Go Down

Topic: Battery choice/source help? (Read 1 time) previous topic - next topic

justjed


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.
... it is poor civic hygiene to install technologies that could someday
facilitate a police state. -- Bruce Schneier

mauried

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.


xl97

thanks for the replies..

(Im learning little by little here)  :)


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?


mauried

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.


xl97

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) :)


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!
















Go Up