Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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  #21   Report Post  
Old July 11th 03, 06:35 PM
Ted Edwards
 
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Default AA battary capacity, Ah (?)

lcoe wrote:

Ted, or anyone, i bot a RShack "Auto Sensing" model (for ni-cad and lithium).
the manual and box says, "automatically senses full charge and shuts off".
further, in the manual it says, '`...charge only fully discharged cells...'


That's a bad sign. A smart charger should be detecting end of charge by
watching for delta-V (a slight drop in voltage). I am concerned that
they say NiCd and lithium (what lithium?) but do not mention NiMH.

another feature is a "backup" fixed timer, 1.5hr for nicad, 2.0 for lith.
it's RS model 23-405, 50% off recently. it's heavy, brick shaped, but
is it really fully automatic?


Personally, I would not go for it. Sounds wrong.

Ted



  #22   Report Post  
Old July 11th 03, 06:35 PM
Ted Edwards
 
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Default AA battary capacity, Ah (?)

Len S wrote:

One by one, people will realize that NiMH never really lives up to
expectations.


Actually, all 4 sets of 4 (116 cells) NiMH AA's that I have have
exceeded expectations. Sounds like you may have tried very early cells.

gotten years on my Li-Ion Notebook and camera without battery


Well, mine died in two years. This is about average life from what I
have read although a few have done better.

replacement. There is a lot of BS circulating about NiMH (like any
other technical topic).


Li-ion suffers from the same thing such as the statements below

From 1st hand experience:
1) NiMH does have memory effect (they may not call it that, but what
else can you call it when you are told to deep cycle a battery to
"fix" it?


There are several effects in batteries that are eroneously called memory
effect. Li-ion suffers from some of these too.

2) NiMH self discharge is far worse than Li-Ion.


This is true but

something that has been charged withing a few weeks and finding it
dead. If you have NiMH cells, get used to this.


Either you are storing your units in a *very* warm place or your
appliance has an ureasonably high standby current. (This is not all
that infrequent.) Over the winter I do not get out for as many walks as
I would like (asthma) so my GPS sees much less use. I changed batteries
on Feb 2, recharged the dead set and left them in my desk drawer. On
Mar 7, the batteries in GPS died so I switched sets *without* recharging
the set from the drawer. These were in use until Mar 20 (almost two
months since being charged) and delivered their usual approx. 14 hours
running time. I suggest you check the standby current on your
instruments.

4) NiMh performance may, on paper, be close to Li-ion, but in "real
world" electronic products, my experience is that NiMH is far behind.


As you can see, I'm questioning your "real world" experience. My
*measurements* corrolate well with Dave Etchell's in
http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM and the data in
http://www.dp-now.com/index.html

Do not believe that you will get more charge-discharge cycles from
NiMH. Maybe in a contractor's cordless drill that normally gets run to
empty every time, But not in a camera, phone, or PDA, where it's very
normal to partially drain the battery, NiMH hates this, but Li-Ion is
very happy with this kind of use.


Sorry, but this is patently false for NiMH being charged with a smart
charger.

5) Notice that no decent notebook computer or cell phone uses NiMH any
more.


These products also have a high status factor. The average business
persons notebok gets replaced because it is "out of date" not because it
doesn't do the job it was purchased for. Li-ion is a status item.

Ted

  #23   Report Post  
Old July 11th 03, 06:38 PM
Dave Martindale
 
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Default AA battary capacity, Ah (?)

lcoe writes:

do you, or anyone know the cutoff voltage for the charge cycle? was thinking
of testing it by charging some partially discharged alkalines.


There isn't a "cutoff voltage". NiMH and NiCd cells are charged while
monitoring voltage over time. As the cells reach full charge, the
terminal voltage rate of change goes to zero, and then negative (i.e.
the voltage *drops*). This is what the chargers sense. They may also
sense the rapid rise in temperature at end of charge.

Don't put alkalines in this charger. Alkalines won't accept high charge
currents, and they'll probably burst or leak.

