battery current ratings

Organic Farmer
Organic Farmer Solar Expert Posts: 128 ✭✭
in Solar Beginners Corner #1
I was looking at golf-cart / floor sweeper batteries, and trying to compare numbers. It seems that the abilities of batteries are a wide spectrum.

So I looked at a few random Trojan batteries and I see that they do not have one single current rating, but a table of ratings over time.

To compare apples to apples, I need to first know which hour's rating for current is the one I should be looking at.

Can anyone explain how this system works, please?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: battery current ratings

    The standard used for RE application is the "20 hour rate": how much it can managed discharged over a period of 20 hours. Some batteries will have a 24 hour rate, which can also be used as the difference between the two is fairly small.

    The shorter the hour rate the higher the discharge rate and the lower the overall capacity.
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  • Organic Farmer
    Organic Farmer Solar Expert Posts: 128 ✭✭
    #3
    Re: battery current ratings

    Okay, Thank you.


    :)
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  • Chris
    Chris Solar Expert Posts: 135 ✭✭
    #4
    Re: battery current ratings

    not to hijack your thread but I had a question to do with this,

    I was looking at some Surette's this afternoon, they said 460 AH......but when I read the specs it said 460 @ 100hrs.....so does mean you would divide that by five? they're really 92HR?

    Sorry this is something that was confusing me as well, as they didn't list a 20hr rating
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: battery current ratings
    Chris wrote: »
    not to hijack your thread but I had a question to do with this,

    I was looking at some Surette's this afternoon, they said 460 AH......but when I read the specs it said 460 @ 100hrs.....so does mean you would divide that by five? they're really 92HR?

    Sorry this is something that was confusing me as well, as they didn't list a 20hr rating

    Unfortunately it is not linear. There is a quite complicated formula involving Peukart's Law for converting one "hour rating" to another. You can find info on it here: http://www.smartgauge.co.uk/technical1.html#peukert

    Concorde has this chart which show the same batteries at various discharge rates: http://www.solar-electric.com/concorde-sun-xtender-pvx-solar-deep-cycle-batteries.html Alas not 20 hour or 100 hour.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #6
    Re: battery current ratings

    the muddle of hour rates, reminds me of 70's stereo power ratings. 385 peak watts into 3 ohms w/20% distortion (or 23 RMS watts) (or 5 pure sinewave watts) No brand matched any other brand.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #7
    Re: battery current ratings

    And different types of batteries will have different 20 vs 100 Hour ratings...

    AGM batteries have very low "internal resistance" so that the 20 hour vs 100 hour capacity ratings will be similar.

    Flooded cell deep cycle batteries have more "internal resistance" and will have a wider spread between 20 hour and 100 hour ratings.

    The Peukert number is an experimental value that takes into account both true electrical resistance and electro/chemical activity of the plates+acid+etc....

    The "Hour Rate" is dependent on how fast you discharge (and recharge) the battery bank... 20 hours works out pretty well for Off Grid...

    Assume 5 hours per night to 50% discharge. That is 10 hours to 50% or 20 hours to 100% discharge (aka 20 hour discharge rate).

    C/20 is also the 5% "minimum" recharging rate we recommend. C/10 is the 10% rate--and as you can guess, it a little bit less efficient at charging (higher current means a little more waste heat being dissipated).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: battery current ratings
    BB. wrote: »
    Assume 5 hours per night to 50% discharge. That is 10 hours to 50% or 20 hours to 100% discharge (aka 20 hour discharge rate).

    typo: should be Assume 5 hours per night to 25% discharge.

    Bill, please delete this post if you edit yours --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #9
    Re: battery current ratings

    Here are some of the Rolls that are for RE, they list the 100, 20 & 10 hour rates.

    http://www.rolls-battery.com/content/specifications-renewable-flooded
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