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  • Peukert Law, Batteries, and You

    Peukert Law, Batteries, and You
    Time for another STICKY THREAD. This is more bad news for you off-grid battery folks. Peuket law is like Death and Taxes, you will pay, and for 99% of you a lot more than you have too. Peukert Law simply states for flooded lead acid batteries: "The higher the discharge rate (Amps) the less capacity the battery actually has". For example your 100 amp hour battery can be as low as 30 AH if discharged at the 1 hour discharge rate of 100 amps. Or as high as 160 AH at the 100 hour rate of 1 amp.

    In theory only with batteries:

    Amp Hours = Amps x Hours
    Hours = Amp Hours /Amps
    Amps = Amp Hours / Hours.

    Well that theory only applies at the discharge rate the manufacture specifies the battery at which is typically 20 hour rate. So for example if you have a a 100 AH battery the 20 hour rate is 5 amps 5 amps = 100 Amp Hours / 20 Hours). From that formula a layman would assume if you had a 100 AH battery you should be able do discharge that battery at 1 amp for 100 hours, or 1 hour at 100 amps. YOu would be wrong, very WRONG, Mr Peukert will not allow it. If you were to discharge that 100 AH battery at 1 amp Mr. Peukert smiles and will makes your battery a 133 AH battery meaning you can discharge it for 133 hours at 1 amp. On the other hand if you were to discharge it at 100 amps or the 1 hour rate Mr. Peukert frowns and robs you with only allowing you 30 AH or a mere 18 minutes when you expected 60 minutes. Surprise!

    Here is Mr Peukert in real terms a Rolls 30H125. It is a 125 AH 12 volt battery. Look at the Discharge Rate table. At 100 hours it is a 166 AH battery. At 1 hour it is a 45 AH battery.

    To make life simple over the years I and other battery professionals have come up with a generic Peuket derating Correction Factor called C. It can be used to ball park determine or adjust if you will for your actual discharge rate where True Amp Hours = C x Rated AH @ 20 hour rate. To bget actual numbers will have to come from the specific battery manufacture and model number. But this will get you close for preliminary design.

    1 Hour = .3
    2 Hour = .5
    3 hour = .6
    4 hour = .65
    5 hour = .7
    6 hour = .75
    8 hour = .8
    10 hour = .85
    12 hour = .9
    16 hour = .95
    20 hour = 1
    24 hour = 1.05
    36 hour = 1.1
    72 hour = 1.25
    100 hour = 1.30

    So for example if you have a 100 AH battery and discharge at the 2 hour rate (50 amps), then 100 AH x .5 = 50 AH.
    Last edited by Sunking; 08-17-2016, 03:06 PM.
    MSEE, PE

  • #2
    Originally posted by Sunking View Post
    Time for another STICKY THREAD. This is more bad news for you off-grid battery folks. Peuket law is like Death and Taxes, you will pay, and for 99% of you a lot more than you have too. Peukert Law simply states for lead acid batteries The higher rate you discharge (amps) the less capacity the battery actually has. For example your 100 amp hour battery can actually be as little 30 AH if discharged at the 1 hour rate of 100 amps.

    In theory only with batteries:

    Amp Hours = Amps x Hours
    Hours = Amp Hours /Amps
    Amps = Amp Hours / Hours.

    Well that theory only applies at the discharge rate the manufacture specifies the battery at which is typically 20 hour rate. So for example if you have a a 100 AH battery the 20 hours rate is 5 amps. From that formula a layman would assume if I had a 100 AH battery I should be able do discharge that battery at 1 amp for 100 hours, or 1 hour at 100 amps. WRONG, Mr Peukert will not allow it. If you were to discharge that 100 AH battery at 1 amp Mr. Peukert smiles and will makes your battery a 133 AH battery meaning you can discharge it for 133 hours at 1 amp. On the other hand if you were to discharge it at 100 amps or th e1 hour rate Mr. Peukert frowns and robs you with only allowing you 30 AH or a mere 18 minutes when you expect 60 minutes. Surprise!

    Here is Mr Peukert in real terms a Rolls 30H125. It is a 125 AH 12 volt battery. Look at the Discharge Rate table. At 100 hours it is a 166 AH battery. At 1 hour it is a 45 AH battery.
    Good sticky as usual, Dereck. Perhaps you could elaborate more on the Peukert factor of different types of batteries? ie, flooded, sealed, etc. Of course manufacturer specs are the last word but there are some generalities.

