# How to calculate Energizer NiMH Charging Times

Discussion in 'Digital Photography' started by newsgroup2003@gmail.com, Apr 29, 2006.

1. ### Guest

I have the Energizer CHDC charger and I checked online and I cant
figure out how htye are calculating the charging times:
http://data.energizer.com/PDFs/chdc.pdf

I have a set of 2300 mAH Energizer batteries and I don't want to charge
them too long.

Anyone know what "math" Energizer seems to be using?

Thanks

, Apr 29, 2006

2. ### Bob SalomonGuest

In article <>,
wrote:

2500 x 1.25/360 will get you close.

--

Bob Salomon, Apr 30, 2006

3. ### ASAARGuest

On 29 Apr 2006 15:25:02 -0700, wrote:

> I have a set of 2300 mAH Energizer batteries and I don't want to charge
> them too long.
>
> Anyone know what "math" Energizer seems to be using?

For AAA cells, dividing the mAh rating by 100 will give you the
identical results shown in Energizer's charging time table. Their
math wasn't quite as precise for AA batteries, but if you divide the
mAh rating by 300 you'll get very close. So for your 2,300 mAh AA
cells, 2,300 / 300 == 7.7 hours.

But you might want to do yourself and your batteries a favor.
Get a better charger, one that stops when the batteries are fully
charged, and use this CHDC charger only as a backup. These are
called "Smart" chargers. The problem is that to calculate the
correct CHDC charge times you'll need to use a more complex formula
that will reduce the 7.7 hours based on two factors.

The first is that your battery's capacities will progressively
diminish as they age, so while using 2,300 when they're new will
work, a year from now they might have dropped to 1,900, and that
would mean that the batteries would now only need 6.3 hours to reach
a full charge. Keeping them in the charger for the full 7.7 hours
that new 2,300 mAh batteries need would only help to further shorten
their lives.

The second factor is the charge state of the batteries when you
put them in the charger. If they're fully discharged, then 7.7
hours would be an appropriate amount of time to leave them in the
charger. But you'll often be putting the batteries back in the
charger before they've been fully discharged. Just because a camera
or other device says that the batteries need to be recharged, that
doesn't mean that the batteries are fully discharged. Put them in
some other devices and they may continue operating for hours!

Another example. Suppose that you fully charge a set of batteries
and don't use them for a month or two. Due to self discharge, they
might have lost 1/2 of their charge. Put these back in the CHDC
charger and they'd only need 3 or 4 hours to reach a full charge, so
if you let them charge for 7.7 hours they'd be "overcooking" in the
charger for several hours, and that would also shorten their lives.

That's the bad news. The good news is that this is a very slow
charger, faster than a trickle charger but not by a lot. So the
batteries won't be severely overheated, and the amount of their life
that's lost by overcharging will probably not be a lot. Instead of
them lasting for 3 or 4 years, they might only last 2 or 3, and
after a couple of years, even if they're still performing fairly
well, you might want to replace them with a new set of 3,300 mAh
batteries.

ASAAR, Apr 30, 2006
4. ### Joseph MeehanGuest

wrote:
>I have the Energizer CHDC charger and I checked online and I cant
> figure out how htye are calculating the charging times:
> http://data.energizer.com/PDFs/chdc.pdf
>
> I have a set of 2300 mAH Energizer batteries and I don't want to
> charge them too long.
>
> Anyone know what "math" Energizer seems to be using?
>
> Thanks

Too many variables to have an accurate answer. Get a good charger and
don't worry.

--
Joseph Meehan

Dia duit

Joseph Meehan, Apr 30, 2006
5. ### Guest

Thanks everyone. What's a good charger that can keep up with
increasing capacity of the batteries? I recall the Energizer has (at
least in the past) capped the maximum mAh in their larger chargers.

, Apr 30, 2006
6. ### GuestGuest

Thanks everyone. What's a good charger that can keep up with
increasing capacity of the batteries? I recall the Energizer has (at
least in the past) capped the maximum mAh in their larger chargers?

Guest, May 2, 2006
7. ### Bob SalomonGuest

In article <dRC5g.105075\$P01.77643@pd7tw3no>, <>
wrote:

> Thanks everyone. What's a good charger that can keep up with
> increasing capacity of the batteries? I recall the Energizer has (at
> least in the past) capped the maximum mAh in their larger chargers?

The new Ansmann Energy 8 Pro is rated for AA NiMh up to 6400 mAh.

