What is the C Rate for Lead-Acid and Lithium Batteries? How to Calculate
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- Опубліковано 22 чер 2022
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In this video, I will unravel the concept of C-rate in battery systems and why it's crucial for anyone involved in solar power to understand it. My name is Nick, and my mission is to make solar power understandable for everyone. C-rate, a term often encountered when discussing battery specifications such as nominal voltage, internal resistance, and ampere-hours, essentially tells us how fast a battery can be charged or discharged. It's usually represented as C followed by a number, for example, C20 or 0.05C, which can sometimes lead to confusion.
C-rate is derived from the battery's capacity in Ampere hours, serving as a guideline for its charging and discharging speeds. For instance, a lead-acid battery with a C-rate of 20 means if the battery has a 100 ampere-hour rating, it can safely charge and discharge at 5 amps. Similarly, for lithium batteries at a 1C discharge rate, we can charge and discharge at 100 amps, which significantly impacts how we design and utilize our solar systems.
Understanding the difference between placing the number before or after the "C" is crucial. If the number precedes the "C", like 20C, you multiply it by the battery's capacity. If it follows, as in C20 or 0.05C, you divide the capacity by that number. This distinction affects how we calculate the necessary charge and discharge currents for our batteries, especially when considering their application in solar power systems.
When we delve into practical applications, the importance of C-rate becomes even more apparent. For solar power systems, especially in settings where batteries like lead-acid or lithium are used, knowing the C-rate helps in accurately sizing the system. Lead-acid batteries typically have lower C-rates than lithium, meaning they can't handle as high charging or discharging currents. This is a critical consideration when planning to power high-demand appliances or when deciding on the battery type for your solar setup.
Moreover, the built-in Battery Management System (BMS) in lithium batteries plays a vital role in managing these rates, shutting down the battery to prevent damage if high currents are drawn. This protective measure is something lead-acid batteries lack, making the understanding and application of C-rates even more essential for ensuring the longevity and efficiency of your solar energy system.
Today, I've covered the essentials of what is c rate, what is c rate of a battery, and how to apply the c rate formula and c rate battery calculation to optimize your solar setup. Whether you're dealing with the discharge rate of lithium-ion batteries or calculating cable thickness for solar panel wires, understanding C-rates is key to a successful solar power system.
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Thank you for the information. Well done
Thank for info. Very clear explanation.
Thanks for the video 👍
Hello @cleversolarpower and thank you for the video. Could you please confirm if the formulas and numbers in minute 1:05 are ok? with a C rate of 20, a battery rated 100 Ah should discharge or charge at 2000 A in 3 minutes, like you shown in the table.
C20 is different than 20C. When the number is in front of the C, you multiply and when the number is behind the C, you divide. At 1:05 you can see C20 is the same as 0.05C.
@@cleversolarpower Maybe term to be used should be number before C or after C.
Front or behind is confusing.
hope this finds you well and safe, can you provide us about connecting solar panels to batteries with MPPT
I have an article about connecting a charge controller to the battery on my website.
nice video, 1 suggestion can you make a video doing a diagram about Off the grid solar system with Micro inverters and batteries with all the parts needed 👍🏻
I'm working on that as an addition to the book. Later I will upload a few videos talking about the different systems. Thanks for the suggestion.
Can you calculate the c rate? I have panasonic up-vw1245p1 seald lead acid battery and i would like to know the c rate. 12v 9ah
You cannot calculate the c-rate. The c-rate is given in the datasheet of the battery. You have to look up the battery tape and it's recommended c-rate.
Good series of videos. You should do one on the Peukert effect. It's kind of related to this topic. Lead batteries with a Peukert of 1.25 lose a lot of their capacity at high C rates of discharge, where as LiFePO4 batteries with a Peukert number of 1.02 to 1.05 can still supply almost all of their energy at high C rates. en.wikipedia.org/wiki/Peukert's_law
Thank you for the many excellent videos you have produced. Many people have had seemingly good results employing used forklift batteries as the storage for home systems. They find used batteries and often spend about $100 US for them, then spend a month or more reconditioning the batteries, often using a single solar panel to “boil” the batteries which removes the stratification from the plates. Eventually the batteries have very high capacity. They also contend these batteries can be drawn well below 50% of capacity regularly and still bounce back for many years. This runs against the normal lead acid logic but I believe them. They are running off grid homes and are running normal grid tied loads daily. Do you have any experience or opinion on these batteries? Thanks ColoradoKeith
Hello Keith, you can run lead acid below 50%, but it will always have an impact on cycle life. Remember that people like to show off their system online. So take some of these with a pinch of salt. It's definitely possible, but not very practical to find such batteries. The boiling is sulfation removal and chargers have these built in. Should run once a month. Voltage is a bit higher than normal during charging.
