battery life help
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Hello everyone
i am designing a project which is going to be battery powered
and i do need some help in calculating the battery life.
the circuit would operate at 5v and takes 50mA
if i were to use a 9v rectangular battery,the battery -life would be
Capacity(500mAh)/50mA=10 hours
But this is were i get confused , if i now decide to use 2 AAA batteries in
series to give 3v and a stepup-switch mode
power supply to get my fixed 5v
since the Capacity for AAA batteries is 1000mAh
would the battery -life be would be Capacity(2000mAh)/50mA=40 hours
OR
Capacity(1000mAh)/50mA=20 hours
Isaac
i am designing a project which is going to be battery powered
and i do need some help in calculating the battery life.
the circuit would operate at 5v and takes 50mA
if i were to use a 9v rectangular battery,the battery -life would be
Capacity(500mAh)/50mA=10 hours
But this is were i get confused , if i now decide to use 2 AAA batteries in
series to give 3v and a stepup-switch mode
power supply to get my fixed 5v
since the Capacity for AAA batteries is 1000mAh
would the battery -life be would be Capacity(2000mAh)/50mA=40 hours
OR
Capacity(1000mAh)/50mA=20 hours
Isaac
Comments
> i am designing a project which is going to be battery powered
>and i do need some help in calculating the battery life.
>the circuit would operate at 5v and takes 50mA
>if i were to use a 9v rectangular battery,the battery -life would be
>Capacity(500mAh)/50mA=10 hours
>But this is were i get confused , if i now decide to use 2 AAA batteries in
>series to give 3v and a stepup-switch mode
>power supply to get my fixed 5v
>since the Capacity for AAA batteries is 1000mAh
>would the battery -life be would be Capacity(2000mAh)/50mA=40 hours
> OR
>Capacity(1000mAh)/50mA=20 hours
>
>Isaac
hi Isaac,
It will be more like 1000 mAh /75 ma = 13.3 hours. The reason for
that is that the switcher will draw enough current from the 3 volt
battery to supply the power needed by the load: 5 volts * 0.050 amp
= 3 volts * 0.67 amp. The switcher is not 100% efficient, and the
batteries will drop in voltage, taking more current, and that is why
I used 75 ma instead of 67 ma.
Most batteries are rated for some number of Amp Hours when discharged
over about a day (actually rounded down to 20 hours). So a 100 Amp Hour
car battery discharged at the 20 hour rate (5 Amps) will last 20 hours.
BUT, if the battery is discharged at a higher rate, say 20 Amps it will
NOT last 5 Hours, but maybe something like 1 hour. Conversly if
discharged at 100 ma will last way longer than 1,000 hours, probably
many thousands of hours.
The common 9 Volt Alkaline battery is rated at about 3.5 hours with a 50
ma load ( or 175 maH) and about 14 hours with a 25 ma load (350 maH).
If your load is 50 ma @ 5 Volts and you used a 100% efficient SMPS then
you would expect the SMPS to draw 50 ma * (5/3) = 83 ma, but because of
efficiency it will draw more, so for 80% efficiency you will pull 83 ma
/ 0.8 or 104 ma.
Looking at the Energizer A92 Alkaline AAA data sheet shows a life of
somewhere in the 3 to 10 hour range depending on what cell voltage you
say is a dead battery (0.8 Volts to 1.2 Volts). Remember that as the
battery voltage goes down the SMPS will pull even more current. So
using a SMPS adds a lot of cost and you get less capacity than with the
9 Volt battery.
I'm working on a PIC project and plan to use the 123 photo battery, it's
a LiMnO2 chemistry and has 3.0 Volts with a capacity of 1.4 Amp Hours.
I use this battery in a number of the battery adapters I make, see
http://www.PRC68.com
Have Fun,
Brooke Clarke, N6GCE
A god source for battery info is: http://data.energizer.com/
>Date: Wed, 12 Nov 2003 21:59:55 -0000
> From: "Isaac. Aiyanyo" <isaac.aiyanyo@n...>
>Subject: battery life help
>
>
> Hello everyone
> i am designing a project which is going to be battery powered
>and i do need some help in calculating the battery life.
