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Mike Fox
Guest
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 Posted:
Sun Dec 19, 2004 9:41 pm Post subject:
To Battery Mavins |
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A little off topic, but I got so aggrevated with NiMH batteries
pooping out in my GPS that I decided to test them and get rid of the
marginal ones. When I looked into battery testers, they seemed to
start about $100, at which time I decided to make my own, but I need
some advice on what load to test the batteries at.
I got an old analog travel clock that runs on a single AA battery and
an external AA battery holder and soldered the connections together so
the external battery runs the clock. Then I soldered some connectors
into the circuit so I can put various loads in parallel with the clock
but in series with an ammeter. When the clock stops, I've got hours
and milliamps.
What I need advice on is what load is too much and will damage the
batteries? The eTrex Legend draws somewhere about 100 milliamps (mA),
but with a load of 118 mA, it took over 14.7 hours to discharge a
brand new fully charged 2500 mAh battery; that's way too long to wait.
[As an aside, that's only 1730 mAh out of a brand new 2500 mAh
battery. Anybody have any thoughts on why?]
Anyway, I can put on loads of 250, 350 and 600 mA. Does anybody have
a feel if 600 mA is too big a load and will damage a battery?
Thanks
Mike |
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Guest
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| Posted:
Sun Dec 19, 2004 10:37 pm Post subject:
Re: To Battery Mavins |
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On Sun, 19 Dec 2004 16:41:44 GMT, Mike Fox <mikefox@satx.rr.com> wrote:
| Quote: | [As an aside, that's only 1730 mAh out of a brand new 2500 mAh
battery. Anybody have any thoughts on why?]
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They are rated at so many milliamp-hours AT A CERTAIN LOAD. If you load
it less than the drain spec, you'll get more mAh out of a cell, but load
it more and you'll get less than advertised.
gm
--
Replace x in adr with c |
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Fred Hiltz
Guest
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| Posted:
Sun Dec 19, 2004 10:37 pm Post subject:
Re: To Battery Mavins |
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Mike Fox wrote:
| Quote: | A little off topic, but I got so aggrevated with NiMH batteries
pooping out in my GPS that I decided to test them and get rid of
the marginal ones. When I looked into battery testers, they
seemed to start about $100, at which time I decided to make my
own, but I need some advice
[snip]
on is what load is too much and will damage the
batteries? The eTrex Legend draws somewhere about 100 milliamps
(mA), but with a load of 118 mA, it took over 14.7 hours to
discharge a brand new fully charged 2500 mAh battery; that's way
too long to wait. [As an aside, that's only 1730 mAh out of a
brand new 2500 mAh battery. Anybody have any thoughts on why?]
Anyway, I can put on loads of 250, 350 and 600 mA. Does anybody
have a feel if 600 mA is too big a load and will damage a battery?
|
Dave Etchells describes his battery testing equipment and methods at
http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM with comments
on constant-load versus constant-power testing.
http://www.batteryuniversity.com/index.htm has more than you
probably want to know about testing, including minutiae like the
improvement after a few cycles of discharge and the dependence of
measured capacity on the current drain and temperature. Have fun!
--
Fred Hiltz, fhiltz at yahoo dot com |
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Brian Morrison
Guest
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| Posted:
Mon Dec 20, 2004 4:04 am Post subject:
Re: To Battery Mavins |
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On Sun, 19 Dec 2004 14:28:34 -0700, in article
<tesbs0546t1o3guekplu239c8v0mdcvepd@4ax.com> mxduffie@axtxom.net wrote:
| Quote: | On Sun, 19 Dec 2004 16:41:44 GMT, Mike Fox <mikefox@satx.rr.com> wrote:
[As an aside, that's only 1730 mAh out of a brand new 2500 mAh
battery. Anybody have any thoughts on why?]
They are rated at so many milliamp-hours AT A CERTAIN LOAD. If you load
it less than the drain spec, you'll get more mAh out of a cell, but load
it more and you'll get less than advertised.
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And a new cell usually takes several cycles for the claimed capacity to be
achieved.
--
Brian Morrison
please observe reply-to address |
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Roy Lewallen
Guest
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| Posted:
Mon Dec 20, 2004 8:10 am Post subject:
Re: To Battery Mavins |
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Brian Morrison wrote:
| Quote: | On Sun, 19 Dec 2004 14:28:34 -0700, in article
tesbs0546t1o3guekplu239c8v0mdcvepd@4ax.com> mxduffie@axtxom.net wrote:
On Sun, 19 Dec 2004 16:41:44 GMT, Mike Fox <mikefox@satx.rr.com> wrote:
[As an aside, that's only 1730 mAh out of a brand new 2500 mAh
battery. Anybody have any thoughts on why?]
They are rated at so many milliamp-hours AT A CERTAIN LOAD. If you load
it less than the drain spec, you'll get more mAh out of a cell, but load
it more and you'll get less than advertised.
And a new cell usually takes several cycles for the claimed capacity to be
achieved.
I've tested a lot of NiMH cells of various brands under various |
constant-current loads. It's very rare for one to meet its
specification, even under a pretty light load. Some of the good name
brands come close, but some like Lenmar consistently have considerably
lower capacity than specified (around 85% is typical). With intense
competition among brands, capacity specification seems to be created
more and more by marketing and advertising departments rather than being
based on engineering test data.
