
but generate no more heat than necessary. Too little energy or too
much energy is worse than just right. That's why suggestions to
use a car battery are bad. Little chance of getting it just right.
Way too much chance of getting enough energy to explode something.

500uF AND 200V is WAY too much.

The process leaves the hole in the insulator/separator.
The field density is high and the dendrite wants to grow back.
And discharge thru the hole causes the high self-discharge rate.

I've had a lot of success restoring 40 year old F-NiCd's for
uses that don't require more than a few days storage life.
But, these days, you can get equivalent capacity in a pair of
AA NiMH cells.

Don't discount the safety issues with high voltage.
The "experts" who look at only part of the problem will call me an idiot,
because 200V probably won't kill you.
Two problems with that..."probably" is great for statistics, but
provides little solace to your family when you're the ONE who died.
And B, the shock isn't the only problem.
I've got scars where the muscle contractions that thru me across the
room caused me to rip my arm open on some sharp object in the path.
Luckily, I haven't fallen and cracked my head open on the furniture...
yet...

Eye Protection is a MUST. Sparks fly.

I built a little box for this process several years ago, and it seems
to work.
It consists of a transformer, a voltage doubler, and a large capacitor.
A push-button switch triggers an SCR that lets the capacitor discharge
into
the bad cell (sort of like a one-shot CD ignition).


I'll give this serious thought. The worst that can happen is that the
battery is ruined. (!!!) Thanks.

I'm still curious about the battery's unnaturally high voltage.

William Sommerwerck wrote:
"Dave M" wrote in message
...


There have been several procedures published on the net as to how to
remove dendrites (search for "nicad dendrites"). One process involves
charging a large electrolytic capacitor (eg, 500uF) to a few hundred
volts, discharging it through the bad cell, then running the cell
through a couple of charge/discharge cycles.

I assume the discharge is + to +.


I built a little box for this process several years ago, and it
seems to work.
It consists of a transformer, a voltage doubler, and a large
capacitor. A push-button switch triggers an SCR that lets the capacitor
discharge into the bad cell (sort of like a one-shot CD ignition).


I'll give this serious thought. The worst that can happen is that the
battery is ruined. (!!!) Thanks.


Yes, + to + on the CD pulse and normal charge/discharge.

Dave M

"William Sommer****** "

When I put the third battery on charge again, it rose to about 7.5V, even
before charge was terminated. I let it sit overnight, and it
self-discharged (?) to about 5.5V. (The others //did not// show
significant self-discharge.) It still wouldn't power the unit.

"Obviously" this battery pack is defective. I'm just wondering if anyone
knows what's going on.


** You are describing the standard "old age" failure mode of most NiCds.

1. The internal resistance of some or all the cells in a pack rises - often
dramatically.

2. The energy capacity drops by a large factor.

3. The pack will not hold charge due to internal leakage.

4. The terminal voltage is depressed, from 1.25V to about 1.2V per cell.

A single overheating event can result in the same outcome - whether by
overcharging or otherwise.

Reason ?

NiCd cells have a small amount of water in them - lose that and the cell is
stuffed.



.... Phil

"Phil Allison"


4. The terminal voltage is depressed, from 1.25V to about 1.1V per cell.


.... Phil

Fine. Nothing new. But why the high voltage?

"William Sommer****** the Over Snipper form HELL "

Fine. Nothing new.


** All new to YOU ****head.

But why the high voltage?


** When on charge - point 1 applies.

Cease charge the pack and the voltage drops almost immediately.

V = I x R ..........

Wot an idiot.



..... Phil

"Phil Allison" wrote in message ...

Fine. Nothing new.

** All new to YOU, ****head.

I've killed men for less than that.

I wasn't expecting you to repeat common knowledge about rechargeable
batteries.


But why the high voltage?

** When on charge - point 1 applies.
** Cease charge the pack and the voltage drops almost immediately.
** V = I x R ..........
** Wot an idiot.

You don't see it, do you? Of course not.

The same thought crossed my mind. The question is... why should a cell's
voltage -- which is supposedly determined by the battery's chemistry --
essentially double (assuming only one cell is bad)? Why should the cell become
a sort of electrochemical chameleon, trying to match the voltage across it?

"William Sommer******"


Fine. Nothing new.

** All new to YOU, ****head.

I've killed men for less than that.

** Another idiotic lie.

I wasn't expecting you to repeat common knowledge about rechargeable
batteries.

** And I didn't.

To your claim of "odd battery problem" - I replied:
--------------------------------------------------------------------------------

You are describing the standard "old age" failure mode of most NiCds.

1. The internal resistance of some or all the cells in a pack rises - often
dramatically.

2. The energy capacity drops by a large factor.

3. The pack will not hold charge due to internal leakage.

4. The terminal voltage is depressed, from 1.25V to about 1.2V per cell.

A single overheating event can result in the same outcome - whether by
overcharging or otherwise.

Reason ?

NiCd cells have a small amount of water in them - lose that and the cell is
stuffed.

------------------------------------------------------------------------------------

** The above is NOT common knowledge and is ONLY true of NiCd cells.



But why the high voltage?

** When on charge - point 1 applies.
** Cease charge the pack and the voltage drops almost immediately.
** V = I x R ..........
** Wot an idiot.

You don't see it, do you? Of course not.


** There is nothing new or "odd" to see.


The same thought crossed my mind. The question is... why should a cell's
voltage -- which is supposedly determined by the battery's chemistry --
essentially double (assuming only one cell is bad)?

** You never put that ******ing mad idea** forward before ??????

Not only do you over snip and change context at whim - now invent entirely
new stuff and pretend it is not new.

FYI ****wit:

YOU claimed to have three 6V NiCd packs - means 5 cells in each.

So the normal, rest voltage is 1.25V x 5 = 6.25V

On charge, with good cells and at the recommended rate, voltage peaks to
about 1.45V then falls to about 1.35V per cell.

That means the pack will rise to 7.25V then fall to 6.75V as the cells get
warm.

If the cells are old and bad, the voltage will rise higher and may never
fall while on charge.

At rest the same faulty pack may well drop to a 1.1V per cell = 5.5V.

This correlates with your story, 100%.

Nothing odd, totally normal.

Shame the same is NOT true of steaming great ****wits like YOU !!!!!!!!!!




.... Phil

I attacked the "bad" Sony battery pack with a Dremel-powered cutoff disk. It
was stuffed with five huge prism cells, each measuring 3 x 7/8 x 1/4. At least
two of them appeared to have excessively low voltage.

I have no intention of trying to restore or replace these cells, especially as
they aren't interconnected in the way you'd expect.

The question remains... As nicads and NiMH cells are charged by constant
current (theoretically, anyway), what would cause the total post-charge
voltage to hit nearly eight volts?

On 01/11/2014 12:49 PM, William Sommerwerck wrote:
I attacked the "bad" Sony battery pack with a Dremel-powered cutoff
disk. It was stuffed with five huge prism cells, each measuring 3 x 7/8
x 1/4. At least two of them appeared to have excessively low voltage.

I have no intention of trying to restore or replace these cells,
especially as they aren't interconnected in the way you'd expect.

The question remains... As nicads and NiMH cells are charged by constant
current (theoretically, anyway), what would cause the total post-charge
voltage to hit nearly eight volts?

I'm no expert, but why not ask you question he

http://batteryuniversity.com/learn/a...ased_batteries

I've used this site for years when I want to figure out something
battery related...

John :-#)#

--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

"John Robertson" wrote in message
...

I'm no expert, but why not ask your question he

http://batteryuniversity.com/learn/a...ased_batteries

Why not? Thanks.