Conference unifix::sailing

    The current issue of Cruising World has an article on batteries.
    
    As I recall, when plates are left exposed or uncharged for a period
    of time, they form a sulfate coating.  If caught quickly, some of
    this coating disolves on re-charging.  As time passes, the coating
    hardens and is essentially permanent.  The coating blocks the battery's
    normal operation and so whatever portion of the plates are sulfated
    permanently are lost forever and unrecoverable.
    
    The bottom line is never let the plates become exposed, and keep
    the battery charged.  Once done, the damage is irreversable.
    
    Rick,
         

    I had the same problem with both batteries at the same time.(broken charger)
    I filled up with water and both batteries died 11 month later.
    Since then I have a cheap amperemeter installed to check if the charger
    is working.
    
    Peter
    

    What special precautions need to be taken with "deep cycle" batteries?
    
    I've heard at least once that they should be discharged completely
    before re-charging.
    
    
    			Joe

>>>    I've heard at least once that they [deep-cycle batteries] should 
>>>    be discharged completely before re-charging.
    
No! The life of a deep-cycle battery is greatly shortened by deep or 
complete discharging. The optimum discharge before recharging is about
50% of the batteries amp-hour capacity. Cruising Equipment and the Ample
Power Company (both in Seattle) have catalogs of high tech battery
charging systems that explain in some detail how to maximize the life of 
your batteries. There are some previous notes that discuss this in more 
detail.

Alan

    Yup, its gone.
    
    I purchsed the Guest Smart switch which has an LED version of an
    expanded scale voltmeter (11.9 to 14.4) in it.  It provides an
    indication of battery state as well as the charger and alternator.
    I wanted a switch that would allow me to get to either battery without
    going thru the both position.
    
    To check the battery that had been "cooked", I got a no load reading
    of 12.6 and then started turning on fans and lights and watched
    the indicator.  The LED's started to go out quickly and soon the
    voltage was less than 12.  The good battery never went below 12.3
    on a high load.  I like the switch.  Not bad functionality for $39
    (it just went to $49 in the new Boat US catalog).
    
    I put a new battery in last weekend.  Now to send the charger back
    to Rayjeff to make sure it is not the culprit.
    
    

    
    Where did you get the Smart Switch for only $39.00?  The lowest
    price I've seen was $45.00.  Does the Smart Switch allow you to
    monitor either battery individually?  How about the load?  I am
    planning to use the Smart Switch in a two switch system with four
    batteries.
                            
    
                                  TO
                                STARTER
                                   |
                                   |
                                  / \
                                 /   \
                                /     \
                    SWITCH 1   O       O  SWITCH 2
                              /|       |\   (Smart Switch)
                             / |       | \
              BATT 1 _______/  |       |  \_____ BATT 4
                               |       |
                   BATT 2______|       |_______ BATT 3
    
    How will this set up work?
    
    Thanks,
    
    John

re -.1: 

Using two switches as you diagrammed will work just fine. But why four 
batteries? Do you have some way other than a conventional engine-driven 
alternator to charge them? If not, I don't see any particular advantage 
to more than two batteries. I'd also suggest that an inexpensive analog 
voltmeter will provide more accurate measurements of battery voltage 
than an LED display (which gives only a very rough estimate of voltage). 
A voltmeter that reads to 0.1 volt is acceptable for everyday life.

    
    I want to install four batteries to increase my battery capacity
    so I can increase my charging capacity.  I am installing a SPA Creek
    Alternator Contoler to increase the Alternator output to allow the
    use of power hungry things like refrigerator, TV, Etc.  If you set
    up your alternator to deliver a constant 40 amps for instance,  you 
    need the battery capacity to soak up all that juice or they will
    just boil over and fry.  I could change things around to make two
    very large batteries but that would mean I would have to get rid
    of the two I have now.
    
    The SPA Creek does have a cut out voltage sensor that shuts it off
    before (hopefully) frying the batteries.  The instructions also
    have a reference list of alternator types and instructions for hooking
    up to each different kind.  My alternator is a DELCO-TRON rated
    at 63 amps.  I hope to get 40 out of it hot, If I can't I'll have
    to upgrade my alternator too.  
    
