How battery capacity is measured and what is Wh? (Watt Hour)
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- Опубликовано: 20 июн 2020
- The most important measure of a battery is how much power you can get out of it on a regular basis. That number is represented by Watt-Hour or Wh. Not Amp Hour or even Milliamp hour that most marketing people like to write in the ads and on the products, that is only part of the answer. (Also remember that older types of batteries, like lead batteries don't survive long if you use more than half of what they contain.)
Let's start by oversimplifying and looking at a battery like a box. You can add stuff, like charging a battery or you can take stuff out when you want to use it. Its capacity is its Volume which is equal to its Length time Width times depth. If any of these change then the total volume will change.
If we simplify a battery capacity we can use the same approach. You can see it as an energy box where the 3 important numbers can be seen as sides of a box. So we calculate the power capacity as Volts times Amps times hours equals capacity in Watt-Hours.
You can use the numbers printed on a battery to calculate a number for its capacity in Wh if its not already there. Most of the time the Amp and the hour have already been multiplied so the equation is just Volts times Amp hour equals Watt hour. That is often what you find printed on a battery.
Unfortunately counting the battery capacity number this way is always too high because the reality is that the battery will always deliver less than this number for several reasons we will look at in the second half of the video. This is the number that the marketing department normally like to print in the specifications because it sound better that the number that you measure getting out of the battery bank.
Ok so let's look a more nuanced view of the battery.
The first reason you don't get as much power as the simplified calculation would suggest is that the Voltage decreases as the battery is being emptied. This can be accounted for if we imagine the container is not shaped like a box but more as a slanting wall. The volume or capacity will decrease.So due to this fact the battery can deliver 10-25% less power than the simple estimation would suggest.
A second reason you get less power is if the battery has to convert its internal voltage level to another that is expected outside. This is the case for all USB power banks that are typically 3-4V internally and have to boost the voltage to 5V which USB requires. This leads to yet more loss of 5-15%.
A third reason for a battery delivering less than expected is when they are working at a high discharge rate. Then the voltage drops even more than normally and the hard work of the batteries causes them to lose energy as heat. In this case it is not unusual to only get 50% out of a battery. With the risk of shutdown due to overheating.
A fourth reason is aging or damaged batteries that do not have all their initial capacity left. When a battery can only reach 80% of the original capacity after fully charging a battery is considered spent, and you can assume that it will degrade fast after this point.
The only reliable way to know how much capacity a battery has is to measure it but that is for another video. For now remember to find out the theoretical Watt Hour capacity and know that the reality will be lower.
Here is an example of the capacity of two batteries
A cell phone on average has 10 watt hours battery capacity. If we let a lego block represent one watt hour it looks like this.
A Currentium Power Bank has a true measured output capacity of at least 65 watt hours when new. It looks like this. In marketing language it would be called a 20000 milliamp hour battery and the Watt hour rating would be higher but that number is not very useful unless you know how the rest of the battery performs.
With the real Watt hour capacity we know that this battery will give this phone over 6 full recharges. That is accurate information. Check out the Currentium home page for more about power banks and solar power.
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Wow! That was a very fast five minutes! Your video gave me more information than the last six videos I watched combined. Thanks for the great information.
Great to hear!
Great video! Hoping to see more energy related videos. Power consumption measurement would be interesting. This was quality content, thanks!
Great suggestion!
Wow this is what I have been looking for. Only smart people know that we learn best with analogies.
Thanks.
Glad it was helpful!
Very lucidly explained, thanks!
Glad it was helpful!
Very useful content, you have earned my subscription ❤️
Awesome, thank you!
Thanks for a good example and expression.
Finally someone who explains this clearly
Happy it was useful
What an explanation. sir You nailed it.
Thanks
Glad it was useful.
When will your batteries be possible to buy?
Very impressive
Thanks
nicely taught
hi, if i need to run a tesla instead of its 100KwA battery, which generator i need to use? The question is not about recharging the 100KWA battery, but about replacing the battery with a generator. In that case, what would be that generator's power? I have seen people charging Tesla with 5KW generators. So can i run that tesla, with 5KW generator as a power source?
Sounds like you should look a hybrid cars which are Electric cars + fossil generators that work together and charge while running. You will not want to try and run a tesla with a large fossil generator in the boot. It probably won't accept charge anyway while running. Its safety features would think that you have forgotten to unplug the charge cable and would not let you drive/run the car until unplugging. Stay Safe.
So basically, that number lets you know how long you battery will last? Kinda like, Yeah it's a 1.5v battery but how long will this battery be able to hold 1.5v of power?
If you have the volt and watt value, you can work out amp.
Just use amps stored and calculate to real world results.
Watt hour was made just to further confuse people.
If a device lists its Wattage is that for one hour ? Trying to determine Watt-Hours so I can be sure I have more than enough power to run a device for an 8 hour work shift. Thanks
Wattage (Watt) rating should refer to max power usage at any point in time. The average should be the same or lower. You should be able to assume that it will give you the max Watt-Hours (Wh) consumed in an hour. If it is important you should test or measure it.
Can a Battery show full charge on a volt meter , and still be missing the Amps - where it won't do anything to crank over an Engine or make Light come on?? Thanks in advance.
Yes, If the (fully charged) battery is really old and worn out its voltage may show the same voltage as a new battery but will drop much faster when trying to use it. If its really bad it will not give enough power (Amps times Volts) to start a car. So it would be storing less usable Electrons (Amps times time) in that case that a new.
Thank you sir
Happy is was of use for you.
It's amazing a standard phone battery is 10wh & a big car battery size lifepo4 battery is 10 smartphone batteries!
Hello, Thanks for the info I learned a lot from you.
If you could help me on my solar system I would appreciate.
