Gentlemen,

NiMh cells are 1.2V IIRC. Would I be right in thinking that these
should be charged individually? IOW, if there's say 6 of them in a
caddy providing 7.2V, you couldn't just hook them up to say 8V and
recharged them all in series?

cheers,

CD

On 21/01/2024 12:54, Cursitor Doom wrote:
> Gentlemen,
>
> NiMh cells are 1.2V IIRC. Would I be right in thinking that these
> should be charged individually? IOW, if there's say 6 of them in a
> caddy providing 7.2V, you couldn't just hook them up to say 8V and
> recharged them all in series?
>
NiMh are OK done like this, but it's a shade more tricky with lithium,
as cells may not all be exactly the same which leads to some cells
overcharging and others undercharging, and overcharged cells are...

KABOOM!

In the model community, where maximum charge is a must chargers and
batteries have balancing connectors to allow each cells voltage to be
monitored and clamped to prevent overcharging

--
"Socialist governments traditionally do make a financial mess. They
always run out of other people's money. It's quite a characteristic of them"

Margaret Thatcher

The Natural Philosopher <tnp@invalid.invalid> wrote:
> On 21/01/2024 12:54, Cursitor Doom wrote:
> > Gentlemen,
> >
> > NiMh cells are 1.2V IIRC. Would I be right in thinking that these
> > should be charged individually? IOW, if there's say 6 of them in a
> > caddy providing 7.2V, you couldn't just hook them up to say 8V and
> > recharged them all in series?
> >
> NiMh are OK done like this, but it's a shade more tricky with lithium,
> as cells may not all be exactly the same which leads to some cells
> overcharging and others undercharging, and overcharged cells are...

NiMH are ok with it because they burn off the overcharge as heat. That's
fine assuming the current is low. If you want to fast charge NiMH at a
high current then you do need per-cell connections, since there's only
so much heat they can take, and one method of detecting charge termination
is by spotting this temperature rise which needs probes on a per-cell basis.

You still get the same variation in charge states as lithium, but you are
safe to overcharge some cells while waitng for the others come up to full
charge.

(a decent charger will back off the charging current as the voltage
increases so as not to overcharge other cells in the pack too much)

Theo

On 1/21/2024 7:54 AM, Cursitor Doom wrote:
> Gentlemen,
>
> NiMh cells are 1.2V IIRC. Would I be right in thinking that these
> should be charged individually? IOW, if there's say 6 of them in a
> caddy providing 7.2V, you couldn't just hook them up to say 8V and
> recharged them all in series?
>
> cheers,
>
> CD
>

https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride

"Well-designed NiMH chargers include Negative Delta V, voltage plateau,
delta temperature (dT/dt), temperature threshold and time-out timers
into the full-charge detection algorithm."

Other text in the article says the NDV detection is weak, corresponds
to a 5mV drop in voltage, and is only really visible if the cells
support fast charge.

Nickel Cadmium bears some similarities, such as the same difficulties
detecting the endpoint.

https://batteryuniversity.com/article/bu-407-charging-nickel-cadmium

Charging the cells separately, does a better job of filling them up,
as each item charged could receive custom treatment. Like, if a cell
is half full, as long as there is a working termination method, the
cell should not be overfilled.

You can do anything you want with batteries (the exception being the
ones that catch fire). But depending on the extremes of behavior,
not following best practice can be pretty expensive in the long run.

I could wear my wool suit in the shower. Nothing prevents it. But
that would not be a "best practice" :-)

Paul

On Sun, 21 Jan 2024 10:19:27 -0500, Paul <nospam@needed.invalid>
wrote:

>On 1/21/2024 7:54 AM, Cursitor Doom wrote:
>> Gentlemen,
>>
>> NiMh cells are 1.2V IIRC. Would I be right in thinking that these
>> should be charged individually? IOW, if there's say 6 of them in a
>> caddy providing 7.2V, you couldn't just hook them up to say 8V and
>> recharged them all in series?
>>
>> cheers,
>>
>> CD
>>
>
>https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride
>
> "Well-designed NiMH chargers include Negative Delta V, voltage plateau,
> delta temperature (dT/dt), temperature threshold and time-out timers
> into the full-charge detection algorithm."
>
>Other text in the article says the NDV detection is weak, corresponds
>to a 5mV drop in voltage, and is only really visible if the cells
>support fast charge.

I didn't find this article very helpful, I'm afraid. They make
frequent reference to "C" without defining what "C" is. They also
didn't specify what the charging algorithm is. So two key omissions at
least.

