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  • #6023
    Webmaster
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    Hi All

    I was wondering if anyone knows the answer to my question.The batteries
    are the stock Bosch and state that they are 140AH each but these are
    big batteries!(Around 20″long) I think I remember reading someplace that
    European Batteries are rated on 10hrs and North America is 20 hrs, any
    thoughts? 😕

    #7181
    Webmaster
    Participant

    A little confused by what you are asking but, if this helps;

    All Batteries are rated by either CCA-Cold Cranking amps, which is usually a short term (30secs) ability to deliver very high starting amps, or more usually the rating is known as Ah – Amp Hours.

    We normally describe a battery by it’s amp hour rating because that gives an idea of how big or or how much power it can deliver for a given time.

    For instance, your 140Ah battery is ideally suited for a domestic battery, because it can cope with deeper cycles – big discharges.

    The way to think of it is, if you have a light that draws 2 amps, then over 3 hours that would be 6 hours drawn – 6Ah. So your battery can deliver 140 amps for one hour, or 1.4 amps for 100 hours.

    Deep cycle, domestic batteries are physically big because of they need more plates of a bigger size to store more charge. Engine start batteries are physically smaller and smaller in terms of Ah rating (typically 70-80 Ah) but can deliver BIG amps (up to 1700A) for short periods.

    You probably have two equal size batteries because it is a compromise, the engine battery can be used for domestic use if needed. This isn’t a good situation really, the engine battery should always be solely dedicated to engine start only and never used for domestic use.

    So calculate what loads you are using typically and size your domestic battery to cope with the discharging and bear in mind the bigger the battery the longer to re-charge back up again!

    Hope I havent patronised you and been of some help!

    Steve May.

    “Betty Blue”
    B36

    #7183
    Webmaster
    Participant

    Hi Stuart

    I think I understand the question.

    The 10 hours rating would mean the battery capacity is tested using a discharge of nominally 14 amps (i.e. to discharge the battery in 10 hours). The 20 hour rating would use a discharge rate of 7 amps.

    If that is the case, I think the 10 hour rating is harder to achieve than the 20 hour. However, in reality I suspect it doesn’t make much difference whether the battery is spec’d against the 10 or 20 hour rating.

    The important factor is the size and composition of the plates. For a service battery you need deep discharge capability but not (necessarily) high amps (unless you want to power an 800W microwave!). BTW – the number of plates in a 12V battery is always six!

    Now – what was the question?

    #7184
    Webmaster
    Participant

    I may have not answered the question directly!

    Roger is right in saying that basically the differance in 10hrs and 20hrs is discharge times. Battery manufacturers use a standard method to determine how to rate their batteries. The battery is discharged at a constant rate of current over a fixed period of time, such as 10 hours or 20 hours, down to a set terminal voltage per cell. So a 100 ampere-hour battery is rated to provide 5 A for 20 hours at room temperature. The efficiency of a battery is different at different discharge rates. When discharging at a low rate, the battery’s energy is delivered more efficiently than at higher discharge rates. This is known as Peukert’s Law.

    Apologies Roger but I must correct you when you say that a 12V battery always has six plates. A 12V battery always has six Cells, each Lead Acid cell being 2V which when connected in series gives 6 x 2V =12V. A cell must have at least 2 plates one being positive the other being negative, and cells can often have more than just two plates!

    So again apologies for patronising anyone but the REAL answer is that it isnt really important the grand scheme of things wether a battery is rated in terms of a 10 or 20 hour discharge, as long as you select the right battery for the application!

    Steve.

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