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Thread: amp-hour rating of each cell in a battery question

  1. #1 amp-hour rating of each cell in a battery question 
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    Hi,

    I was trying to calculate the amp-hour rating of each cell in a battery pack for an electric vehicle.

    the kWh storage of the battery is 61.9kWh
    the battery has a total cell count of 6831 and the maximum voltage in each cell is 3.8V

    I divided the storage capacity by the total cell count and then divided that by the max cell voltage to get an answer of 2.38 Ah per cell

    Just want to check if this sounds right? I'm alway suspicious when things seem easy.

    Thanks


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  3. #2  
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    Quote Originally Posted by johnoshea View Post
    Hi,

    I was trying to calculate the amp-hour rating of each cell in a battery pack for an electric vehicle.

    the kWh storage of the battery is 61.9kWh
    the battery has a total cell count of 6831 and the maximum voltage in each cell is 3.8V

    I divided the storage capacity by the total cell count and then divided that by the max cell voltage to get an answer of 2.38 Ah per cell

    Just want to check if this sounds right? I'm alway suspicious when things seem easy.

    Thanks
    I might be full of it, but since the battery is given as able to provide a certain amount of total energy, the part lacking here is essentially how quickly can it dump 61.9KWH? The battery output voltage is 3.8 V., but it's own "internal resistance" determines it's ability to maintain 3.8 V. at up to some maximum current level, after which it's output voltage will begin to drop.

    I see the problem as indeterminate. Harold? What do you say? jocular


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    Quote Originally Posted by johnoshea;452404I
    divided the storage capacity by the total cell count and then divided that by the max cell voltage to get an answer of 2.38 Ah per cell

    Just want to check if this sounds right? I'm alway suspicious when things seem easy.
    That's about right, and is typical of 18650 lithium ion cells.
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  5. #4  
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    Quote Originally Posted by jocular View Post
    I might be full of it, but since the battery is given as able to provide a certain amount of total energy, the part lacking here is essentially how quickly can it dump 61.9KWH?
    Not an issue in this question. Maximum power is not the same as maximum energy. Different battery technologies can have widely varying energy and power ratings. LiCo, for example, has a fairly high energy density but low overall power output. LiFePO4 has a lower energy density but much higher power output.
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  6. #5  
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    Quote Originally Posted by jocular View Post
    Quote Originally Posted by johnoshea View Post
    Hi,

    I was trying to calculate the amp-hour rating of each cell in a battery pack for an electric vehicle.

    the kWh storage of the battery is 61.9kWh
    the battery has a total cell count of 6831 and the maximum voltage in each cell is 3.8V

    I divided the storage capacity by the total cell count and then divided that by the max cell voltage to get an answer of 2.38 Ah per cell

    Just want to check if this sounds right? I'm alway suspicious when things seem easy.

    Thanks
    I might be full of it, but since the battery is given as able to provide a certain amount of total energy, the part lacking here is essentially how quickly can it dump 61.9KWH? The battery output voltage is 3.8 V., but it's own "internal resistance" determines it's ability to maintain 3.8 V. at up to some maximum current level, after which it's output voltage will begin to drop.

    I see the problem as indeterminate. Harold? What do you say? jocular
    You're right. The amp-hour rating will vary depending on how fast the battery is discharged, and there doesn't seem to be any fixed standard. Battery manufacturers use different discharge times to rate their batteries. A longer, slower, discharge rate will generally extract more of the stored energy than a quick discharge.
    What is an Amp Hour and How to Calculate Battery Capacity | OverlandResource.com
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