--

Bob Salomon, May 2, 2006
8. ### Thomas T. VeldhouseGuest

wrote:
> Thanks everyone. What's a good charger that can keep up with
> increasing capacity of the batteries? I recall the Energizer has (at
> least in the past) capped the maximum mAh in their larger chargers?

Maha C401FS .... it is an awesome little piece of equipment.

--
Thomas T. Veldhouse
Key Fingerprint: 2DB9 813F F510 82C2 E1AE 34D0 D69D 1EDC D5EC AED1

Thomas T. Veldhouse, May 2, 2006
9. ### Guest

Thanks again. Curious though, quick or rapid chargers are recommended.
I was under the impression it's better for the batteries to be slow
charged?

, May 3, 2006
10. ### SMSGuest

wrote:
> Thanks again. Curious though, quick or rapid chargers are recommended.
> I was under the impression it's better for the batteries to be slow
> charged?

The batteries will have a larger number of cycles if they aren't charged
with a very high current. Probably not worth worrying much about, but
the better chargers don't charge at a high rate.

SMS, May 3, 2006
11. ### SMSGuest

wrote:
> Thanks everyone. What's a good charger that can keep up with
> increasing capacity of the batteries? I recall the Energizer has (at
> least in the past) capped the maximum mAh in their larger chargers?

Technically, they have a timer that times out, after what used to be
sufficient time to charge even the highest capacity batteries. I'm sure
that they'll come out with updated models that don't have this
limitation. The timer is supposed to be a fail-safe way of terminating
charging, if the other detection methods don't work for some reason.

The charger makers may want to put a switch on the charger for high
capacity batteries, to increase the duration of the timer from three
hours to maybe six hours.

SMS, May 3, 2006
12. ### ASAARGuest

On 2 May 2006 21:51:21 -0700, wrote:

> Thanks again. Curious though, quick or rapid chargers are
> recommended. I was under the impression it's better for the
> batteries to be slow charged?

Yes, if you're using an old timer based charger, since there were
many ways that the charger could end up charging the batteries well
beyond the point where they reached a full charge. If a fast
charger was used, the batteries could be severely overheated,
shortening their lives. With "smart" chargers, even if the very
fast ones aren't quite as gentle as the slower chargers, significant
damage won't occur, and you'll get long life (many charge cycles)
whether a fast or a slow charger is used. I use a slower charger
more often, but only because it's smaller and more convenient. I
rarely need to quickly charge a large number of batteries, but that
need arises, I've got several fast (30 and 60 minute) chargers
available. More important than whether you get a fast or slow
charger, is to get one that charges each cell independently. If you
find a charger that only charges batteries in pairs, skip it.

ASAAR, May 3, 2006
13. ### Thomas T. VeldhouseGuest

wrote:
>
> Thanks again. Curious though, quick or rapid chargers are recommended.
> I was under the impression it's better for the batteries to be slow
> charged?
>

It is better to charge slow, mostly because of the fact that a battery will
take a charge more efficiently and take more of a charge when it is cool in
temperature. Fast charging raises the temperature of a battery. There are
other reasons I believe, but that is a large one.

--
Thomas T. Veldhouse
Key Fingerprint: 2DB9 813F F510 82C2 E1AE 34D0 D69D 1EDC D5EC AED1

Thomas T. Veldhouse, May 3, 2006
14. ### Bob SalomonGuest

In article <44589d85\$0\$277\$>,
"Thomas T. Veldhouse" <> wrote:

> It is better to charge slow, mostly because of the fact that a battery will
> take a charge more efficiently and take more of a charge when it is cool in
> temperature.

Some chargers, like the Ansmann Digispeed and Digispeed Ultra have a
temperature controlled exhaust fan in the charger to draw heat off from
the cells when the temperature rises during charging. These automatic
fans keep the batteries at the proper temperature even in the Digispeed
Ultra which charges most cells in 10 minutes to full charge.

--

Bob Salomon, May 3, 2006
15. ### Thomas T. VeldhouseGuest

Bob Salomon <> wrote:
> In article <44589d85\$0\$277\$>,
> "Thomas T. Veldhouse" <> wrote:
>
>> It is better to charge slow, mostly because of the fact that a battery will
>> take a charge more efficiently and take more of a charge when it is cool in
>> temperature.

