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  • #6093
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    The service batteries fitted to my 2000 B31 are 2-off Numax 135Ah (age unknown). When I bought my B31 last October, the service batteries were reading a bit low on my battery meter on the instrument panel. They were reading approx 12V, whereas my starting battery read (and still reads) approx 13.5V on the same meter.

    This season, the battery meter has been showing the service batteries to by approx 11V, sometimes even lower, but everything seemed to be working fine. I suspected the meter. However, when on holiday last week, anchored in Brodick Bay for a couple of days without running the engine, the service batteries went flat, requiring me to run the engine for a while to bring them back up to their “normal” voltage.

    Last weekend I took the batteries off the boat and tested them with a voltmeter at home. One was 12.7V and the other 13V. They would have been charged up when I motored back to Rhu (in no wind but glorious sunshine) the previous Sunday, but I didn’t expect them to be so high.

    I’ll be taking the batteries to be tested at D&W Wilson in Glasgow this week, but I wondered if anyone had any comments or suggestions? e.g.

    1. Why is my battery meter reading lower than the reading I get at home with my multi-meter.
    2. The standard B31 fit is one 140Ah service battery. If both my batteries are truly dud, would one battery suffice.

    Alastair Cameron

    #7368
    Webmaster
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    Hi,

    I also get a lower reading on my battery meter than my multi meter so I would suspect the quality or accuracy of the battery meter. My batteries are 140 each and a similar age. I am begining to suspect the life left in my batteries as they also seem to run down too quick. If you get them properly load tested you should have the answer.

    Regards, John
    Loblolly.

    #7378
    Webmaster
    Participant

    Thanks for the reply John.

    I took both batteries to DW Wilson on Friday. They ran them through a few tests. One battery had a dud cell, and the other was only giving about 60% output. I bought 2 new 120Ah batteries to replace them.

    I contacted the previous owner, who told me that the batteries were bought in July 2005. Two years doesn’t seem like a very good life, even if they were being deep cycled fairly often.

    Even after fitting the two new batteries, the meter is still reading low. It is odd, because it seems to read ok when switched to read the single starting battery. Maybe it’s a poor connection somewhere in the wiring from the batteries to the meter.

    Alastair
    Electra 2

    #7379
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    Alastair,

    when you say they are reading a ‘little low’, how low is low?
    A reading of 12.7 – 12.9 volts would be acceptable for new batteries, and if they were dry charged and the electrolite added just before you purchased, the lower reading could be normal until they had cycled a few times.

    If when fully charged the voltage increases a lot (0.2 volts +) when you take a reading from just one battery, perhaps there is a current draw or earth leakage on the other, which may account for a different reading when using a handheld meter.

    rgs
    Paul

    #7391
    Webmaster
    Participant

    The reading was reading less than 12V for the service batteries. In fact now the meter needle swings about between 5V and 13V, so I definitely think it is inaccurate for the service batteries. It seems fine for showing the charge in the starting battery however, so it may well be something in the wiring.

    The new service batteries seem to be holding charge fine, and I’m content that “all is well” despite the meter reading. Thanks to all for your advice.

    On a similar note, I had a strange experience last weekend. While on shore power at Rhu Marina, the shore power tripped out. This seemed to drain ALL the power out of my starter battery. I had to use jump leads to get the engine started. Since doing this and charging it up for a couple of hours while motoring, it has been absolutley fine again. Could there have been some sort of sudden discharge FROM my battery TO the shore power?

    Alastair

    #7394
    Webmaster
    Participant

    Alastair

    Interesting problem!

    I don’t think there could have been any direct discharge from your engine battery to the shore power, since the battery is 12V DC and shore power is 240 V AC (apologies if I am stating the obvious). However, there could be a discharge through the battery charger or into the service battery.

    Do you have a split charge system using diodes, a voltage sensitve relay (VSR) or maybe a manual switching arrangement? Without more details of your set-up it is difficult to guess what the problem might be.

    Roger

    #7399
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    I agree it is an interesting one. Although the problem hasn’t recurred (I was back at Rhu last weekend, and connected up to the shore power with no problems) it would be nice to understand the mechanism by which it happened.

    The charging system is a split system. I’m not sure of it is split through diodes or a VSR. It could be the latter, as the engine battery always takes priority.

    Alastair

    #7407
    Webmaster
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    @Electra2 wrote:

    I agree it is an interesting one. Although the problem hasn’t recurred (I was back at Rhu last weekend, and connected up to the shore power with no problems) it would be nice to understand the mechanism by which it happened.

    The charging system is a split system. I’m not sure of it is split through diodes or a VSR. It could be the latter, as the engine battery always takes priority.

    Alastair

    Hi,

    I have just been through the unhappy determination of unserviceable batteries.

    The first thing to understand is that the modern charging systems will keep batteries in reasonable trim so long as they are tied to an almost constant mains supply or charge regime. However the voltage (pd., or potential difference) will drop off quite quickly when charging by any mode ceases. Once mine reached 10 volts unassisted (ie., when sailing) my radar and instruments began to malfunction. I am using 2 Silver-Alloy, sealed batteries of 170ah’s, these have a window showing the state of charge that under certain circumstances can mislead however if a disconnection of charging is introduced then the window colour will be found to change quite quickly from green (good charge) to black (requires charge) and when out of service to white at which point they are ready for the knacker’s yard almost without hesitation.
    I have now adopted (due to no further options in Greece) to using Bosch Tecmaxx Silver-Alloy batteries of 170ah’s, the deep cycling or not of these batteries is a unknown or at least that is the conclusion my research has reached.

    Not too sure if this helps but basically unless the battery holds 12.5 or more volts for more than say 48 hours unassisted and without load being applied it is likely on it’s way to the NY.

    Yours, Chris,
    SV., Pickled Tink.

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