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Battery Bank Maintenance

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    Battery Bank Maintenance

    Hey there, I was hoping to get a response in regards to battery bank testing and maintenance for DC supply in a Substation, switch yard. Many years my company has done impedance and ripple current testing annually and a discharge testing about every five years. When completing impedance testing and verifying voltage reads from every cell within that bank, if the cells are out of range (lowest to highest) 5% of each other we are given the go ahead to do an equalize charge for whatever the manufacturer specify's (48 hours normally). After said charge and a day later, we go back and check individual cell voltages. Most of the time the cells voltages are about the same, but within a month they are back to being + - 1.5% to 2.5% differing in cell voltage, 2.17vdc cell could be as low as 2.11 or high as 2.23 or higher. I am to the point where I think, if we aren't doing discharge testing every year, that turning the AC charger off for a discernible amount of time would really be exercising all the cells equally, in theory, essentially. If we have a bad cell it would be distinguishable when turning the charger back on. I am thinking preventative maintenance but the employer believes otherwise. Just want some feedback on what other people are doing with their battery banks. Thanks in advance

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    Quote Originally Posted by africanamber View Post
    Hey there, I was hoping to get a response in regards to battery bank testing and maintenance for DC supply in a Substation, switch yard. Many years my company has done impedance and ripple current testing annually and a discharge testing about every five years. When completing impedance testing and verifying voltage reads from every cell within that bank, if the cells are out of range (lowest to highest) 5% of each other we are given the go ahead to do an equalize charge for whatever the manufacturer specify's (48 hours normally). After said charge and a day later, we go back and check individual cell voltages. Most of the time the cells voltages are about the same, but within a month they are back to being + - 1.5% to 2.5% differing in cell voltage, 2.17vdc cell could be as low as 2.11 or high as 2.23 or higher. I am to the point where I think, if we aren't doing discharge testing every year, that turning the AC charger off for a discernible amount of time would really be exercising all the cells equally, in theory, essentially. If we have a bad cell it would be distinguishable when turning the charger back on. I am thinking preventative maintenance but the employer believes otherwise. Just want some feedback on what other people are doing with their battery banks. Thanks in advance
    So a battery discharge test is a destructive test so you don't want to drain the batteries any more that necessary. Have you done a cell impedance test or specific gravity? This would tell you if an individual cell has an issue. Some cells being high would indicate the voltage may not have stabilized. When I worked for a utility, we would turn off the charger and cycle the breakers and then measure voltage. I can't imagine that there would be an issue with turning the charger off, letting it sit for a short time and then measuring the voltage. This would not effect the life of the batteries. I am guessing they are flooded lead acid.

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    Quote Originally Posted by baccuskt View Post
    So a battery discharge test is a destructive test so you don't want to drain the batteries any more that necessary. Have you done a cell impedance test or specific gravity? This would tell you if an individual cell has an issue. Some cells being high would indicate the voltage may not have stabilized. When I worked for a utility, we would turn off the charger and cycle the breakers and then measure voltage. I can't imagine that there would be an issue with turning the charger off, letting it sit for a short time and then measuring the voltage. This would not effect the life of the batteries. I am guessing they are flooded lead acid.
    I just hit this question on a sample test. You can use a hydrometer to measure the density of the electrolyte in ratio to the density of water, right?

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    Quote Originally Posted by cotton View Post
    I just hit this question on a sample test. You can use a hydrometer to measure the density of the electrolyte in ratio to the density of water, right?
    Yes, specific gravity.

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