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'selection of battery for power consumption of 300m'
1998\06\08@170010 by David Wong

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Where can I find data or a web site on batteries in general.  I'm looking to
spec in a battery to power a Pic and a bunch of other electronics for about
20 hours.  The current consumption of the parts would be about 300mA/hour.
What would be the ideal battery?  Also can anyone direct me to some
companies that do fast charger IC's as well as gas gauges for batteries.
And any parts that you may recommend.

Thanks
DW

1998\06\08@224850 by Clyde Smith-Stubbs

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On Mon, Jun 08, 1998 at 11:45:16AM -0400, David Wong wrote:
> Where can I find data or a web site on batteries in general.  I'm looking to
> spec in a battery to power a Pic and a bunch of other electronics for about
> 20 hours.  The current consumption of the parts would be about 300mA/hour.

A lead-acid gel-cell battery would be the best choice, unless weight is critical
,
in which case you might want to look at Nimh (Nickel-metal hydride) or Lithium-i
on
batteries, but the gel-cell will be cheaper, and can be float charged with const
ant
voltage. The others require fancy charging circuitry. A "gas-gauge" for a gel-ce
ll is
basically a voltmeter.

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1998\06\08@234134 by Bob Blick

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www.duracellnpt.com/techref.d/refind.html

Has some specs on duracell batteries. Note that in practice what you get
is about 75% of the rating. Also note that they expect you to take the
cells down to something like .8 volts

Cheers,
Bob

1998\06\09@050542 by Mike Keitz

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On Tue, 9 Jun 1998 07:55:36 +1000 Clyde Smith-Stubbs <clydespamKILLspamHTSOFT.COM>
writes:
>On Mon, Jun 08, 1998 at 11:45:16AM -0400, David Wong wrote:
>>battery to power a Pic and a bunch of other electronics
>for about
>> 20 hours.  The current consumption of the parts would be about
>300mA/hour.
>
You mean the operating current is 300 mA (at 5V, I assume)?  This is
quite a bit of power.  The battery is going to be rather unweildly.  It
would be advantageous to look at reducing the power by using micropower
techniques or implementing standby/sleep modes.

On the other hand, if the capacity required is 300 mA-hr, (operating
current of 15 mA for 20 hours), just about any sort of medium sized
battery such as 4 "AA" cells will have lots of capacity.  Specify a
battery with plenty of extra capacity, then it will be less necessary to
have a gas gauge or rapid charge.  Also the battery will wear out more
slowly, and it's "useful life" will extend further into the wear-out
phase.


(The rest of this is assuming 300mA * 20 hr = 6 A-hr)
>A lead-acid gel-cell battery would be the best choice, unless weight
>is critical,
>in which case you might want to look at Nimh (Nickel-metal hydride) or
>Lithium-ion
>batteries, but the gel-cell will be cheaper,

I think the lead-acid is about the only practical choice.  If the weight
(about 5 lbs for a 10 A-hr 6V gell-cell) is a problem you will do much
better to reduce the power consumption rather than deal with exotic
batteries.

and can be float charged
>with constant
>voltage. The others require fancy charging circuitry. A "gas-gauge"
>for a gel-cell is
>basically a voltmeter.

Yes, easy to charge with just a constant-voltage, current-limited
arrangement.  However, it is not recommended to charge faster than 4
hours.  Measuring the voltage does give a meaningful indication of the
energy remaining.  Be sure your circuit has a cut-out that will keep the
battery from overdischarging, as this is very bad for them.

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1998\06\09@051245 by Dennis Plunkett

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At 02:41 PM 8/06/98 -0700, you wrote:
>http://www.duracellnpt.com/techref.d/refind.html
>
>Has some specs on duracell batteries. Note that in practice what you get
>is about 75% of the rating. Also note that they expect you to take the
>cells down to something like .8 volts
>
>Cheers,
>Bob
>
>

I don't agree with the 75% of capacity, we get 100 to 115% consistntly, note
that the capacity tests are done with a light load! Not a huge 1AMP  or
something like that. 0.8V is quite OK for most things, also note the
internal impedance of the cell at this voltage.

Dennis

-=====================================================================-

Dennis Plunkett: Embedded Hardware, Software design
NEC Australia DRMASS
ph 03 9264-3867

-=====================================================================-

1998\06\09@052256 by Dr. Imre Bartfai

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It seems for me as a total capacity of 6Ah theoretically (a small remark:
the measure 300 mA/hour makes no sense; the current is measured in mA). I
would suggest a jelly type lead battery.

Imre


On Mon, 8 Jun 1998, David Wong wrote:

{Quote hidden}

1998\06\09@105053 by 'Grif' w. keith griffith

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At 07:55 AM 6/9/98 +1000, you wrote:
>On Mon, Jun 08, 1998 at 11:45:16AM -0400, David Wong wrote:
>> Where can I find data or a web site on batteries in general.
>A lead-acid gel-cell battery would be the best choice, unless weight is
critical,
>in which case you might want to look at Nimh (Nickel-metal hydride) or
Lithium-ion
>batteries,

snip,hack

Gel cells are great, as long as you get them back on charge after use, if
they are going to be left in a discharged state, use something else.  Oh,
and for the float charger is great mind set, don't forget if you set the
float for 13.6 or so, and don't do anything "fancy" my memory is telling me
you only get about 80% of capacity.  Seems like some of the power one
charger wall warts do a 14.6 volt end point constant current then pop over
to a float.