On 21/01/2024 21:55, Cursitor Doom wrote:
> On Sun, 21 Jan 2024 10:19:27 -0500, Paul <nospam@needed.invalid>
> wrote:
>
>> On 1/21/2024 7:54 AM, Cursitor Doom wrote:
>>> Gentlemen,
>>>
>>> NiMh cells are 1.2V IIRC. Would I be right in thinking that these
>>> should be charged individually? IOW, if there's say 6 of them in a
>>> caddy providing 7.2V, you couldn't just hook them up to say 8V and
>>> recharged them all in series?
>>>
>>> cheers,
>>>
>>> CD
>>>
>>
>> https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride
>>
>> "Well-designed NiMH chargers include Negative Delta V, voltage plateau,
>> delta temperature (dT/dt), temperature threshold and time-out timers
>> into the full-charge detection algorithm."
>>
>> Other text in the article says the NDV detection is weak, corresponds
>> to a 5mV drop in voltage, and is only really visible if the cells
>> support fast charge.
>
> I didn't find this article very helpful, I'm afraid. They make
> frequent reference to "C" without defining what "C" is. They also
> didn't specify what the charging algorithm is. So two key omissions at
> least.

"C" is the batteries Ah capacity. A charge at "C" implies a charge in
Amps at the Amp-hour capacity of the battery.

I thought the article was good.

On Sun, 21 Jan 2024 22:26:38 +0000, Fredxx wrote:

> On 21/01/2024 21:55, Cursitor Doom wrote:
>> On Sun, 21 Jan 2024 10:19:27 -0500, Paul <nospam@needed.invalid> wrote:
>>
>>> On 1/21/2024 7:54 AM, Cursitor Doom wrote:
>>>> Gentlemen,
>>>>
>>>> NiMh cells are 1.2V IIRC. Would I be right in thinking that these
>>>> should be charged individually? IOW, if there's say 6 of them in a
>>>> caddy providing 7.2V, you couldn't just hook them up to say 8V and
>>>> recharged them all in series?
>>>>
>>>> cheers,
>>>>
>>>> CD
>>>>
>>>>
>>> https://batteryuniversity.com/article/bu-408-charging-nickel-metal-
hydride
>>>
>>> "Well-designed NiMH chargers include Negative Delta V, voltage
>>> plateau,
>>> delta temperature (dT/dt), temperature threshold and time-out
>>> timers into the full-charge detection algorithm."
>>>
>>> Other text in the article says the NDV detection is weak, corresponds
>>> to a 5mV drop in voltage, and is only really visible if the cells
>>> support fast charge.
>>
>> I didn't find this article very helpful, I'm afraid. They make frequent
>> reference to "C" without defining what "C" is. They also didn't specify
>> what the charging algorithm is. So two key omissions at least.
>
> "C" is the batteries Ah capacity. A charge at "C" implies a charge in
> Amps at the Amp-hour capacity of the battery.
>
> I thought the article was good.

Why do people use abreviations, when they spell it out anyway..?

Cursitor Doom wrote:

> I didn't find this article very helpful, I'm afraid. They make
> frequent reference to "C" without defining what "C" is.

They do have an article on that, wouldn't hurt them to link to it from
the first mention of "C" in the NiMH article ...

<https://batteryuniversity.com/article/bu-402-what-is-c-rate>

Well, a lot of devices do do that, and the end result is often some dud
cells where they get reverse charged by the unit when its running as they do
not mach. Having said that, Recharging them one at a time seems hit and miss
also. I have found about half have a very long life and the rest, not so
much. I put this down to the way they are in series when used. If you get a
number which match, then they seem to carry on that way, but have one that
goes down before the others and its knackered in a few weeks. Now that has
been my finding, and only mine, so if you are lucky with choosing the paris
or however many are in series, then you get a long life.
Brian

--

--:
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
briang1@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"Cursitor Doom" <cd@notformail.com> wrote in message
news:co4qqilk5n5tg58bqcfa1v4qgdf9egoajn@4ax.com...
> Gentlemen,
>
> NiMh cells are 1.2V IIRC. Would I be right in thinking that these
> should be charged individually? IOW, if there's say 6 of them in a
> caddy providing 7.2V, you couldn't just hook them up to say 8V and
> recharged them all in series?
>
> cheers,
>
> CD

I would say that they do not like being in series in any way, see my
previous post.
Brian

--

--:
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
briang1@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"The Natural Philosopher" <tnp@invalid.invalid> wrote in message
news:uoj4md$6a1c$5@dont-email.me...
> On 21/01/2024 12:54, Cursitor Doom wrote:
>> Gentlemen,
>>
>> NiMh cells are 1.2V IIRC. Would I be right in thinking that these
>> should be charged individually? IOW, if there's say 6 of them in a
>> caddy providing 7.2V, you couldn't just hook them up to say 8V and
>> recharged them all in series?
>>
> NiMh are OK done like this, but it's a shade more tricky with lithium, as
> cells may not all be exactly the same which leads to some cells
> overcharging and others undercharging, and overcharged cells are...
>
> KABOOM!
>
> In the model community, where maximum charge is a must chargers and
> batteries have balancing connectors to allow each cells voltage to be
> monitored and clamped to prevent overcharging
>
>
>
>
> --
> "Socialist governments traditionally do make a financial mess. They always
> run out of other people's money. It's quite a characteristic of them"
>
> Margaret Thatcher
>

