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Hey gang-

maybe someone with more battery experience can shed the light on this holy grail!  lol

I have a project/pcb/circuit..  its a minimal Arduino circuit with on-board microSD card.. (designed to play PWM audio output on D9..using SimpleSDAudio lib)

I have it all breadboarded up..to mirror he minimal components the PCB will have..and have tested it just fine..

Im at the stage where schematic/board layout and firmware/code is pretty much complete...  (and soon to order some pcbs for population/assembly)

in the design stage. I was loosely thinking a +3v CR2032 would 'work'.. but be at is bare minimum...

However that turned out NOT to be the case..  while I believe the +3v is fine... I dont believe these can deliver enough current for the project.

I tested on my PSU and having it at +3v was fine..  but turning down the current.. I eventually got the same results/reaction as I did when running off the CR2032 coin cell.


my question(s) are as follows:

1.) How much current can the CR2032 give?  I have looked and not only do I see different numbers.. I usually only see it for mAh...  not mA?  Im thinking I need about

I understand that these CR2032's are mostly for high energy, low power projects...

and I guess Im needing the opposite... or at least just more current.

2.) The space/area I have to work with.. really is only suited for a 'coin cell' type of battery...  it can be a little 'bigger' (23mm diameter I think I have room for?.. maybe a bit more if needed)...  Is there anything out there that can work for my needs?

3.) Is there a value/sepc on these datasheets Im supposed to be looking for/at to see if the battery can DELIVER the current I need?



Secondary question... about my PSU (benchtop Mastech HY1803DL)

I set the voltage to +3v
I set the current to be 'about' .10-.11 Amps  (100-110mA)

when I connect it to my project..and power it on..

I see the current LCD screen 'jump'.. to about .06A....... when I press the button and trigger an audio clip to play.. I see the current LCD screen on my PSU jump to about .08A

Im curious as to what my current LCD screen is 'reflecting' (telling me).. is this the current 'draw' of my project?  (kinda cool/nice if it is...nice way to 'tell')




thanks!!


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my question(s) are as follows:

1.) How much current can the CR2032 give?  I have looked and not only do I see different numbers.. I usually only see it for mAh...  not mA?  Im thinking I need about
1mA? 2mA?  Certainly very little indeed.
Quote

I understand that these CR2032's are mostly for high energy, low power projects...
Strictly micro-power applications only, like calculators (a few tens of uA)
Quote

and I guess Im needing the opposite... or at least just more current.
For an SDcard you need a regulated 3.3V and perhaps upto 150mA - SDcards can be power hungry, different cards take
different currents, and more when writing.
Quote

2.) The space/area I have to work with.. really is only suited for a 'coin cell' type of battery...  it can be a little 'bigger' (23mm diameter I think I have room for?.. maybe a bit more if needed)...  Is there anything out there that can work for my needs?
Do you need the capacity of an SDcard?  An EEPROM might be less power hungry.  You will really struggle to find anything for that
size, but the best power density is LiPo, the best voltage match might be LiFePO4.  Well having said that 23mm diam, but how long?
Quote

3.) Is there a value/sepc on these datasheets Im supposed to be looking for/at to see if the battery can DELIVER the current I need?
When you can find a datasheet for a battery it will have discharge curves - these are perhaps the best info.  The datasheet only
covers one type of cell from one manufacturer.
Quote


Secondary question... about my PSU (benchtop Mastech HY1803DL)

I set the voltage to +3v
I set the current to be 'about' .10-.11 Amps  (100-110mA)

when I connect it to my project..and power it on..

I see the current LCD screen 'jump'.. to about .06A....... when I press the button and trigger an audio clip to play.. I see the current LCD screen on my PSU jump to about .08A

Im curious as to what my current LCD screen is 'reflecting' (telling me).. is this the current 'draw' of my project?  (kinda cool/nice if it is...nice way to 'tell')

thanks!!
Yes, you're powering up the SDcard at that point perhaps, and perhaps an audio amp, so the current will rise.  80mA is actually quite
modest in fact
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HI

thanks for the reply..


Cant really use an Eeprom at this point..  (audio files are user changeable)

The SD card seems to work fine at down to even 2.8-2.9......