I have 8 Panels each 350watt mono,
I have 8 batteries of 150amp gel, 3000 deep cycle, connected in series, it is 48v sysytem
STECA SOLARIX PLI 5000-48 INVERTER HYBRID INVERTER- indicated 80amp, no controller needed.
I got 160amp fuse for solar wire before it get into the invertor, One point to consider my system is not high tech like yours, I am communicating with you from far away in Africa.
I tried to explain my system so you understand what I got,
My problem, during the day time the Invertor charges the batteries and they get to 53.6¬53.8 volts, but this is where it get complicated in the evening or sun-set the invertor start beeping error (04) by saying low power from battery, then switches back to the grid=no use at the evening!
This made me mad, the setting is set to 44, if battery get law than to 44 then only Invertor to go back to the grid. Investigations I measured the batteries and each is showing 12.6 to 13.4 volts each.
Do you come across this kind of faults where the battery is full and come in the sunset no power to give, where it should hold at least few hours, but it gives up at sunset.
Please ask any diagnostic questions, if I missed any, thanks in advance
Thanks in advance Alex
I have a question I hope you could answer. There is an argument or debate going on in the tool community about fairness when comparing tools with different batteries. Specifically watt hours and cells. If one of the battery packs is 24 volts rated at 120 watt hours using standard discharge 18650 cells comparable to using an 18 volt battery pack rated at 108 watt hours using high discharge 21700 cells? Would that be a fair comparable test? Which battery pack has the advantage or would they both operate with the same power? Also someone said that a 18 volt battery pack rated at 108 watt hours with 21700 high discharge cells is actually producing twice the watt hours since it’s using high discharge cells. Is that true? Sorry to bombard you with all these questions. I’m very interested in learning the technology behind the different battery cells and the way they operate. Hopefully these are questions you could answer for me. Thank you for your time. Hope to hear from you
The question is How do you test and compare fairly and meaningfully battery pack or power banks. Eg which is better 24v 120Wh of 18650cells vs 18V 108Wh of 21700 “high discharge” cells.
Let me answer it generally like this:
The short answer is if your batteries are getting hot or really hot when you are using them then the are probably to weak for the task if you want them to last as long as possible.
The longer answer is, first its really important to keep Watt(W) (how hard it is/can work) and What Hour(Wh) (how long a battery can work before empty) separate.
The answer is it depends on at what power level (W) you are pulling out of the battery pack. The limit is a combination of the chemistry and the quality of connections. The closer you are to the max that a specific pack can deliver the more is lost to heat. If the (W) you are pulling out are used where you need them or if a large part is lost as heat because you are running the batteries as hard as they can work. If the batteries get hot then you are losing usable Watt hours (Wh) that is not going to the work you want done, and the battery chemistry is pushed hard resulting isn shorter life of the pack. This can significantly affect results.
So any test has to be done at given power (W) Level that is relevant to the use you want to compare. At that power you measure Wh delivered and compare.
@@currentium thank you so much for getting back to me. Thanks for educated me on how these cells and battery packs work. The main focus of the debate in this particular issue though is, does a battery pack containing 21700 high discharge cells, produce twice the amount of watt hours while under load? The rating on the battery pack says 108 watt hours, but when under load ( in use ) does it produce 200+ watt hours? If would think not but someone is saying it does
A battery will NEVER deliver more total energy (Wh) when under heavy load than when working at low load. There will always be more or less loss to heat. A larger battery capable of higher discharge will lose less to heat.
@@currentium thank you. Ever since you first messaged me back a couple weeks ago I’ve been studying lithium ion cells and discharge rates, discharge curves, c rates, etc etc. I’ve learned quite a bit but there’s still plenty more the learn. The main thing I was getting wrong was associating watts with WH and amps with AH. Knowing the difference between power and energy and charge capacity Vs energy capacity makes things a lot easier to understand. Thank you for all your help my friend. I really appreciate you getting back to me
@@IMPACT-NATION A little correction. A battery does not produce Wh. That's like saying a car produce gasoline. No. It uses Wh (amount of energy) like a car uses fuel. Now, what you want to ask is probably one battery is able to produce X Watt (power output) similar to a car producing X HP (power output).
Pushing battery to output high power close to its maximum ability is just as bad as revving your car to recline since it significantly wears it down.
Can you tell me if a battery that is fully charged and one that is flat have the same watt hours and if one is rated at say 274w/h on the side is at fully charged and if it was discharged to say 10% would it still be 274w/h?
I understand that you are asking this because of Airline regulations that have a limit of a singel 160Wh (or several 100Wh) as handluggage. When we talk Wh we normally want to know what is the maximum amount of energy that can be stored in that battery. That is typically its rating. By discharging the battery it still has the same rating even if it is safer to transport discharged batteries.
@@currentium Thanks, I understand this is the rating on the side of the battery but i met with CASA who govern air travel in Australia and they said that a battery that is discharged in real life wont be 274wh and in theory could travel on board. I wanted to see if i could find something that proved this as Dangerous goods asked for more information. I am struggling to find anything or understand if this is true and your video was the best i could find, thankyou for replying too.
i know i know this but A×V=W... so it's just how many hours the battery can deliver those amps at its nominal voltage until it's "dead" so what I'm finally understanding now... is... that watts are a meaningless unit that only confuse the consumers of electricity
It can be confusing but they all say different things when you get used to them. To help remember you can think of Watts like the measure of how hard and fast you are peddling a training bike in a gym. And add time to give Watt-Hours as how long you can go at that speed before being exhausted.
Title: How battery capacity is measured. Dude says "Only reliable way to know how much capacity a battery has is to measure it, but thats for another video" ?????
I never knew such a short video could drag for so long. Get to the point.
Thanks