I have noticed that the chargers for rechargeable batteries invariably stop
charging the AA and AAA when they are fully charged and the on charge light
goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and you are
just told to charge them for a certain time - no light going out when they are
full.

Why is this there difference?

On 06/12/2016 13:43, Right said Fred wrote:


I have noticed that the chargers for rechargeable batteries invariably stop
charging the AA and AAA when they are fully charged and the on charge light
goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and you are
just told to charge them for a certain time - no light going out when they are
full.

Why is this there difference?

Crap charger.

Mike

Right said Fred wrote:


I have noticed that the chargers for rechargeable batteries invariably stop
charging the AA and AAA when they are fully charged and the on charge light
goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and you are
just told to charge them for a certain time - no light going out when they are
full.

Why is this there difference?


Because the 9v batteries are a set of cells in series so the normal
methods of detecting full charge do not apply (individual cells may be
in a different state of charge). Hence the instruction to slow charge
for a minimum interval that ensures that all cells are fully charged at
a charge rate that is low enough not to damage through over-charge.

Chris K

On 06/12/2016 15:02, ChrisK wrote:
Right said Fred wrote:


I have noticed that the chargers for rechargeable batteries invariably
stop
charging the AA and AAA when they are fully charged and the on charge
light
goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and
you are
just told to charge them for a certain time - no light going out when
they are
full.

Why is this there difference?


Because the 9v batteries are a set of cells in series so the normal
methods of detecting full charge do not apply (individual cells may be
in a different state of charge). Hence the instruction to slow charge
for a minimum interval that ensures that all cells are fully charged at
a charge rate that is low enough not to damage through over-charge.

Chris K
Then how do power tool chargers manage it?

Mike

Muddymike wrote:

ChrisK wrote:

9v batteries are a set of cells in series so the normal
methods of detecting full charge do not apply (individual cells may be
in a different state of charge).

Then how do power tool chargers manage it?

Extra "balance" connections between individual cells within battery and
charger.

In article ,
Right said Fred wrote:
I have noticed that the chargers for rechargeable batteries invariably
stop charging the AA and AAA when they are fully charged and the on
charge light goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and you
are just told to charge them for a certain time - no light going out
when they are full.

Why is this there difference?

With multiple cell batteries you can't sense the change in terminal
voltage in the same way as single cell types.

--
*Ambition is a poor excuse for not having enough sense to be lazy *

Dave Plowman London SW
To e-mail, change noise into sound.

Muddymike wrote:
On 06/12/2016 15:02, ChrisK wrote:
Right said Fred wrote:


I have noticed that the chargers for rechargeable batteries invariably
stop
charging the AA and AAA when they are fully charged and the on charge
light
goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and
you are
just told to charge them for a certain time - no light going out when
they are
full.

Why is this there difference?


Because the 9v batteries are a set of cells in series so the normal
methods of detecting full charge do not apply (individual cells may be
in a different state of charge). Hence the instruction to slow charge
for a minimum interval that ensures that all cells are fully charged at
a charge rate that is low enough not to damage through over-charge.

Chris K
Then how do power tool chargers manage it?

Mike

Much the same way I guess - and they still tend to use NICADs which are
much more robust wrt charging. Lion power tools use more complex
charging algorithms like laptops. Still not sure I like the idea of
charging series connected Lions without individual cell monitoring but
it seems to work for laptops and the like. Perhaps the cells are more
carefully matched at the outset.

Chris K

Andy Burns wrote:
Muddymike wrote:

ChrisK wrote:

9v batteries are a set of cells in series so the normal
methods of detecting full charge do not apply (individual cells may be
in a different state of charge).

Then how do power tool chargers manage it?

Extra "balance" connections between individual cells within battery and
charger.


Not for NiCads that I've seen. Just series charging of strings of
cells. I have an EoR 36v (30 cell) battery pack I got from B&Q for £1
as a source of cells - just 30 cells in series.

