EEVblog #140 - Battery Capacity Tutorial

[CharlietoKind]

nice, very informational videos!

[mariomaslonek]

lol you should be on the discovery channel... i love it. and easy to understand.

[mariomaslonek]

lol you should be on the discovery channel...lol i love it. and easy to understand.

[Technoguy3]

Good video. I didn't really understand milliampHours. Totally off topic, does anyone know what this 30-pin video connector I have is called? It only uses 16 of the pins. It came out of an old (the oldest) Gateway Profile.

[Schmiki24]

Uhm, at 19:50 it's mOhms, not Ohms, because a battery with 40 Ohms IR would really suck. :-P

[EEVblog]

@Schmiki24 No, it's 10 to 40 Ohms for a CR2032 battery

[MrTranxistor]

i really should have watched this video first before commenting on the other one and i would have answered my own question... so it's true that these numbers really are just consummer nonsence. now lts talk about getting the 9000 joules our of a AA.. theoretically speaking*wink wink* whats the formula to determine that in farads? =]

[tupham81]

I am astounded by ur awesomeness... Keep up ur awesome videos and I hope u win the iinet top geek award :)

[jonhdoe1395]

WRITTEN MAN, WRITTEN :p

[tupham81]

So how do we know that different battery manufacturers are being fair and going by the same constant current/voltages for their mAh capacities?

In other words, how can I know that a no-name branded battery that claims to be 2800mAh is equivalent to an energizer? It would definitely explain why the cheapo ones I bought off eBay didnt last very long when the energizer niMh batteries last much longer.

Also how do we know what the capacity is after n amount of charge cycles?

[EEVblog]

@tupham81 You don't, and they aren't. You have to read the datasheets. If thee data is not on their then you have to measure it yourself.

[luppa79]

You're saying that the mAh definition assumes a certain voltage, but you're making that assumption yourself. You would need to assume some voltage level if you want to calculate energy with a simple multiplication, but that's not the fault of the definition of Ah. Neither does it call for keeping the current constant. For example, 1h of 200mA + 1h of 400mA usage equals 600mAh, no matter what the voltages are.

What is capacity? Does that mean energy or Ah capacity or something else? I don't know.

[EEVblog]

@luppa79 True battery capacity is measured in Wh

[Microhard2012]

@EEVblog Actually we both go it wrong! From wikipedia it's 1J=1 W . s =1 W .h / 3600. So it's

1J=1 W . s = 2.7778×10^(−4) W.h .

Multiplying all part with 3600 we have: 3600J=3600 W.s=1 W.h which is quite logic if you think that 3600sec=1h.

So 1.4 W.h is 1.4*3600J=5040J and 2.5W.h=2.5*3600J=9000J.

[superdau]

Think about this: an average person needs around 9000 kJ a day (not talking about manual labor or athletes here; they can easily use tripple the amount). That's equivalent to the energy stored in 1000 AA batteries or a cube a little larger than 21x21x21cm³ stuffed with batteries. Running a human on batteries wouldn't be cheap ;-) . And if you have rechargeables: even with those 4x15min quick chargers you'd need 3 of these charges stuffed 24/7 to have enough energy.

[Microhard2012]

Great educative Video! There is a little mistake at the Joule conversion equation 6:43 .

It's 1J=1 W . s *3600=1 W .h

[ReefMimic]

save me 28 mins next time and just tell us the best ones to get

[EEVblog]

@ReefMimic I'm giving you the information so you can work it out for yourself. You're welcome.

[EEVblog]

@Certifiedfunds They will have a lower self discharge rate when colder, and hence a longer shelf life in theory.

[kwakkwak123]

Thank you for the video Dave, very interesting! I'm also studying electrical engineering, but not in english. And I'm always having problems understanding what the 'load' is you are always talking about. Is it the current your circuit has to create, or is it the resistance it sees?

[zzzlt]

would it be posibal to make labscope from microphone?

