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Sci.Electronics.Basics -> Two battery related questions ...
There are 3 messages in this thread.
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Author: purple_starsDate: 23:09 12-12-06
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Hi folks,
I use a bank of NiMH batteries to power some mobile equipment and I
currently charge the bank with a small 6.5 watt folding solar panel.
Works great. One nice extra of this setup is that the banks are made
from AA batteries so I can swap out charged batteries from the banks
and put them into electronics I use while in the outdoors, like my GPS
receiver for example, and put the spent/drained batteries back into the
bank where they eventually recharge. But using this system has brought
up two questions in my mind that I would like answers to ...
#1 - My battery banks are made out of 4 banks, each bank having 10 NiMH
AA cells wired in series to make 12 volts. Those 4 banks are wired in
parallel to supply the amps I want. They are all made of AA batteries.
As I said above I sometimes swap batteries out and use the banks like
a battery charger for personal electronics, very convenient. What I
would like to do is make one of the banks out of AAA batteries instead
of AA batteries for that very reason, so I could also charge up AAA
batteries. Some of my electronics use AAA instead of AA.
So the question is .... What will happen if instead of using 4
identical banks wired up in parallel I instead use 3 banks made of AA
batteries and 1 bank made of AAA batteries. They would all still be 12
volt banks, but the AAA bank would have much less capacity. What will
that do to my overall "battery" when it recharges ? Will it still
fully charge using the solar panel even though one of the banks has a
smaller capacity ?
#2 - Right now I am using just the solar panel to recharge the banks,
but it would be great to have the flexibility of using other charge
sources that are available. If I was near an outlet I would love to
use a 12 volt wall wart or even an automobile alternator to recharge my
battery bank. Problem is I don't know if it will work. For one thing
I do know that the NiMH batteries get warm if they are given a lot of
current, how warm I have never tried to find out .. would they burn up
or something ? Would they burn up a 12 volt supply by eating up too
many amps while recharging ? The solar panel setup is kind of
self-regulating in that it can only supply about 1/2 of an amp on a
full sunny day, so the batteries can't recharge but so fast. But if I
hook the batteries up to an automobile electrical system they could
have all the amps they want, what is going to happen if I do that ?
That is all rather long winded I know ... but I wanted to make sure I
was clear about what I was doing. Does anyone know the answer to these
two questions ?
Thanks in advance!
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Author: ehsjrDate: 00:43 13-12-06
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purple_stars wrote:
> Hi folks,
>
> I use a bank of NiMH batteries to power some mobile equipment and I
> currently charge the bank with a small 6.5 watt folding solar panel.
> Works great. One nice extra of this setup is that the banks are made
> from AA batteries so I can swap out charged batteries from the banks
> and put them into electronics I use while in the outdoors, like my GPS
> receiver for example, and put the spent/drained batteries back into the
> bank where they eventually recharge. But using this system has brought
> up two questions in my mind that I would like answers to ...
>
> #1 - My battery banks are made out of 4 banks, each bank having 10 NiMH
> AA cells wired in series to make 12 volts. Those 4 banks are wired in
> parallel to supply the amps I want. They are all made of AA batteries.
> As I said above I sometimes swap batteries out and use the banks like
> a battery charger for personal electronics, very convenient. What I
> would like to do is make one of the banks out of AAA batteries instead
> of AA batteries for that very reason, so I could also charge up AAA
> batteries. Some of my electronics use AAA instead of AA.
>
> So the question is .... What will happen if instead of using 4
> identical banks wired up in parallel I instead use 3 banks made of AA
> batteries and 1 bank made of AAA batteries. They would all still be 12
> volt banks, but the AAA bank would have much less capacity. What will
> that do to my overall "battery" when it recharges ? Will it still
> fully charge using the solar panel even though one of the banks has a
> smaller capacity ?
>
> #2 - Right now I am using just the solar panel to recharge the banks,
> but it would be great to have the flexibility of using other charge
> sources that are available. If I was near an outlet I would love to
> use a 12 volt wall wart or even an automobile alternator to recharge my
> battery bank. Problem is I don't know if it will work. For one thing
> I do know that the NiMH batteries get warm if they are given a lot of
> current, how warm I have never tried to find out .. would they burn up
> or something ? Would they burn up a 12 volt supply by eating up too
> many amps while recharging ? The solar panel setup is kind of
> self-regulating in that it can only supply about 1/2 of an amp on a
> full sunny day, so the batteries can't recharge but so fast. But if I
> hook the batteries up to an automobile electrical system they could
> have all the amps they want, what is going to happen if I do that ?
>
> That is all rather long winded I know ... but I wanted to make sure I
> was clear about what I was doing. Does anyone know the answer to these
> two questions ?
>
> Thanks in advance!
>
It's not the best way to charge NiMh, but you can probably
get away with it. The auto system won't overcharge the packs -
unless there is a defect, like a shorted cell, in a pack - if
you charge each pack through a diode. (If one cell is shorted,
you can overcharge the other cells.) It also won't charge the
packs fully. In general, you can figure the auto system will
deliver ~ 14.4 volts when running. The diode will drop ~ .6 V
so the NiMh pack will get ~ 13.8. (The diode also prevents
discharging the NiMh packs into the car's battery.) For full
charge, the pack needs ~ 14.1 volts. If the car is not running,
the charge on the packs will be even less.
Ed
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Author: jasenDate: 14:18 13-12-06
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On 2006-12-13, purple_stars <webnews1@hotmail.com> wrote:
> So the question is .... What will happen if instead of using 4
> identical banks wired up in parallel I instead use 3 banks made of AA
> batteries and 1 bank made of AAA batteries. They would all still be 12
> volt banks, but the AAA bank would have much less capacity. What will
> that do to my overall "battery" when it recharges ? Will it still
> fully charge using the solar panel even though one of the banks has a
> smaller capacity ?
likely the smaller will overcharged and damaged.
> #2 - Right now I am using just the solar panel to recharge the banks,
> but it would be great to have the flexibility of using other charge
> sources that are available. If I was near an outlet I would love to
> use a 12 volt wall wart or even an automobile alternator to recharge my
> battery bank. Problem is I don't know if it will work.
hook thre wall-wart to the input of your charge controller insted of the
solar panel.
> For one thing I do know that the NiMH batteries get warm if they are
> given a lot of current, how warm I have never tried to find out ..
> would they burn up or something ?
boil dry.
> Would they burn up a 12 volt supply by eating up too many amps while
> recharging ?
the charge controller should stop that.
> The solar panel setup is kind of
> self-regulating in that it can only supply about 1/2 of an amp on a
> full sunny day, so the batteries can't recharge but so fast. But if I
> hook the batteries up to an automobile electrical system they could
> have all the amps they want, what is going to happen if I do that ?
something like that
> That is all rather long winded I know ... but I wanted to make sure I
> was clear about what I was doing. Does anyone know the answer to these
> two questions ?
first off it sounds like your charging setup is incomplete
secondly series charging of different batteries, or ones
with different histories, is not a good for them.
get a 12V operated NiMh charger
Bye.
Jasen
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