Chris K

ChrisK wrote:

Andy Burns wrote:

Muddymike wrote:

Then how do power tool chargers manage it?

Extra "balance" connections between individual cells within battery and
charger.

Not for NiCads that I've seen.

Maybe not NiCads but certainly for Lithium based ones, hence all the
extra terminals on the pack.

ChrisK wrote:
Andy Burns wrote:
Muddymike wrote:

ChrisK wrote:

9v batteries are a set of cells in series so the normal
methods of detecting full charge do not apply (individual cells may be
in a different state of charge).

Then how do power tool chargers manage it?

Extra "balance" connections between individual cells within battery and
charger.


Not for NiCads that I've seen. Just series charging of strings of
cells. I have an EoR 36v (30 cell) battery pack I got from B&Q for £1
as a source of cells - just 30 cells in series.

Chris K
Nicad power tool chargers use a different system based on temperature
instead of terminal voltage changes.

On Tue, 6 Dec 2016 14:42:32 +0000, Muddymike wrote:

On 06/12/2016 13:43, Right said Fred wrote:


I have noticed that the chargers for rechargeable batteries invariably stop
charging the AA and AAA when they are fully charged and the on charge light
goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and you are
just told to charge them for a certain time - no light going out when they are
full.

Why is this there difference?

Crap charger.

Mike


Do you have a pointer to a 9v charger which will work differently then?

"Muddymike" wrote in message
...
On 06/12/2016 15:02, ChrisK wrote:
Right said Fred wrote:


I have noticed that the chargers for rechargeable batteries invariably
stop
charging the AA and AAA when they are fully charged and the on charge
light
goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and
you are
just told to charge them for a certain time - no light going out when
they are
full.

Why is this there difference?


Because the 9v batteries are a set of cells in series so the normal
methods of detecting full charge do not apply (individual cells may be
in a different state of charge). Hence the instruction to slow charge
for a minimum interval that ensures that all cells are fully charged at
a charge rate that is low enough not to damage through over-charge.

Chris K
Then how do power tool chargers manage it?

And laptops.

"Andy Burns" wrote in message
...
Muddymike wrote:

ChrisK wrote:

9v batteries are a set of cells in series so the normal
methods of detecting full charge do not apply (individual cells may be
in a different state of charge).

Then how do power tool chargers manage it?

Extra "balance" connections between individual cells within battery and
charger.

Cant be, there are only two connections to the battery where it goes in the
charger.

"Dave Plowman (News)" wrote in message
...
In article ,
Right said Fred wrote:
I have noticed that the chargers for rechargeable batteries invariably
stop charging the AA and AAA when they are fully charged and the on
charge light goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and you
are just told to charge them for a certain time - no light going out
when they are full.

Why is this there difference?

With multiple cell batteries you can't sense the change in terminal
voltage in the same way as single cell types.

But power tools and laptops don’t get charged on time alone.

At a rough guess its because the single cell chargers can tel when its
charged as there is only one cell, but as all 9v batteries have lots of
cells in series, you will always find that you are overcharging some cells
more than others making the detection of fully charged very ambiguous. If
sad batteries had an internal circuit that could detect each cell then you
could do this, but they don't.
Brian

--
----- -
This newsgroup posting comes to you directly from...
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"Right said Fred" wrote in message
...


I have noticed that the chargers for rechargeable batteries invariably
stop
charging the AA and AAA when they are fully charged and the on charge
light
goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and you
are
just told to charge them for a certain time - no light going out when they
are
full.

Why is this there difference?

No see the answer I gave earlier.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Muddymike" wrote in message
o.uk...
On 06/12/2016 13:43, Right said Fred wrote:


I have noticed that the chargers for rechargeable batteries invariably
stop
charging the AA and AAA when they are fully charged and the on charge
light
goes out to tell you that they are completed.

BUT: the ones I have had do not stop charging the 9v batteries - and you
are
just told to charge them for a certain time - no light going out when
they are
full.

Why is this there difference?

Crap charger.

Mike