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    • #3
      Originally posted by FloridaSun View Post
      Good sticky as usual, Dereck. Perhaps you could elaborate more on the Peukert factor of different types of batteries? ie, flooded, sealed, etc. Of course manufacturer specs are the last word but there are some generalities.
      Already did that See what you thunk? AGM is not as severe because they have lower internal resistance, and Gel is significantly higher because of the higher internal resistance. The post refers to Flooded Lead Acid true deep cycle batteries.

      As a general rule the higher the internal resistance, the higher the Peukert factor excluding NiCd. From worse to best.

      NiFe
      Lead Acid (Gel, Flooded, AGM in that order)
      NiCd/NiMh
      Lithium
      MSEE, PE

      Comment


      • #4
        Originally posted by Sunking View Post
        Already did that
        that's odd, the whole post did not come up when I read it first time.

        Comment


        • #5
          Originally posted by FloridaSun View Post
          that's odd, the whole post did not come up when I read it first time.
          I was probably editing when you posted.
          MSEE, PE

          Comment


          • #6
            Originally posted by Sunking View Post
            I was probably editing when you posted.
            and you can give more info off the top of your head than I could post with an hour research.

            Comment


            • #7
              Nice, thanks for sharing the info...in before the sticky!
              1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

              Comment


              • #8
                Originally posted by Sunking View Post
                Time for another STICKY THREAD. This is more bad news for you off-grid battery folks. Peuket law is like Death and Taxes, you will pay, and for 99% of you a lot more than you have too. Peukert Law simply states for lead acid batteries The higher rate you discharge (amps) the less capacity the battery actually has. For example your 100 amp hour battery can actually be as little 30 AH if discharged at the 1 hour rate of 100 amps.

                In theory only with batteries:

                Amp Hours = Amps x Hours
                Hours = Amp Hours /Amps
                Amps = Amp Hours / Hours.

                Well that theory only applies at the discharge rate the manufacture specifies the battery at which is typically 20 hour rate. So for example if you have a a 100 AH battery the 20 hour rate is 5 amps 5 amps = 100 Amp Hours / 20 Hours). From that formula a layman would assume if you had a 100 AH battery you should be able do discharge that battery at 1 amp for 100 hours, or 1 hour at 100 amps. YOu would be wrong, very WRONG, Mr Peukert will not allow it. If you were to discharge that 100 AH battery at 1 amp Mr. Peukert smiles and will makes your battery a 133 AH battery meaning you can discharge it for 133 hours at 1 amp. On the other hand if you were to discharge it at 100 amps or the 1 hour rate Mr. Peukert frowns and robs you with only allowing you 30 AH or a mere 18 minutes when you expected 60 minutes. Surprise!

                Here is Mr Peukert in real terms a Rolls 30H125. It is a 125 AH 12 volt battery. Look at the Discharge Rate table. At 100 hours it is a 166 AH battery. At 1 hour it is a 45 AH battery.

                To make life simple over the years I and other battery professionals have come up with a generic Peuket derating correction factor called C. It can be used to determine or adjust if you will for your actual discharge rate where True Amp Hours = C x Rated AH @ 20 hour rate.

                1 Hour = .3
                2 Hour = .5
                3 hour = .6
                4 hour = .65
                5 hour = .7
                6 hour = .75
                8 hour = .8
                10 hour = .85
                12 hour = .9
                16 hour = .95
                20 hour = 1
                24 hour = 1.05
                36 hour = 1.1
                72 hour = 1.25
                100 hour = 1.30

                So for example if you have a 100 AH battery and discharge at the 2 hour rate (50 amps), then 100 AH x .5 = 50 AH.
                Awesome info... thank you for posting it!
                [CENTER]SunLight @ Night[/CENTER]

                Comment


                • #9
                  Should like discussion on Peukert concerning LFP
                  Reed

                  Comment


                  • #10
                    Originally posted by reed cundiff View Post
                    Should like discussion on Peukert concerning LFP
                    Reed
                    No not really unless you plan on extended high discharge rates of C1 or greater.
                    MSEE, PE

                    Comment


                    • #11
                      This is too short, I want to find a long one ,where can I find it ? http://www.genstattu.com/

                      Comment


                      • #12
                        Too short ? meaning the power does not last long enough ? or too small, and you have space for a larger battery pack ?
                        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                        solar: http://tinyurl.com/LMR-Solar
                        gen: http://tinyurl.com/LMR-Lister

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