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Keeping NiMh batteries charged without overcharging them

 
 
Daniel Prince
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      07-17-2006
I know that this is off topic for this newsgroup but there is a lot
of battery discussion here.

My brother just bought a set of two FRS radios that came with NiMh
rechargeable battery packs and a charging stand (Motorola Talkabout
T5000R). The manual says that the battery packs are Nicad but they
are NiMh. The manual says to charge the battery packs for 16 hours
the first time and then after the first charge 14 hours. The manual
also says that the battery packs should not be charged for more than
16 hours.

Can I keep these battery packs fully charged by putting the charger
on a timer? If so, how many minutes per day should they be charged?
Thank you in advance for all replies.
 
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Dennis Pogson
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      07-17-2006
Daniel Prince wrote:
> I know that this is off topic for this newsgroup but there is a lot
> of battery discussion here.
>
> My brother just bought a set of two FRS radios that came with NiMh
> rechargeable battery packs and a charging stand (Motorola Talkabout
> T5000R). The manual says that the battery packs are Nicad but they
> are NiMh. The manual says to charge the battery packs for 16 hours
> the first time and then after the first charge 14 hours. The manual
> also says that the battery packs should not be charged for more than
> 16 hours.
>
> Can I keep these battery packs fully charged by putting the charger
> on a timer? If so, how many minutes per day should they be charged?
> Thank you in advance for all replies.


The answer to this conundrum is dependant on how much you have used the
batteries each day plus a small amount of self-discharge. I wouls say it is
not possible to use a timer effectively unless it is connected to a charger
which switches off once the batteries are fully charged. There are many such
chargers around.


 
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Roger Whitehead
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      07-17-2006
In article <(E-Mail Removed)>, Daniel Prince
wrote:
> I know that this is off topic for this newsgroup but there is a lot
> of battery discussion here.


Here's a useful resource - http://www.batteryuniversity.com .


Roger

 
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=?iso-8859-1?Q?mark=5Fdigital=A9?=
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      07-17-2006

"Daniel Prince" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>I know that this is off topic for this newsgroup but there is a lot
> of battery discussion here.
>
> My brother just bought a set of two FRS radios that came with NiMh
> rechargeable battery packs and a charging stand (Motorola Talkabout
> T5000R). The manual says that the battery packs are Nicad but they
> are NiMh. The manual says to charge the battery packs for 16 hours
> the first time and then after the first charge 14 hours. The manual
> also says that the battery packs should not be charged for more than
> 16 hours.
>
> Can I keep these battery packs fully charged by putting the charger
> on a timer? If so, how many minutes per day should they be charged?
> Thank you in advance for all replies.


Do you think it was a typo or do you think the instructions are actually for
Nicads?
Applying what I know about NiMh cells in a hybrid car, they are generally
topped off to the 3/4 full capacity and generally not allowed to drain below
1/4 remaining capacity. It's meant to extend the life of the cells.
What we do know about your batteries is they will lose their charge. If we
go by a guideline of 1% loss each day then maybe about 10 minutes on the
charger will maintain the batteries at what ever level they may be at. In
other words, if the batteries have 1/2 their power reserve, 10 minutes on
the charger will keep them at 1/2 their power reserve. If we use 14 hours as
the "going from dead to full charge state" then it would be about 8 minutes
a day.
If it were me I would just get a battery tester and go from there.
mark_

 
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Daniel Prince
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      07-17-2006
"Dennis Pogson" <(E-Mail Removed)> wrote:

>Daniel Prince wrote:
>> I know that this is off topic for this newsgroup but there is a lot
>> of battery discussion here.
>>
>> My brother just bought a set of two FRS radios that came with NiMh
>> rechargeable battery packs and a charging stand (Motorola Talkabout
>> T5000R). The manual says that the battery packs are Nicad but they
>> are NiMh. The manual says to charge the battery packs for 16 hours
>> the first time and then after the first charge 14 hours. The manual
>> also says that the battery packs should not be charged for more than
>> 16 hours.
>>
>> Can I keep these battery packs fully charged by putting the charger
>> on a timer? If so, how many minutes per day should they be charged?
>> Thank you in advance for all replies.

>
>The answer to this conundrum is dependant on how much you have used the
>batteries each day plus a small amount of self-discharge. I wouls say it is
>not possible to use a timer effectively unless it is connected to a charger
>which switches off once the batteries are fully charged. There are many such
>chargers around.