    You see, your total battery capacity is directly proportional to your 
    maximum charging rate.  
    
    

re .8:

I think you'll want a much larger alternator. Assume that you have four 
105 amp-hr batteries and that you discharge all four halfway (the 
optimum discharge). This means that you've taken 210 amp-hrs from the 
batteries. Recharging isn't perfectly efficient, so you'll have to 
return more amp-hrs to the batteries than you used. At a 40 amp charging 
rate, you'll need to run your engine for over 6.5 hours to recharge the 
batteries (assuming an 80% recharging efficiency). At a 100 amp charging 
rate (which is 25 amps per battery), you'll still need to run the engine 
for over 2.5 hours to recharge (and a 25 amp charge rate is high -- as I 
recall, the final charging rate should be about 10 amps for a 105 amp-hr 
battery). Prolonged high charging rates reduce battery life and produce 
a lot of hydrogen gas (which isn't exactly safe). 

Perhaps this much engine running time is acceptable to you. I prefer a 
day of sailing with no engine running time at all. By the way, I'm a tad 
doubtful that a normal 60 amp alternator will be able to produce 40 amps 
continuously, especially on a hot day in a hotter engine room. 

    
    Re: .9
    
    We are really talking about a working range of the battery bank
    of 50% to 85% of the total battery capacity.  At 400 A this gives
    you a range of 200 to 340 or 140 amp hours of usable capacity. 
    At 40 amps this gives a charge time of 3.5 hours or 4 hours if you
    consider some loss.  There is also a maximum charging rate based
    on Battery capacity that you have to consider.  If that rete is
    exceeded, batteries boil, produce a lot of hydrogen like you say,
    and are damaged.   
    
    I think that this is the best upgrade I can do without spending
    a whole lot more money.
    
    

    I think I will buy the `Ample' book.  I need the instruction.
    
    Can I ask what may be a dumb question.  I have two batteries each
    rated at 70 ah.  They are in separate banks, so I can use; both,1,
    or 2 as I please.  Assuming that `1' has been used overnight for
    lighting etc., and is at 50% capacity, and `2' is at say 75% because
    it was not used after a `both' charging cycle, what happens to each
    battery in the next `both' charge.  Is the cut out/reduction in
    charging determined by the fuller of the two batteries.   
    

re -.1:

For once life is nice and simple. When charging two or more batteries in
parallel, the charging current is divided unequally between the 
batteries so that the least charged battery gets the most charging 
current. This is because your alternator is essentially a constant 
voltage current source whose voltage is greater than the battery
voltage. The more discharged a battery, the greater the charging current 
must be to raise the voltage at the battery's terminals to a given 
value. Since the batteries are in parallel and are being charged from 
the same alternator, the current into the batteries must be such that 
voltage at the terminals of all of the batteries is the same (neglecting 
an voltage drops in the battery cables). As the batteries reach the same 
state of charge, the currents into them become more or less equal.

I usually parallel my three batteries when starting the engine and leave 
them paralleled until I stop the engine. I then switch to a single 
battery. If one battery is quite discharged, I may charge it alone for a 
while.

    Re: last 2
    
    I use a different scheme since my engine use is probably not typical.
    My boat is on the Merrimac and when the engine is used to get into
    port it is used for a long time ( >1 hour is easy ).  I don't want
    my batteries cycling between 80-100 % all the time and this would
    be common given my particular pattern of usage so here is what I
    do.....
    
    Wire the boat with two distinct power buses; call one the panel
    bus and call the other the engine bus.  Equip each battery with
    its own switch such that it can be attached to either or both buses.
    So, two batteries=2 switches, 3=3, etc..
    
    In practice you use the panel bus to discharge your batteries down to
    the optimum level (50%) by attaching them in a rotating sequence
    as required.  The 2nd through nth batteries are used as spares or
    engine bus supplies and are therefore kept at 100% until their turn
    comes on the panel bus.
    
