NIMH battery charging.

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"ASAAR" wrote:

As I understand it, PCR (periodic current reversal) has a beneficial
effect on the physical structure of a metallic cathode as it's
formed, rather than a chemical effect.

There are at least 2 effects.

In fact, I believe PCR is required in electroplating, otherwise the
plated material is too spongy to be useful. In a battery, this can
mean dendrite formation.

My own electroplating experiments (without PCR) when I was young
produced very soft deposits.

This has been knowm by electroplates since the year dot. Almost all EP
is done by ofset AC current so as the get a sound solid plate. If the
metal is prone to growing dendrite of crystals, the current reversal
is concentrated at the dendrite and quickly removes it.

The other effect is stopping an `overvoltage' layer forming and the
resultant gassing off. This is also known as surface charge, and can be
quite significant.

Sealed NiCd and NiMH cells generate a lot more heat once they are fully
charged, and this temp rise reduces the series resistance of the cell
*LOTS*. It is this that causes the drop in voltage rise rate on charge
and discharge that can be used to signal end of charge.

Note that with NiCds, charging at low tempps is VERY bad news. Keep
them above 20C at the start. I don't know if this is a problem with
NiMH cells.

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

 

[ASAAR]

I agree on your points .. I was not aware of the "newer"(?) negative
pulse charging systems that probably do a better job in preserving the
microcrystaline structure of the "internal chemical battery soup" ...
as to "smart chargers" is there any other method that can be
considered "intelligent" than monitoring the voltage dip ? If a
charger doesn't use this method, I for one would not qualify it as an
"intelligent charger"

I suppose that measuring current would be about as useful, but I
agree that the smart chargers probably do monitor the voltage. What
I meant though, was that smart chargers don't necessarily have to
use current pulses to charge batteries. I think a truly smart
charger would require smart batteries that have a very small amount
flash RAM. That would allow the charger to write information to the
batteries identifying their last couple of charge cycles, with
date/time info. as well as design capacity and recent capacity.
That would allow the chargers to easily handle temporary loss A.C.
power during the charger cycle and also let you know when it might
be approaching the time to replace the batteries.. I don't know if
any of the "Info-Lithium" batteries do this of if the tracked
information is stored in the laptop or PDA that the batteries are
used with.

 

[ASAAR]

The chart recorder was set to display zero current at chart center
so that any reversal of current that might be described as
"Flex Negative charging current" would be displayed as a negative
value. The charging current never went negative! But this run was
done on a set of new cells, so maybe the "Flex" part didn't need to be
executed. I can imagine applying a momentary resistive load would
result in a "negative" pulse of charging current, so it might happen,
but I never saw it.

Thanks for the information. Now I'm curious as to how Flex
Negative Pulse Charging actually works. I imagine that since it has
a name, it should also have a description somewhere. Do you know if
it's a somewhat generic term, of if it's only used by one charger
manufacturer?

 

[Bob Salomon]

Thanks for the information. Now I'm curious as to how Flex
Negative Pulse Charging actually works. I imagine that since it has
a name, it should also have a description somewhere. Do you know if
it's a somewhat generic term, of if it's only used by one charger
manufacturer?

It sounds like the Ansmann Refresh mode in their Energy series chargers.
www.ansmann.com

 

[Ian Stirling]

I suppose that measuring current would be about as useful, but I
agree that the smart chargers probably do monitor the voltage. What
I meant though, was that smart chargers don't necessarily have to
use current pulses to charge batteries. I think a truly smart
charger would require smart batteries that have a very small amount
flash RAM. That would allow the charger to write information to the

Alternatively, if you're happy charging in only one charger - a barcode
may work almost as well.

 

[John Beardmore]

I think a truly smart
charger would require smart batteries that have a very small amount
flash RAM. That would allow the charger to write information to the
batteries identifying their last couple of charge cycles, with
date/time info. as well as design capacity and recent capacity.
That would allow the chargers to easily handle temporary loss A.C.
power during the charger cycle and also let you know when it might
be approaching the time to replace the batteries.

I would have thought the actual performance of the cell would be the
better indicator for determining replacement.


J/.

 

[imbsysop]

I suppose that measuring current would be about as useful, but I
agree that the smart chargers probably do monitor the voltage. What
I meant though, was that smart chargers don't necessarily have to
use current pulses to charge batteries. I think a truly smart
charger would require smart batteries that have a very small amount
flash RAM. snip ..

guess we are talking about a different type of technology now ?
maybe it will happen but maybe not with cheap AA NiMH's ?
It is my feeling that many people do not care too much about efficient
charging of their batteries and as such discard an astronomic lot of
"faulty" batteries that actually have no problem at all except bad
charging ?

 

[Markus L]

On Wed, 28 Sep 2005 11:08:05 -0700, Chuck Olson wrote:
Thanks for the information. Now I'm curious as to how Flex
Negative Pulse Charging actually works. I imagine that since it has
a name, it should also have a description somewhere. Do you know if
it's a somewhat generic term, of if it's only used by one charger
manufacturer?

Have built a so-called reflex charger (that's the term to google for) myself
some years ago, based on the ICS1702 chip made by www.galaxypower.com (can't
reach their website today). In the datasheets of their ICs, the reflex
charging principle is described in detail. As far as I remember, a cycle
takes around 1 second and is made up of about 950ms forward (charge) current
and about 20ms reverse (discharge) current. In between there are short
pauses to make sure one source is shut off before the other one is
activated. These pauses are also used to measure the open-circuit voltage of
the cell. The reverse current is around 2.5 times the forward current. My
results with reflex charging were good. Today I'm using a commercial charger
made by www.orbitronic.de that can also do reflex charging.

