Victron BMV600 how to setup battery Capacity AH

fca1
fca1 Solar Expert Posts: 124 ✭✭
in Off Grid Solar & Battery Systems #1
Hi there, i will install a BMV602 to monitor my battery bank, reading the manual i need to give the battery capacity (logic)...
Now reading the manual they say " Batterycapacity -The battery capacity in amp hours(Ah) at a 20 h discharge rate."

My battery's are rated at 5h rate i mean they say 255AH at C5, so should i give the bmv a 255ah capacity or i must convert the 255ah @c5 to c20 ?

And how to this conversion from 255ah at c5 to c20 rate?

thanks
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Victron BMV600 how to setup battery Capacity AH

    Yes, you can convert to the 20 Hour Rate for more accurate battery capacity (as a percent of full/partial charge). A few people here, on purpose, program the battery bank as ~1/2 the "real" capacity. This lets them work 100% to 0% indicated capacity, while leaving a 50% capacity in reserve (generally, recommend trying not to discharge below 50% for long life).

    If you want the 20 Hour rate, usually, the battery Mfg. will give you a chart with different AH Capacity vs discharge rate.

    Or, there are calculations (Puekert Factor) that can be made--But you need the Puekert Factor number from the Battery Mfg.--Which you may not have.

    Lastly, you could compare to similar construction batteries (from same or different vendor) and estimate the battery 20 Hour capacity.

    Note that AGM/GEL type batteries have a much smaller spread between C/5 and C/20 discharge rates (AGM's are more efficient) vs Flooded Cell batteries.

    If you can give us the Battery Brand and Model Number, somebody here may have a link to the technical specifications.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • fca1
    fca1 Solar Expert Posts: 124 ✭✭
    #3
    Re: Victron BMV600 how to setup battery Capacity AH

    Hi the batteries are exide epzv255 ah @c5 i'm using Peukert factor 1.2, and using the spreadsheet on "http://www.smartgauge.co.uk/calcs/peukert.xls"
    with this input

    Peukert's Exponent 1,2
    Batt Capacity 255
    At hour rating 5



    i get a realamps of 324ah at 15amp (255/20 = 12,5 15 is the closest to 12,5) discharge rate , so this means my batts are 20ah rate have 324 ah capacity ?

    i should put on the victron 324 ah ?



    thanks





    BB. wrote: »
    Yes, you can convert to the 20 Hour Rate for more accurate battery capacity (as a percent of full/partial charge). A few people here, on purpose, program the battery bank as ~1/2 the "real" capacity. This lets them work 100% to 0% indicated capacity, while leaving a 50% capacity in reserve (generally, recommend trying not to discharge below 50% for long life).

    If you want the 20 Hour rate, usually, the battery Mfg. will give you a chart with different AH Capacity vs discharge rate.

    Or, there are calculations (Puekert Factor) that can be made--But you need the Puekert Factor number from the Battery Mfg.--Which you may not have.

    Lastly, you could compare to similar construction batteries (from same or different vendor) and estimate the battery 20 Hour capacity.

    Note that AGM/GEL type batteries have a much smaller spread between C/5 and C/20 discharge rates (AGM's are more efficient) vs Flooded Cell batteries.

    If you can give us the Battery Brand and Model Number, somebody here may have a link to the technical specifications.

    -Bill
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
    Re: Victron BMV600 how to setup battery Capacity AH
    fca1 wrote: »
    My battery's are rated at 5h rate i mean they say 255AH at C5, so should i give the bmv a 255ah capacity or i must convert the 255ah @c5 to c20 ?

    It really depends on how you use your batteries. If you are operating a forklift and discharging your batteries over 8 hours, a C8 rate would be most useful. If you are running a lightbulb and your battery could power it for 100 hours, a C100 rate would be most useful.

