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NiMH cell voltage



 
 
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  #11  
Old September 15th 08, 06:50 PM posted to rec.photo.digital
Steve B[_3_]
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Default NiMH cell voltage



"nospam" wrote in message
...
In article
,
ransley wrote:

My sanyo Eneloops are fully charged at 1.5v and wont run my camera at
1.29v My Sony came with Nimh, Get new batteries or charger.

nimh batteries do not put out 1.5v.


Right, go buy a new V meter and some Eneloops and a good charger. I
just got done charging 3 sets. And I supose you think a cars lead acid
battery is charged at 12v. Nimh-Nicad are basicly dead at 1.2v


there's nothing wrong with my meter or charger. perhaps it is you who
needs a replacement or at least learn how to use what you have.
furthermore, go read up on the chemistry of nimh batteries. the
nominal voltage of nimh/nicad batteries are 1.2v.


From my own (accurate) readings on many NiMh cells over the years, 1.29v
usually means there's plenty of life left in a cell. A voltage reading
unfortunately gives zero information as to the health of the cell, i.e. it's
internal resistance, so if it doesn't work properly in a camera at this
off-load voltage then be very suspicious of it's state of health.

NiMh voltage plateaus in use at around 1.20 - 1.24v for most makes, low
self-discharge ones may be a little higher, but it plummets rapidly in use
once it has fallen to 1.15v. This makes 1.15v - 1.19v a good region for a
camera to shut down, my Pentax K100D shuts down at 4.76v, i.e. 1.19v per
cell. It would give better battery life at 1.15v but there's always the
risk the camera would die during a flash recharge or autofocus current surge
which would pull the battery voltage below the threshold for a second or
two, probably making the camera try to shutdown.


  #12  
Old September 15th 08, 11:42 PM posted to rec.photo.digital
ASAAR
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Default NiMH cell voltage

On Mon, 15 Sep 2008 15:02:07 -0700 (PDT), ransley wrote:

Well I better go see if my meter is bad and get a new one, but my car
and car battery charger are also about the same when I double check
voltages. I have felt heat from the cells so maybe these sony chargers
are not very good. They are the standard charger that comes with their
cameras and 2 sony aa Nimh cells. I just charged another pair and
after a few hours 1.4v is what I read.


If your NiMH cells seem to be getting a decent charge I wouldn't
fret too much about the Sony chargers*. Most chargers heat
batteries, some more than others, but usually not much heat is
produced until the cells approach full charge. I assume that you're
using a digital meter but if it's analog, their accuracy is a
certain percentage of the full scale voltage, which can produce
large inaccuracies if you're not using the scale that gets the
largest needle excursion.

* If the Sony chargers can only charge cells in pairs, you might
want to consider getting one that charges cells independently and
has either an LED or LCD display for each cell, showing its charge
progress. You can spend more for better chargers that show the
actual voltages (and other information) for each of the cells, but
they won't necessarily do a better job of charging than the more
inexpensive ones will.

  #13  
Old September 16th 08, 08:47 AM posted to rec.photo.digital
Ron Hunter
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Default NiMH cell voltage

ransley wrote:
On Sep 14, 11:21 pm, ASAAR wrote:
On Sun, 14 Sep 2008 20:32:27 -0700 (PDT), ransley wrote:
ransley wrote:
My sanyo Eneloops are fully charged at 1.5v and wont run my camera at
1.29v My Sony came with Nimh, Get new batteries or charger.
nimh batteries do not put out 1.5v.
Right, go buy a new V meter and some Eneloops and a good charger. I
just got done charging 3 sets. And I supose you think a cars lead acid
battery is charged at 12v. Nimh-Nicad are basicly dead at 1.2v

Totally wrong, as a quick glance at NiMH manufacturer's data
sheets will show. Eneloops have the same voltage characteristics as
standard NiMH batteries. This is from one of Energizer's old NiMH
AA engineering data sheets :

Designation: ANSI-1.2H2
Battery Voltage: 1.2 Volts
Average Capacity: 1850 mAh (to 1.0 volts)
(Based on 370 mA (0.2C) discharge rate)

and this is from Duracell's Tech Bulletin :

