Battery power calculation from its capacity 1

[ameenbassam]

Hi There,
In an article called 'An Energy Management System of a Fuel Cell/Battery Hybrid Boat', the author assumed values of charging, discharging, and optimum power of the battery as follows:

charging, discharging, and optimum power values for battery (Poptchar, Poptdis, and PBATopt ),
where charging power equals to discharging power with 30% capacity of battery and optimum power value is 20% capacity of the battery; the battery has 360 Ah and 560 V.

My question is, How the battery capacity will be converted to power ?
I know that Battery total energy = 360*560 Wh. So, i can calculate energy of 30% and 20% of it. But i need time to convert it to power.

If nominal current is 72 A. Then time for 30% of the capacity = 0.3*360/72 = 1.5 h and for 20% capacity is 1 hour. If I divide the energy of 30% capacity and 20% of the capacity over time of 1.5 hr and 1 hr, I have the same amount of power of 40320 W. What am i missing ? or it is a mistake of the article author ?

Many Thanks in advance

 

[VEBill]

If the battery is 560 volts (that's quite the battery) and the nominal current is 72A, then the nominal power being provided by the battery is 560 v x 72 A = 40320 watts.

 

[ameenbassam]

@VE1BLL
Thank you for your kind reply.
How can I convert the capacity to power ??
If nominal current is 72 A. Then time for 30% of the capacity = 0.3*360/72 = 1.5 h and for 20% capacity is 1 hour. If I divide the energy of 30% capacity and 20% of the capacity over time of 1.5 hr and 1 hr, I have the same amount of power of 40320 W.

 

[IRstuff]

I'm not 100% convinced that you've interpreted those parts of the article. I think when they refer to 20% or 30% of capacity, they're talking about 0.2C or 0.3C, which they also use, which refer to the allowable discharge currents where 0.2C means 0.2*Ahr_capacity/hr, which is relatively consistent with typical battery manufacturer recommendations to discharge at less than 0.2C to get the maximum ampacity from a battery.

TTFN
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[ameenbassam]

@IRstuff
Thank you for your kind reply.
I read this article so many times trying to understand but it is written exactly as follows:
'' charging power equals to discharging power with 30% capacity of battery and optimum power value is 20% capacity of the battery ''

You can find it in

http://www.mdpi.com/1996-1073/7/5/2799/htm

 

[IRstuff]

Yes, I've looked at the article, hence the uncertainty. However, on the face of it "optimum power value is 20% capacity of the battery" makes no sense if it's actually referring to the total capacity of the battery, since there's nothing in the chemistry or operation or specifications that relates to "optimum power" to the total battery capacity. I refer you specifically to Table 3, wherein "Life cycle (0.3C, 80% DOD)" is one of the entries. 80% DOD means 80% depth of discharge of the total capacity of the battery, at 30C discharge rate, i.e., at 18A.

TTFN
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[ameenbassam]

@IRstuff
Thank you for your kind reply. I am agree with you that there is no sense in relating capacity to power and i am trying to contact with the author of this article.

Regarding Table 3, it is written that continuous current at 0.5C and life cycle is measured at 0.3C. What i should use ?
In Simulink, nominal current of such a battery should be 72 A.

What i am sure of is that 30% of the capacity equals to 108 Ah and 20% of the capacity is equals to 72 Ah. How can i calculate the power ?

 

[IRstuff]

"What i am sure of is that 30% of the capacity equals to 108 Ah and 20% of the capacity is equals to 72 Ah"

Again, I think that 30% refers to 108A current and 20$ refers to 72A current. The power question was answered by the other poster already.

TTFN
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