    There is a side benefit to this in that your electronics are never
    connected to anything but clean power.
    

    Re .11 
    
    When using battery switches be cautious about using the "Both"
    switch postion. I am assuming a bare switch, i.e. it does not 
    have built in isolator diodes. 
    
    When you are dealing with "like" batteries which are at widely
    seperate state of charges, as might occur when one is used to
    run lights over night, then the voltage difference between them
    can cause large currents to flow from one battery to the other.
    This current is limited only by the internal resistance of the 
    battery. This same effect can occur if you use highly different
    battery types, by capacity or deep verses standard starting batt.
    
    It is often best to maintain relatively equal states of charge if
    you are using the "Both" switch position. Two other things will
    normally avoid the surge current. If you insure that the switch
    is not placed in "both" without the charging source operating,
    then when you do switch to "both" the charging voltage will normally
    be high enough to prevent the cross current and the charge will
    be proportional as mentioned in reply .13.
    
    Finally if you want to avoid these issues, consider using a battery
    isolator, with or without switch.
    
    Jerry
    

    Previous reply:
    
    Sometimes, when trying to start, one needs the power from both
    batteries. That means putting the battery switch to "both", when
    there is no charging voltage from the alternator. So you can't escape
    switching to "both" at some time or another and the issue of one
    battery discharging, with high current, into the other in some
    situations just can't be avoided, unless you have an isolator. And
    often, we don't want to use isolators because of the potential drop
    of roughly .7v.
    
    There's never an easy answer.......
    
    Tally-ho,
    
    Ray

    Maybe i can kickstart this topic (and hope everyone uses "next unseen")

    I  am trying to evaluate the condition of the batteries on my
    new-to-me boat. They are 2 8D wet cell batteries installed in 1985, i
    haven't looked for the manufacturer's name.

    The problem i think is that they have just about had it. The following
    are some symptoms i've observed. (please note that all the voltage
    readings could be low by about .13v; i will get my RS meter calibrated
    properly and report back if i find a bad error).

    1   The batteries are in a steady state: they have been charging on the
        charger for a couple of days with no load, and a small load (1.5a)
        is applied and the battery switch set to BOTH. The shore power
        battery charger (the original 1980 Sentry 15a) goes on when the
        battery voltage goes down to 12.60 and clicks off at 13.35. The
	cycle time is about 5 min with the 1.5 a load. 

	Questions:
	    Is this normal behavior?
	    Should the off voltage be more?
	    Would that value be the float voltage?
	    Does the fact that small load decreases the battery voltage
		from 13.35 to 12.60 in about 5 min mean the capacity's
		shot?

    2   I tired a small capacity test. I kept the charger on for 24 hours.
        Turned it off and observed a voltage of 12.95, and going down. I
        removed the load and came back 24 hours later. Now the voltage was
        12.31 and the specific gravity was about 1.175, which i assume to
        be the steady state voltage that can be used to indicate charge
        level. If so, a chart i found in Ocean Navigator says the charge
        level is about 75%. I then put a 4.0a load on it and noted the
        following readings.
	    time    reading
	    1730    12.31
	    1745    11.92
	    0700     2.42
        Obviously the next morning the battery was deader than a gaseous
        human waste event. It's charging right now.

	Questions:
	    75% of 210 a-h (for a group 8D) is about 157, yet i observed at
	    most 54 a-h (i don't know when the voltage went below 10.5).
	    Does this mean the battery has about gone?

    I don't know the history of the battery, but i'm sure it's had its fair
    share of abuse. Is it time for new ones?

    tnx,
    paul
    

    Paul,
    
    Have you tried working the batteries one at a time?  Sometimes
    batteries which are in parallel won't charge properly, and that makes
    getting to the bottom of your symptoms more difficult.   If one of your
    batteries is shorted internally, it's going to discharge a good
    battery which is in parallel with it.   
    
    I'd start poking the batteries one at a time.
    
