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  1. #21
    Join Date
    Jul 2003
    Location
    West Australia
    Posts
    11,609

    Default Re: Charging engine battery via 1-2-both switch

    An alternive for OP might be to simply buy and fit one of these. ie 10w solar panel no controller. Wired directly to engine battery via diode. https://www.ebay.com/itm/10-100W-5V-...5a5fa70b7abad8
    Here is a suitable diode fitted at the battery connection so no need for fuse. https://www.ebay.com/itm/50PCS-1N581...YAAOSw4sNb9gsQ
    ol'will

  2. #22
    Join Date
    May 2009
    Location
    Wirral
    Posts
    673

    Default Re: Charging engine battery via 1-2-both switch

    You will find that these panels also have a 5v usb output so you dont get the panels full output for charging a 12v battery.
    Leisure Owners Association

  3. #23
    Join Date
    Apr 2002
    Location
    Cornwall
    Posts
    8,784

    Default Re: Charging engine battery via 1-2-both switch

    Quote Originally Posted by lw395 View Post
    I've always switched to both as soon as the engine is started, and to 1 (or whichever is Domestic) as soon as it's stopped. It's what you do, like turning the key so the oil pressure alarm shuts up, or turning the gas off when the kettle has boiled. Isn't it what nearly everyone did from about the mid 70s (or was it even before that?) when sailing boats started to have two batteries to about the late 90s when most new boats started to have bigger house batteries and more complex systems?
    Most of us don't motor for long enough to worry about over charging the engine battery from the alternator.
    That's how it was in the 70's, also had blocking diodes and Lucas relay controlled by alternator warning light. But it was early 80's we bought in more complex systems, not late 90's.

    Brian
    Kddpowercentre VASR charge

  4. #24
    Join Date
    May 2007
    Posts
    37,244

    Default Re: Charging engine battery via 1-2-both switch

    Quote Originally Posted by halcyon View Post
    That's how it was in the 70's, also had blocking diodes and Lucas relay controlled by alternator warning light. But it was early 80's we bought in more complex systems, not late 90's.

    Brian
    The simple systems were fitted for a long while in smaller boats, especially racing boats.

  5. #25
    Join Date
    Apr 2002
    Location
    Cornwall
    Posts
    8,784

    Default Re: Charging engine battery via 1-2-both switch

    Quote Originally Posted by lw395 View Post
    The simple systems were fitted for a long while in smaller boats, especially racing boats.
    We supplied lots of boats down to 18 foot, and a lot of Westerly's raced but yes a lot of out and out racers and day boats were simple.

    Brian
    Kddpowercentre VASR charge

  6. #26
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    7,698

    Default Re: Charging engine battery via 1-2-both switch

    Quote Originally Posted by BabaYaga View Post
    Some info missing in the example above.
    Not sure what you think is missing, seems clear enough to me. The example i quoted is a cut and paste from the boat owners email. It was posted because it clearly shows how a faulty battery, in a bank of more than one, can quickly discharge all of the batteries in that bank, if the 1-2-B is on B, the engine battery is included in the bank. It also demonstrates how a system with separate switches and a split charge system can easily cope with a battery failure.

    But the fact that the alarm went off (stopped) when the engine was started suggests to me that the faulty domestic battery indeed was taking some charge, at least enough to stop the voltage from falling to a very low level while the engine was running.
    No, the failed battery has a shorted cell, it cannot have its voltage raised to a sufficient level to silence the low voltage alarm. The reason the alarm went off was because of the alternator output was going to the good battery and trying to raise that voltage, but primarily the terminal voltage would be influenced by the engine battery voltage and the alternator output. Remove those and the domestic bank promptly drops to 10.5v This isn't an uncommon mode of failure, i've seen it several times and have had it happen to me twice, on different boats.

    How was the split charging arranged? If a VSR, surely that would have opened if it had sensed a 'non-charging' system voltage? In that case the domestic battery would have been disconnected from the alternator and the alarm (possibly a low voltage alarm from some equipment) had come on again?
    Instead, the customer reports a fast dropping voltage after engine shut down.
    The boat is fitted with a Victron Cyrix VSR, this is dual sensing and would have closed due to the alternator output at the engine battery, that's how it's supposed to work. The monitor has no way of knowing the battery has a shorted cell, all it "sees" is that the voltage at the engine battery exceeds the set point for closing the relay. If it closed because the domestic bank was low on voltage it would be a pretty useless thing.