5.1 General Characteristics
The discharge characteristics of the nickel-metal
hydride cell are very similar to those of the nickelcadmium
cell. The charged open circuit voltage of both
systems ranges from 1.25 to 1.35 volts per cell. On
discharge, the nominal voltage is 1.2 volts per cell and
the typical end voltage is 1.0 volt per cell.

http://www.duracell.com/oem/recharge...metal_tech.asp


I just read a few spec sheets showing 1.35-1.4 being a stablised full
charge of Nimh, My sony charger peaked it out at 1.5 and today on 2
different meter I am showing 1.38-1.4v on Eneloop cells, at 1.2v they
are basicly discharged and wont even power up my camera at 1.29v,
These are nearly the same voltage patterns as I have seen from Nicads.
Eneloops do take 1.5v to peak on my 2 sony Nimh chargers.


I have never seen a battery that will put out more voltage than the
chemical action allows, and for NiMH, that is about 1.24-1.3 volts. The
1.3 volt reading is a no-load condition on a battery fresh out of the
charger, and should be considered 'transient'. A discharged NiMH would
measure about 1.0 to 1.1 volt. I suspect you have a meter inaccuracy,
and please send the URL for those 1.39-1.4 voltage numbers.
  #14  
Old September 16th 08, 02:02 PM posted to rec.photo.digital
David J Taylor[_6_]
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Default NiMH cell voltage

ransley wrote:
[]
In using 2 digital meters that in other usage has been shown accurate.
Today after taking a few shots even with flash I am showing 1.38v, Its
time to verify my meter or get a new one. What does everyone else show
for V on a fully charged NiMh


I test into a 1.3 ohm load, and show 1.25V typically. I would prefer to
know the on-load voltage, not the open-circuit value, as it is more
representative of actual use, and may indicate the cell condition a little
better (i.e. poor cells will show lower voltage).

I just tested some newer cells which I charged about a day ago and they
show 1.34/1.35V open-circuit, and 1.28/1.29V with the 1.3-ohm load. This
is slightly higher than I expected.

David


  #15  
Old September 16th 08, 04:24 PM posted to rec.photo.digital
SMS
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Default NiMH cell voltage

Daniel Prince wrote:
Sometime ago, I bought a used camera on eBay. It uses two AA cells.
I noticed that I was not getting very good battery life with Kodak
2.1 ah pre-charged cells.

Yesterday when the camera said that it needed new batteries, I
checked the voltage of the cells. One was 1.288 volts and the other
was 1.292 volts.


As someone else pointed out, you need to test the batteries under load.

Buy the battery tester at

"http://www.nimhbattery.com/zts-mbt-1-battery-tester.htm" or
"http://www.thomasdistributing.com/zts-mini-mbt-battery-tester.htm"

which will do a pulsed load test on your batteries. Of course the cost
of such a tester would buy a lot of new batteries.

You can see a graph of battery capacity versus voltage on the battery
data web site, at "http://nordicgroup.us/battery/nimhdischgrid.gif" but
it's for four 2700 mAH batteries, so adjust accordingly. Basically, once
the voltage falls below 1.2V, the remaining capacity falls very rapidly.

The flat discharge curve of NiMH batteries is both a blessing and a
curse. The problem is that it's extremely difficult to have an accurate
battery fuel gauge for NiMH cells because the voltage falls by such a
small amount for most of the capacity.
  #16  
Old September 16th 08, 07:32 PM posted to rec.photo.digital
SMS
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Posts: 2,312
Default NiMH cell voltage

Daniel Prince wrote:
wrote:

On Sun, 14 Sep 2008 07:48:08 -0700, Daniel Prince
wrote:

Sometime ago, I bought a used camera on eBay. It uses two AA cells.
I noticed that I was not getting very good battery life with Kodak
2.1 ah pre-charged cells.

Yesterday when the camera said that it needed new batteries, I
checked the voltage of the cells. One was 1.288 volts and the other
was 1.292 volts.

These voltages seem much too high for "dead" batteries to me. I
checked the menus on the camera and the manual and did not find a
setting for battery type.

Is this camera defective and rejecting batteries at too high a
voltage? Thank you in advance for all replies.