On Mon, 22 Jan 2024 09:54:40 -0000, "Brian Gaff"
<brian1gaff@gmail.com> wrote:

>Well, a lot of devices do do that, and the end result is often some dud
>cells where they get reverse charged by the unit when its running as they do
>not mach. Having said that, Recharging them one at a time seems hit and miss
>also. I have found about half have a very long life and the rest, not so
>much. I put this down to the way they are in series when used. If you get a
>number which match, then they seem to carry on that way, but have one that
>goes down before the others and its knackered in a few weeks. Now that has
>been my finding, and only mine, so if you are lucky with choosing the paris
>or however many are in series, then you get a long life.
> Brian

Well the plan is to just keep them in series (there are 15 of them
providing about 19V when fully charged) and hook them up to a 20V
supply via a suitable current limiting resistor so they charge very
slowly and with minimum stress. I'm still not sure if that's a good
idea or not, though.
Background. This is to power up a vintage Hacker Sovereign radio made
in about 1970 which is a bit of a battery scoffer and eats through 2x
PP9s within 3 months. It just seemed like I was for ever swapping out
PP9s. So bought four 4x packs of JCB NIMh AA cells and am trying my
luck with them.

On 21/01/2024 21:55, Cursitor Doom wrote:
> On Sun, 21 Jan 2024 10:19:27 -0500, Paul <nospam@needed.invalid>
> wrote:
>
>> On 1/21/2024 7:54 AM, Cursitor Doom wrote:
>>> Gentlemen,
>>>
>>> NiMh cells are 1.2V IIRC. Would I be right in thinking that these
>>> should be charged individually? IOW, if there's say 6 of them in a
>>> caddy providing 7.2V, you couldn't just hook them up to say 8V and
>>> recharged them all in series?
>>>
>>> cheers,
>>>
>>> CD
>>>
>>
>> https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride
>>
>> "Well-designed NiMH chargers include Negative Delta V, voltage plateau,
>> delta temperature (dT/dt), temperature threshold and time-out timers
>> into the full-charge detection algorithm."
>>
>> Other text in the article says the NDV detection is weak, corresponds
>> to a 5mV drop in voltage, and is only really visible if the cells
>> support fast charge.
>
> I didn't find this article very helpful, I'm afraid. They make
> frequent reference to "C" without defining what "C" is. They also
> didn't specify what the charging algorithm is. So two key omissions at
> least.

C is capacity divided by charge time in hours

It then becomes the charge current.
So a 5Ah battery charged at one C is charged at 5A. At 2C , 10A, and so on.
It is a cell capacity-independent way to specify how fast a particular
chemistry can be safely charged (or discharged: they are different).

So a 30C rated battery may safely be discharged in two minutes. Ideal
for jump starters.

If its charge rate is 1C however, it needs an hour to be safely recharged.

--
"An intellectual is a person knowledgeable in one field who speaks out
only in others...”

Tom Wolfe

On 1/22/2024 12:11 AM, Smolley wrote:
> On Sun, 21 Jan 2024 22:26:38 +0000, Fredxx wrote:
>
>> On 21/01/2024 21:55, Cursitor Doom wrote:
>>> On Sun, 21 Jan 2024 10:19:27 -0500, Paul <nospam@needed.invalid> wrote:
>>>
>>>> On 1/21/2024 7:54 AM, Cursitor Doom wrote:
>>>>> Gentlemen,
>>>>>
>>>>> NiMh cells are 1.2V IIRC. Would I be right in thinking that these
>>>>> should be charged individually? IOW, if there's say 6 of them in a
>>>>> caddy providing 7.2V, you couldn't just hook them up to say 8V and
>>>>> recharged them all in series?
>>>>>
>>>>> cheers,
>>>>>
>>>>> CD
>>>>>
>>>>>
>>>> https://batteryuniversity.com/article/bu-408-charging-nickel-metal-
> hydride
>>>>
>>>> "Well-designed NiMH chargers include Negative Delta V, voltage
>>>> plateau,
>>>> delta temperature (dT/dt), temperature threshold and time-out
>>>> timers into the full-charge detection algorithm."
>>>>
>>>> Other text in the article says the NDV detection is weak, corresponds
>>>> to a 5mV drop in voltage, and is only really visible if the cells
>>>> support fast charge.
>>>
>>> I didn't find this article very helpful, I'm afraid. They make frequent
>>> reference to "C" without defining what "C" is. They also didn't specify
>>> what the charging algorithm is. So two key omissions at least.
>>
>> "C" is the batteries Ah capacity. A charge at "C" implies a charge in
>> Amps at the Amp-hour capacity of the battery.
>>
>> I thought the article was good.
>
> Why do people use abreviations, when they spell it out anyway..?
>

It's a shorthand, and it does have its uses.