Most of the time the batteries will not be used at all.

Here are some pictures of one of the battery packs:

http://img242.imageshack.us/my.php?i...ict0354gt2.jpg

http://img119.imageshack.us/my.php?i...ict0352up0.jpg

Are there automatic chargers that will work with these battery
packs?
 
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Daniel Prince
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      07-17-2006
mark_digital© <(E-Mail Removed)> wrote:

>
>"Daniel Prince" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed).. .
>>I know that this is off topic for this newsgroup but there is a lot
>> of battery discussion here.
>>
>> My brother just bought a set of two FRS radios that came with NiMh
>> rechargeable battery packs and a charging stand (Motorola Talkabout
>> T5000R). The manual says that the battery packs are Nicad but they
>> are NiMh. The manual says to charge the battery packs for 16 hours
>> the first time and then after the first charge 14 hours. The manual
>> also says that the battery packs should not be charged for more than
>> 16 hours.
>>
>> Can I keep these battery packs fully charged by putting the charger
>> on a timer? If so, how many minutes per day should they be charged?
>> Thank you in advance for all replies.

>
>Do you think it was a typo or do you think the instructions are actually for
>Nicads?


The instructions and table of contents say "NiCd" several times and
never mention NiMh. The battery packs are clearly marked NiMh. I
think the manual was written when they used NiCd battery packs and
not updated when they switched to NiMh technology.

>If it were me I would just get a battery tester and go from there.


What kind of tester would I need for the battery packs in the
pictures below?

http://img242.imageshack.us/my.php?i...ict0354gt2.jpg

http://img119.imageshack.us/my.php?i...ict0352up0.jpg

 
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ASAAR
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      07-17-2006
On Mon, 17 Jul 2006 11:35:54 -0700, Daniel Prince wrote:

> What kind of tester would I need for the battery packs in the
> pictures below?
>
> http://img242.imageshack.us/my.php?i...ict0354gt2.jpg
>
> http://img119.imageshack.us/my.php?i...ict0352up0.jpg


It wouldn't be very practical to try to test those battery packs.
Relatively inexpensive testers can be had, but they're usually
designed to test individual cells. From the images, it appears that
those battery packs contain 3 AAA NiMH cells. Perhaps AAA was used
to minimize the size, but Motorola also makes several very small FRS
radios that use 3 AA batteries, so if you ever plan to get
additional FRS radios, look for them. As NiMH batteries can now be
easily found with capacities in the 2,500 to 2,700 mah range, that
would give them 4 times the capacity of the rather anemic battery
packs used by your Motorola FRS radios.


> Can I keep these battery packs fully charged by putting the charger
> on a timer? If so, how many minutes per day should they be charged?


The best way to keep the batteries charged depends to a great
extent on how often you use the radios. What complicates the matter
is that your charger doesn't appear to be a "smart" charger that
knows when to stop charging. You should have at least on more
battery pack than you have radios. From your battery's standpoint,
it would be best for them if you use the radios frequently enough so
that any battery pack in the radio would be fully depleted in
anywhere from one day to several weeks. Whenever the battery pack
goes dead, pop in the spare battery pack that's fully charged, and
put the dead battery pack back in the charger for another 14 hours
of charging. The spare battery (like most rechargeable batteries)
will slowly lose charge while sitting unused, but if it's eventually
used in one of the radios within several weeks of its last session
in the charger, it will be close enough to being fully charged so
that whatever charge it lost won't be a significant amount.

The problem for the batteries would occur if you don't use the
radio very frequently. Then you'd often be in the position of
needing to recharge battery packs that still have a good amount of
charge left in them, and it would be best for the batteries if they
were charged only long enough to be fully charged. Whether this
would be 2, 5, 7 or 11 hours, you'd have no way to tell, and could
only guess based on experience. At least your charger is a very
slow one, so overcharging probably wouldn't overheat the batteries
very much, which is very hard on them. What's even worse for
batteries is non-use. If you get tired of using the radios at the
end of this summer and pack them away for next year's use, this can
greatly reduce the battery's performance. Unlike some rechargeable
battery types (ie, some lithium formulations) that can be totally
ruined if they go a year or more between charges, NiMH probably
wouldn't be ruined, but they might lose a substantial amount of
their capacity.