>
> Some chargers, like the Ansmann Digispeed and Digispeed Ultra have a
> temperature controlled exhaust fan in the charger to draw heat off from
> the cells when the temperature rises during charging. These automatic
> fans keep the batteries at the proper temperature even in the Digispeed
> Ultra which charges most cells in 10 minutes to full charge.
>

I'll tell you what. If a fan is required, then the core of that battery is
going to be hot ... and it will not charge efficiently. Also, heat is not the
only fact, resistance is another, and of course, how the battery has been
conditioned (the better Maha chargers claim to have an algorithm they use to
charge the battery that eliminates the need to condition a battery).

10 minutes ... I suspect the charger is manufacturer is figuring that its
users would prefer to replace batteries more often then to charge slowly. I
find it a rare case that I actually need to quick charge. I keep a couple of
batteries charged as spares and then charge at slow speeds for most charges.
There are cases I want power fast and I will use the fast charge (like a
spontaneous photo opportunity and I need to power my flash), but they are few
and far between.

--
Thomas T. Veldhouse
Key Fingerprint: 2DB9 813F F510 82C2 E1AE 34D0 D69D 1EDC D5EC AED1

Thomas T. Veldhouse, May 3, 2006
16. ### SMSGuest

Thomas T. Veldhouse wrote:

> I'll tell you what. If a fan is required, then the core of that battery is
> going to be hot ... and it will not charge efficiently. Also, heat is not the
> only fact, resistance is another, and of course, how the battery has been
> conditioned (the better Maha chargers claim to have an algorithm they use to
> charge the battery that eliminates the need to condition a battery).

The ultra high-rate chargers such as the Ansmann Digispeed and Digispeed
Ultra should be avoided. There is rarely a need to charge the batteries
that fast, and the high charging current and high heat has a very
negative effect on battery life. The fan will dissipate the heat into
the air, but it doesn't help the battery life.

SMS, May 4, 2006
17. ### Bob SalomonGuest

In article <4459726d\$0\$96921\$>,
SMS <> wrote:

> The fan will dissipate the heat into
> the air, but it doesn't help the battery life.

Certainly has not hurt the cells to date.

--

Bob Salomon, May 4, 2006
18. ### Bart van der WolfGuest

"Bob Salomon" <> wrote in message
news:...
> In article <4459726d\$0\$96921\$>,
> SMS <> wrote:
>
>> The fan will dissipate the heat into
>> the air, but it doesn't help the battery life.

>
> Certainly has not hurt the cells to date.

Is there any evidence for that, e.g. a link to some research? I'm
serious, all I've ever heard/read over the years is that rapid
charging reduces useful life of NiCd/NiMH batteries. It's to do with
the heat generated when the cells reach approx. 80% of their capacity,
more heat changes the chemical ability to recharge. I'd love to see a
good study on that subject.

Bart

Bart van der Wolf, May 4, 2006
19. ### Paul RubinGuest

"Bart van der Wolf" <> writes:
> Is there any evidence for that, e.g. a link to some research? I'm
> serious, all I've ever heard/read over the years is that rapid
> charging reduces useful life of NiCd/NiMH batteries. It's to do with
> the heat generated when the cells reach approx. 80% of their capacity,
> more heat changes the chemical ability to recharge. I'd love to see a
> good study on that subject.

The rapid chargers that I know of stop charging when that happens.
They switch over to a slow charge, so to get a complete charge takes
several hours. But being able to get the cells up to 80% in 15
minutes is very useful.

Paul Rubin, May 4, 2006
20. ### SMSGuest

Bart van der Wolf wrote:
>
> "Bob Salomon" <> wrote in message
> news:...
>> In article <4459726d\$0\$96921\$>,
>> SMS <> wrote:
>>
>>> The fan will dissipate the heat into
>>> the air, but it doesn't help the battery life.

>>
>> Certainly has not hurt the cells to date.

>
> Is there any evidence for that, e.g. a link to some research? I'm
> serious, all I've ever heard/read over the years is that rapid charging
> reduces useful life of NiCd/NiMH batteries. It's to do with the heat
> generated when the cells reach approx. 80% of their capacity, more heat
> changes the chemical ability to recharge. I'd love to see a good study
> on that subject.

Remember, Bob Salomon is the distributer for the Ansmann chargers. So of
course he's going to say what he says.

The fact is that high rate charging, which raises the temperature of the
batteries considerable, reduces the number of charge cycles.

As Isidor Buchmann writes "High temperature during charge and standby
kills batteries."

It'd be interesting to test the number of cycles of the same battery
type using both a normal rate and a high rate charger to see just what
the difference in the number of cycles would be.

It's not usually necessary to charge batteries at such a high rate, so
those very high rate chargers should be avoided unless someone really
needs a super-fast charge.

SMS, May 4, 2006