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'[EE]: Battery life calculation'
2011\03\12@211030 by Andre Abelian

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Hi all,

What's the best way to calculate battery life if boost converter is evolved..
1. I have boost converter that starts at 0.9v and batteries I used are 2xAA     at this moment I have 2 rechargeable batteries each one is 2000 mah total voltage battery side
   is 2.4v and output of boost converter is 3.3v
  standby current boost converter takes 6ma assuming every thing else is disabled or in sleep.
  I made a mistake in schematic by not enabling burst mode. it suppose to be 38uA on stand by mode not 6ma. LTC3402
  mod can be done but any time I do the mod the chip burns out. 2. I use PIC24FJ256GB110 according to datasheet it takes 1ma run time assuming 2v power but the clock is not mentioned so I do not know.     I am using 4mhz 3.3v and run time takes 5ma. I changed the crystal to 1mhz I see very small difference in load. I used 4mhz
   only because of USB requirement. I am able to switch internal clock to 4.000.000 when usb is not used and 48.000.000
  when usb is plugged in.

my question is how should I calculate battery life based on 8ma load since there is a boost converter that runs at 0.9v and I know from passed that 80% of battery should be used. I know its rated as current per hour lets say

80% of 2000ma = 1600ma/0.008ma=200.000 hours

I am just adding extra 2 ma incase of enabling other IC chips.
does this make sense? 200.000 hours

thanks

AA


2011\03\12@213719 by Bob Blick

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On Sat, 12 Mar 2011 18:10 -0800, "Andre Abelian" wrote:

> What's the best way to calculate battery life if boost converter is
> evolved.
wattage out / efficiency of conversion = wattage in

{Quote hidden}

The USB peripheral probably is to blame for the higher-than-predicted
current. But other peripherals you have enabled may also be having some
effect.


{Quote hidden}

Small correction, I think you mean 8 mA not .008 mA

I'd calculate the current required first by the wattage into the boost
converter.

If you need 3.3V at .005A that is .0165 W. If your boost converter is
80% then you need .020625 W in. At 2.4 V in that is .0086 A

So your .008 A estimate is pretty close only if you need .005 A out. But
your battery voltage will not always be 2.4 so you can figure it better
if you know the average.

But basically I would say 200 hours is not a bad estimate. But not if
you need another 2 mA for other chips.

Friendly regards,

Bob

-- http://www.fastmail.fm - Access all of your messages and folders
                         wherever you are

2011\03\12@221333 by RussellMc

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> What's the best way to calculate battery life if boost converter is evolved.


Andre

The following may APPEAR o be "pedantic" - just picking at a small and
unimportant "mistake" but in fact in this case there are two possible
interpretations of what you wrote, which differ by a factor of1000,
and it is impossible to be sure which one you intend

You need to pay careful attention to your units so that we can be sure
we are all talking about the same thing.

Your answer could be interpreted as meaning

"about 200 hours"   which would be very very very  roughly correct.

"about 200000 hours" which would be very very very wrong.

Writing 200.000 is very misleading.
It implies either a prevision to 1/1000 of whatever unit you are using
(hours?) OR that the "." is being used as a 1000's separator  so that

  200.000  = 200,000    = = =  200.000

Because you have used 0.008 mA where your figures SUGGEST that either
8 mA or 0.008 A should have been used, it IS possible that you do
intend the incorrect figure of 200000 hours.

Please check your information provided and update so that we can be
sure of what you are saying.

____

as Bob notes.
Battery energy capacity / aberage energy use is a reasonable first try.
But ONLY a first try.

Per cell  average voltage AVAILABLE is about 1.15 Volt.
Battery voltage = 1.3 V average.
Available energy = 2.3 x 2000 mAh x 80% ~~~= 3680 mWh

IF load is 8 mA
IF Vload = 3V3.
IF boost efficiency ~~~= 80%

Power to converter = 8 x 3.3 x 1/80% = 33 mW

Battery life ~~~~= 3680 / 33 = 11.5 hours or about 1100 hours.
Or about 120
Or about 150
or ...
depending on other assumptions which can be discussed.

