[C320-list] Alternator Wiring Question

[Larry Frank]

It does seem strange that there would be a fuse in the ground.   But as suggested maybe it has a different function than what we consider the traditional function for a fuse.

I have a Balmar 100 amp with the positive output wired directly to the house batteries. I have a 150 amp circuit breaker at the battery end of the positive cable.  I guess if this tripped while the engine is running it would blow out the diodes in the alternator, but they can be replaced at a repair shop at a fraction of the cost of a new alternator.  The purpose of the breaker is to protect the positive side of the charging circuit in the event of a short circuit which could happen for example f the insulation on the positive cable chafed through and shorted to ground.  Without the breaker or a fuse there would be a unacceptable chance of a fire.  This could happen if the engine was running or not and maybe with no one on board.  I would rather get the alternator fixed than replace the boat.  It is a safety thing.  A fuse in the ground would not protect the circuit like the fuse or breaker in the positive cable located close to the battery.

If you are worried about a fuse or breaker opening up and taking out the alternator diodes you can install one of these devieces - Balmar TSP-12 Spike Ground Protector 12V.

If there is any question if an alternator is functioning properly, take it to a repair shop where they will test it for you.

Larry
WindSwept C320 #246

On 6/30/20, 6:24 PM, "C320-list on behalf of Mark Seyler" <c320-list-bounces at lists.catalina320.com on behalf of mseyler at cox.net> wrote:

    I had no idea my alternator issue would cause confusion.  Here’s a little more detail, for anyone who is interested.  But I understand that the question facing most members of the list on receiving this e-mail may be whether to hit "next" or "delete."

    According to what I have been able to read on-line, the point of the fuse in the ground wire is to protect the diodes in the rectifier on the alternator.  The semiconductor fuse is supposed to be a faster-blowing fuse for that reason.  I have read that it is in the ground wire to eliminate the overcurrent path to ground if the power is lost to the field windings while the alternator is running.  

    In my case, the fuse also blew when a wrench dropped so as to briefly short between the B+ and the B-, or ground connection, on the alternator.  That accident apparently sent lots of amps to ground, blowing the fuse (and hopefully bypassing the alternator completely).  But just to make things confusing, even when the fuse is blown there is still an alternate path to ground through the ground wire.  That means you can measure 12 volts between B+ and B- on the alternator, and think the fuse has not blown.  However, the alternate path to ground goes away when you turn the key on to start the engine, and there is no longer 12V between B+ and B-.  (I still haven't figured out why -- I think that a circuit gets energized.)  Without 12V between B+ and B- on the alternator the field windings are not energized, and the alternator doesn't generate power when running.  My hope is that because it never had 12V to the field windings, I won't have blown the diodes, and my new alternator won't be an expensive paperweight.  I'll know after the new fuse arrives, and I can start it up with power to B+ and a good connection from B- to ground.

    I learn something from this list almost every time a new thread starts.  If anyone has a better understanding than what I have stated above, please share it and I'll learn something more.

    Mark Seyler
    S/V Reality, 
    Catalina 320, #232
    New Orleans, LA



    -----Original Message-----
    From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of Scott Thompson
    Sent: Tuesday, June 30, 2020 11:10 AM
    To: C320-List at Catalina320.com
    Subject: Re: [C320-list] Alternator Wiring Question

    So what would cause an alternator fuse to blow except for a problem with the alternator itself? I have no fuse despite having the Balmar setup. 
    (As far as I know --- I didn't do the install myself.) And would a blown fuse fry an external regulator such as the Balmar?


    On 6/30/2020 10:13 AM, Jack Brennan wrote:
    > I’m a little puzzled by an earlier reference to the fuse being in the ground wire. Why would that be?
    >
    > I know there has been some controversy about whether to fuse the positive wire from the alternator because, if the fuse blows, it will take out the alternator.
    >
    > That’s not really an issue for me because I use the standard 55-amp alternator on my Yanmar, which costs about $100 online. But that would be an issue if I had one of those expensive Balmar setups that people like.
    >
    > Jack Brennan
    > Sonas, 1998 Catalina 320
    > Tierra Verde, Fl.
    > Dolphin Cruising Club of Tampa Bay
    >
    >
    >
    >
    >
    >
    > Sent from Mail for Windows 10
    >
    >

    --
    Scott Thompson
    Surprise, #653