1C, 0.2C Do I understand the numbers correctly?

I looked ataSamsung 22F data sheet so wondering if I understand it?

Assembling a20P pack.

If the cell tests in an Opus at 2500ma (assuming 100% accuracy), is 1C = 2500mAh?

Spec sheet says 100% of the energy is available at 0.2C so that means I can draw10amps from the pack?

Do people shoot for 0.2C for power walls or come at it from a different angle?

Thanks,

Jeff

Hello jeffl98

1C means that You use all available power in 1 Hour.

0.2C means that You use 5 hours to use up all the power.

It is a bit more complicated: Example: a specific cellmay have a 1C rating of 2000 mAh and a 0.2C rating of 2250 mAh

Actual Data sheet for the cell in question state MAX Discharge current is 4.4 Amps or 2C. (2200 mA(h) * 2 )

You can pull 10 Amps, but You will severely shorten the life of Your cell.

Most members here design their cell banks to contain 80 or 100 cells. A 14S80p powerbank can deliver 4+ KW at 1C.
I do not think many care about the 0.2C rating. I dont.

I hope this clarifies things a bit.

ChrisD

Definition from IEC61960-2003 standard:
3.5 Rated capacity
Quantity of electricity declared by the manufacturer which a single cell or battery can deliver during a 5hr period.

If the cell tests in an Opus at 2500ma (assuming 100% accuracy), is 1C = 2500mAh?

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No.
1C is the capacity which the cell gave out during the 5hr discharge according to the manufacturers conditions and holding 1-4hr pause between end of charge and start of discharge.
Opus is not suitable for measuring capacity with good accuracy. You can't even set the discharge cut-off voltage.

Spec sheet says 100% of the energy is available at 0.2C so that means I can draw 10amps from the pack?

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No. Datasheet says that the rated capacity is XXXXmAh at 0.2C discharge which means that the XXXX which is taken as 1C is the capacity delivered by the cell during a 5hr discharge test.
If you discharge the cell at a higher rate, say 0.8C, the capacity will be lower, so you'll have one capacity at 0.2C discharge and another at 0.8C discharge BUT to make it easier to deal with the data we assume that 1C is the 5hr discharge capacity. Look at my tests, there are discharge tests at different rates and you'll see how the results differ.


BTW, max discharge rate doesn't depend on capacity rating. So if your cell is rated at 2500mAh it does not mean that you can discharge it at 10A or 25A))

1C rating:
2000mAh: 2A
2200mAh: 2.2A
1800mAH: 1.8A
600mAh: .6A

.2C rating
2000mAh: .400A
2200mAh: .440A
1800mAH: .360A
600mAh: .120A

1C = mAh/1000

This is based off of the original specs, not what the cell does after a long life. So if it was designed at 2200mAh, and it now only reaches 1500mAh, then 1C still is 2.2A, not 1.5A

Maybe some terminology clarifications....
The C rating is measured in amps that you could draw from a cell over time.
Like said above,
0.2C is the current you could draw for 5 hours to empty a cell,
1C is the current you could draw for 1 hour to empty a cell, etc

Unless you have better measurement gear, the Opus reading for mAhrs may be all the info you've got.
So if the Opus reads 2500mAhr capacity and the Opus test took 5 hours to discharge the cell from full, then that might be the 0.2C rating.
The Opus would have pulled 2500mAhrs/5hrs = 500mA for 5 hours in this case.

For your pack of 20p, the 0.2C current would be 20 x 500mA = 10A total for the pack.

People seem to typically draw less than 0.2C from their packs, basically lighter loading and reducing max/min cell voltages significantly prolongs cell life.
Short bursts of higher current shouldn't hurt but cells with lower current ratings may heat internally more.

Thanks! LOL! I knew mentioning the Opus would cause some problems. I shouldn't have mixed theoretical with reality.

Yeah, I was trying to figure out how much I could draw from this baby pack safely without prematurely shortening it's life or heating it upso all comments were helpful.

All I have currently is an Opus and a Zanflare so I've already noticed a difference in reporting. Interestingly, my Zanflare is reporting higher by about 90ma. I've seen the Opus is usually higher.

Is there something that is accurate enoughwithout the professional test equipment price or is the Opus/Zanflare good enough? What are you guys using? (or is that a Mac vs Windows question)? haha!

Jeff

The charger results are a baseline. You charge all your cells with the same charger and build your packs based on that one chargers results. Don't mix chargers are you'll get different results.

The exception is when you build more than one string. So if string A is all charged with opus, and string B is charged all with zanflare. Don't mix the results if you can help it.

You can make the opus more accurate with some mods, but you won't get the opus and zanflare returning the same results each time. So it's best to keep them separate

Redpacket said:

0.2C is the current you could draw for 5 hours to empty a cell,

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Yes

Redpacket said:

1C is the current you could draw for 1 hour to empty a cell, etc

Click to expand...

No. If you discharge at 1C you'll end up sooner than 1hr because "C" is defined at 0.2C discharge, not 1C.

For example. We have a 3000mAh rated cell.
C=3000 which means its capacity is 3000mAh at 600mA (0.2C) discharge.
At 3000mA or 1C discharge its capacity goes down to 2730mAh, for example.
So when you discharge the cell at 3000mA (1C) you'll end up in 2730/3000*60 minutes which is 54.6min - less than 1 hour or 60 minutes.
The higher is the discharge current - the less is the discharge time compared to 1/X (at XC discharge rate).