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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  #11   Report Post  
Old July 10th 03, 08:10 PM
Dave Martindale
 
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Default AA battary capacity, Ah (?)

(Remove SPAM From Address to Reply) writes:

Please don't do that! Those cheap chargers are either constant current
or timer terminated.


That's partly correct. Yes, the cheap chargers are constant-
current, but no, they are not a problem. For most NiMH cells,
the "cheap" chargers are charging at a rate less than C/10, and
are no problem even if left plugged in all day.


There are two different types of cheap charger. They're both constant
current with no detection of end of charge. One type uses a low enough
charge rate that a full charge takes 14 hours; that's what you're
talking about. If the batteries start out partially charged, not
completely discharged, they will be overcharged - but at such a low
current that it won't hurt them.

However, the *timed* cheap chargers use a higher current that will
recharge the batteries in about 5 hours. They are a problem because
they will properly recharge *only* a specific capacity of battery, and
*only* if it's fully discharged before charging. If the battery is
higher capacity than the charger is designed for, the timer will shut
off before full charge is reached. If the battery is the correct
capacity but isn't fully discharged, then the charger will overcharge
it, and with a current large enough to damage the battery.

So, avoid the timed chargers completely. 14-hour chargers are OK but
slow. Fast chargers with end-of-charge detection are OK and fast.

Dave

  #12   Report Post  
Old July 11th 03, 12:30 AM
Ted Edwards
 
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Default AA battary capacity, Ah (?)

Dave Martindale wrote:

There are two different types of cheap charger. They're both constant
current with no detection of end of charge. One type uses a low enough
charge rate that a full charge takes 14 hours; that's what you're
talking about. If the batteries start out partially charged, not
completely discharged, they will be overcharged - but at such a low
current that it won't hurt them.


From my reading, this seems to be somewhat cotroversial, some authors

and manufacturers claiming C/10, some C/20 and some saying even lower.
My MAHA 204 charges at C/60 after the end of the fast charge cycle.

It's probably on sacle of decreasing badness. :-)

Ted


  #13   Report Post  
Old July 11th 03, 12:30 AM
Ted Edwards
 
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Default AA battary capacity, Ah (?)

The Masked Marvel wrote:

Alternately look at cameras using propriatary Li-Ion batteries.


The problem with those are proprietary packs of any cell chemistry sell
at extorsionist prices. For the price of one spare Li-ion pack, I can
buy several sets of NiMH cells and, at todays performance levels, the
NiMH are very little behind similar volume Li-ion packs in performance.

Ted

  #16   Report Post  
Old July 11th 03, 08:00 AM
Ted Edwards
 
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Default AA battary capacity, Ah (?)

Dave Martindale wrote:

I never use anything but fast chargers now myself. But slow chargers
are better for the batteries than timed chargers, and so it's useful to
distinguish between them.


Agreed but a smart charger is so inexpensive considering how many safe
effective recharges you will get, not to mention the convenience.

Ted


  #17   Report Post  
Old July 11th 03, 09:41 AM
Len S
 
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Default AA battary capacity, Ah (?)

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. Now I CAREFULLY check for Li-Ion when buying a new toy. I've
gotten years on my Li-Ion Notebook and camera without battery
replacement. There is a lot of BS circulating about NiMH (like any
other technical topic). 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?
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.
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. I've had one of those tiny
Casio camera for 6 months now and I can take pictures (on and off) for
2 weeks before it needs charging. Also some makers (I think Sony and
Konica) have cameras that use Li-Ion and AA Alkalines (of course you
could use AA NiMH if you like too)
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.
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.
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.

end of rant


LiIon also have the pseudo-advantage that the manufacturer *has* to
supply a decent charger for them. You can get equally good NiMH
chargers, but a lot of the NiMH chargers sold are junk. You have to do
a bit of research to get a good one.

Dave

  #18   Report Post  
Old July 11th 03, 05:14 PM
Sofie
 
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Default AA battary capacity, Ah (?)

Icoe:
Yes, actually.... the Radio Shack #23-405 is only for NiCad and NiMH....
NOT for LITHIUM.
and, yes, it is microprocessor controlled and is designed to specifically
sense the unique charging curves of NiCad or NiMH, switch selectable and
will shut off when it achieves full charge as detected by the chip...... or
failing that, it's backup timer will shut it off.
It is a nicely built unit and if used properly should work just fine....
the business about charging only fully discharged cells applies mainly to
NiCad .... by fully discharging them, the "memory effect" is negated. You
really do not want to fully discharge NiMH every time you charge them....
and you don't have to.... there is no memory effect to worry about.....
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
--------------------------------------------


"lcoe" wrote in message
news:[email protected]

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...'

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? Thanks! --Loren






  #19   Report Post  
Old July 11th 03, 05:51 PM
lcoe
 
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Default AA battary capacity, Ah (?)

In rec.crafts.metalworking Sofie wrote:
Icoe:
Yes, actually.... the Radio Shack #23-405 is only for NiCad and NiMH....
NOT for LITHIUM.


yes, i mis-spoke, thanks for noticing.

and, yes, it is microprocessor controlled and is designed to specifically
sense the unique charging curves of NiCad or NiMH, switch selectable and
will shut off when it achieves full charge as detected by the chip...... or
failing that, it's backup timer will shut it off.
It is a nicely built unit and if used properly should work just fine....
the business about charging only fully discharged cells applies mainly to
NiCad .... by fully discharging them, the "memory effect" is negated. You
really do not want to fully discharge NiMH every time you charge them....
and you don't have to.... there is no memory effect to worry about.....
-- Best Regards, Daniel Sofie Electronics Supply & Repair


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

i see some newer chargers on-line that have a switch selectable "dis-charge"
then/charge mode. i believe it works for either type battery. Thanks! --Loren
`
--------------------------------------------



"lcoe" wrote in message
news:[email protected]


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...'

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? Thanks! --Loren






  #20   Report Post  
Old July 11th 03, 06:06 PM
Sofie
 
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Default AA battary capacity, Ah (?)

Icoe:
I would very strongly suggest that you NOT put alkaline batteries in your
Radio Shack #23-405 charger..... it is only designed for NiCads and NiMH.
DO NOT put alkalines in ANY charger not specifically designed for
alkalines..... they may explode or at the very least, get hot and make a
hell of a mess.
The cut-off voltage and charging curve is different for NiCad versus NiMH
..... that is why the charger has a 2 position selection switch..... make
certain it is set correctly for the type of battery you are charging....
notice that there is NOT a 3rd selection position for Alkaline...... do NOT
attempt to recharge alkaline batteries in this charger.
The automatic discharge and then recharge feature of some chargers and
reconditioners was meant mainly for NiCads..... to help minimize the "memory
effect" ...... not really needed for NiMH although there are those that say
it helps and others that say that regular deep cycling of NiMH is not
beneficial or even good for the battery..... my experience suggests the
latter.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
--------------------



"lcoe" wrote in message
news:[email protected]

do you, or anyone know the cutoff voltage for the charge cycle? was

thinking
of testing it by charging some partially discharged alkalines.

i see some newer chargers on-line that have a switch selectable

"dis-charge"
then/charge mode. i believe it works for either type battery.

Thanks! --Loren
`






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