As far as battery 'size' goes...  'coin cell' sized.... but can be a bit 'bigger' in OD than the 2032...  up to maybe 23mm...
as far as 'long'...  not much.  normal 'height' of a coin cell..maybe a bit bigger then the 2.5mm of the 2032.. but not much..


I think I have seen +3.3v and +3.6v coin cells before?  (I'll have to search around a bit)...
maybe one of these will give me the 80-100mA I need?



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Not for long... I use a little flashlight W/2 2032's and 5 - 6 hours @ 20 mA until the light is useless. 100 - 160 mAH total capacity so put current/mAH 100 mA/160 mHA = 1.6 hrs... IF you are lucky. The 2032 simply wasn't intended for that service.

Bob
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thanks!..


I figured since its not 'working' smiley


any sorta of replacement, that can me the current needed?  (but in a similar footprint?)

really the footprint is the 'key' here.. the space is really 'tight'..  

I was thinking trying some other smaller watch batteries.. and running two in parallel to increase the capacity...etc..

then noticed these are only 1.5v!!  LOL   (foiled again!)  

so I guess Im looking to order something.. that 'fit the bill' so to speak...  (looking like I need 100mA output)

any suggestions?

I find the specs misleading.. or better put Im not clear on what Im supposed to 'look' for?


take this link for example:  http://www.batteryjunction.com/maxell-cr2450.html
*(might be too 'thick'.. but worth looking to.. if can delivery the 'current' needed)

CR2450's:  
Specifications-
    Brand / Type: Maxell
    Model: CR2450
    Chemistry: Lithium
    Output Voltage: 3V
    Height: 5mm

Now looking around some more...

I find this link to some CR2450's..

http://www.megabatteries.com/item_details2.asp?id=14443&sid=shopgoogle&gclid=CLvPzunjqrUCFfBDMgodKV8AyA

with these specs.. (probably a bit more realistic?..but who knows...??)
Specifications:
    Nominal Voltage: 3.6V
    Size: 2450
    Capacity: 120 mAh
    Chemistry: Lithium Ion (Li-Ion)
    Brand: Power Portable
    Included Qty: 2


one says +3v... one says +3.6v..   HUGE difference in capacity..  
    Weight: 6.3g
    Diameter: 24.5mm
    Capacity: 620mAh





double up on some LI2016's?  (not sure on their capacity out either though.....looks like only 18mA or so though?) LOL..
a 2325?

a 2430?

thanks!
« Last Edit: February 09, 2013, 10:49:31 pm by xl97 » Logged


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With battery powered projects, the main issue is how long do you want the battery to last, before it has to be replaced.
Coin cells have extremely low capacity, 100 mah or so is typical.
They are mainly designed for backup, watches, anything that draws extremely low current , 10s of uA.
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How about this battery
http://www.hobbyking.com/hobbyking/store/__11874__ZIPPY_138mAh_20C_Single_Cell_.html
Dimensions: 37x26x3.2mm
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@ mauried-

yes.. I know about the CR2032 (that it wont work).. the question is about finding a suitable replacement (similar footprint but with more current output)



@BillHo-

thanks.. if for some reason the 'coin cell' shaped/styled battery can be forgone....  I'll look into this type..

for right now though the round, coin cell shaped battery is what 'fits'..  maybe up (maybe) up to 25mm in diameter...  Id like to keep thickness and 'thin' as I can though..

I need a battery that can fit in the footprint.. as well as have a Typical (sometimes called Background or Continuous) Drain of at least (I think maybe 50-60mA... and a Pulse Drain of maybe 80mA)

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Still need to know how long you want the battery to last for.
You say you need a battery that can supply 80 ma, but for how long?
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If Im going off what my benchtop PSU is saying on the current LCD screen..

when I power up my Arduino/project... it says/shows 0.05-0.06A... which Im led to believe means my project is pulling 50-60mA...  correct?


When I press the button... (which plays an audio clip from the SD card.. as well as PWM fads a couple leds)...  the LCD screen for the current shows/display/jumps to 0.07-0.08A  (which is 70-80mA)...  correct?


this is just a 'display' prop so run time isnt 'too' important.. and can be a bit of a trade off.. if size and current can be 'found'..  smiley

maybe 1 hour?  I'll take whatever (the most) I can get!  lol..