Some chemistries, you can trickle charge forever (abuse) a cell,
at C/10 or C/20 ("capacity over ten" or "capacity over twenty") .
That's NiCd. That's how Black and Decker used to charge my screwdriver.
No precision charger there. Charge circuit cost them ten cents.
Capacity over twenty means it would take twenty hours to charge up.

You can't do that for Lithium ion. It calls for a precision charger,
with cutoff behavior, to stop charging the cell when it is full.
You may charge at C/3 (fast charging?), but it still requires
prompt termination (no trickle charging after it is full). The
reason it has to be a precision charger, is it drives the device
to the edge of stability. That's how you "pick" the capacity, by
determining "when it starts to smoke".

Lithium Iron Phosphate is a bit more tolerant. Some of those have
been powered by tiny solar cells (trickle the current in continuously),
without them catching fire. But those also have lower energy density.

The unit of C is scalable. It doesn't matter how big the battery is.
If C was 3000 maH, C/3 charge rate is 1000ma or one amp. If
the cell was room sized (lead acid scales to room sized),
and C was 300000, then C/3 would be 100000 mA or 100 amps.

If someone writes:

"The key advantage of the lithium-titanium based technology is the
high speed charge and discharge. Typical charge and discharge rates
are defined up to 5C (in comparison with 0.5C for LFP).
The peak discharge rates are up to 10C continuous"

And that is what the Proterra transit bus uses. A blade charger
lowers onto the roof of the bus, and the bus charges at 500kW.
Their charge cycle doesn't quite fill the bus battery full, but
it does achieve a charging interval of ten minutes, before the bus
drives off. It's a bit better than the car characteristic.

An ultracapacitor is not a battery (a battery has a non-linear
curve, the ultracapacitor is linear and voltage drops at a
constant rate when discharged at a constant current draw). But
compared to a battery, it charges at 2000C. Those can do
a million charge cycles, but aren't practical for vehicles
(except for drag racers). The limitations on those would
tend to be thermal. Even with wide tabs on each cell,
the "peak" rating for the device implies you'd come close
to burning the tabs off. Dropping a screwdriver across a
suitcase full of those, would be "very bad for your screwdriver".
They sell a six-pack of those (sort of looks like an automotive
battery), to people who put a 1kW sub in the boot, and the
device "buffers" the car battery,and improves the battery
impedance characteristic. When the sub thumps, it thumps
with authority.

The charge rate, in units related to capacity C, gives you
some idea how whizzy an item you are dealing with. Or
potentially, how dangerous it might be (ultracaps would not
be fitted with protection devices if you really wanted to
harvest their characteristic properties).

Automotive batteries don't have protection devices, because
you "want those 600 cranking amps". A buddy in uni, was wearing
a loose fitting watch with metal strap while working on his
Mini, and the strap somehow shorted the battery. This is why they tell
you not to wear metallic jewellery when working around such things. His
wrist had the link pattern of the watch, burned into his wrist.
You don't wear the watch while that heals :-) Once you see an
injury like that, you'll have new respect for the battery in
the car.

Paul

On 1/21/2024 4:55 PM, Cursitor Doom wrote:

>
> I didn't find this article very helpful, I'm afraid. They make
> frequent reference to "C" without defining what "C" is. They also
> didn't specify what the charging algorithm is. So two key omissions at
> least.
>

https://batteryuniversity.com/article/bu-407-charging-nickel-cadmium

"Nickel-based batteries also charge with constant current but the
voltage is allowed to rise freely. Full charge detection occurs by
observing a slight voltage drop after a steady rise [NDV]. This may
be connected with plateau timing and temperature rise over time (more below)."

That amounts to single stage constant current, with a complex termination
characteristics unrelated to absolute cell voltage.

Nickel metal hydride is similar.

https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride

"The charge algorithm for NiMH is similar to NiCd with the exception
that NiMH is more complex. Negative Delta V to detect full charge is faint,
especially when charging at less than 0.5C. A mismatched or hot pack reduces
the symptoms further."

