wesnewell
100 GW
And all that would be great if anyone gave a rats *ss. Doesn't change the fact that to find the rated max amperage of a 20C discharge rated battery is determined by 20 X AH. Which is wtf I said in the first place.
NCM vs lifepo4?
- Thread starter emaayan
- Start date
wb9k
10 kW
Not for your one example....just everything else that depends on knowing C-rate, which you defined totally incorrectly. Details matter.
major
10 kW
The language and terminology is particularly confusing here. Does C mean charge? Or is it the abbreviation for the unit of charge, the Coulomb? Or is it a temperature unit? Or the speed of light? And then there is also _rate_ which is the differential with respect to time, or speed at which things happen. Or is it referring to the value assigned to a certain attribute by the manufacturer describing the product capability? Like what is the rated rate? Rated C means something different than C-rate.
The context of how the word or term or symbol is used has a lot to do with the interpretation.
The context of how the word or term or symbol is used has a lot to do with the interpretation.
johnrobholmes
10 MW
C means capacity. A 20ah pack has 20ah capacity. It can be used for charge or discharge descriptions. A 1c charge would be one hour, or 1 x 20a. 2c charge would be 30 minutes, or 2 x 20a. A 10c discharge would be 10 x 20a = 200amps. A 10c discharge rate takes 6 minutes. etc etc
wesnewell
100 GW
The C in C-rate means Charge rate. Technically, it means this.
http://en.wikipedia.org/wiki/Battery_charger#Charge_rate
It has nothing to do with capacity. It's only value is to determine the max rated charge and discharge rates for a particular battery. The formula for that is C-rate times times ah rating, which I stated earlier, and was erroneously corrected for. It appears that some people just want to confuse others with details which which are totally irrelevant to that fact. All this crap I had to learn some 45 years ago where I was responsible for servicing a 48V battery room in a telephone central office that was used fro backup of power failures. Yes, it was huge. Don't recall ah rating but each single cell lead acid battery was over 100 lbs. Over charge those babies and you could take the whole building out.
http://en.wikipedia.org/wiki/Battery_charger#Charge_rate
It has nothing to do with capacity. It's only value is to determine the max rated charge and discharge rates for a particular battery. The formula for that is C-rate times times ah rating, which I stated earlier, and was erroneously corrected for. It appears that some people just want to confuse others with details which which are totally irrelevant to that fact. All this crap I had to learn some 45 years ago where I was responsible for servicing a 48V battery room in a telephone central office that was used fro backup of power failures. Yes, it was huge. Don't recall ah rating but each single cell lead acid battery was over 100 lbs. Over charge those babies and you could take the whole building out.
Ypedal
100 TW
and then from the link you provided..
try again jack.
melodious
100 kW
which has more wH?
1.2# of LiFEPO4
or (insert drum roll)
1# of NCM
d-('-')z now if that isn't a troll post then give me a spoon and I'll give you one of my eyeballs.
I'm going outside. I need fresh green life nourishing air. lol I give up
1.2# of LiFEPO4
or (insert drum roll)
1# of NCM
d-('-')z now if that isn't a troll post then give me a spoon and I'll give you one of my eyeballs.
I'm going outside. I need fresh green life nourishing air. lol I give up
wesnewell
100 GW
I guess you want to join the rank of those that want to confuse people. OK, I have a 37V battery with a C rate of 20C, What;s the capacity of my battery. Get the point now?
melodious
100 kW
I'd do the math, but I'm pre-occupied with my own matters lolwesnewell said:
FWIW, I too along with many folk here enjoi the topic.
wesnewell
100 GW
That was neant for ypedal.
SamTexas
1 MW
I disagree with wesnewell. C is for capacity just like all others said. This is not a matter of opinion. It's well defined.
2C discharge rate means the battery can be discharged in 1/2 hour regardless of it capacity. C is used for charge/discharge rate so that the actual discharge currents (A) does not have to be specified for different battery size with the same chemistry/characteristic.
Without C:
2A discharge for 1Ah "ABC" battery
4A discharge for 2Ah "ABC" battery
10A discharge for 5Ah "ABC" battery
20A discharge for 10Ah "ABC" battery....
With C:
2C discharge for "ABC" battery.
2C discharge rate means the battery can be discharged in 1/2 hour regardless of it capacity. C is used for charge/discharge rate so that the actual discharge currents (A) does not have to be specified for different battery size with the same chemistry/characteristic.
Without C:
2A discharge for 1Ah "ABC" battery
4A discharge for 2Ah "ABC" battery
10A discharge for 5Ah "ABC" battery
20A discharge for 10Ah "ABC" battery....
With C:
2C discharge for "ABC" battery.
wesnewell
100 GW
Type c rate into google, then click on the MIT pdf and tell them they are wrong too.SamTexas said:
SamTexas
1 MW
I am not going to do that. But I will tell MIT or Stanford or CalTech ... that they are wrong when they are wrong. The title, the reputation of a person or an organization does not guarantee correctness all the time. I have seen smart, reputable people admitting being wrong all the time. That make them also respectable.
spinningmagnets
100 TW
Since the C-rate is listed in the cell specs, and there's no listing for that chemistries C-rate per pack size, I was under the impression that it was the "Current" output ability per cell (I could be wrong, clearly I don't have a proper understanding of something here).