'Grif' N7IVS

1998\06\09@122516 by tjaart

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'Grif' w. keith griffith wrote:

> At 07:55 AM 6/9/98 +1000, you wrote:
> >On Mon, Jun 08, 1998 at 11:45:16AM -0400, David Wong wrote:
> >> Where can I find data or a web site on batteries in general.
> >A lead-acid gel-cell battery would be the best choice, unless weight is
> critical,
> >in which case you might want to look at Nimh (Nickel-metal hydride) or
> Lithium-ion
> >batteries,
>
> snip,hack
>
> Gel cells are great, as long as you get them back on charge after use, if
> they are going to be left in a discharged state, use something else.

...unless it is a Hawker (Gates) They are the only Pb's that can take it.

--
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Tjaart van der Walt
.....tjaartKILLspamspam.....wasp.co.za

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1998\06\09@131929 by Reginald Neale

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Bob said:
>>Has some specs on duracell batteries. Note that in practice what you get
>>is about 75% of the rating. Also note that they expect you to take the
>>cells down to something like .8 volts
>>

and Dennis replied:
>I don't agree with the 75% of capacity, we get 100 to 115% consistntly, note
>that the capacity tests are done with a light load! Not a huge 1AMP  or
>something like that. 0.8V is quite OK for most things, also note the
>internal impedance of the cell at this voltage.
>

"Capacity" is meaningful only when both the load current and endpoint
voltage are specified. AFAIK, all batteries give maximum capacity for
lightest possible loads and (obviously) lowest possible endpoint voltages.
The range of capacities for a given battery can be dramatic. Example: an
automotive battery may be rated for 100 ampere-hours, but that rating is by
convention at the 10-hr rate, which makes the numbers look high but is not
useful in trying to determine how long you can crank an engine. You aren't
even going to come close to being able to supply 100 amps for an hour.

Bottom line, determine what endpoint voltage makes sense in your
application, and how much current is required; then make your own
measurements on candidate battery types to get the most useful answers.
Allow a generous fudge factor to take care of unit-to-unit variations. Also
note that capacity varies with temperature range in a manner specific to
each battery technology, generally dropping with temperature. Many types
lose most of their capacity at freezing temperatures.

Good luck with your project!

Reg Neale

1998\06\09@134416 by Bob Blick

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On Tue, 9 Jun 1998, Dennis Plunkett wrote:
>
> I don't agree with the 75% of capacity, we get 100 to 115% consistntly, note
> that the capacity tests are done with a light load! Not a huge 1AMP  or
> something like that. 0.8V is quite OK for most things, also note the
> internal impedance of the cell at this voltage.

Maybe it's a conversion problem from American to Australian amp-hours :-)
Seriously, though. The specs published by Duracell are the optimum. It is
almost impossible to get what they claim. The original post was from
someone with a 300mA requirement. I had previously done tests of Duracell
D-cells at that exact load, with temperature varying between 50 and 70
degrees F. I got a fraction over 12 amp hours. The cells are rated 15 amp
hours by Duracell. I think I gave a valid answer to his exact question,
and to the majority of users.

Cheerful regards,
Bob

1998\06\10@005956 by tjaart

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Bob Blick wrote:

> On Tue, 9 Jun 1998, Dennis Plunkett wrote:
> >
> > I don't agree with the 75% of capacity, we get 100 to 115% consistntly, note
> > that the capacity tests are done with a light load! Not a huge 1AMP  or
> > something like that. 0.8V is quite OK for most things, also note the
> > internal impedance of the cell at this voltage.
>
> Maybe it's a conversion problem from American to Australian amp-hours :-)
> Seriously, though. The specs published by Duracell are the optimum. It is
> almost impossible to get what they claim. The original post was from
> someone with a 300mA requirement. I had previously done tests of Duracell
> D-cells at that exact load, with temperature varying between 50 and 70
> degrees F. I got a fraction over 12 amp hours. The cells are rated 15 amp
> hours by Duracell. I think I gave a valid answer to his exact question,
> and to the majority of users.

You are right. The 'capacity' quoted by manufacturers are the integralof the current over time for a
really 'light' load. When you slap on your
current guzzlers, you get to experience the rise in internal resistance,
temperature effects and other mysterious properties that make your
life a misery.

This is why you have to check for a discharge curve at the load you
want to work with.

A very important thing about batteries : *NEVER* believe the reps.
Check it out for yourself. We've seen really cheap no-name NiCd
batteries outperform (and outlast) all the NiCd brand makes. I've
heard such crap comming from these reps that I went the mile and
made a bit of a study. It is really worth it.

Three weeks ago one of these a**holes told me that the Hawker
batteries aren't very good because they don't do well in temp extremes.
Bull!! They are the *only* batteries to still work (and charge) well
from -20DC to +80DC.

So, bottom line, do your homework. Study all the types, and then
choose a Hawker Pb gel. ;) I think there is a link on my home page
to Hawker.

--
Friendly Regards

Tjaart van der Walt
tjaartspamspam_OUTwasp.co.za

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