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  • Vented Battery Box!

    9 December 2013 - The battery manufacturer confirmed the correct calculations. -------- Below calculations highlighted in RED are not correct.

    I recently manufactured a couple of battery boxes, each to house a 123 Ah AGM. What I couldn't find was off the shelf was; battery boxes that complied with the Australian Standards in regard to ventilation. There is plenty of information out there offering various calculations to do such, although not to the requirements of Australian Standards. There various international or country specific standards, or industry standards, although it is the Australian Standards of which we must comply with. [Extracts from the Australian Standards are littered all over the net on this topic.]


    If you have a naturally ventilated enclosure, (such as a simple battery box that quite a few of us use to house our batteries.) the required opening is rather large in comparison to mechanical exhaust ventilation rate as per the Australian standard, due to the 0.1 m/s ventilation rate used for natural ventilation.

    I have several 120Ah AGM batteries - and are an VRLA type even though they commonly referred to as a sealed type. Two in my camper and two in my 4WD in currently inadequately vented boxes.

    The batteries are predominately charged from CTeK D250S units whilst driving of which they have a regulated output float voltage of approx 13.6 and a maximum charge current of 20 amps - 14.4V. I charge 2 x 120Ah batteries from this unit at the same time whilst on the go. I also normally set my portable charger at 16Amps although has a range from 8, 16, 35 Amps.

    If I calculate an exhaust ventilation rate as per the extract from the Australian Standard AS3011.2 posted in another thread, http://www.myswag.org/index.php?acti...ch=67818;image of which utilises the same calculations in AS4086.2 I get the following.

    Calculations below are for one battery only.

    Charge Rate
    Condition II (i) 0.5 A per 100 A.h at the 3 h rate of discharge of battery capacity of lead - acid batteries;
    C 3 rate of discharge. 120Ah Century C12-120DA
    123 Ah / 3 = 41 Amps (41/123 = 0.3333 C rate)41 Amps x 0.5 = 20.5Amps C3 (0.16665 C rate)

    (20 hr rate @ 1.75 V per cell x 6 cells = 10.5 V: 6.17 Amps x 20 hr = 123.4 A.h)
    3 hr rate @ 1.75 V per cell x 6 = 10.5 V: 29.72 Amps x 3 hr = 89.16 A.h (3 hour rate as per battery manufacturers Amp table corresponding to hours.)
    89.1 Ah: The charging rate "I" is: 0.5 x (89.1/100) = 0.4455 Amps

    Exhaust Ventilation Rate - for one battery
    Exhaust rate qv = 0.006
    0.006 X 6 cells (one battery consisting of 6 individual cells) X 20.5 Amps = 0.756 l/s

    0.006 qv x 1 battery x 6 cells x 0.4455 Amps = 0.016038 l/s

    Natural Ventilation Rate
    I'm proposing the natural ventilation rate to avoid fitting fans and alert devices. Would the following calculation be correct for the natural ventilation of which is also to be not less than 0.1m/s. opening (X 2) one high & one low)?

    A = 100 qv (natural ventilation rate)
    where
    A = the minimum area of the apertures, in square centimetres
    qv = the minimum exhaust rate in l/sec. (With assumed natural ventilation of at least 0.1m/s is assumed through the apertures.)
    100 A (qv) X 0.756 l/s = 75.6 cm2 (Minimum open area)

    A = 100 x qv 100 x 0.016038 = 1.6038 cm2 (minimum effective cross sectional area for an inlet aperture, or, an outlet aperture)

    To qualify; natural ventilation rate
    0.016038 l/s X 0.1 m/s X 1000 = 1.6038 cm2.

    I'm just not 100% sure if I have got the Natural Ventilation equation is correct for a single battery, consisting of 6 cells.

    I have checked on most of the major battery manufacturers sites and they all state that their AGM's are Valve regulated and some of the email advice states I must ventilate and comply with the relevant standards.


    Cheers.
    Attached Files
    Last edited by CC2005; 04-10-14, 09:12 PM.
    PB MY11 LS 4D56 - auto, with stuff.