>the circuit would operate at 5v and takes 50mA
>
>if i were to use a 9v rectangular battery,the battery -life would be
>Capacity(500mAh)/50mA=10 hours
>But this is were i get confused , if i now decide to use 2 AAA batteries in
>series to give 3v and a stepup-switch mode
>power supply to get my fixed 5v
>since the Capacity for AAA batteries is 1000mAh
>would the battery -life be would be Capacity(2000mAh)/50mA=40 hours
> OR
>Capacity(1000mAh)/50mA=20 hours
>
>
>Isaac
>
It sounds like he's describing a DC to DC Boost Converter. I thought
that with these converters, the input power has to equal the output
power, plus any losses of course. No practical converter is 100%
power efficient, but I get different numbers than you. He mentioned a
5V @ 50mA load:
(5 * 50mA) = (3 * 83mA)
So battery life would be 1000mAh / 83mA = 12 hours. Probably would be
even less than that when you figure in switching and conduction
losses, plus as batteries deplete their internal resistance goes up
further aggravating things. Am I wrong here? Best regards.
-Dave
>
>
> hi Isaac,
>
> It will be more like 1000 mAh /75 ma = 13.3 hours. The reason for
> that is that the switcher will draw enough current from the 3 volt
> battery to supply the power needed by the load: 5 volts * 0.050
amp
> = 3 volts * 0.67 amp. The switcher is not 100% efficient, and the
> batteries will drop in voltage, taking more current, and that is
why
> I used 75 ma instead of 67 ma.
Right you are. It should be about 83 ma plus whatever is lost to
inefficiency. (5volts * 50mA) = (3volts * 83mA) = 0.25 watt. And at
2.5 volts (1.25 per cell--close to end of life), it becomes a drain
of 100mA plus the loss due to inefficiency, worse due to increasing
battery resistance.
-- Tracy
>Hi Tracy,
>
>It sounds like he's describing a DC to DC Boost Converter. I thought
>that with these converters, the input power has to equal the output
>power, plus any losses of course. No practical converter is 100%
>power efficient, but I get different numbers than you. He mentioned a
>5V @ 50mA load:
>
>(5 * 50mA) = (3 * 83mA)
>
>So battery life would be 1000mAh / 83mA = 12 hours. Probably would be
>even less than that when you figure in switching and conduction
>losses, plus as batteries deplete their internal resistance goes up
>further aggravating things. Am I wrong here? Best regards.
>
>-Dave
>
>
>>
>>
>> hi Isaac,
>>
>> It will be more like 1000 mAh /75 ma = 13.3 hours. The reason for
>> that is that the switcher will draw enough current from the 3 volt
>> battery to supply the power needed by the load: 5 volts * 0.050
>amp
>> = 3 volts * 0.67 amp. The switcher is not 100% efficient, and the
>> batteries will drop in voltage, taking more current, and that is
>why
> > I used 75 ma instead of 67 ma.
>
missed the question -- though they were informative.
The question was:
If I put 2 1000 mAH batteries in series, do
I get 2000 mAH out of the pair? Or only 1000 mAH
at the higher voltage?
I assume you get 1000 mAH at the higher voltage.
Power = I*V. Let's assume 100 mA.
With one 1.5 volt battery, at 100 mA you'd get
.15 watts. With 2 1.5 volt batteries, at 100 mA
you'd get .30 watts.
It makes sense to me that adding the extra
battery would double the power. My analysis
experience breaks down at this point -- I don't
know enough yet to be able to relate the
doubling in power to mAH. Any help?
--- In basicstamps@yahoogroups.com, "Isaac. Aiyanyo"
<isaac.aiyanyo@n...> wrote:
>
> Hello everyone
> i am designing a project which is going to be battery powered
> and i do need some help in calculating the battery life.
> the circuit would operate at 5v and takes 50mA
>
> if i were to use a 9v rectangular battery,the battery -life would be
> Capacity(500mAh)/50mA=10 hours
> But this is were i get confused , if i now decide to use 2 AAA
batteries in
> series to give 3v and a stepup-switch mode
> power supply to get my fixed 5v
> since the Capacity for AAA batteries is 1000mAh
> would the battery -life be would be Capacity(2000mAh)/50mA=40 hours
> OR
> Capacity(1000mAh)/50mA=20 hours
>
>
> Isaac
circuit. This should help you understand that the answer to your question is
NO. You will only get 1000 mAhr out of the series combination.