    The C20 rate is typically most useful for most of us. Some battery manufacturers use a C24 rate.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Crotalus
    Crotalus Solar Expert Posts: 26 ✭
    #5
    Re: Victron BMV600 how to setup battery Capacity AH

    I think you will like the Victron battery monitor. I have one in my travel trailer and has proved useful. I have a single Trojan 27TMH and I sent an email to the people at Trojan where they supplied me with the Peukert number of 1.22. Charge efficiency of 89% and the charge voltage of 14.8V, float voltage of 13.2V, and the equalize Voltage is 15.5V. I used their values to program the monitor. The 20 hour rate was on the battery as 115Ah @ 20Hr. I have set the alarm for the SOC at 50%.

    You might try to find out if there is a support site for your battery. The manufacture should be able to help you if they care to do so.
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  • fca1
    fca1 Solar Expert Posts: 124 ✭✭
    #6
    Re: Victron BMV600 how to setup battery Capacity AH

    what do you mean with "most of US"
    Here you have the stats of my usage in watts for the lastweek

    Start: 2013/04/17 11:37
    End: 2013/04/24 11:37
    Minimum: 44.0 @ Abr 18 13:40
    Maximum: 1475.0 @ Abr 20 16:34
    Average: 281.71844615082364
    so 281/24 i an average amp consumption of ~12ah...
    this rate hour for what i understood will only influence the time remaining of the victron

    Regards


    vtmaps wrote: »
    It really depends on how you use your batteries. If you are operating a forklift and discharging your batteries over 8 hours, a C8 rate would be most useful. If you are running a lightbulb and your battery could power it for 100 hours, a C100 rate would be most useful.

    The C20 rate is typically most useful for most of us. Some battery manufacturers use a C24 rate.

    --vtMaps
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: Victron BMV600 how to setup battery Capacity AH

    For off grid use... C/20 (20 hour rate) seems to be, roughly, the average discharge rate that make sense for evaluating a battery bank for off grid use...

    If you discharge the battery 25% per night (2 days no sun, 50% maximum discharge = battery 4x daily load) and guess that the lights/power usage is ~5 hours per evening--That is about a 4 days * 5 hours per night = 20 hour discharge curve.

    Also, for charging we recommend a nominal range of 5% to 13% rate of charge (for solar arrays) which works out to ~C/20 to C/8 rate of charge--So again, on the low side of the charging spectrum, that C/20 hour rate shows up.

    In the end, most deep cycle batteries have a 20-24 hour rate listed and it maps well to the typical off grid system use--So we have "crafted" all of our rules of thumbs around that battery bank capacity.

    Remember that battery capacity is a rough number that goes up (to rated AH) as the battery bank is cycled the first 10-20 times or so, and eventually drops again as the battery sulfates/wear & tear, etc... A manufacturer may call a battery "failed" if it has lost 20% or more of its stated capacity.

    For an off grid user, the battery may be dead if it lost 50% of its capacity (cannot support 50% or 2 day discharge). Or if the battery can no longer support the surge/well pump startup requirements.

    More or less, I like to suggest (using the 20 hour capacity) an average heavy discharge rate of C/8 and for maximum surge of C/2.5 for flooded cell batteries.

    AGM/GEL batteries can support higher currents--But that also needs larger copper wire, fuses, etc... AGM are great for heavy/short loads (well pump for home use, etc.). However, since most homes/cabins have a few hours per night of steady loads--the flooded cell banks are large enough to support high surge currents for the well pump/microwave oven use.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • williaty
    williaty Solar Expert Posts: 60 ✭✭
    #8
    Re: Victron BMV600 how to setup battery Capacity AH

    The specific monitor he's talking about, the Victron BMV-600, must be told the full 20-hour rate capacity, Peukert's Constant, and the charge efficiency factor. It then computes a real state of charge (as a percentage) that's compensated for those factors. The TTG display also counts the time down to 50% SoC, not 0%, so it's telling you how much more running time you have to a safe discharge level (not to killing you the batteries).

    It's a very, very good battery meter and I'm extremely happy with the ones I've installed. Once you start using its datalogging capabilities as well, you'll be amazed at how much more you'll learn about your systems behavior.
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  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    #9
    Re: Victron BMV600 how to setup battery Capacity AH

    Yes great monitors. Thanks for pointing out how the time to go works. I have my discharge floor set to 50% so at 50% discharge the time to go will be zero.
    Thanks
    Regards Peter
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
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