It would help to know what camera you are speaking of.


It is a Canon PowerShot A510.


Hmm, if there's one type of camera I wouldn't bother to buy used it'd be
the Canon A series. For some reason this series is priced ridiculously
low, maybe because everyone is buying the super small, super slim cameras.

I picked up a second A570 IS at a closeout sale at Sears for $130. The
A590 IS was worsened a bit with poorer video capability and a higher
resolution, higher noise sensor. I think they couldn't do 30 fps at the
higher resolution (8 megapixels versus 7.1) so they cut it down to 20
fps which is too jerky.
  #17  
Old September 16th 08, 07:35 PM posted to rec.photo.digital
[email protected]
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Default NiMH cell voltage


I have never seen a battery that will put out more voltage than the
chemical action allows, and for NiMH, that is about 1.24-1.3 volts. The
1.3 volt reading is a no-load condition on a battery fresh out of the
charger, and should be considered 'transient'. A discharged NiMH would
measure about 1.0 to 1.1 volt. I suspect you have a meter inaccuracy,
and please send the URL for those 1.39-1.4 voltage numbers.


You can get a honest 1.4 volt reading of a NIMH battery when
measured immediately after charging. The voltage will drop after a
few hours to about 1.35 volts.
  #18  
Old September 16th 08, 11:54 PM posted to rec.photo.digital
ASAAR
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Default NiMH cell voltage

On Tue, 16 Sep 2008 11:32:52 -0700, SMS wrote:

I picked up a second A570 IS at a closeout sale at Sears for $130.


How bizarre. That's the same camera that you recently criticized
numerous times because of its inability to take more than 10 or 20
shots from a pair of fresh batteries. We knew that wasn't true, and
now apparently so do you, although far be it for you to correct your
obviously bogus criticism.

  #19  
Old September 18th 08, 12:39 AM posted to rec.photo.digital
ASAAR
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Posts: 6,057
Default NiMH cell voltage

On Wed, 17 Sep 2008 13:36:01 -0700 (PDT), ransley wrote:

I just tested a few new-old Duracell Alkaline, in the original packs.
1.5v aa -aaa and came up with 1.6v new. Is this in spec? or do I have
2 meters that are innacurate. My experiance is all cells v. and Lead
Acid car batteries are more than nominal ratings. Check your car, It
wont start in winter with 12v. 13.3 is a peak saturated voltage, 12.8
a mean 100% charge. A 12 v system is in fact optimal at 13v.. A 12v
car battery is 75% dead at 12v.


That's about right. I seem to recall getting open circuit
voltages with fresh alkalines ranging from about 1.56 to 1.6 volts.
If I recall correctly, lead acid cells have a 2.2v nominal voltage,
not 2v, so a 6 cell battery should provide 13.2 volts, or slightly
more while being charged. From Energizer's App. Manual :

Battery Testing
Measuring the open circuit voltage (OCV) of a battery to determine
the amount of service life will yield a rough estimate. A more accurate
method is to measure the closed circuit voltage (CCV) of the battery.
This is accomplished by putting the battery under load for one to two
seconds and measuring the CCV. If the battery voltage is greater than
or equal to 1.1 volts, the battery has approximately 20% service left.
The load is determined by the size and type of battery. In the case of a
single cylindrical 1.5 volt Alkaline or Carbon Zinc battery, the load
would be approximately 8 ohms. Otherwise, an OCV reading of 1.5
volts or greater for a single cylindrical 1.5 volt Alkaline or Carbon Zinc
battery indicates essentially an undischarged battery or one that has
been discharged less than 10%.


Don't believe the "greater than or equal to 1.1 volts" though.
That implies that a reading of 1.4 volts would also indicate 20%
service left. Also, the amount of life remaining depends on the
current draw as well as the device's minimum operating voltage since
the batteries have their own internal resistance. Some of my analog
radios operate (at moderately low volume) with cell voltages below
0.4 volts. They draw only about 10-15ma, vs. the 100ma, 250ma,
500ma and greater currents that Energizer normally uses in its
battery life charts, so at 1.1volts, those alkalines have much more
than 20% service life remaining.

 




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