Dave
  #24   Report Post  
Old July 11th 03, 07:01 PM
Dave Martindale
 
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Default AA battary capacity, Ah (?)

(Len S) writes:
One by one, people will realize that NiMH never really lives up to
expectations. I have gone through a small fortune in cell phones,
digital cameras, and other doodads (OK, I'm a gadget hound) over the
last five years. Many developed useless NiMH batteries in only a few
months.


How did you charge them? Did you use a good fast charger?

I've had a number of NiMH cells fail, but they were 5 years old or
more.

1) NiMH does have memory effect (they may not call it that, but what
else can you call it when you are told to deep cycle a battery to
"fix" it?


There are several use-related and charging-related effects that may
affect the apparent capacity of a NiMH cell. You don't need to learn
about them if you don't want, but that doesn't justify calling it
"memory effect" when it's something else.

From what I've read (the Cadex book), NiMH cells should be given a full
discharge once a month or once every couple of months to keep the nickel
electrode in good shape. If you recharge every day, that's a tiny
fraction of the charge cycles.

2) NiMH self discharge is far worse than Li-Ion. I hate picking up
something that has been charged withing a few weeks and finding it
dead. If you have NiMH cells, get used to this.


NiMH self-discharge *is* higher than LiIon. However, it takes many months
for them to be dead. In a few weeks, you might see 20 or 30% reduction
in capacity. If your cells are dead in "a few weeks", either you have
bad cells, or they're in a device that puts a constant load on them.
For example, many electronic devices with electronic "power" switches
actually draw current when "off".

When I know I'm going to use a device with NiMH batteries, and I haven't
used it for a while, I'll just pop the batteries into a fast charger.
They're back to *full* charge in 15 minutes, ready to use. It's pretty
seldom that I don't have 15 minutes advance warning of needing a
battery-powered device.

3) Yes, Li-Ion cells are proprietary, but who cares if you can plug in
a camera and then use it for a few days.


Some people care what a spare battery costs. Some people like having a
"pool" of NiMH cells that they can use in any device. Some people like
having a choice of chargers.

5) Notice that no decent notebook computer or cell phone uses NiMH any
more. These products now have brutal price pressure so the makers
would love to use cheaper batteries. They did use NiMH for a while,
but had to stop because the performance was just too crappy.


I think this had more to do with weight. A LiIon battery storing a
certain amount of energy is about half the weight of an equivalent
NiMH battery. The battery is a significant chunk of the weight of
either a cellphone or laptop.

It just so happens that I have a laptop computer with a LiIon battery.
The battery is nearly dead, and provides only 5-10 minutes of running
time. The battery cannot be taken apart and rebuilt with new cells; I
have to buy a new one. (New ones cost CDN$200-300!) This doesn't mean
that all LiIon batteries are bad, but it does provide a counterexample
to the "LiIon batteries are always wonderful" message.

Dave
  #25   Report Post  
Old July 11th 03, 09:34 PM
Dave Martindale
 
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Default AA battary capacity, Ah (?)

lcoe writes:

so i popped them in and the camera fired up fine, and i reviewed pictures
taken w/these same batteries. then i went to 'record', it tried, but
shutdown. again, sameo, sameo.


This is really just demonstrating that alkalines aren't suitable for
your digital camera - too much internal resistance.

Rechargeable alkalines, even on their first use, are worse than
single-use ones, Later discharges get worse yet because internal
resistance increases. I don't expect single-use alkalines that have
been recharged are any different in this respect.

the choice still remains to install fresh alkalines, assuming the
balance of the battery cap. could be utilized, and if i am willing
to put up with the intemittant operation of the camera. for now,
it's going to be Ni-mh, but i will not be able to resist further
testing.


Forget the alkalines. You've demonstrated that they're useless except
as an absolute last resort. Use NiMH for day to day use. Buy a set of
single-use lithium AAs for backup if you can't always be sure of having
enough NiMH batteries for a trip.