[noparse][[/noparse]Non-text portions of this message have been removed]
so i now know that i would get 1000mA
U R a great bunch
Isaac
Original Message
From: "Allan Lane" <allan.lane@h...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, November 13, 2003 3:14 PM
Subject: [noparse][[/noparse]basicstamps] Re: battery life help
> Amazingly enough, all 4 previous responses
> missed the question -- though they were informative.
>
> The question was:
> If I put 2 1000 mAH batteries in series, do
> I get 2000 mAH out of the pair? Or only 1000 mAH
> at the higher voltage?
>
> I assume you get 1000 mAH at the higher voltage.
> Power = I*V. Let's assume 100 mA.
>
> With one 1.5 volt battery, at 100 mA you'd get
> .15 watts. With 2 1.5 volt batteries, at 100 mA
> you'd get .30 watts.
>
> It makes sense to me that adding the extra
> battery would double the power. My analysis
> experience breaks down at this point -- I don't
> know enough yet to be able to relate the
> doubling in power to mAH. Any help?
>
> --- In basicstamps@yahoogroups.com, "Isaac. Aiyanyo"
> <isaac.aiyanyo@n...> wrote:
> >
> > Hello everyone
> > i am designing a project which is going to be battery powered
> > and i do need some help in calculating the battery life.
> > the circuit would operate at 5v and takes 50mA
> >
> > if i were to use a 9v rectangular battery,the battery -life would be
> > Capacity(500mAh)/50mA=10 hours
> > But this is were i get confused , if i now decide to use 2 AAA
> batteries in
> > series to give 3v and a stepup-switch mode
> > power supply to get my fixed 5v
> > since the Capacity for AAA batteries is 1000mAh
> > would the battery -life be would be Capacity(2000mAh)/50mA=40 hours
> > OR
> > Capacity(1000mAh)/50mA=20 hours
> >
> >
> > Isaac
>
>
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wrote:
> Amazingly enough, all 4 previous responses
> missed the question -- though they were informative.
I didn't think we missed the question, just gave him a little more
information than he wanted perhaps [noparse]:)[/noparse]. He wanted to know what the
battery life comparisons would be if he went from supplying a 5V,
50mA load with a straight 9V battery as opposed to a 3V to 5V boost
converter. He didn't really specify how he was going to drop the
voltage from 9V to 5V though, I assume a regulator of some sort which
would throw off his initial guess of getting 500mAh/50mA=10 hours
since no regulation or conversion device is 100% efficient.
> I assume you get 1000 mAH at the higher voltage.
> Power = I*V. Let's assume 100 mA.
>
> With one 1.5 volt battery, at 100 mA you'd get
> .15 watts. With 2 1.5 volt batteries, at 100 mA
> you'd get .30 watts.
> It makes sense to me that adding the extra
> battery would double the power.
> I don't
> know enough yet to be able to relate the
> doubling in power to mAH. Any help?
Well in the above description you are saying to keep the current at a
constant 100mA. In a series circuit, doubling the voltage while
keeping the current constant causes a doubling in power.
-Dave
>
> The question was:
> If I put 2 1000 mAH batteries in series, do
> I get 2000 mAH out of the pair? Or only 1000 mAH
> at the higher voltage?
>
> I assume you get 1000 mAH at the higher voltage.
> Power = I*V. Let's assume 100 mA.
>
> With one 1.5 volt battery, at 100 mA you'd get
> .15 watts. With 2 1.5 volt batteries, at 100 mA
> you'd get .30 watts.
>
> It makes sense to me that adding the extra
> battery would double the power. My analysis
> experience breaks down at this point -- I don't
> know enough yet to be able to relate the
> doubling in power to mAH. Any help?
>
> --- In basicstamps@yahoogroups.com, "Isaac. Aiyanyo"
> <isaac.aiyanyo@n...> wrote:
> >
> > Hello everyone
> > i am designing a project which is going to be battery powered
> > and i do need some help in calculating the battery life.
> > the circuit would operate at 5v and takes 50mA
> >
> > if i were to use a 9v rectangular battery,the battery -life would
be
> > Capacity(500mAh)/50mA=10 hours
> > But this is were i get confused , if i now decide to use 2 AAA
> batteries in
> > series to give 3v and a stepup-switch mode
> > power supply to get my fixed 5v
> > since the Capacity for AAA batteries is 1000mAh
> > would the battery -life be would be Capacity(2000mAh)/50mA=40
hours
> > OR
> > Capacity(1000mAh)/50mA=20 hours
> >
> >
> > Isaac