LiFePO4 actual capacity?

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juanito
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LiFePO4 actual capacity?

Does anyone know how much of a percent of a LiFePO4 battery can be used before harming the battery?

For an example if you have a 40Ah pack can you really only use, let's say, 30Ah before the cells reach 2.5V? Lead acid batteries are consided to saftly give up to 80% of their usable energy before harming them.

What about C rate and temperature? A 40Ah lead acid battery may only give you 20Ah depending on how fast it is discharged. In reality, you can only get the full 40Ah if you discharge it very slowly. Is the same true of LiFePO4's?

The reason why I'm asking is because I'm trying to figure out the range of an electric scooter I would like to build and I seem to get outrageous numbers. It would be a 12kw 72V scooter with one of two battery options. Here are the estimated specifics:

With 100Ah pack:

Total weight including 200lb rider: 567lb

0-60MPH: 22.8 sec or 0.23 miles

Effeciency at 60MPH about 78%

If all 100Ah are usable then: 146 starts and stops to 60MPH

Also if drag causes deceleration from 100 to 95 kph in 10 seconds then range is: 349 miles (never stopping)

With 100Ah pack:

Total weight including 200lb rider: 753lb

0-60MPH: 30.3 sec or 0.30 miles

Effeciency at 60MPH about 78%

If all 100Ah are usable then: 220 starts and stops to 60MPH

Also if drag causes deceleration from 100 to 95 kph in 10 seconds then range is: 526 miles (never stopping)

I don't know. Maybe it will have much more drag than I am anticipating. But still. Could it be that a 100Ah battery really doesn't put out 100Ah in the real world. An EV that goes 526 miles doesn't seem right. Of course this is a vehicle that is
almost all battery.

juanito
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Re: LiFePO4 actual capacity?

Ok never mind. I was calculating the drag way off. For an example if it decelerated from 100 to 95 kph in let's say more like 3 seconds it would only have a range of 210 miles with the 200 Ah and only 139 miles with the 100 Ah.

But still. I wonder what the actual amp-hours really are.

Oh and by the way. Up there I ment to put 200Ah in the second list.

jdh2550_1
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Re: LiFePO4 actual capacity?

Hi juanito,

To get best battery life you should use no more than 80% DOD with LiFePO4 as well. So your 40Ah batteries will deliver 32Ah of usable capacity. Peukert's effect with LiFePO4 is negligible so even at >1C rates you'll get around 32Ah out of the batteries. Our tests of Thundersky batteries confirm this.

With lead acid Peukert's effect is a lot more noticeable - with a hypothetical 40Ah battery, used to 80% DOD with >1C rates you might only expect to get 20Ah. And of course it's bigger and heavier too.

Lead is dead! ;-)

John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employer
Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.

juanito
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Re: LiFePO4 actual capacity?

Thanks so much! Oh and I typoed again. I ment 4 seconds not three.

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