    What temperatures are you talking about?  If it's outside here in the
    balmy northeast, that will likely have an impact on how long you can
    effectively draw power from the batteries.  
    
    Not a technical answer, but maybe it'll help a bit.
    
    djc
    
    

re .16:

>>> The problem i think is that they have just about had it. 

I think you're right. 1985 is old for the usually (mis)treated boat 
battery. As a battery ages, it loses capacity. If a battery is
chronically undercharged, which is likely for a battery the size of 
yours, especially if your engine has a wimpy OEM alternator, the plates
sulfate, which is more or less synonomous with reduced capacity and
death. 

Part of the trouble may also be your battery charger. To fully charge a 
battery requires raising its voltage to somewhere around 13.8 to 14.1 
volts (depending on battery type). Maintaining the voltage at 13.35 V
will, I think, result in chronic undercharging. 

Once charging has been stopped, it takes quite a while (up to 24 hours) 
for the battery's voltage to drop to a steady state. Battery voltage is 
only a good measure of the state of charge and capacity for a battery in 
good condition. A fully charged battery should have a voltage of 12.8 V or 
more (again depending on type) 12 to 24 hours after charging ends. 

A good 200 A-hr battery should deliver more than 200 A-hr at a 4 A load. 
As I recall, A-hr capacity is usually specified for a discharge current
of A-hr capacity divided by 20 (which would be about 10 A for your
batteries). Capacity is higher at lower discharge currents and lower at
higher currents. 

But, it is very harmful to the battery to discharge it deeply (which 
means below about 10.5 V). Again depending on type and construction, the 
cycle life of a battery deeply discharged (much less than 10 volts)
might vary from 1 or 2 cycles to maybe 400. If the discharge is limited
to 50% of capacity, life is much longer. 

I've been doing some load testing on my batteries to gather data that 
will allow me to estimate when they are 50% discharged. I built a box 
that applies a constant load (+/- about 1% adjustable between 1 and 10
A) to the battery, measures the on time, and shuts the load off when the
voltage drops below an adjustable limit value. I also have a regulated
10A DC charger (it was built about 20 years ago as a regulated,
current-limited 12 V power supply, possibly for a computer, which I
bought recently new for $10) so that I can more or less repeatably
recharge the batteries to 13.8 V. 

Preliminary results indicate that our two year old 85 A-hr batteries are 
delivering about 75 A-hrs with a 3.00 A load and a lower limit voltage 
of 10.5 V. If I use a lower limit of 12.0 V, the voltage will rise to 
about 12.5 volts 12 to 24 hours after discharging stops. For our 
batteries, 12.5 V is roughly half charged.

We also have a low voltage alarm on the boat so that we don't 
accidentally discharge the batteries too far. 

You might want to get an Ample Power catalog. Lots of useful information. 
Battery charging isn't as simple as it seems. There is a good article 
in the latest Cruising World about batteries by Nigel Calder (he does 
seem be actually knowledgeable). I assume you've read the other notes in 
SAILING about high-output alternators and the like so I won't repeat 
myself.

Alan

    Yah, when I read 13.35 for a charge I thought it was low. Most lead
    acid batteries I've dealt with consider 13.8V fully charged. In
    automotive applications, where recharging is done all the time and the 
    abuse of the battery is less, my truck charges to 14.45V and my car to
    13.8V. The car battery is dead. 
    	But as you went on to describe the discharge rate it sounded like
    the batteies wern't doing all that great anyway. Yah, checking them
    individually could show one to be better than the other, but 8.5 years
    on a lead acid battery is a very long life. 
    	What crosses my mind as I sit here and type is a means of diagnosing
    things without the price on a new battery (though it sounds like you'll
    want one or two this season). Perhaps if you have access to a good
    automotive battery, put it on the same charger, alone, and check what 
    level it charges to. Perhaps the battery is so poor that it can't
    achieve the 13.8 volt level. If the charger charges a known good battery  
    to a more appropriate level I would take that to imply a very dead
    battery being the reason for the very low level. 
    