Now, at one time, I used to read articles (not from that site), claiming
one chemistry was NDV, the other was plateau, and the claim it was plateau
was because nobody could observe the small amount of NDV :-)

That means, for precision charging (charging not based on time, as a very crude
indicator it is done), is best done on individual cells. It's easier
to spot the signal for the noise, when working with individual cells.
But it still requires a "fast charge" NiMh, to ensure the NDV is the
mentioned 5 millivolts or so. That's why the charging method has
multiple terminations, including "time", if you blow past all the
other termination events (max temperature).

All the observations are from the same root cause. The temperature
rises when the cell is full. The pressure rises. The voltage behavior
is affected by the pressure inside the cell. They're trying to pick a
proxy for the physical effects, without measuring the physical effects.

If NiCd or NiMh had pressure sensors and two terminals on the outside
of the device, that might allow endpoint determination. Or using
thermistors (a bit more practical), you could measure the temperature
inside the cell. NDV as a proxy, is fine, as long as the cell and charger,
can work within the limitations.

There used to be some 8AH D-cell sized NiCd for sale. Why didn't
I buy some ? Well, they weren't fast charge (it would not be reasonable
to pour a lot of amps into them). No charger would ever be offered,
on the same web page as the cells. How many charge cycles would
you get out of a thing like that, without an intelligent charger ?
I think development would have continued on those... if it was not
the end of the NiCd era.

Paul

On Mon, 22 Jan 2024 11:48:41 -0500, Paul <nospam@needed.invalid>
wrote:

>On 1/21/2024 4:55 PM, Cursitor Doom wrote:
>
>>
>> I didn't find this article very helpful, I'm afraid. They make
>> frequent reference to "C" without defining what "C" is. They also
>> didn't specify what the charging algorithm is. So two key omissions at
>> least.
>>
>
>https://batteryuniversity.com/article/bu-407-charging-nickel-cadmium
>
> "Nickel-based batteries also charge with constant current but the
> voltage is allowed to rise freely. Full charge detection occurs by
> observing a slight voltage drop after a steady rise [NDV]. This may
> be connected with plateau timing and temperature rise over time (more below)."
>
>That amounts to single stage constant current, with a complex termination
>characteristics unrelated to absolute cell voltage.
>
>Nickel metal hydride is similar.
>
>https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride
>
> "The charge algorithm for NiMH is similar to NiCd with the exception
> that NiMH is more complex. Negative Delta V to detect full charge is faint,
> especially when charging at less than 0.5C. A mismatched or hot pack reduces
> the symptoms further."
>
>Now, at one time, I used to read articles (not from that site), claiming
>one chemistry was NDV, the other was plateau, and the claim it was plateau
>was because nobody could observe the small amount of NDV :-)
>
>That means, for precision charging (charging not based on time, as a very crude
>indicator it is done), is best done on individual cells. It's easier
>to spot the signal for the noise, when working with individual cells.
>But it still requires a "fast charge" NiMh, to ensure the NDV is the
>mentioned 5 millivolts or so. That's why the charging method has
>multiple terminations, including "time", if you blow past all the
>other termination events (max temperature).
>
>All the observations are from the same root cause. The temperature
>rises when the cell is full. The pressure rises. The voltage behavior
>is affected by the pressure inside the cell. They're trying to pick a
>proxy for the physical effects, without measuring the physical effects.
>
>If NiCd or NiMh had pressure sensors and two terminals on the outside
>of the device, that might allow endpoint determination. Or using
>thermistors (a bit more practical), you could measure the temperature
>inside the cell. NDV as a proxy, is fine, as long as the cell and charger,
>can work within the limitations.
>
>There used to be some 8AH D-cell sized NiCd for sale. Why didn't
>I buy some ? Well, they weren't fast charge (it would not be reasonable
>to pour a lot of amps into them). No charger would ever be offered,
>on the same web page as the cells. How many charge cycles would
>you get out of a thing like that, without an intelligent charger ?
>I think development would have continued on those... if it was not
>the end of the NiCd era.
>
> Paul

That was *very* well explained; many thanks, Paul.

On 22/01/2024 09:56, Brian Gaff wrote:

> I would say that they do not like being in series in any way, see my
> previous post.

Well there are NiMH PP3s (the little 9V batteries) which have to be
recharged with the cells in series as they are made with (presumably 6)
cells in series.

--
Max Demian

On 22/01/2024 18:00, Max Demian wrote:
> On 22/01/2024 09:56, Brian Gaff wrote:
>
>> I would say that they do not like being in series in any way, see my
>> previous post.
>
> Well there are NiMH PP3s (the little 9V batteries) which have to be
> recharged with the cells in series as they are made with (presumably 6)
> cells in series.
>
Nickel cells can be left on trickle charge indefinitely when placed in
series.
They all end up fully charged

--
"The most difficult subjects can be explained to the most slow witted
man if he has not formed any idea of them already; but the simplest
thing cannot be made clear to the most intelligent man if he is firmly
persuaded that he knows already, without a shadow of doubt, what is laid
before him."