Using a low C-rate chemistry in a very large pack improves the max amps that can be drawn from the pack, and also reduces the amps drawn from each cell. if it is technically correct to use the term "C-Rate" for both the individual cell chemistry and the fully assembled pack, I am confused...
edit: some of my misunderstanding may stem from the well-known rule-of-thumb that drawing high amps from a pack will provide less capacity, while drawing low amps for a longer time will provide a higher capacity. The C-Rate of the chemistry doesn't change, but the capacity is conditional?
Using a low C-rate chemistry in a very large pack improves the max amps that can be drawn from the pack, and also reduces the amps drawn from each cell. if it is technically correct to use the term "C-Rate" for both the individual cell chemistry and the fully assembled pack, I am confused...
edit: some of my misunderstanding may stem from the well-known rule-of-thumb that drawing high amps from a pack will provide less capacity, while drawing low amps for a longer time will provide a higher capacity. The C-Rate of the chemistry doesn't change, but the capacity is conditional?
melodious
100 kW
Unless the quality control is spot.on.all.day.pHucking.long. The pack will have inconsistencies and some cells will degrade & decay over time.
In a perfect utopian society, yes. Here on earth. No. We're all too preoccupied with things other than the big picture.
I think NCM cells cost less to make. And they are just as "environmentally friendly" as LiFEPO4 (Jebus, I love typing that)
In a perfect utopian society, yes. Here on earth. No. We're all too preoccupied with things other than the big picture.
I think NCM cells cost less to make. And they are just as "environmentally friendly" as LiFEPO4 (Jebus, I love typing that)
wesnewell
100 GW
Well, I try to just enlighten people. Since you seem not to care about that, you can just remain benighted. If you change your mind, this will help.SamTexas said:
http://www.google.com/search?q=c+rate
SamTexas
1 MW
The C-rate (discharge rate) does not change at all regardless of the size of the battery.spinningmagnets said:
Example:
o A 5Ah battery cell (single cell) has a discharge rate of 3 (or 3C). So 15A (3*5) can be drawn from that single cell.
o 3 of those cells are paralleled to form a 15Ah pack. The discharge rate remains the same, 3 or 3C. So 45A (3*15) can be drawn from that pack.
o 40 of those cells are used to build a 10s4p pack. The discharge rate still remains the same. The pack capacity is 20Ah (4*5) and the discharge rate is 3 or 3C. So 60A (4*15) can be drawn from this 10s4p pack.
That's the advantage of using C. There is no need to specify the actual discharge current for all the various capacity packs built around identical cells. The actual discharge current is easily obtained by multiplying the discharge rate by the pack's capacity.
SamTexas
1 MW
I sense that you are getting more and more defensive. So this will be my last response to you on this subject. You can have the last word.wesnewell said:
OK, so I just googled as you suggested, and read the first link, word for word, top to bottom:
http://batteryuniversity.com/learn/article/what_is_the_c_rate
Nothing in there disagree with me and the rest of the people. C is for capacity.
Say what you wish, I will not respond to you on this subject anymore.
nicobie
100 MW
If I was a newb thinking about going electric on my bike and reading this, I'd give up on the idea and go ICE.
999zip999
100 TW
More info on the different NCM cells with price. Do they have a tab difference like the A123's. can they solder or must be clamped or laser welded only ? I do like the enderal 16ah pack as 16s pack. I guess about 700.usd plus a bms and what charger ? This is for a bike and we are worry about price.
spinningmagnets
100 TW
Quote from the MIT PDF linked above:
999zip999
100 TW
Is this still a NCM vs lifepo4 thread. Or blow my trumpet thread. Get the train back on track. Why is this thread so frock up ?
wb9k
10 kW
wesnewell said:
20C is not the C rate, it's a discharge rating, or a charge rating. Rarely are even those numbers the same, but they are generally expressed in terms of the cell's C rate. Get the point? (You don't give enough data to answer your own question above, btw.) It's possible the lingo you learned years ago in the phone world is different from what the battery world itself generally does. The old phone company's jargon often was different from the rest of the world. Forgive me if I was a bit too zealous with my correction, but I work for a battery company, and C-rate means something very specific to everyone in this industry--and it is not any kind of max current rating. It's exactly what Y-pedal and I are saying. This is a board full of people--many of them neophytes in electronics, batteries, or both--who are into playing with stuff that has the potential to kill them. It's pretty important to actually know what you're doing with this stuff. Throwing around the wrong terminology is confusing to the people who need clarity the most. Doing it as if you're and industry insider when it's pretty clear you're not is just wrong.
Now I can certainly be wrong. Just in the last couple days I've been called out for incorrect use of the unit psi in describing stack pressure. I'm happy to be corrected when I'm wrong. But I'm not wrong about the current, most widely accepted definition of C-rate.
wb9k
10 kW
spinningmagnets said:
Cell impedance changes with discharge rate. I believe this is usually a function of electrochemistry, not a purely electrical phenomenon. Higher cell impedance means more heat and more loss across the cell itself. Hence, lower capacity.
wb9k
10 kW
999zip999 said:
Fair enough. FWIW, the biggest downside I see for NCM chemistry is all those precious metals and rare earth minerals. It's not that you can't use that stuff, but it's not a be-all end-all chemistry, and widespread adoption for EV's is, IMO questionable. Li batteries that use Li metal electrodes have the same liability IMO, and I'm not alone in that assessment.
Sorry about the trumpet solo.....
