Velocity Reviews > How long to charge AA NiMH?

# How long to charge AA NiMH?

Ed Wicks
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 12-28-2006
I have a Sony BC-CS1 charger. Apparently the charging light never goes
out.
How long should I charge a AA NiMH battery? Thx. Ed

Cgiorgio
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 12-28-2006
Until it is fully charged. When charged with a fairly high current (greater
than about 1/4th of capacity), NiMH batteries start to heat up, (most of the
energy is converted to heat) and the terminal voltage drops slightly. Decent
chargers will detect this state for every single cell and either switch the
charge current off or switch to trickle charge for maintaining the charge. I
do not know about the Sony BC-CS1. For example the better models from GP and
others work fine this way. As a rule of thumb, a fully discharged new NiMH
battery can be charged with 1.4 times its capacity before overcharging sets
in.

"Ed Wicks" <(E-Mail Removed)> schrieb im Newsbeitrag
news:281220060820456637%(E-Mail Removed)...
>I have a Sony BC-CS1 charger. Apparently the charging light never goes
> out.
> How long should I charge a AA NiMH battery? Thx. Ed

Bob Salomon
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 12-28-2006
In article <281220060820456637%(E-Mail Removed)>,
Ed Wicks <(E-Mail Removed)> wrote:

> I have a Sony BC-CS1 charger. Apparently the charging light never goes
> out.
> How long should I charge a AA NiMH battery? Thx. Ed

Until it is charged. How long does that take?

Take the mAh rating of the battery. Add 30% and divide that by the
chargers output. That is how long it takes that charger to recharge that
battery if that cell is fully uncharged.

--

=?iso-8859-1?B?bWlubmVz+HR0aQ==?=
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 12-28-2006

Ed Wicks wrote:
> I have a Sony BC-CS1 charger. Apparently the charging light never goes
> out.
> How long should I charge a AA NiMH battery? Thx. Ed

The NiMH batteries are known for high tolerance to overcharging. If you
charge your battery for 8 hours, it will definetely be charged (there
are no other chargers which are made for charging for longer).

Mardon
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 12-28-2006
Bob Salomon <(E-Mail Removed)> wrote:

> Until it is charged. How long does that take?
>
> Take the mAh rating of the battery. Add 30% and divide that by the
> chargers output. That is how long it takes that charger to recharge that
> battery if that cell is fully uncharged.

Close but not quite. The "Operating Instructions" sheet packed with my
Sony BCG-34HUF charger specify a 15 minute charge time for 2500mA NH-AA
batteries. The charging output is specified as 7.5 amps at 5.6 volts DC.
You formula calculates 26 minutes. If you deduct the 30% instead of adding
it, the formula calculates 14 minutes. Did you mean to say "add 30%" or
should it have been "subtract 30%" or does this particular charger just

Ken Weitzel
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Posts: n/a

 12-28-2006
Ed Wicks wrote:
> I have a Sony BC-CS1 charger. Apparently the charging light never goes
> out.
> How long should I charge a AA NiMH battery? Thx. Ed

Hi...

That charger is little more than a trickle charger; it charges at only
70 mil's. So if you were charging 2500 mA batteries from "empty" to
completely topped up, it would take a little more than two days to finish.

Take care.

Ken

ASAAR
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 12-28-2006
On Thu, 28 Dec 2006 08:20:45 -0500, Ed Wicks wrote:

> I have a Sony BC-CS1 charger. Apparently the charging light never goes
> out.
> How long should I charge a AA NiMH battery? Thx. Ed

How long have you waited for the light to go out? Some old
chargers have lights that don't indicate when the batteries have
reached a full charge, and use the light only to indicate that the
charger is powered on and is still charging, even if the batteries
have been charged so long that they're now being overcharged.

A figure can't be given for that charger unless you know the
actual capacity of the AA batteries. The BC-CS1 is an old, *slow*
charger that took 13 hours to charge 1,750mAh AA batteries. If you
have the original AA cells that came with the charger, they're
probably pretty old and have lost a lot of their original capacity.
So if by now they're providing only 1,200mAh, they'd charge quicker,
taking about 9 hours to reach full charge. But if you buy new
2,700mAh batteries, they would need just over 20 hours to complete
charging. Such old chargers usually had timer cutoffs, so that they
might stop charging after about 15 hours, and the 2,700mAh batteries
wouldn't fully charge with only a single charge cycle. If the
charger's charging light went out at 15 hours, the 2,700mAh
batteries would only be 75% charged.

You should probably get a new "smart" charger, one that knows when
the batteries are fully charged and stops charging at that point,
instead of continuing to charge until a time limit is reached.
They'll be able to deal with modern high capacity NiMH cells, and
depending on the model, can fully charge AA cells in less than a
couple of hours. There are some very high current chargers that can
fully charge AA cells in as little as 15 minutes, but the NiMH
batteries would probably last longer if you get a gentler charger
that takes an hour or more to finish charging.

Paul Allen
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 12-28-2006
On Thu, 28 Dec 2006 08:20:45 -0500
Ed Wicks <(E-Mail Removed)> wrote:

> I have a Sony BC-CS1 charger. Apparently the charging light never goes
> out.
> How long should I charge a AA NiMH battery? Thx. Ed

Here's the summary I wrote up back in 2002, including a link to
definitive backup material by Marc Venis and a handy Java charging
time calculator:

http://paulngail1.home.comcast.net/batteries.html

Charging time does matter. If your charger is not one of the newer
automatic types, you must know the charging current and the capacity
of your batteries in order to calculate the approximate time to a
full charge. If your charger does not have its charging current
listed on its label, throw it out and buy a better one.

Paul Allen

Just Another Digital Fan
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 12-28-2006

Ken Weitzel wrote:

> That charger is little more than a trickle charger; it charges at only
> 70 mil's. So if you were charging 2500 mA batteries from "empty" to
> completely topped up, it would take a little more than two days to finish.

LOL I got my first N-Mh AA 2600mA cells last week and only have an old
Uniross charger which states it charges at 150 mA.

I make that around 24.6 hours for a full charge! Must get a modern
charger....

The rule of thumb I used with slow charge Ni-Cd's is capacity/10 for 14
hours.

Freedom55
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 12-28-2006
Ed Wicks wrote:
> I have a Sony BC-CS1 charger. Apparently the charging light never goes
> out.
> How long should I charge a AA NiMH battery? Thx. Ed

I have 2500 NiMH batteries which take 27 hours to charge in my 140mA
charger.

Ron

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Where I belong I'm right
Where I belong.

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