Now in LiFePo4 batteries cells specification we see the P Rate from Power Rate, 0,5P is half Wh of battery.
That's not C rate.
Thank you so am I right in saying for an AGM leisure battery the lower the C rate the better?
It's better to have a low current draw/charge than a high current draw for any battery. 0.2C is the maximum an AGM - lead-acid battery. Lower is best.
@@cleversolarpower thank you I'm trying to decide between three AGM batteries. One is 100Ah at C20 one is 120Ah at C100 and the third one is 120Ah at C20 .
On those figures which do you think would be the best to buy?
Thank you so much for trying to help me - I'm very confused and can't decide out of the three which to choose
hi. 5200 mAh, 3 H and 50 C are given. Voltage is not given. How to calculate power of this battery? Thanks.
You need to figure out how many cells there are. Every cell has it's own voltage depending on chemistry.
Should power consumption include inverter losses in addition to appliance consumption?
Yes. Measure the standy consumption of your inverter and multiply by 24 hours.
thank you finally a video on C ratings that is easy to understand, although my battery has 2 C ratings C20 82ah and C100 90ah I'm guessing the C100 rating is max capacity so would the 82ah C20 rating be it's usable capacity?
At C20 you battery can deliver 82Ah, at C100 the same battery can deliver 90Ah. You battery capacity changes if the load is lower. The advertised capacity for this battery should be 82Ah.
@@cleversolarpower thank you
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Saya memiliki battery lifepo 3,2v ,50amp....apa artinya?
Can you rephrase in English?
I have a 50 ampere 3c lifepo4 battery, what does that mean it can be charged up to 150 amperes
@@ririanakmuslim5191 3C is overstated for lifepo4. It's more like 1C.
Can you clear the contradiction please? Because in another video, you said the C-rate for a lead acid battery is 0.2.
Some lead-acid batteries are 0.05C like flooded lead-acid. Others like GEL and AGM is 0.2C. You can find it on the battery datasheet.
In your sample 20C you divide AH by 20, but on the table it should be multiplied, am i missing something? 😂
You got me confused. 1:20 Why do you multiply capacity of 100 Ah by 1 for a Lithium battery with a discharge C rating of 1, but in the previous example you divide (you don't multiply) capacity of 100 Ah by 20 for a Lead-Acid battery with a C "rating" (unspecified type of rating) of 20? You also go on to say that the Lithium battery can charge and discharge at 100 amps. How do you know that the charge and discharge C ratings are the same for the Lithium battery, and if they are the same, why would they not be the same for the Lead-Acid battery?
1:33 This table did make it easier to understand. I can see where my confusion comes from (I didn't have time to sit through the whole video when I made the first comment). 20C and C/20 is not the same thing. 0.05C and C/20 is the same, but 20C and C/20 is not. Just like 5 dollars is not the same as 1/5 dollar. (The difference is evident from pluralization alone. Five dollars is more than one dollar; one fifth of a dollar is not even a single dollar.) Likewise, 20C is a factor of 20, and C/20 is a factor of 1/20. The slash hints that it's a fraction.
All this is saying is that division by 20 is multiplication by 1/20. But who on Earth doesn't know that, and yet wants to learn about C-rates for batteries? This is basic math. It's not necessary to make it so complicated. Changing the formula or the form of the formula just because you dip into fractions once you go below 1C to make it easy on the noobs is a total waste in my opinion and only adds to further confusion.