Amongst other things you use a figure of 80% for available battery energy.
That MAY have be the same as the 80% converter efficincy that I assumed.
If so then increase hours by 1/.8 = 1.25 x.
BUT using only 80% of battery capacity is wise.
But lets get the basics right first and hen we can discuss such details.

200.000 = 200 ?

or 200.000 = 200000 ?


         Russel

2011\03\13@174859 by Andre Abelian

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Hi Bob,

Thanks for your replay. According to my co worker boost converter was taking 6 ma
but after I checked it every things different now. According to my test boost converter takes only 0.24ma not 6ma and that 6 ma cames from Zbee module that I didn't know that default settings sleep pin was disabled. I removed the zbee and now total
current is 0.24ma. in this case assuming 80% of 2000 ma 1600/0.24= 6666 hours for safety I say 5000 hours.
The only thing I do not know can rechargeable battery last longer or none rechargeable like duracell etc?
my circuit doesn't charge batterys.
thanks

Andre



________________________________
From: Bob Blick <spam_OUTbobblickTakeThisOuTspamftml.net>
To: Microcontroller discussion list - Public. <.....piclistKILLspamspam@spam@mit.edu>
Sent: Sat, March 12, 2011 6:37:18 PM
Subject: Re: [EE]: Battery life calculation



On Sat, 12 Mar 2011 18:10 -0800, "Andre Abelian" wrote:

> What's the best way to calculate battery life if boost converter is
> evolved.
wattage out / efficiency of conversion = wattage in

{Quote hidden}

The USB peripheral probably is to blame for the higher-than-predicted
current. But other peripherals you have enabled may also be having some
effect.


{Quote hidden}

Small correction, I think you mean 8 mA not .008 mA

I'd calculate the current required first by the wattage into the boost
converter.

If you need 3.3V at .005A that is .0165 W. If your boost converter is
80% then you need .020625 W in. At 2.4 V in that is .0086 A

So your .008 A estimate is pretty close only if you need .005 A out. But
your battery voltage will not always be 2.4 so you can figure it better
if you know the average.

But basically I would say 200 hours is not a bad estimate. But not if
you need another 2 mA for other chips.

Friendly regards,

Bob

-- http://www.fastmail.fm - Access all of your messages and folders
                         wherever you are

2011\03\13@182024 by Kerry Wentworth

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Alkaline batteries will last longer.

1) They have a higher mAH capacity

2) They have a higher voltage, so the current will go down. (I assume you are measuring current into the converter)

3) They don't self-discharge the way most rechargeables do. 5000 hours, at 8 hours a day, 40 hours a week, is 2 1/2 years.

Kerry


Andre Abelian wrote:
{Quote hidden}

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2011\03\13@183832 by Michael Watterson

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On 13/03/2011 23:13, Kerry Wentworth wrote:
> Alkaline batteries will last longer.
>
> 1) They have a higher mAH capacity
>
> 2) They have a higher voltage, so the current will go down. (I assume
> you are measuring current into the converter)
>
> 3) They don't self-discharge the way most rechargeables do. 5000 hours,
> at 8 hours a day, 40 hours a week, is 2 1/2 years.
>
> Kerry

At cool temperatures a Alkaline can last 5 years or more.

A rechargeable can self discharge in 2weeks to 16 weeks depending on exact type. NiMH seem worse than NiCd

Lithium Primary cells can last 10 years

2011\03\13@205104 by Forrest W Christian

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Michael Watterson wrote:
> A rechargeable can self discharge in 2weeks to 16 weeks depending on
> exact type. NiMH seem worse than NiCd
>
> Lithium Primary cells can last 10 years.
>   The newer 'precharged' NiMH cells are actually rather good in the 'long term storage of charge' category.  Much better than 16 weeks.  See http://en.wikipedia.org/wiki/Low_self-discharge_NiMH_battery - some people report much lower discharge rates than is described in this article.