  • #2
    Originally posted by CC2005 View Post
    I recently manufactured a couple of battery boxes, each to house a 123 Ah AGM. What I couldn't find was off the shelf was; battery boxes that complied with the Australian Standards in regard to ventilation. There is plenty of information out there offering various calculations to do such, although not to the requirements of Australian Standards. There various international or country specific standards, or industry standards, although it is the Australian Standards of which we must comply with. [Extracts from the Australian Standards are littered all over the net on this topic.]

    I've probably got it wrong with my battery box enclosure build, AND probably still have! And I'm more than happy to be corrected so I can get it right. I just want to keep the insurer at bay if ever the situation arises.

    If you have a naturally ventilated enclosure, (such as a simple battery box that quite a few of us use to house our batteries.) the required opening is rather large in comparison to mechanical exhaust ventilation rate as per the Australian standard, due to the 0.1 m/s ventilation rate used for natural ventilation.

    Exhaust Ventilation Rate
    E.g. 6 cell battery at a charging rate of *20 Amps:
    Exhaust rate (clause 3.3.2) qv = 0.006 0.006 X 6 cells X 20 Amps = 0.72 l/s

    For Natural Ventilation - 0.1 m/s
    Natural ventilation rate (clause 3.3.4.2) A = 100 qv Based on a natural ventilation rate of 0.1 m/sec (m/s)
    A = Minimum area of the apertures in square centimetres.
    A 100 (qv) X 0.72 l/s = 72 cm2
    To qualify; natural ventilation rate 0.72 l/s X 0.1 m/s X 1000 = 72 cm2
    Or
    0.72 l/s ÷ 0.1 m/s ÷ 1000 = 0.0072 m2 0.0072 m2 X 10000 = 72 cm2.

    So for my "naturally ventilated enclosure" 120 Ah battery(s) I would need 2 x 85mm X 85mm vents (one high and one low) or at least 10 x 30mm dia holes located both top and bottom of which to supply adequate flow across the battery.

    * 0.5 A for the 100 Ah at the 3 hr rate of discharge in my situation = approx 20 Amps. (17.63)


    Cheers

    http://postimg.org/image/e7r7lqjyl/


    Why would you want to vent AGM batteries??

    Comment


    • #3
      Originally posted by TheTaipan View Post
      Why would you want to vent AGM batteries??


      Took the words out of my mouth

      I have 3 AGMs buried somewhere in the boat only used AGM because they dont need venting


      Could be wrong

      Comment


      • #4
        Originally posted by TheTaipan View Post
        Why would you want to vent AGM batteries??
        I have been advised that my, and most AGM batteries still incorporate a valve relief in the event the battery is recharged at high volume. Granted they are commonly termed as a sealed battery although that does not exclude them from the Australian Standards. If they are Valve Regulated they are encapsulated in the standards. They have the potential and provision to release hydrogen gas; they have a valve.

        My battery supplier provided the following links for me to work out the ventilation requirements for my AGM batteries.
        http://www.intelepower.com.au/index....=90&Itemid=108
        http://www.intelepower.com.au/index....=91&Itemid=109

        I have also looked at several other battery manufacturers information. And some of them also state that their AGM batteries shall be ventilated also. And they are Valve Regulated types.

        Exide has a VRLA statement in their general faq's http://www.exidebatteries.com.au/battery-faq/
        Extract from Exide
        AGM stands for Absorbed Glass Mat. An AGM battery is a VRLA battery that has its entire amount of electrolyte "absorbed" in the separator material. The separator acts like a sponge and is saturated to approximately 98% (over 100% would mean free acid in the battery). This is why an AGM battery is spill-proof and can be mounted in virtually any position.


        Full River information: AGM Battery VRLA http://www.fullriver.com/products/ad.../DC120-12B.pdf
        http://www.fullriver.com/products/ad...nstruction.pdf

        http://www.energymatters.com.au/rene...rgy/batteries/
        http://www.energymatters.com.au/full...-dc-p-170.html

        I have had my batteries installed in under ventilated battery boxes.

        So are my calcs correct?


        Originally posted by lizard View Post
        Took the words out of my mouth

        I have 3 AGMs buried somewhere in the boat only used AGM because they dont need venting


        Could be wrong
        You might want to check out the ; National Standard for Vessels - Same info as the Aust Standard, plus more.
        Last edited by CC2005; 30-11-13, 12:34 PM. Reason: add oat info
        PB MY11 LS 4D56 - auto, with stuff.

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