 

[ASAAR]

I would have thought the actual performance of the cell would be the
better indicator for determining replacement.

It would, if you can make some assumptions. But as Ian pointed
out (using barcodes) if you're not restricted to a single charger
that can compile a history, how would a different charger seeing a
cell for the first time know what I referred to as the "design
capacity" of the cells? While it has been almost a year since I
bought NiMH AAs having less than 2,500 mah capacities, only a few
months ago I bought a radio that for some odd reason was supplied
with four brand new 1,100 mah NiMH cells. I wouldn't want to use
them in a camera, but they do an adequate job in the radio. The
"smart" charger would need some way to differentiate between these
batteries and 2,500 mah batteries that through use now only have 1/2
their "design capacities" remaining. While it's true that they'd
also be adequate for use in the radio, I'm not aware of any charger
smart enough to know what kind of device the batteries would be used
in. For that it would be beneficial if in addition to the chargers,
we also have "smart" users.

 

[ASAAR]

guess we are talking about a different type of technology now ?
maybe it will happen but maybe not with cheap AA NiMH's ?
It is my feeling that many people do not care too much about efficient
charging of their batteries and as such discard an astronomic lot of
"faulty" batteries that actually have no problem at all except bad
charging ?

Different technology for sure, but nothing that hasn't been done
at low cost for many years. Some backup tapes have had solid state
memory for many years. While that would have been too expensive for
use in batteries then, memory cost is a tiny fraction of what it was
then. The RayOVac 15-minute chargers rely on a different, simple
type of "smart" technology built into their batteries and they are
more expensive. But most of the expense was probably of the "what
the market will bear" variety than due to manufacturing costs.

You're right about bad charging being a major problem. But if the
chargers that store battery histories could have USB ports and
periodically (say every month or two) send their data to a PC, good
software on the PC could recognize bad charging habits and wag a
virtual finger at the user.

 

[ASAAR]

Have built a so-called reflex charger (that's the term to google for) myself
some years ago, based on the ICS1702 chip made by
www.galaxypower.com (can't reach their website today). In the
datasheets of their ICs, the reflex charging principle is described in
detail. As far as I remember, a cycle takes around 1 second and is made
up of about 950ms forward (charge) current and about 20ms reverse
(discharge) current. In between there are short pauses to make sure
one source is shut off before the other one is activated.

Thanks for the info. Something like that was going on in my
otherwise unsatisfactory RayOVac chargers (for renewal alkalines and
NiCad batteries) based on nothing more than the cyclical slight
dimming of the LEDs while charging. They did in fact use pulse
charging, but the documentation didn't say anything about "reflex"
charging or negative pulses.

 

[imbsysop]

Have built a so-called reflex charger (that's the term to google for)
myself
some years ago, based on the ICS1702 chip made by www.galaxypower.com
(can't
reach their website today). In the datasheets of their ICs, the reflex
charging principle is described in detail. As far as I remember, a cycle
takes around 1 second and is made up of about 950ms forward (charge)
current
and about 20ms reverse (discharge) current. In between there are short
pauses to make sure one source is shut off before the other one is
activated. These pauses are also used to measure the open-circuit voltage
of
the cell. The reverse current is around 2.5 times the forward current. My
results with reflex charging were good. Today I'm using a commercial
charger
made by www.orbitronic.de that can also do reflex charging.

thnx very much for the pointers .. while searching google I came across this
one ..

http://www.mpoweruk.com/chargers.htm

it seems quite informative for those that want to learn more about charging
systems ..
HTH

 

[John Beardmore]

It would, if you can make some assumptions. But as Ian pointed
out (using barcodes) if you're not restricted to a single charger
that can compile a history, how would a different charger seeing a
cell for the first time know what I referred to as the "design
capacity" of the cells?

It wouldn't, though it might be able to tell you what the cell was
actually capable of.

While it has been almost a year since I
bought NiMH AAs having less than 2,500 mah capacities, only a few
months ago I bought a radio that for some odd reason was supplied
with four brand new 1,100 mah NiMH cells. I wouldn't want to use
them in a camera, but they do an adequate job in the radio. The
"smart" charger would need some way to differentiate between these
batteries and 2,500 mah batteries that through use now only have 1/2
their "design capacities" remaining.

Why ?

While it's true that they'd
also be adequate for use in the radio, I'm not aware of any charger
smart enough to know what kind of device the batteries would be used
in. For that it would be beneficial if in addition to the chargers,
we also have "smart" users.

I would have thought that if the charger could report on the state of
the cell, it would be up to the user to determine how to use it ?


Cheers, J/.

 

[Nostrobino]

[ . . . ]

thnx very much for the pointers .. while searching google I came across
this one ..

http://www.mpoweruk.com/chargers.htm

it seems quite informative for those that want to learn more about
charging systems ..
HTH

*Very* informative! Thanks for the link!

N.

 

[Nostrobino]

[ . . . ]

thnx very much for the pointers .. while searching google I came across
this one ..

http://www.mpoweruk.com/chargers.htm

it seems quite informative for those that want to learn more about
charging systems ..
HTH

Very informative! Thanks for the link.

N.