[Films4You]

Battery Capacity is important because of land fill issues. The quicker a Battery loses power the quicker it will end up in a land-fill.

[EEVblog]

@kd5gua It depends entirely on how you define the battery capacity and it's end use into a particular load type. By the very definition, mAh or Wh capacities are implying a constant current or power discharge rate.

[GTXAbunada]

@Afrotechmods I am sorry but what does calculus has to do with my question. The integral of v with repsect to time, gives a unit of v.s which is not a unit of energy. The thing that I was missing is the fact that constant current is assumed.

[GTXAbunada]

@dosmaster88 I yeah I see, I forget about that. Of course. That's the same reasoning behind putting battery capacity in Ah or mAh, assuming constant voltage throughout the battery's life cycle. Correct?

[monstercameron]

veri technical, do it for dummies next time!

[gbowne1]

@Certifiedfunds yeah, I've done this but often wondered why myself.

[valajbeg]

GRAET TUTORIAL

[detectiveinspekta]

I have a 3.3V MCU wondering what sort of battery to use. 9V - buck converter, or 3x1.5V to regulator. I think did some rough calculations and could get 10 days of use putting the MCU to sleep 9/10 of the time.

[EEVblog]

@detectiveinspekta AA's will have more capacity than a 9V battery, AAA's it might be a toss up. But you'd have to do some ballpark calcs.

[shiftplusone80]

Thank you.

[ubuntututorials]

Who hates the new YouTube homepage?

[popson4]

@ubuntututorials

Absolutely I hate it.

[hipnocesar]

i've never worried about the cut off voltage, thanks again Dave you are the best.

[hitachi088]

this guys is better than most of the Electronic Teacher out there .

[electrodacus]

Good video.

LiFePo4 are quite close to a constant voltage for most of the capacity.

It will go down from 3.2V to 3.0V from 100% down to 10% of the capacity.

Probably my next video will be about this rechargeable battery.

The best rechargeable battery for EV and renewable energy.

[GTXAbunada]

I don't understand how can capacity, an energy unit, be the area under the curve of voltage vs. time with units V.s. Could someone please explain.

[Afrotechmods]

@GTXAbunada Like Dave said, 1 joule = 1 watt.second. If you haven't done calculus yet look up integration and integrals, and you will learn that the area under the curve equals the number of joules given up during the discharge cycle. Khan academy would probably have some good videos on basic calculus.

[Orthosonic]

@GTXAbunada

Because of the assumption of constant current load. So the actual area is in 'volt hours'. But multiplied by a constant current you get watt hours.

[EEVblog]

@Orthosonic Actually it's not a constant current (although you could assume that). You have to log the cell current as well when calculating power.

This is shown in my next video on measurement, but I decided not to include it in this one.

[dosmaster88]

@GTXAbunada

Hope you are following post ;)

area is because we assume we are running constant current load while measuring voltage drop over time!!!

So in such case we have Volt*Amper*Time(h) = Wh or in case you don't take voltage drop into account the youll have just load current(mA)*time(h)= mAh

hope it helps ;)

[ryanstewart86]

why does the resistance increase when the temperature drops, you would have thought it would be the opposite!?

[Afrotechmods]

@ryanstewart86 Probably because the capability of the battery to deliver current is dependent on a chemical reaction, and normally chemical reaction rates increase as temperature increases.

[GTXAbunada]

Perfect, I've always wanted to know some of this stuff

[dosmaster88]

supa dupa cool stuff !!! go for rechargeable batteries, NiMh, LiPol, Lion. Discharge characteristics, charging techniques !!!

Thumbs up :)

[QBMan]

Naa constant resistance would be like good for lamps (bicycle or so). I think thats why they got that types in there. There are batteries "specialised" for light/lamps. I dont think that it has any or much effekt on lamps what battery you use but well thats marketing xD

[clovekkk]

First

[ubuntututorials]

@clovekkk faill....

[artifactingreality]

you hold that battery like a pro. making me wet.

[Nanovirus5995]

@artifactingreality ó_ó ?