Also, keeping track of where the C letter is, if it's in front of the number or behind the number is completely unnecessary. Just take 100 Ah and multiply by 0.05 like it says on the far left (0,05C). It's the same as dividing 100 Ah by 20. Because of this extra step, you actually managed to confuse yourself in the video. 1:48 You said "if it's after the number, you divide it by battery capacity". It's not capacity. You meant to say divide it by the C-rate number, not by capacity. Capacity is 100, C-rate number is 20 (C/20). You're dividing by 20, not by 100.
Knowing the difference between divisor and dividend is much more useful than knowing where the C letter is positioned within something as obscure as a battery's C-rating. Basic knowledge usually is most important. Now I can better understand why so many people are having a hard time with C-ratings. They don't know math well enough. There are no shortcuts to getting the basics down right.
I understand your confusion. I didn't invent the way the C-rate is written down. There are two ways that are being used so I explained both. If in doubt, refer to the table for clarification.
@@cleversolarpower What does the "C" in "C-rate" stand for? Charge? Current? Capacity? Neither? I know the answer is not on Wikipedia. I have also looked at other sources. From Wikipedia article on battery charger: "Charge and discharge rates are often given as C or C-rate, which is a measure of the rate at which a battery is charged or discharged relative to its capacity."
Also, I wonder if these C-rate numbers hold up to what it says on the label? Have you ever tested them to confirm? I am by no means in battery business, or in solar panel business. So I don't know much about these things. But I have worked as an electrician, and I went to a practical secondary school (gymnasium) in Sweden to learn the trade, so I do understand the basics of batteries and electricity in general. I only recently came across the term "C-rate" and was wondering what it is, so I googled and landed here.
The only unit of measurement I know of that uses "C" is Coulomb. But it doesn't fit the description here. C-rate is not a measure of electric charge. It's a "rate" of charge. In other words, it measures speed! Rate is just a fancier word for "speed". So C-rate stands for "charge rate" then? Charge speed, in other words. It might be! If it wasn't for the fact that the same term is used for both charge and discharge! So it's kind of broken right there. It's badly defined to be a measurement of anything. Using a single letter for double meaning and open up for free interpretation. You can have it mean whatever you wish. Current, capacity, charge... it's all good. But that's not science.
If C-rate means charge rate, then logically, discharge rate should be abbreviated as "D-rate", right? But it's not. Instead, everything is just "C-rate", including burst discharge rate (how about "BD-rate" for short?). I think it would be a good fit to use C-rate for charge rate, and D-rate for discharge rate. Because the maximum charge rate and maximum discharge rate of a battery is hardly ever equal.
I think C-rate is one of those "measurements" that don't carry much scientific significance. It's the battery equivalent of a "shoe size". If C-rate was a universal unit of a physical quantity, it would be better defined, well documented, scientifically accepted, and it would be included in the SI system of units. It would not need to be made "relative" to the battery capacity to be relevant.
C-rate reminds me of gravity. Everyone can feel its effects, some of us can explain it, a few can do calculations on it, but no one really knows what it is.
You can think of C-rate as the speed at which you can drive a car from New York to San Francisco on a full tank, relative to the size of your gas tank. You can have a fast car that consumes a lot of gas to get there faster, but if your gas tank is too small, you will never get to your destination. The higher the consumption and the smaller the gas tank, the faster you will get stranded. What really matters in the long run is capacity. This is also why it's printed on every rechargeable battery, even when C-rate is not.
@@samirgunic C-rate doesn't have a unit. I exist because a battery with an advertised capacity of 100Ah can have more capacity and less capacity. If it is discharged fast (at a high c-rate) then the capacity is reduced because of heat generation. If the battery is discharged slowly it will have more than 100Ah. To make the manufacturers use one unit and not falsely advertise, they use a 0.2C rate for lead-acid. If the same 100Ah battery gets tested at a 0.5C rate the capacity will be reduced. If it is tested at 0.1C rate, then the capacity is more than 100Ah.
@@cleversolarpower i think you was a little bit wrong, because I found in datasheets for a different kind of lead acid batteries there a many acceptable values for C-rates (different charts are there), it's only affects time for work in that special range of voltage and current (something looks like available amount of power for special battery mode). If I'm not wrong, there are only two issues with lead acid battery which affect life cycles: depth of charge (undercharge) and incorrect max charging voltage value (overcharge).