Although I agree - for the poster's purposes, non-rechargeables seem to be the way to go.  And probably just good quality Alkaline is best because of the low current draw.  I don't think Lithium gains you anything to speak of in this application - Alkalines seem better suited to low-discharge applications, and Lithium seems to do better in bursty high-current applications like cameras, although the exact nature of the application would probably have to be analyzed.

-forres

2011\03\14@054003 by Jonathan Hallameyer

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On Sun, Mar 13, 2011 at 8:51 PM, Forrest W Christian <EraseMEforrestcspam_OUTspamTakeThisOuTimach.com> wrote:
{Quote hidden}

Speaking of bursty... Lithium primary cells aren't anywhere near as
bursty, leakage wise, than alkaline. Which may be another reason to
use them in something you're going to let sit for a while.

--
Jonathan Hallameyer

2011\03\14@055610 by Michael Watterson

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On 14/03/2011 09:39, Jonathan Hallameyer wrote:
> On Sun, Mar 13, 2011 at 8:51 PM, Forrest W Christian<forrestcspamspam_OUTimach.com>  wrote:
>>
>> Michael Watterson wrote:
>>> A rechargeable can self discharge in 2weeks to 16 weeks depending on
>>> exact type. NiMH seem worse than NiCd
>>>
>>> Lithium Primary cells can last 10 years.
>>>
>> Although I agree - for the poster's purposes, non-rechargeables seem to
>> be the way to go.  And probably just good quality Alkaline is best
>> because of the low current draw.  I don't think Lithium gains you
>> anything to speak of in this application - Alkalines seem better suited
>> to low-discharge applications, and Lithium seems to do better in bursty
>> high-current applications like cameras, although the exact nature of the
>> application would probably have to be analyzed.
>>
>> -forrest

The Camera type Primary Lithium  batteries (non-rechargable) may not be the same kind as used in Memory/Clock backups, not sure. They almost certainly perform better in constant low current drain than in intermittent high peak current applications though.

AFAIK only NiCd especially likes bursty use as then nickel dendrites don't grow?

>> --
> Speaking of bursty... Lithium primary cells aren't anywhere near as
> bursty, leakage wise, than alkaline. Which may be another reason to
> use them in something you're going to let sit for a while.
>
Some PCs CMOS (originally clock power and the 64 bytes RAM in same chip) used Alkaline batteries. Later they changed to large 2/3rd ish AA size Primary Lithium
Some early 286  used NiCd. These tended to go flat and also corrode motherboard

Now they all use a CR2032 or similar Primary Lithium coin cell

2011\03\14@071520 by Forrest W Christian

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Michael Watterson wrote:
> The Camera type Primary Lithium  batteries (non-rechargable) may not be
> the same kind as used in Memory/Clock backups, not sure. They almost
> certainly perform better in constant low current drain than in
> intermittent high peak current applications though.
>   I meant in comparison to Alkaline - and in applications where a larger (say AA-sized) battery would be in use.

The 'rated' capacity of a Lithium AA and an Alkaline AA are nearly the same - about 3000mAh.  However, the Alkaline can only provide that at the low end of the current scale - say under 50mA of load.   So, if you're drawing under 50mA, and within normal temperature ranges, it doesn't seem to make any fiscal sense to use Lithium over Alkaline, considering Lithiums are easily 2x the price of an Alkaline.     For better comparison between the two, the datasheet at http://data.energizer.com/PDFs/l91.pdf seems to do a really good job.

You can also compare to the datasheet of an 'industrial' Alkaline at http://data.energizer.com/PDFs/l91.pdf .   Of particular interest are the 'busty' voltage curves on this and the datasheet above.

I will say that Lithiums are definitely more usable in a wider range of temperatures and applications.  Personally, the 'Emergency Primary' batteries I keep in the car are almost all Lithium cells.  For memory backup, I'd use a lithium coin any day over about anything else - except perhaps a supercap capacitor (1F or larger) if the amount of time for backup was in line with what could be stored in the capacitor.