It would be good to be able to estimate (roughly) when the
batteries need to be recharged. Check your manual. It might show
how long batteries last for both receiving (affected by audio
volume) and transmitting. Then if you think that the radio has used
up at least 3/4 of its charge, swap it with the spare battery if
you're near the charger. If you're away from home and using the
radio, continue using it until you see a battery warning (assuming
that the Motorola shows one) and then swap battery packs.

 
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=?iso-8859-1?Q?mark=5Fdigital=A9?=
Guest
Posts: n/a
 
      07-18-2006

"Daniel Prince" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> mark_digital© <(E-Mail Removed)> wrote:
>
>>
>>"Daniel Prince" <(E-Mail Removed)> wrote in message
>>news:(E-Mail Removed). ..
>>>I know that this is off topic for this newsgroup but there is a lot
>>> of battery discussion here.
>>>
>>> My brother just bought a set of two FRS radios that came with NiMh
>>> rechargeable battery packs and a charging stand (Motorola Talkabout
>>> T5000R). The manual says that the battery packs are Nicad but they
>>> are NiMh. The manual says to charge the battery packs for 16 hours
>>> the first time and then after the first charge 14 hours. The manual
>>> also says that the battery packs should not be charged for more than
>>> 16 hours.
>>>
>>> Can I keep these battery packs fully charged by putting the charger
>>> on a timer? If so, how many minutes per day should they be charged?
>>> Thank you in advance for all replies.

>>
>>Do you think it was a typo or do you think the instructions are actually
>>for
>>Nicads?

>
> The instructions and table of contents say "NiCd" several times and
> never mention NiMh. The battery packs are clearly marked NiMh. I
> think the manual was written when they used NiCd battery packs and
> not updated when they switched to NiMh technology.
>
>>If it were me I would just get a battery tester and go from there.

>
> What kind of tester would I need for the battery packs in the
> pictures below?
>
> http://img242.imageshack.us/my.php?i...ict0354gt2.jpg
>
> http://img119.imageshack.us/my.php?i...ict0352up0.jpg
>


I have NiCad's their charger wouldn't charge anymore, and at $90 per battery
pack it turned my stomach to discard them. I gave them to my son-in-law and
cycled them thru a "mindless" charger (a charger with the same
characteristics as yours). I got them back and when it came time to
recharge them my charger did just that. So, there's pros and cons to
dedicated automatic chargers.
Bring the battery pack to Radio Shack (or similar outfit) and they'll show
you a simple multi-tester with probes.
You say you or your brother won't be using the batteries most of the time.
Is it because you'll be using an adapter or you won't be using the radios
often? I'm not familiar with those radios and whether or not they can be
powered by an ac to dc power supply or from a vehicle's electrical system.

mark_

 
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Daniel Prince
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      07-19-2006
mark_digital© <(E-Mail Removed)> wrote:

>Bring the battery pack to Radio Shack (or similar outfit) and they'll show
>you a simple multi-tester with probes.


I have several digital multimeters but from what I have read it is
not possible to determine the state of charge of NiCd or NiMh
batteries just by measuring the voltage of the cells or packs. If
it is possible, what voltage would correspond to what state of
charge?

For example what would the voltage of this pack be when it was 50
percent charged?

What would the voltage of this pack be when it was 25 percent
charged?

What would the voltage of this pack be when it was ten percent
charged?

>You say you or your brother won't be using the batteries most of the time.
>Is it because you'll be using an adapter or you won't be using the radios
>often?


We use the radios when we go out together to large stores, swap
meets, parks and amusement parks etc. Sometimes we use the radios
two or three days a month and sometimes we go a couple of months
without using them.
--
Never ever let your brain explode. It's VERY bad for you and
it leaves a terrible mess for someone to clean up.
 
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EDM
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      07-19-2006
"Daniel Prince" <(E-Mail Removed)> wrote in message news:(E-Mail Removed)...
> mark_digital© <(E-Mail Removed)> wrote:
>
> >Bring the battery pack to Radio Shack (or similar outfit) and they'll show
> >you a simple multi-tester with probes.

>
> I have several digital multimeters but from what I have read it is
> not possible to determine the state of charge of NiCd or NiMh
> batteries just by measuring the voltage of the cells or packs. If
> it is possible, what voltage would correspond to what state of
> charge?


Chargers don't measure charge state by voltage. They do it by
resistance. When cells are at or near their capacity, resistance
skyrockets.



 
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