To answer the OP's question, you won't harm the cells by discharging at
600 mA or considerably more. Don't discharge cells connected in series
unless you have a way to monitor battery voltage and stop the discharge
before any cells can get reverse charged. This isn't a problem when
discharging a single cell at a time. You'll get a little less capacity
at the higher discharge rates, but not a really big difference. It'll
still be easy to identify bad cells.
The "bad" cells might be due to your charger prematurely terminating the
charge. I've had a lot of trouble with this, especially with new cells
until they've been cycled a half dozen times or more. That is, it might
be a charger problem rather than a battery problem.
Roy Lewallen |
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Chap
Guest
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| Posted:
Tue Dec 21, 2004 3:38 am Post subject:
Re: To Battery Mavins |
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On Sun, 19 Dec 2004 14:28:34 -0700, mxduffie@axtxom.net wrote:
| Quote: | They are rated at so many milliamp-hours AT A CERTAIN LOAD. If you load
it less than the drain spec, you'll get more mAh out of a cell, but load
it more and you'll get less than advertised.
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If 2300mAh batteries are charged in a charger that normally charges
2100mAh batteries will they receive a full charge?
TIA |
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Roy Lewallen
Guest
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| Posted:
Tue Dec 21, 2004 7:50 am Post subject:
Re: To Battery Mavins |
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Chap wrote:
| Quote: |
If 2300mAh batteries are charged in a charger that normally charges
2100mAh batteries will they receive a full charge?
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Yes. It'll just take slightly longer, assuming that the "2300 mAh"
batteries actually have more capacity than the "2100 mAh" batteries.
Often the difference in specification just reflects the creativity of
the marketing department, rather than having anything to do with actual
capacity.
Roy Lewallen |
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GSV Three Minds in a Can
Guest
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| Posted:
Tue Dec 21, 2004 10:38 pm Post subject:
Re: To Battery Mavins |
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Bitstring <10sf3rjfu1pl6a4@corp.supernews.com>, from the wonderful
person Roy Lewallen <w7el@eznec.com> said
| Quote: | Chap wrote:
If 2300mAh batteries are charged in a charger that normally charges
2100mAh batteries will they receive a full charge?
Yes. It'll just take slightly longer, assuming that the "2300 mAh"
batteries actually have more capacity than the "2100 mAh" batteries.
Often the difference in specification just reflects the creativity of
the marketing department, rather than having anything to do with actual
capacity.
|
Actually it depends on the =type= of charger. Something which decides
to quit based on a timer (yes, they still sell plenty like that) will
not fully charge the higher capacity batteries (probably not the 2100
mAHr either).
If it's a decent charger that quits when it detects 'battery full' based
voltage or similar, then it'll charge anything (and will do sensible
things if you feed it half-discharged batteries, which the timer models
don't).
--
GSV Three Minds in a Can
Outgoing Msgs are Turing Tested,and indistinguishable from human typing. |
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Roy Lewallen
Guest
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| Posted:
Wed Dec 22, 2004 5:43 am Post subject:
Re: To Battery Mavins |
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GSV Three Minds in a Can wrote:
| Quote: |
Actually it depends on the =type= of charger. Something which decides
to quit based on a timer (yes, they still sell plenty like that) will
not fully charge the higher capacity batteries (probably not the 2100
mAHr either).
If it's a decent charger that quits when it detects 'battery full' based
voltage or similar, then it'll charge anything (and will do sensible
things if you feed it half-discharged batteries, which the timer models
don't).
|
Gad, I didn't realize anybody was selling a NiMH charger, especially for
that capacity cell, that uses a simple timer. If you have one of those,
the difference between a cell specified as 2100 mAh and 2300 mAh is the
least of your worries.
Roy Lewallen |
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David Lesher
Guest
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| Posted:
Wed Dec 22, 2004 6:23 am Post subject:
Re: To Battery Mavins |
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I have a Battery Mavin query:
I've got CH1HR Eveready charger. It's fine with most of my AA/AAA NiMH
cells, but I have several Hitech/GN P320AAA-303's and it always labels
them as "bad" when inserted. (i.e. blinking LED...)
Why? A slow dumb charger does fine on them.....
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433 |
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GSV Three Minds in a Can
Guest
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| Posted:
Wed Dec 22, 2004 4:16 pm Post subject:
Re: To Battery Mavins |
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Bitstring <10shgpta8j3p731@corp.supernews.com>, from the wonderful
person Roy Lewallen <w7el@eznec.com> said
| Quote: | GSV Three Minds in a Can wrote:
Actually it depends on the =type= of charger. Something which
decides to quit based on a timer (yes, they still sell plenty like
that) will not fully charge the higher capacity batteries (probably
not the 2100 mAHr either).
If it's a decent charger that quits when it detects 'battery full'
based voltage or similar, then it'll charge anything (and will do
sensible things if you feed it half-discharged batteries, which the
timer models don't).
Gad, I didn't realize anybody was selling a NiMH charger, especially
for that capacity cell, that uses a simple timer.
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Yep. Ansmann Photocam 4.
| Quote: | If you have one of those, the difference between a cell specified as
2100 mAh and 2300 mAh is the least of your worries.
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It works OK as long as you always insert fully discharged batteries, and
as long as you didn't want them fully charged when it finishes. 8>.
--
GSV Three Minds in a Can
Outgoing Msgs are Turing Tested,and indistinguishable from human typing. |
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