-forrest

2011\03\14@084859 by Sean Breheny

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While there is a lot of good info in this thread, I think that you may
be confusing two different kinds of Lithium Primary cells.

The ones which are targeted as replacements for Alkaline batteries are
Lithium Iron Disulfide. They have better high-current discharge
abilities and I believe that they are also lighter than Alkaline. New
cells have an open-circuit voltage a little above 1.5V (Wiki says
1.8V). I do not think that they have better shelf life than Alkaline.

The ones used for battery back-up for real-time clocks, etc., are
Lithium Manganese Dioxide. They have a voltage of about 3V and have a
shelf life several times longer than Alkaline.

http://www.nexergy.com/lithium-manganese-dioxide.htm


On Mon, Mar 14, 2011 at 7:15 AM, Forrest W Christian <@spam@forrestcKILLspamspamimach.com> wrote:
{Quote hidden}

>

2011\03\14@085213 by Sean Breheny

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Another good link comparing all three technologies (Alkaline, Lithium
Iron Disulfide, and Lithium MnO2)

http://data.energizer.com/PDFs/lithiuml91l92_appman.pdf


On Mon, Mar 14, 2011 at 8:48 AM, Sean Breheny <KILLspamshb7KILLspamspamcornell.edu> wrote:
{Quote hidden}

>> -

2011\03\14@114608 by Bob Blick

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On Mon, 14 Mar 2011 05:39 -0400, "Jonathan Hallameyer" wrote:

> Speaking of bursty... Lithium primary cells aren't anywhere near as
> bursty, leakage wise, than alkaline. Which may be another reason to
> use them in something you're going to let sit for a while.

And they operate at lower temperatures - Alkaline batteries don't work
very much below freezing.

If you want really super low temperature performance you can use lithium
thionyl batteries, a bit pricey but good for military applications where
you just need it to work.

But even standard off-the-shelf lithium cells have great low temperature
performance.

Cheerful regards,

Bob

-- http://www.fastmail.fm - A no graphics, no pop-ups email service

2011\03\14@123804 by Michael Watterson

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On 14/03/2011 15:46, Bob Blick wrote:
> If you want really super low temperature performance you can use lithium
> thionyl batteries, a bit pricey but good for military applications where
> you just need it to work.

yes used to see those on some PCs and industrial controllers 3.x volts and about 2/3rds AA size. Those were what I was thinking of.

They can last till you lose interest in what they where fitted to.

Don't dispose of in fire. Probably

2011\03\14@131956 by William \Chops\ Westfield

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On Mar 14, 2011, at 9:37 AM, Michael Watterson wrote:

>> you can use lithium thionyl batteries..

> yes used to see those on some PCs and industrial controllers 3.x volts
> and about 2/3rds AA size.


Actually available in an wide variety of sizes.
http://www.tadiranbat.com/ is a major supplier.

Note that these are also designed for low discharge rates.

BillW

2011\03\14@150747 by Bob Axtell

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While the ideas presented here are good, I'd have absolutely NO confidence in any
calculation. The only time I'd feel confident is to:

1. Purchase the exact battery that the customer will use, whatever that is, and install
it into the breadboard. PURCHASE is a keyword; anything you have laying about is
stale.

2. Subject the product to the temperature range expected.

3. Using a small A/D converter and timer (a PC application is fine), monitor the battery usage.

4. When the batteries are too low to operate the product, that is the end of the battery's
life.

5. Do this at least 3 times, with 3 different batteries, to handle normal variation.

NOW you have good data; the average of the 3 is the battery lifetime.

Everything else is BULL----.

--Bob




On 3/14/2011 5:48 AM, Sean Breheny wrote:
{Quote hidden}

>> -

2011\03\14@152836 by Bob Ammerman

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{Quote hidden}

This is all lovely, but what if your expected battery lifetime is on the order of months or even years? At some point you have to trust the manufacturers' data.

