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'[OT]: advice sought on buying an NiMH battery char'
2001\01\23@125304 by Simon Nield

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I am planning to buy an NiMH fast charger so I can feed my digital camera, gameboy, palm and so on a
little more economically, and avoid having to bulk-buy duracells.
[rumour has it you also get more of the rated capacity out of an NiMH than a standard alkaline in
this type of high-drain application too]

A surf of the web revealed a fair number of good reviews of this beast:
http://www.mahaenergy.com/products/consumer/mhc204f.htm

The spec looks good, but... any comments on / experience of this unit, or recomendations for other
similar products ?

[I live in the UK so getting hold of this particular unit is going to mean waiting a few weeks...
hence the desire to get it right.]

thanks,
Simon

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2001\01\23@132418 by Bob Blick

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The main advice I can give is pretty generic - throw the charger's lid
away - for every 10 degrees cooler you keep the batteries when charging,
you'll double the number of cycles you get out of them.

As regards the claim of "no danger of overcharging", I still would get
them out as soon as they are done.

And remember that nimh lose 10% of their charge per day on average.

-Bob

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2001\01\23@150212 by Paul Hutchinson

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> A surf of the web revealed a fair number of good reviews of this beast:
> http://www.mahaenergy.com/products/consumer/mhc204f.htm
>
> The spec looks good, but... any comments on / experience of this
> unit, or recomendations for other
> similar products ?

I got one when I ordered a 12VDC powered NiCad/NiMH battery charger from
Kodak.com (for my Kodak digital camera) 2 months ago.

So far it works great.

Paul

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Chief Engineer
Maximum Inc., 30 Samuel Barnet Blvd.
New Bedford, MA 02745
spam_OUTphutchinsonTakeThisOuTspamimtra.com
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=========================================

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2001\01\24@065706 by Roman Black

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Bob Blick wrote:

> And remember that nimh lose 10% of their charge per day on average.
>

Is this really true? I bought NiMh AAA batteries for
a device I use, as these had higher capacity than
the equivalent NiCd batteries. But this device only gets
used every now and then...
-Roman

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2001\01\24@080304 by Alan B. Pearce

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> And remember that nimh lose 10% of their charge per day on average.
>

>Is this really true? I bought NiMh AAA batteries for
>a device I use, as these had higher capacity than
>the equivalent NiCd batteries. But this device only gets
>used every now and then...

yeah I was wondering that too. 10 days shelf life from charge? does not really
sound right to me. I would have thought nearer 1% worst case, and that is still
less than a 1/3 of a year.

I do not have expertise with these but 10% does sound somewhat off as a figure.

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2001\01\24@081758 by Simon Nield

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bob b:
>> And remember that nimh lose 10% of their charge per day on average.

roman:
>Is this really true?

it is apparently a topic of hot debate. i had heard (see link below) that NiMH self discharge is
only about twice that of NiCd, and more like 2% per day in typical conditions.

http://www.cliffshade.com/dpfwiw/batteries.htm

if you are the type to want something closer to fact than opinion then check out this graph to see
how self discharge varies with temperature:
http://www.duracell.com/OEM/Rechargeable/Nickel/selfdis.html

and this one to see how NiMH stacks up against NiCd:
http://www.bti.ca/selfdis.htm

[google search: http://www.google.com/search?q=nimh+self+discharge ]


so how occasionally do you use them ?

could be that a trickle charger would suit your application - negligable memory effect with NiMH (
unlike NiCd):
http://www.duracell.com/OEM/Rechargeable/Nickel/voltdep.html

and they are kinder to the environment, which can't be a bad thing.


Regards,
Simon

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2001\01\24@083016 by Roman Black

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Simon Nield wrote:
{Quote hidden}

Thanks for the info and the good links!
:o)
-Roman

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2001\01\24@094001 by Dale Botkin

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On Wed, 24 Jan 2001, Alan B. Pearce wrote:

> > And remember that nimh lose 10% of their charge per day on average.
> >
>
> >Is this really true? I bought NiMh AAA batteries for
> >a device I use, as these had higher capacity than
> >the equivalent NiCd batteries. But this device only gets
> >used every now and then...
>
> yeah I was wondering that too. 10 days shelf life from charge? does not really
> sound right to me. I would have thought nearer 1% worst case, and that is still
> less than a 1/3 of a year.
>
> I do not have expertise with these but 10% does sound somewhat off as a figure.

If my cellular and laptop NiMH batteries are any indication, I would not
be surprised at 5% at least, maybe higher.  The self-discharge really does
become a problem.

