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Thread: Battery Switch Question???

  1. #1

    Question Battery Switch Question???

    Is there any harm in switching a Perko while underway? I personally haven't because I didn't know if the alternater freak out if it didn't have a load on it. I've done this to vehicles (older ones, not new) and it wasn't any problem. The only reason I ask, is more than once, I have shut down to switch to a different battery because I forgot to earlier. I suffer from CRS syndrome (Can't remember Sh**).
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  2. #2
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    Depends on what sw and how itís wired.

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    Member NewMoon's Avatar
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    Switch through Both, not through Off.

    Most switches are "make before break."
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    Supporting Member bullbuster's Avatar
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    Default Good question

    Mine is a 4 position switch. My mechanic told me to roll it thru 'all' when switching between batteries. I do, but never worried about it before.
    Can the very brief interruption to the charging circuit cause any damage?


    Mine doesn't have the "stop engines before switching off" statement.
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    Regardless of setup, an important consideration is that the alternator-to-battery + connection must never be broken while the alternator is generating current. Otherwise the energy stores in the alternator inductive coils would produce a large voltage spike, possibly destroying both the alternator rectifier diodes and any connected electronics.

    For this reason I never switch battery when the engine is running.

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    Member Cap'n Ron's Avatar
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    Default Thanks for great advice...

    Seems like our boat dealers should be telling us this, but I never heard of it, and so THANKS Guys!

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    Member NewMoon's Avatar
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    I just looked at the specs for a Perko and a Guest switch. Both of them, and my Blue Seas as well, are designed to make contact before breaking contact, meaning that you can go between 1 and 2 through Both or All (whichever it's labeled) without losing connection to your batteries.

    What you can't safely do is switch through the Off position.

    If you have a very old or cheaply made switch it may not work this way.
    Richard Cook
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  8. #8

    Thumbs up Good to know.

    Thanks for the info. On kind of the same subject, is there an in-line diode I can put on the positive feed to the house circuit that will prevent draining the crank battery if the switch is in the both position?
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    Yes, depending on where you want to put the diode.

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    In older outboards the battery was not required once the motor was running (CDI Ignigion Systems) and you wouldn't have a problem interrupting the battery connection. These motors use a charge coil(AC) that is rectified to DC, as opposed to an alternator such as on an inboard or your car. Newer generations of motors, EFI, EFI Four Stroke, and Direct Injection Two Stroke require a minimum of 12v from the battery constantly. Any drop below that in battery voltage or a disconnect (rolling the switch through "OFF") will cut the engine. This is also why you should use a nyloc nut rather than a wing nut on your battery terminals, to avoid a loose connection. Inboard alternators also will not tolerate the disconnection as stated in a prior post.

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