-- Bob Ammerman
RAm Systems

2011\03\14@215447 by RussellMc

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On 15 March 2011 08:07, Bob Axtell <TakeThisOuTengineerEraseMEspamspam_OUTcotse.net> wrote:
> While the ideas presented here are good, I'd have absolutely NO
> confidence in any
> calculation. The only time I'd feel confident is to:...

All points well taken.
BUT sometimes you don'y have the luxury of eg 15 to 30 year testing.

I'd say that given any system of *well defined*  battery, load and
overall environment a competent engineer should be able to get the
uncertainty down to a factor of say less than 2:1, and in many cases
much better than that.  It's the engineers job to ensure that "well
defined" is what it says and is well enough known.

In most cases, the accuracy of the assumption set and match of theory
to reality are the limiting factors. Otherwise known as applied
engineering :-). Even believing the manufacturer depends greatly on
who the manufacturer is and which product you are dealing with.

Bob and I are generally in agreement though - if the volume is large
enough and the answer important enough then a substantial amount of
work may be required to get a half good answer for an apparently
simple requirement.

As an aside - where power levels get so low that "many years" of
backup or operation are aimed at, use of "energy harvesting" may well
provide an extremely valuable contribution.
eg a 2000 mAh energy store operated over 5 years provides about 50
microamps continuous current.
At say 3V that's about 150 uW power.

2 cm^2 of modern silicon PV material exposed to 0.01 sun (200 mm^2 and
10 millisun if Olin is asking) continually. Or* 250 millisun (25% of
full sun for people who want the figure  to leap out at a glance) for
1 hour per day would provide this power level . E&OE.

A few cm^2 of PV panel storing to a supercap MAY provide long term
powering needs relatively  easily and cheaply in many such
applications.


Russell

* Beware people who start sentences with "Or ..." :-)

2011\03\15@101621 by William Couture

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On Mon, Mar 14, 2011 at 9:54 PM, RussellMc <RemoveMEapptechnzspamTakeThisOuTgmail.com> wrote:
{Quote hidden}

Actually, this is straying into an area I've been thinking of lately.

My local "dollar store" has solar stakes (for only $1 ! ).  In case you
haven't seen them, they are little self-charging lights that you can use
to outline your sidewalk or whatnot.  (see the attached image.  Only
the dollar store ones are not as nicely finished).

Inside is the solar cell, an unidentified 4-wire component (I think it
is some sort of comparitor / switch), a resistor, a white LED, and
a 200mA Nicad AA cell (1.2V).

When in the light, the cell charges.  In the dark, the LED lights.

So,
  1) Could you use something like this for your project?

  2) What can other people on this list think of to do with
      such a toy?

Bill

-- Psst...  Hey, you... Buddy...  Want a kitten?  straycatblues.petfinder.org


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2011\03\16@153227 by Bob Axtell

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On 3/14/2011 12:28 PM, Bob Ammerman wrote:
>> While the ideas presented here are good, I'd have absolutely NO
>>
> is is all lovely, but what if your expected battery lifetime is on the
> order of months or even years? At some point you have to trust the
> manufacturers' data.
>
> -- Bob Ammerman
> RAm Systems
>
I won't beat this horse again after this...

- - - -

Are you saying that manufacturers have 30-yrs of data for a product they invented a year ago?
All they have is conjecture, and bull---- .

You can tell the client ("The battery maker indicates that battery life can be as long as 30 years") but in no way can you "calculate" battery life..

Does anyone remember what happened at Ramtron? When the ferroelectric  process was cooked up, the company FELT that the cell would be good for at least 10 years, but to be precise, it never.SAID 10 years. Now they believe it will last 40 years, but that's because the cells have have held for 25+ years. Only NOW is their data good enough to make even plausible life assumptions.

Anybody notice that I NEVER design in a PIC less than 2 years old?

All I am saying is: don't get caught up in bull----.

--Bob

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