Dale
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2001\01\24@102233 by Roman Black

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Dale Botkin wrote:
{Quote hidden}

Try taking them out of the device. With my walkman I
found that they go flat in a few days if left in,
but last for weeks when not in the device. I think
NiMh have poor performance with very low currents
like the device standby current?? Maybe that is partly
responsible for the rumours of high self-discharge
rates?
-Roman

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2001\01\24@105530 by Simon Nield

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dale:
>If my cellular and laptop NiMH batteries are any indication, I would not
>be surprised at 5%

one of the duracell graphs i mailed a link to earlier (repeated below) shows self-discharge vs
temperature:

http://www.duracell.com/OEM/Rechargeable/Nickel/selfdis.html

taking the 30 day discharge and working back to a daily rate (not really valid as it's not quite
linear):
0 celsius => between 0.15% and 0.35% discharge per day
20 celsius => between 0.5% and 0.85% per day
45 celsius => between 2% and 2.5% per day
(measuring the 30 day discharge to the closest 5%)

...

taking another manufacturer's datasheet (see page 9):
http://www.mahaenergy.com/download/pdf/mhaa155.pdf

suggests a similar maximum self-discharge rate of 2% per day (making the same approximation of it
being almost linear over the 30 day measured period)

...

had a look for specs on sanyo cells as they seem to be pretty popular, but their website was not
forthcoming.

...

assuming you are not living somewhere extremely warm with no aircon and are not leaving your laptop
& phone in direct sunlight all the time (or locked in a hot car all day), i would make an educated
guess that either your batteries are very old and are not charging up to full capacity any more, or
your devices are not really as 'off' as you think they are.

Regards,
Simon

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2001\01\24@110410 by Alan B. Pearce

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>your devices are not really as 'off' as you think they are.

I suspect this is the situation a lot these days in anything that might have a
micro in it - it is easier to turn it off and on under software than have a
proper off/on switch to properly isolate the battery.

I have just bought a Panasonic radio with a digital tuner, and was most
surprised to find that the station tuning is kept in ram, if there are no
batteries in it and the mains is off for more than 5 minutes it loses its
station settings - are EPROM's that much more expensive???

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2001\01\24@113910 by Bob Blick

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On Wed, 24 Jan 2001, Simon Nield wrote:
> taking another manufacturer's datasheet (see page 9):
> suggests a similar maximum self-discharge rate of 2% per day (making the same approximation of it
> being almost linear over the 30 day measured period)

That's the problem with manufacturer data - it's wrong. Another poster
mentioned 5% per day based on his experience and I said 10% based on my
experience. We're both right, and the manufacturers are very optimistic.

Hi-capacity nicads are not much better. I have a THS720 scope, and 4
battery packs. If I charge all the packs, wait a week, I can barely get
25% life from each pack. If I've left one in the scope, it'll run maybe 5
minutes(supporting the low-drain theory has merit).

Battery manufacturers have ALWAYS LIED, get used to it. Duracell also
claims a D-alkaline has 18AH, and I have tested them under their
conditions and never gotten better than 13 or so.

Cheerful regards,

Bob Blick

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2001\01\24@173729 by Morgan Olsson

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Hej Bob Blick wrote:

>That's the problem with manufacturer data - it's wrong.

Certainly har to read - if You can ever get anything... but I have actually got nice and apparently correct data from VARTA, Panasonic and some Taiwan mfg.

> Another poster
>mentioned 5% per day based on his experience and I said 10% based on my
>experience. We're both right, and the manufacturers are very optimistic.

I would´nt say you are wrong, but far away from my experiences.
I would believe some of this is the reason:

1) The cells are damaged by overcharging or overheating by a bad charger, overdischarged in application (does it really turn off completely in time) or other damage

2) The appliance (or the battery meter electronics found in some laptop batterypacks?) use idle current?

I have personally had good experience with Both NiCd, and even better with NiMH.

I had my *two year old* original cell phone (NOKIA) battery pack (NiCd) lying some (3?) months, without use, and when plugging it in the phone i was surprised the phone indicated "2/3" (and really worked)!

Almost all my battery powered things (mostly DVMs) i have NiMM cells in.

Chargers, I have had some bad experiences regarding overcharging.

"Forgetting" discharged cells lying on the shelf is no good either - charge before storing, to avoid them "overselfdischarge"!

-snip-

>Battery manufacturers have ALWAYS LIED, get used to it. Duracell also
>claims a D-alkaline has 18AH, and I have tested them under their
>conditions and never gotten better than 13 or so.

I personally dislike a lot of battery manufactueres for difficulties in getting data in earlier projects, Duracell too, difference is Duracell is just a lot more expensive...
Pity, i heard they bought VARTA, which I used before...

Well Battery chemistry is no easy task, very temperature dependant etc, but data is usually very hard to get.  Like have you seen capacity marking on primary batteries in normal stores?  And the Duracell TV-ads about their cells giving a lot more life to toys, although independant tests have shown that it is no big difference, and some even slightly better and much cheaper.  Sorry i forgot which, now... i only learned to avoid Duracell.  (BTW word play: "Dyracell" in swedish = "Expensivecell")
Doesnt matter, NiMH rules!

-Not just techically, also economically and environmentally :)

And lithium is coming :)

/Morgan

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2001\01\26@084655 by Peter L. Peres

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I confirm that NiMh off the shelf batteries have a rather high self
discharge rate. They also seem to lose capacity faster than NiCd over
cycles. Maybe it's a quality thing, I've used no-name cells. Next time I
will buy brand.

Peter

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