Conference unifix::sailing

    I replaced an alternator in an MD7A last year, but kept the old
    one.  Cost around $400!!!!
    
    I'd like to repair the old one and keep it as a extra.  Can you tell
    me where I can get this book.   Thank you in advance!
    
    Gary

    Glad you were successful but beg to differ on the purpose of the
    diodes. The exiter current is supplied to the armature through
    carbon brushs supplied by the regulator. This is how the alternator
    is turned on and off. When the regulator sees low voltage (<~13VDC)
    it switchs the armature current on. When >~14.5VDC it turns it off.
    The stator is actually a 3 phase AC generator with its output voltage
    impedence limited only. The diodes are hooked up as either a full
    wave (six) or a half wave (three) rectifier. The altenator can
    generate stator voltages at no load (Infinate output inpedence)
    of 60-70 perhaps even higher. The diodes usually don't have peak
    inverse voltage limits of more than 50. The diodes are high
    current devices and high PIV ratings would make them expensive.
    With a battery connected the PIVs don't exceed 14.5 VDC. Thats
    why you should never run an exited alternator without a load...

    The cost to rebuild the 60+ amp Delco alternator on a Perkins 4-236
    was $60 here in Seattle.  Are the parts for Volvo that much more
    expensive?
    
    	Howard

    He said the cost for a rebuild, off the shelf. Its hard to find anyone
    who will actually rebuild yours for you. You usually have to do it
    yourself. Sort of like tring to find a rebuilding kit for a water pump
    these days...                                         

    re: .1
    
    Gary,
    The name of the book is " The 12 Volt Doctor's Alternator Book" by
    Edgar J. Beyn, from SPA CREEK INC., Annapolis MD.  It's published
    by C. Plathe North American Division, 222 Severn Ave., Annapolis,
    MD 21403. The book cost me 19.95 at the Arm Chair Sailor, 1500
    westlake Ave. N., Seattle WA 98109. They apparently ship frequently
    to the east coast.
    
    re. .4
    
    Hmmm.. well by that book, which is all I know about alternators, there
    is more than one way to excite a rotor. For this variety of alternator
    the original current is supplied to the rotor by this second or
    "auxiliary" set of 3 diodes. Anyway past that it's probably best that
    I refer the book which looks at a few different ways excite current
    is accomplished in todays alternators.
    
    
    Cheers
    Jeff Kass

    I'am not sure I understand why an alternator would supply DC to the
    rotor through diodes???? Generally DC is supplied directly to the
    rotor through brushes from the battery. The current is limited
    to a static maximum number of amps by the resistance (length) of
    the wire. The geometry and material of the rotor will create
    an M field of sufficient flux density and shape to induce an
    optimum current in the three stator windings,hence 3 phase.
    Since the rotor field rotates so does the polarity and amplitude
    of the stator current, hence AC. In a generator the field is
    static,  (fixed magnet) hence DC.

    Thanks for correcting me!  I looked a my book again and the excite
    current is supplied from the battery through a keyswitch and alternator
    warning lamp. Also connecting to the same point on the regulator were
    the open diodes. Their purpose is not to provide excite current but a
    separate 12VDC supply and sampling point for the regulator. The reason
    for these diodes are "to make alternators self contained units with
    internal or attached voltage, and with a minimum of external wiring 
    connections.  Thanks again, I hate wrong information! If you want
    to contact me I'm at DTN 545-4326.
    
    Jeff Kass

    Most modern Alternators are as you describe,self-contained, but not
    all. DELCO as I recall introduced them first but you can still find
    units with external regulators and armature connections. Some have
    a single armature connection,allowing a return to ground through the
    unit body,and some isolate the armature and require two wires. Some
    require the external point to be grounded to excite the unit and some
    require 12VDC. Make sure you know what you have before you start
    hooking up power though... 

    Another alternative for those (like myself) who aren't trained
    in electrical machines, is a place called Automotive Components, Inc
    in Hudson, MA (508) 568-0461.  The guy is super honest, will rebuild
    any starter or generator (or combination) for $107, and he is full
    of information.

    If you have a Yanmar engine, try an auto junk yard and look for a
    Nissan.  They use the Hitachi alternator just like the Yanmar.
    
    

re .10:

Automobile alternators should NOT be used aboard a boat, most especially
if you have a gasoline engine. Marine alternators have been specially
modified to reduce the risk of fire and explosion from internal
sparking. Same is true of starter motors. 

    What about using marine alternators in your car.....?
    
    Gregg

re .12:

No reason not to ..... except that marine alternators are much more 
expensive than automobile alternators, especially rebuilt or used ones. 

    No you can't.  They'll get salt water on your engine block.
    

    Re: .11
    
    I usually agree with Alan's comments but ----, I see little
    risk using automotive parts on a boat IF the boat is powered with
    a diesel engine. Alan did correctly point out that starter motors
    should be considered as a potential hazard. In fact, a starter presents
    greater risks than an  alternator because the starter's brushes
    are a sofrom the commutaat the armature's commutator. 
    
    An alternator also uses brushes but they are used to energize the
    fields without the use of a commutator. In addition, the field
    current is relatively small, 1-3 amperes but the starter's armature
    current is high, 50-75 amperes is not unusual.
    
    Joe
                                                             

    The last line in the 1st paragraph got gobbled by my editor, sorry.
    
    It should have read, "In fact, a starter presents greater risks 
    than an alternator because the starter's brushes are a source for
    arcing at the armutator's commutator."
    
    Joe

    I too have a diesel engine, but have had fear in my heart about
    upgrading my alternator inexpensively with a high output automotive one
    due to fears that my Propane locker, which is next and above my engine
    could leak. It is made of Marine plywood and lots of caulk. If my fear
    is unfounded, I'd like to know. I've seen a picture of what the topside
    of a boat blown off by a propane leak looks like. I believe it was in
    Hal Roth's book "After 50,000 miles. It's not a pretty sight.
    
    Robert

Re: .17--

My comments in response .15 were directed towards risks involved 
with an automotive alternator in a diesel fueled verses a 
gasoline fueled engine. Obviously, if one were to operate 
any electrical or for that matter, mechanical device in the 
presence of volatile, flammable/explosive substances, he should 
use a device rated for that environment. 

I have a diesel engine in my boat and I also have propane. When I 
installed the propane system, I absorbed the added expense of a 
Marine Energy System's propane locker. That locker is vented to 
the outside of the hull to prevent leakage into the bilge. 

Joe

While we're on the topic of explosions...

After I bought my boat this summer, I found a veritable toxic waste dump full
of miscellaneous volatile organic chemicals (e.g. paint thinner, acetone, etc.)
stored below a settee. Some of these chemicals were in steel cans that
were showing signs of rust at the seams. Needless to say, I removed all this
stuff from the boat.

You can't be smug about explosion safety just because you use diesel fuel and
an alcohol stove. Even a BIC lighter contains enough butane to make a huge bang.

--RS

P.S. My boat has an automotive alternator, which I intend to keep because it
works, and it's not at the top of my list of safety improvements.