    Of course the voltage rapidly dropped again when the engine was stopped. The relay would have opened, there would have been no connection to the charged engine battery or alternator and the faulty battery would have again discharged the good one. In fact, it's unlikely that much charge went to the good battery, other than a little surface charge. Again, this is exactly how the system should have operated, the relay opened to protect the engine battery.

    To me it is not clear how this situation could have drained the engine battery if instead a 1-2-B switch set to both had been used while motoring. (Left on both after engine shut down is an other story, of course).
    That depends on the rest of the system. If the alternator could keep up with the drain from the faulty battery and if the switch was turned off immediately the engine was stopped, the engine battery might still start the engine. With the VSR, even if the alternator couldn't keep up the engine battery would be safe, the VSR would open if the voltage dropped to the set point. A faulty battery can impose a massive drain on good batteries, in the example i posted, the faulty battery was still warm the next morning (was left connected to the other two batteries).
    Rainbow Marine.
    www.rainbowmarine.co.uk

  7. #27
    Join Date
    Oct 2001
    Posts
    1,380

    Default Re: Charging engine battery via 1-2-both switch

    Returning to the original post, if I had a good domestic battery and a flat engine battery I'd physically swap them. And take the flat one home. For bench charging/testing/replacing.

    For the OPʼs setup, I'd disconnect the domestic bank at an appropriate battery terminal, then with the 1-2-B switch on B, charging would be directed solely to the engine battery.

  8. #28
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    7,698

    Default Re: Charging engine battery via 1-2-both switch

    Quote Originally Posted by James_Calvert View Post
    Returning to the original post, if I had a good domestic battery and a flat engine battery I'd physically swap them. And take the flat one home. For bench charging/testing/replacing.

    For the OPʼs setup, I'd disconnect the domestic bank at an appropriate battery terminal, then with the 1-2-B switch on B, charging would be directed solely to the engine battery.
    Why ? Just turn the switch to the engine battery and that's all that gets charged.
    Rainbow Marine.
    www.rainbowmarine.co.uk

  9. #29
    Join Date
    Oct 2001
    Posts
    1,380

    Default Re: Charging engine battery via 1-2-both switch

    Quote Originally Posted by PaulRainbow View Post
    Why ? Just turn the switch to the engine battery and that's all that gets charged.
    Because his charger is only connected to his domestic bank. He originally asked if he could get charge to his engine battery using B. Of course he could. But some of us were worried about the impact if something was wrong with a battery.

  10. #30
    Join Date
    Dec 2008
    Location
    Sweden
    Posts
    1,500

    Default Re: Charging engine battery via 1-2-both switch

    Quote Originally Posted by PaulRainbow View Post
    If the alternator could keep up with the drain from the faulty battery and if the switch was turned off immediately the engine was stopped, the engine battery might still start the engine.
    Thanks for your comment. I agree with what is quoted above.
    Your first post to this thread was a bit more categorical:

    Quote Originally Posted by PaulRainbow View Post
    All of the time the switch is in "Both" the batteries are in parallel and any issue that affects one battery affects them all. If a battery fails due to a shorted cell, for instance, that battery will get very hot and discharge any battery connected to it. So, if that happens while you have the switch set to both, you lose all power.
    Quote Originally Posted by PaulRainbow View Post
    If that boat had been using a 1-2-B switch, set to both, the engine battery would also have been flat.
    What your chosen example demonstrates, in my view, is the opposite to what you first claimed. Despite a shorted cell, the faulty battery did not manage to drag down the system voltage enough to open the VSR as long as the engine was running and the alternator putting out.
    This shows that a failed battery does not automatically flattens any other batteries connected in parallel to it.

    NB, I am not saying such a total loss of power could never happen, under other circumstances, if a 1-2-B switch or a 'head lamp relay' is used. There is a risk, but not a huge one. Which I think your example underpins.

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