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'Formula'
1999\01\30@133554
by
darwin
Hi
Can somebody tell me the formula to know how long
will a battery last supplying a 20 ma load.
Thanks
1999\01\30@140933
by
dave vanhorn
At 01:35 PM 1/31/99 0500, Darwin Reynoso wrote:
>Hi
>Can somebody tell me the formula to know how long
>will a battery last supplying a 20 ma load.
>
>Thanks
'snot that simple. You'd think a 20mah battery would last one hour, but it
will typically give you about half that.
The Amp/Hour rating of a battery is called "C". You need a battery with a
rating of at least 2C in order to get an hour's runtime. Depending on the
chemistry, this can get a lot worse. ZincAir cells can give you a huge
amphour rating for their size, but they only like to supply tiny currents.
First, settle on a battery type, (Nicad, Gell, Alkaline..... ) then get
with the manufacturer for current/runtime curves.
1999\01\30@172357
by
darwin

Okey
Using a 9volts Duracell battery
supplying a 20 ma load how long will it lasts
Eduardo R. wrote:
{Quote hidden}> >Can somebody tell me the formula to know how long
> >will a battery last supplying a 20 ma load.
> >
>
> Darwing,
> It depends on the kind of batery you are going to drain that current (20mA)
> from.
>
> For Rechargable type bateries: AA penlight = 500mA/h
> for C type = 1500mA/h
>
> Then we have that AA will last 500mA/20mA = 25 hours when fully charged.
>
> for C type 1500mA/20mA = 75 hours
>
> You need to know the mA/h rate for the batery you are planning to use, or
> calculate it from the above values in case you are using those or similar ones
.
>
> Remember that n batteries in parallel supply n times the current,
> increasing the time they last.
>
> Hope this helps
> Best wishes
> Eduardo R
>
> AC Power Control project based on PIC
>
http://www.geocities.com/SouthBeach/Cove/4535
> ICQ# 10909825
>
spam_OUTeriveraTakeThisOuTumemphis.campus.mci.net
>
> CHILDHOOD CANCER
> "Anyone whose family hasn't been touched by it
> should get down on his knees every night and
> thank the MAN upstairs"...........SAM COOPER
1999\01\30@173654
by
dave vanhorn
At 05:24 PM 1/31/99 0500, Darwin Reynoso wrote:
>Okey
>Using a 9volts Duracell battery
>supplying a 20 ma load how long will it lasts
>
>Eduardo R. wrote:
Well, I'd reccomend a resistor, DVM and a stopwatch. Apply load, measure
battery every 10 minutes, plot a graph.
You also have to define what you mean by "dead battery". If you need 9V,
your battery will be dead a lot sooner than if you only need 6V.
1999\01\31@145857
by
Russell McMahon

Even that's not fully answerable but it's closer.
An ALKALINE 9v "transistor" battery (PP3 etc) has a capacity of
around 500 mAH.
This means that NOMINALLY it can provide about 1 mA for 500 hours or
10mA for 50 hours etc.
For your 20 mA you would expect to get APPROXIMATELY 500/20 = 25
hours. This will depend on temperature, whether you do it in one
burst or eg 10 minutes every hour (battery chemistry gets a chance to
do things while its resting) and very importantly, how many hours you
want to discharge it in (20 in this case) how you define the end
point. An Alkaline battery starts off at about 1.5 volts per cell
(there are 6 cells in a 9 volt battery) drops a few tenths of a volt
fairly quickly then settles into a fairly flat decline until it gets
to around 1 volt per cell and then plunges quite rapidly thereafter.
Below 0.9 to 0.8 volts its fully gone and drops very rapidly to zero.
Manufacturers publish curves of expected performance under various
"standard" conditions.
Rough guide.
For discharge currents of 0.1 x amphour capacity or less:
Time ~ capacity/time
For more rapid discharges
Time ~ capacity / (2 x time)
For very fast discharges  much less than you would expect.
Here are a few TYPICAL capacities for modernish batteries.
All these are in milliamp hours.