- Leo Tolstoy

On 22/01/2024 18:01, The Natural Philosopher wrote:
> On 22/01/2024 18:00, Max Demian wrote:
>> On 22/01/2024 09:56, Brian Gaff wrote:
>>
>>> I would say that they do not like being in series in any way, see my
>>> previous post.
>>
>> Well there are NiMH PP3s (the little 9V batteries) which have to be
>> recharged with the cells in series as they are made with (presumably
>> 6) cells in series.
>>
> Nickel cells can be left on trickle charge indefinitely when placed in
> series.
> They all end up fully charged

But are there any fast chargers for PP3s?

--
Max Demian

On 22/01/2024 18:00, Max Demian wrote:

<snip>
>
> Well there are NiMH PP3s (the little 9V batteries) which have to be
> recharged with the cells in series as they are made with (presumably 6)
> cells in series.
>
Seven actually.

1.2 7 * .
8.4 ok

--
Cheers
Clive

On 22/01/2024 18:36, Max Demian wrote:
> On 22/01/2024 18:01, The Natural Philosopher wrote:
>> On 22/01/2024 18:00, Max Demian wrote:
>>> On 22/01/2024 09:56, Brian Gaff wrote:
>>>
>>>> I would say that they do not like being in series in any way, see my
>>>> previous post.
>>>
>>> Well there are NiMH PP3s (the little 9V batteries) which have to be
>>> recharged with the cells in series as they are made with (presumably
>>> 6) cells in series.
>>>
>> Nickel cells can be left on trickle charge indefinitely when placed in
>> series.
>> They all end up fully charged
>
> But are there any fast chargers for PP3s?
>
Of course. Any delta peak charger with adjustable charge current will work .

https://www.hobbies.co.uk/logic-variable-output-ac-dc-delta-peak-nimh-charger

--
Outside of a dog, a book is a man's best friend. Inside of a dog it's
too dark to read.

Groucho Marx

On Monday 22 January 2024 at 10:31:23 UTC, Cursitor Doom wrote:
> On Mon, 22 Jan 2024 09:54:40 -0000, "Brian Gaff"
> <brian...@gmail.com> wrote:
>
> >Well, a lot of devices do do that, and the end result is often some dud
> >cells where they get reverse charged by the unit when its running as they do
> >not mach. Having said that, Recharging them one at a time seems hit and miss
> >also. I have found about half have a very long life and the rest, not so
> >much. I put this down to the way they are in series when used. If you get a
> >number which match, then they seem to carry on that way, but have one that
> >goes down before the others and its knackered in a few weeks. Now that has
> >been my finding, and only mine, so if you are lucky with choosing the paris
> >or however many are in series, then you get a long life.
> > Brian
> Well the plan is to just keep them in series (there are 15 of them
> providing about 19V when fully charged) and hook them up to a 20V
> supply via a suitable current limiting resistor so they charge very
> slowly and with minimum stress. I'm still not sure if that's a good
> idea or not, though.
> Background. This is to power up a vintage Hacker Sovereign radio made
> in about 1970 which is a bit of a battery scoffer and eats through 2x
> PP9s within 3 months. It just seemed like I was for ever swapping out
> PP9s. So bought four 4x packs of JCB NIMh AA cells and am trying my
> luck with them.

Always on trickle charging works well with Ni*, but does require a slow 24hr+ charge rate.
Vape cells are another option, can't charge those as easily though.

On 1/22/2024 5:31 AM, Cursitor Doom wrote:
> On Mon, 22 Jan 2024 09:54:40 -0000, "Brian Gaff"
> <brian1gaff@gmail.com> wrote:
>
>> Well, a lot of devices do do that, and the end result is often some dud
>> cells where they get reverse charged by the unit when its running as they do
>> not mach. Having said that, Recharging them one at a time seems hit and miss
>> also. I have found about half have a very long life and the rest, not so
>> much. I put this down to the way they are in series when used. If you get a
>> number which match, then they seem to carry on that way, but have one that
>> goes down before the others and its knackered in a few weeks. Now that has
>> been my finding, and only mine, so if you are lucky with choosing the paris
>> or however many are in series, then you get a long life.
>> Brian
>
> Well the plan is to just keep them in series (there are 15 of them
> providing about 19V when fully charged) and hook them up to a 20V
> supply via a suitable current limiting resistor so they charge very
> slowly and with minimum stress. I'm still not sure if that's a good
> idea or not, though.
> Background. This is to power up a vintage Hacker Sovereign radio made
> in about 1970 which is a bit of a battery scoffer and eats through 2x
> PP9s within 3 months. It just seemed like I was for ever swapping out
> PP9s. So bought four 4x packs of JCB NIMh AA cells and am trying my
> luck with them.
>