Dave


  #26   Report Post  
Old July 12th 03, 12:36 AM
Bob Kos
 
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Default AA battary capacity, Ah (?)

Right on the money. Heat kills batteries. Cheap chargers overheat the
batteries. The Maha chargers work nice for reasonable cost. I have NiMH
batteries that still work well after 5 years thanks to the TLC they get in
my cheapie Maha charger. Thomas Distributing is the place to get 'em.

Speaking of heat, you should use caution in using lithium AA throwaway
batteries. They apparently get quite hot during heavy discharge cycles. So
much so that my Olympus D-600L's warranty would be voided if those batteries
were used in it.

Ted Edwards wrote in message ...

Please don't do that! Those cheap chargers are either constant current
or timer terminated. Pay somewhat more and you can charge your
batteries whenever you feel like it without worrying about state of
charge. Ray-o-vac has a good charger but, personally, I like the Maha
line. My 204 isn't as versatile as some of the newer ones but it works
well. I paid Cdn$30 for it a couple years ago.
For example, see
http://www.thomas-distributing.com/batteries.htm

Ted




  #27   Report Post  
Old July 12th 03, 01:07 AM
Old Nick
 
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Default AA battary capacity, Ah (?)

On Fri, 11 Jul 2003 19:34:24 +0000 (UTC), (Dave
Martindale) wrote something
.......and in reply I say!:

PMFJI. You sound as if you are addressing the questions I have.

I have a couple of little Uniden walkie-talkies, that take 4 X AAA
cells. They chew out the cells fairly fast, so I bought NiCds. No go.
The radios appear to have trouble dealing with the lower voltage. I
reckon they are trying to grab max volts to get Tx power up, and
probably should have had an extra battery. Rechargeable ALkalines
worked fine, but as you say deteroriate rapidly.

Sorry. Question. Are NiMH cells better in this regard? I am ringing
battery houses, and one guy said they were. I assume this would be
because they have lower internal resistance. Is this so? I got the
impression the guy knew more about _batteries_ than I do, but less
about electrical theory G

Next G. One shop had several AH capacities, at different prices
(actually they were the only ones to explain this, and will get my
custom). Are there any advantages/disadvantages to getting the lower
capacities, if this means they get discharged better etc?

Thanks for any help. Sick of buying expensive "special" chargers that
then gather dust.

This is really just demonstrating that alkalines aren't suitable for
your digital camera - too much internal resistance.


************************************************** ****************************************
Huh! Old age!. You may hate it, but let me tell you, you can't get by for long without it!

Nick White --- HEAD:Hertz Music
Please remove ns from my header address to reply via email
!!
")
_/ )
( )
_//- \__/
  #28   Report Post  
Old July 12th 03, 02:16 AM
Dave Martindale
 
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Default AA battary capacity, Ah (?)

(Old Nick) writes:

I have a couple of little Uniden walkie-talkies, that take 4 X AAA
cells. They chew out the cells fairly fast, so I bought NiCds. No go.
The radios appear to have trouble dealing with the lower voltage. I
reckon they are trying to grab max volts to get Tx power up, and
probably should have had an extra battery. Rechargeable ALkalines
worked fine, but as you say deteroriate rapidly.


Sounds like the radio is poorly designed. Alkaline cells start at 1.5
volts, but drop pretty much continuously in voltage as they are drained.
Depending on the load, a device needs to operate properly down to 1 V
per cell (light load) to 0.8 V per cell (heavy load) in order to get
most of the energy out of alkalines. So a properly-designed radio
powered by 4 alkaline cells should tolerate 6 V in, but work properly
all the way down to 4 V. NiCd and NiMH cells provide about 1.2 V over
nearly their entire discharge time, over a wide range of load. Thus,
4 cells will provide 4.8 V and the radio *should* work fine.