Alkaline AA 500
Alkaline C 7500
Alkaline D 15000
NiCd AA 500
NiCd C 1800
NiCd D 4000
Your mileage WILL vary.
Tjaart noted a while ago (6/1998) that a Duracell D rated at 15000
mAH nominal will actually provide 12000 mAH at 300ma at 50 to 70
degrees Fahrenheit. (strange new fangled temperature units we don't
know about over here).
From: Darwin Reynoso <.....darwinKILLspam@spam@fuse.net>
{Quote hidden}>Okey
>Using a 9volts Duracell battery
>supplying a 20 ma load how long will it lasts
>
>Eduardo R. wrote:
>
>> >Can somebody tell me the formula to know how long
>> >will a battery last supplying a 20 ma load.
>> >
>>
>> Darwing,
>> It depends on the kind of batery you are going to drain that
current (20mA)
>> from.
>>
>> For Rechargable type bateries: AA penlight = 500mA/h
>> for C type = 1500mA/h
>>
>> Then we have that AA will last 500mA/20mA = 25 hours when fully
charged.
>>
>> for C type 1500mA/20mA = 75 hours
>>
>> You need to know the mA/h rate for the batery you are planning to
use, or
>> calculate it from the above values in case you are using those or
similar ones.
{Quote hidden}>>
>> Remember that n batteries in parallel supply n times the current,
>> increasing the time they last.
>>
>> Hope this helps
>> Best wishes
>> Eduardo R
>>
>> AC Power Control project based on PIC
>>
http://www.geocities.com/SouthBeach/Cove/4535
>> ICQ# 10909825
>>
eriveraKILLspamumemphis.campus.mci.net
>>
>> CHILDHOOD CANCER
>> "Anyone whose family hasn't been touched by it
>> should get down on his knees every night and
>> thank the MAN upstairs"...........SAM COOPER
>
1999\01\31@151109
by
William Chops Westfield
An ALKALINE 9v "transistor" battery (PP3 etc) has a capacity of
around 500 mAH.
:
Here are a few TYPICAL capacities for modernish batteries.
All these are in milliamp hours.
Alkaline AA 500
NiCd AA 500
Those don't corrolate. A typical 9V alkaline battery contains 6 AAAA
cells, so would of necessity have a much lower mAH rating than an AA.
Also, a NiCd usually has significantly less energy than an alkaline
(although a higher current capability) (as with the C/D cell numbers.)
I therefore think that the quoted Alkaline AA capacity is incorrect.
NiCd C 1800
NiCd D 4000
Another thing to watch out for is that many of the "consumer" D cells
are actually C cells in a bigger package (keeps prices lower.)
IIRC, the duracell web site includes a fair amount of technical
information, including the discharge curves for their common batteries.
BillW
1999\01\31@152557
by
Dave Johnson
>Here are a few TYPICAL capacities for modernish batteries.
>All these are in milliamp hours.
>
>Alkaline AA 500
>Alkaline C 7500
>Alkaline D 15000
>NiCd AA 500
>NiCd C 1800
>NiCd D 4000
For comparison, from The Art of Electronics, I get these:
Alkaline:
D 10000  8000
C 4500  3200
AA 1400  1000
AAA 600  400
These are *measured* capacities at a continuous drain down to 1V/cell.
The first number is at 10 mA, the second at 100mA. Note that the
capacities go down significantly, especially with the smaller cells.
So yes, a LOT depends on what kind of current you're drawing and whether
it's continuous or intermittent.
Dave Johnson
'Formula'
1999\02\01@021150
by
Russell McMahon
My table of typical battery capacities gave a wrong value for the
Alkaline AA cell.
The table should have read
All values in mAH
>Alkaline AA 2250
>Alkaline C 7500
>Alkaline D 15000
>NiCd AA 500
>NiCd C 1800
>NiCd D 4000
>
>Your mileage WILL vary.
1999\02\01@104640
by
Matt Bonner
Darwin Reynoso wrote:
>
> Hi
> Can somebody tell me the formula to know how long
> will a battery last supplying a 20 ma load.
>
There's bound to be something here:
http://www.duracell.com/OEM/
Matt
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