Example of a couple PP9s in the back of this. Looks
like a major battery hog. Like a boom box almost.

https://i.ebayimg.com/images/g/Bh8AAOSwghRk0LnE/s-l960.jpg

The general discussion here, is to use a non-SMPS mains supply (linear).

https://groups.io/g/Hackerradiogroup/topic/hacker_mains_adapter/55541525?p=

One thing they mention here, is the PP9s don't stay at 9V for very long.

https://www.batterystation.co.uk/content/datasheets_MSDS/eveready/Eveready%20PP9%20Product%20Spec%20Sheet.pdf

You could just buy four 4-cell rechargers, and recharge the whole
lot of them in one go :-)

A device like this, can tell you how well they match one another. It
includes a battery analyzer.

http://www.economik.com/maha-energy/powerex-mh-c9000pro-wizardone-charger-analyzer-for-4-aa-aaa-nimh-nicd/

The radio would not have a feature, to stop drawing power from the
rechargeables when they're exhausted (UVLO). For example, falling asleep
listening to radio, one of the cells could get reverse biased if
there is no cutoff circuit.

https://en.wikipedia.org/wiki/Cutoff_voltage

When testing the capacity of a NiMH or NiCd battery a cut-off voltage of 1.0 V per cell
is normally used, whereas 0.9 V is normally used as the cut-off voltage of an alkaline cell.

Devices that have too high cut-off voltages may stop operating while the battery still
has significant capacity remaining.

16 * 1.25 = 20V
16 * 1.0 = 16V

But if you look at the curve at the bottom of this page,
a somewhat higher cutoff should be selected.

https://www.powerstream.com/AA-tests.htm

https://www.powerstream.com/z/AA-NiMH-composite.png

16 * 1.18 = 18.9V [ With so many cells in series, don't want to go so far down the knee ]

The effects of temperature are noted here. Picking
a cutoff is more complicated than it looks. Between 20C and 40C,
it's looking pretty good. A wider temperature range, might
take a low power micro or something.

https://data.energizer.com/pdfs/nickelmetalhydride_appman.pdf

But at some point, the more cells you put in series, you
almost have to monitor cells individually to detect discharge-knee-approach.
One cell could fall over the knee before the others (mismatched cells).

Maybe 12 cells would slice the PP9 characteristic better, 6 cells per PP9 replacement.

16 * 1.40 = 22.4 [ Fresh off charger ]
16 * 1.25 = 20.0
16 * 1.18 = 18.9 Stop

14 * 1.40 = 19.6 [ Fresh off charger ]
14 * 1.25 = 17.5
14 * 1.18 = 16.5 Stop

12 * 1.40 = 16.8 [ Fresh off charger ]
12 * 1.25 = 15.0
12 * 1.18 = 14.16 <=== PP9 pair spends most of its life at this voltage, or a bit lower

https://www.eevblog.com/forum/projects/designing-low-voltage-battery-protection-circuit-good-reference-designs/?action=dlattach;attach=263015;image

( https://www.eevblog.com/forum/projects/designing-low-voltage-battery-protection-circuit-good-reference-designs/ )

Your circuit could do this:

+--- V++ or this: +---- V++
| |
PP9 PP9
| |
PP9 +---- Vmid (SPKR return)
| |
+--- GND PP9
|
+---- GND

and the first one is going to be a LOT easier to design
the UVLO (Under Voltage Lock Out) for than the other tree.

( UVLO is terminology from SMPS design, protecting an SMPS from
drawing high current, when the input voltage is abnormally low.
Which is not what we're protecting against here, it is battery
damage due to not having load cutoff behavior available. )

Paul

On Tue, 23 Jan 2024 10:55:39 -0500, Paul <nospam@needed.invalid>
wrote:

>On 1/22/2024 5:31 AM, Cursitor Doom wrote:
>> On Mon, 22 Jan 2024 09:54:40 -0000, "Brian Gaff"
>> <brian1gaff@gmail.com> wrote:
>>
>>> Well, a lot of devices do do that, and the end result is often some dud
>>> cells where they get reverse charged by the unit when its running as they do
>>> not mach. Having said that, Recharging them one at a time seems hit and miss
>>> also. I have found about half have a very long life and the rest, not so
>>> much. I put this down to the way they are in series when used. If you get a
>>> number which match, then they seem to carry on that way, but have one that
>>> goes down before the others and its knackered in a few weeks. Now that has
>>> been my finding, and only mine, so if you are lucky with choosing the paris
>>> or however many are in series, then you get a long life.
>>> Brian
>>
>> Well the plan is to just keep them in series (there are 15 of them
>> providing about 19V when fully charged) and hook them up to a 20V
>> supply via a suitable current limiting resistor so they charge very
>> slowly and with minimum stress. I'm still not sure if that's a good
>> idea or not, though.
>> Background. This is to power up a vintage Hacker Sovereign radio made
>> in about 1970 which is a bit of a battery scoffer and eats through 2x
>> PP9s within 3 months. It just seemed like I was for ever swapping out
>> PP9s. So bought four 4x packs of JCB NIMh AA cells and am trying my
>> luck with them.
>>
>
>Example of a couple PP9s in the back of this. Looks
>like a major battery hog. Like a boom box almost.
>
> https://i.ebayimg.com/images/g/Bh8AAOSwghRk0LnE/s-l960.jpg
>
>The general discussion here, is to use a non-SMPS mains supply (linear).
>
> https://groups.io/g/Hackerradiogroup/topic/hacker_mains_adapter/55541525?p=
>
>One thing they mention here, is the PP9s don't stay at 9V for very long.
>
> https://www.batterystation.co.uk/content/datasheets_MSDS/eveready/Eveready%20PP9%20Product%20Spec%20Sheet.pdf
>
>You could just buy four 4-cell rechargers, and recharge the whole
>lot of them in one go :-)
>
>A device like this, can tell you how well they match one another. It
>includes a battery analyzer.
>
> http://www.economik.com/maha-energy/powerex-mh-c9000pro-wizardone-charger-analyzer-for-4-aa-aaa-nimh-nicd/
>
>The radio would not have a feature, to stop drawing power from the
>rechargeables when they're exhausted (UVLO). For example, falling asleep
>listening to radio, one of the cells could get reverse biased if
>there is no cutoff circuit.
>
>https://en.wikipedia.org/wiki/Cutoff_voltage
>
> When testing the capacity of a NiMH or NiCd battery a cut-off voltage of 1.0 V per cell
> is normally used, whereas 0.9 V is normally used as the cut-off voltage of an alkaline cell.
>
> Devices that have too high cut-off voltages may stop operating while the battery still
> has significant capacity remaining.
>
>16 * 1.25 = 20V
>16 * 1.0 = 16V
>
>But if you look at the curve at the bottom of this page,
>a somewhat higher cutoff should be selected.
>
>https://www.powerstream.com/AA-tests.htm
>
> https://www.powerstream.com/z/AA-NiMH-composite.png
>
>16 * 1.18 = 18.9V [ With so many cells in series, don't want to go so far down the knee ]
>
>The effects of temperature are noted here. Picking
>a cutoff is more complicated than it looks. Between 20C and 40C,
>it's looking pretty good. A wider temperature range, might
>take a low power micro or something.
>
>https://data.energizer.com/pdfs/nickelmetalhydride_appman.pdf
>
>But at some point, the more cells you put in series, you
>almost have to monitor cells individually to detect discharge-knee-approach.
>One cell could fall over the knee before the others (mismatched cells).
>
>Maybe 12 cells would slice the PP9 characteristic better, 6 cells per PP9 replacement.
>
>16 * 1.40 = 22.4 [ Fresh off charger ]
>16 * 1.25 = 20.0
>16 * 1.18 = 18.9 Stop
>
>14 * 1.40 = 19.6 [ Fresh off charger ]
>14 * 1.25 = 17.5
>14 * 1.18 = 16.5 Stop
>
>12 * 1.40 = 16.8 [ Fresh off charger ]
>12 * 1.25 = 15.0
>12 * 1.18 = 14.16 <=== PP9 pair spends most of its life at this voltage, or a bit lower
>
>https://www.eevblog.com/forum/projects/designing-low-voltage-battery-protection-circuit-good-reference-designs/?action=dlattach;attach=263015;image" rel="nofollow" target="_blank">https://www.eevblog.com/forum/projects/designing-low-voltage-battery-protection-circuit-good-reference-designs/?action=dlattach;attach=263015;image
>
>( https://www.eevblog.com/forum/projects/designing-low-voltage-battery-protection-circuit-good-reference-designs/ )
>
>Your circuit could do this:
>
> +--- V++ or this: +---- V++
> | |
> PP9 PP9
> | |
> PP9 +---- Vmid (SPKR return)
> | |
> +--- GND PP9
> |
> +---- GND
>
>and the first one is going to be a LOT easier to design
>the UVLO (Under Voltage Lock Out) for than the other tree.
>
>( UVLO is terminology from SMPS design, protecting an SMPS from
> drawing high current, when the input voltage is abnormally low.
> Which is not what we're protecting against here, it is battery
> damage due to not having load cutoff behavior available. )
>
> Paul

Wow! A lotta useful info there, Paul, well done! That certainly clears
up a lot of incomplete aspects to this issue and gives me the
necessary details I was lacking. Many thanks indeed for that sterling
effort!