If the radio doesn't work on NiCds, and the NiCds were in fact all good,
then it just doesn't operate properly at 4.8 V. If it works at 6 V but
not at 4.8 V, it will start working OK on alkalines, but stop working
when the alkalines are still half-full.

Sorry. Question. Are NiMH cells better in this regard? I am ringing
battery houses, and one guy said they were. I assume this would be
because they have lower internal resistance. Is this so? I got the
impression the guy knew more about _batteries_ than I do, but less
about electrical theory G


NiMH is not better than NiCd in this respect. NiMH actually have higher
internal resistance than NiCd, though still far below alkalines. If
NiCds don't work, NiMH aren't likely to either.

Next G. One shop had several AH capacities, at different prices
(actually they were the only ones to explain this, and will get my
custom). Are there any advantages/disadvantages to getting the lower
capacities, if this means they get discharged better etc?


Lower capacity cells may just be older. But they may also have lower
internal resistance. You can't really tell without measuring. I
wouldn't pay much of a premium for exceptionally high capacity.

Dave
  #29   Report Post  
Old July 12th 03, 02:32 AM
Jim K
 
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Default AA battary capacity, Ah (?)

Like everything else, your mileage will vary. I bought a Toshiba
digital camera around 4 years ago and bought a set of NiMH with
charger for around $25. I'm still using the same set and have taken
thousands of pictures.

On 11 Jul 2003 00:41:15 -0700, (Len S) wrote:

One by one, people will realize that NiMH never really lives up to
expectations. I have gone through a small fortune in cell phones,
digital cameras, and other doodads (OK, I'm a gadget hound) ov

snipped
  #30   Report Post  
Old July 12th 03, 06:31 AM
jakdedert
 
Posts: n/a
Default AA battary capacity, Ah (?)

All the Motorola FRS radios (that I'm familiar with) use three AA cells.
All of their literature states that alkalines or Nimhs *must* be used.
According to Motorola, NiCads are not acceptable.

jak

"Dave Martindale" wrote in message
...
(Old Nick) writes:

I have a couple of little Uniden walkie-talkies, that take 4 X AAA
cells. They chew out the cells fairly fast, so I bought NiCds. No go.
The radios appear to have trouble dealing with the lower voltage. I
reckon they are trying to grab max volts to get Tx power up, and
probably should have had an extra battery. Rechargeable ALkalines
worked fine, but as you say deteroriate rapidly.


Sounds like the radio is poorly designed. Alkaline cells start at 1.5
volts, but drop pretty much continuously in voltage as they are drained.
Depending on the load, a device needs to operate properly down to 1 V
per cell (light load) to 0.8 V per cell (heavy load) in order to get
most of the energy out of alkalines. So a properly-designed radio
powered by 4 alkaline cells should tolerate 6 V in, but work properly
all the way down to 4 V. NiCd and NiMH cells provide about 1.2 V over
nearly their entire discharge time, over a wide range of load. Thus,
4 cells will provide 4.8 V and the radio *should* work fine.

If the radio doesn't work on NiCds, and the NiCds were in fact all good,
then it just doesn't operate properly at 4.8 V. If it works at 6 V but
not at 4.8 V, it will start working OK on alkalines, but stop working
when the alkalines are still half-full.

Sorry. Question. Are NiMH cells better in this regard? I am ringing
battery houses, and one guy said they were. I assume this would be
because they have lower internal resistance. Is this so? I got the
impression the guy knew more about _batteries_ than I do, but less
about electrical theory G


NiMH is not better than NiCd in this respect. NiMH actually have higher
internal resistance than NiCd, though still far below alkalines. If
NiCds don't work, NiMH aren't likely to either.

Next G. One shop had several AH capacities, at different prices
(actually they were the only ones to explain this, and will get my
custom). Are there any advantages/disadvantages to getting the lower
capacities, if this means they get discharged better etc?


Lower capacity cells may just be older. But they may also have lower
internal resistance. You can't really tell without measuring. I
wouldn't pay much of a premium for exceptionally high capacity.

Dave






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