I just dont think a coin cell, even if I do 2 in parallel, will ever get me the current I need?



requirements:
(coin cell shape area.. I have roughly 24mm diameter.. and maybe 4.5-5.0mm thickness for a solution)

has to have enough current

voltage can be +3.0 (probably not enough..but 'will work') to +5v....
and while not 'round' or coin cell shaped...

this 'almost' fits into the SIZE requirements:  https://www.sparkfun.com/products/731

but I dont think that will give me enough current either...  smiley-sad


anything? smiley
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1.) How much current can the CR2032 give?  I have looked and not only do I see different numbers.. I usually only see it for mAh...  not mA?

You know that amp-hours is a measure of the energy available, for example, if a battery can supply 1mA for 10 hours, that's 10mAH. Also if it can supply 2mA for 5 hours, same thing.

The specification you're indirectly looking for is the C-rate, usually listed in the spec table as just "C". But then you'll find max. discharge current listed as a multiple, e.g. 3c. Or, if you're lucky, you'll find spec sheet like this one, which lists the actual current, but note the "2.5c" part. Another example is a LiMn battery which has a discharge rate of 8C, which is quite a bit of current -- I note this page doesn't specifically list C for this battery; I'm just familiar with it. (Max charge current is probably very close to, or equal to "C" for this cell.)

I think you'll just have to dig up real spec sheets on the batteries you're investigating. And I think you're going to need bigger ones.
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The Sparkfun Lipo battery at 110 mah , will easily give you the 80 ma that you need, as its rated at 2C
so can deliver 220 ma .
It will last approx  an hour before needing to be recharged at 80 ma current draw.

 Lipo batteries must not be overcharged, more than 4.2V  or discharged below approx 3V or the battery will be  damaged, which means that if you use one , you need some kind of smart charging arrangement to ensure that overcharge, or extreme discharge does not occur.

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thanks for the replies..

(Im learning little by little here)  smiley


the Li-Po @ Sparkfun...

this is the datasheet:
http://www.sparkfun.com/datasheets/Batteries/UnionBattery-110mAh.pdf

I 'thought'.. the MAX Discharge is the current I can get for a very brief period/burst of time..  not a reflection of what current I can pull normally?

There is a STANDARD DISCHARGE.. and a MAX DISCHARGE listed..

0.2C5A

&


2.C5A

respectively..



I need about 50mA normally (I guess).. and about 80-mA max.. when button pressed?

the 0.2C5A is only about 20mA or so?... correct?.. and hence not enough?

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Max discharge rate means exactly that, the maximum rate that the battery can be discharged at.
No time limit is mentioned nor applicable.
You wont however get the full 110mah capacity at the 2C rate, but at the 0.2C rate you will.

 
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haha..  (I just get more confused)

ok..so MAX is the MAX I can 'constantly' draw?  and not a MAX 'pulse' drain....right? (meaning I can only get that much current draw for a brief period of time)



(still a bit confused on your other comment of 220mA can be delivered because its rated 2C)?..

in relation to the new comment..  "You wont however get the full 110mah capacity at the 2C rate, but at the 0.2C rate you will."

(sorry for being thick here..it'll sink in eventually) smiley


the 0.2C rate (or whatever) worthless to me....  20mA mean nothing in this project scope..

so,...
2C = 220mA (2 x capacity)
1C = 110mA (1 x capacity)
0.2C = (roughly) 20mA  (.2 x capacity)

right?


if MAX discharge is 2C  (220mA)...  this can ONLY be given/pulled for 30 minutes?

110mA (which is it is rated for).. will give me 110mA for 1 hour (or so)

and pulling 20mA (0.2C) will give me 20mA for around 5 hours or so...


am I correct in all this so far?
*I dont think so because you say this: "You wont however get the full 110mah capacity at the 2C rate"
do you just mean it wont run for the full 'hour'?  I'm pulling 2C (220ma)??

so if I want to pull the full 110mA (or close) form the battery pack.. it'll run 1 hour (tops)..

I think i can live with that...  since it wont be @ full draw (80mA) for more than a button press. then back down to its normal 'power needs'...

thanks!















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