    If not I'd probably adjust the charger to charge to a higher level with 
    a new battery. 
    
    	Those dead batteries in the middle of the night that require a half
    hour of charging  every hour really make it hard to sleep next to the
    engine when it's not your watch.
    
    Geoff 

    There is a pretty good section on battery charging in BOAT/us catalog
    that talks about absorbtion, float and bulk recharging.  Darned if I
    can remember all that stuff.  But with two brand new 195ah on board
    I'll not worry for a while yet.
    
    

The specific gravity of the fluid in each cell is a good 1st level indicator
of battery condition. Batteries with problems frequently have cells that
are not all at the same level of charge.

You can get a cheap specific gravity tester at any auto parts place. It
looks like an eye dropper with a bunch of colored balls in it.

Eight years is end-of-life for a typical lead acid battery. It's probably
time to buy a new one.

--RS

    Thanks for all the ideas.

    I have checked both batteries one at a time, and get more or less the
    same result for each. I have checked the specific gravity for each cell
    a couple of times and all the readings are within about .025 of each
    other. I have a tempurature compensated seemingly good quality (though
    fragile) hygrometer (sp?) from NAAPA ($8.50).

    I can only evaluate the AC charging situation; i havn't had the motor
    running yet since i inspected the boat before purchase. It has a 90a
    alternator, which is not a 150a Balmer, but not a wimpy oem either.
    There is also a T-MAC controller so i expect to be able to get as much
    as possible from the alternator.

    I have read all the catalogs, Ocean Navigator (i second the praise on
    Nigel Calder's articles - i am going to get his books), PS, etc. Plus i
    even have an EE background. However, all this stuff still causes my
    eyes to glaze over when i'm staring at $700 for two new batteries, a
    few more hundred for an amp-hour meter so as not to destroy the first
    $700, a few hundred more for for a good AC charger (the current one
    maxes at about 12 a), etc. (with appologies to Al Haig) A few hundred
    here, a few hundred there, the next thing you know you'r talking about
    *real* money...

    I guess the 8.5 years on these batteries is better than the 5 years on
    the originals. Small solace for me, however.

    I have more or less resolved to get new batteries. I'll probably go
    with Prevailers because, they seem to be able to take more abuse. I'll
    stick with the T-MAC and existing AC charger; use my wind generator as
    much as possible, and get a 20 watt solar array to make sure the
    batteries get at least some juice each day. Next year i'll probably pop
    for an a-h meter and regulator and a better AC charger. Maybe the year
    after, a 150a alternator. Who knows. The batteries are required now and
    i can adjust the T-MAC and Sentry for gell-cell levels, so i'll go with
    that.

re .22:

Be a little cautious about using Prevailers with a manual charging 
control such as the T-MAC and a standard regulator. Prevailers must not 
be charged at more than 14.1 volts or so (doing so voids the warranty).
Standard (non-adjustable) regulators are set at about 14.4 volts. It is
also rather easy in general to overcharge and damage batteries with a
manual control. 

Prevailers have a very low self-discharge rate -- a very few percent per 
month. I'd suggest spending the price of a small solar panel on an Ample 
Power adjustable regulator (about $170), a current shunt (about $50 
for a Cruising Equipment 1mV/A 300A shunt), and a good digital voltmeter 
(Fluke 73 or equivalent, under $75). With this you can build a good 
battery charging and monitoring system quite reasonably. 

We use a Fluke 73 to measure battery and alternator voltage (to 0.01 V),
two Cruising Equipment shunts (to measure alternator output current and
battery load current to 0.1 A), an older generation Ample Power
regulator, a diode isolator, and a 100 A alternator to charge/monitor
three Prevailer batteries. Works very well without any additional
charging sources such as solar panel or wind generator. It is also 
totally automatic and idiot-user proof. Another advantage of the Ample
Power regulator is that it reduces the charging voltage as the battery
temperature increases, a desirable feature to prevent battery damage in 
hot weather. 

I hope needless to say, but be sure that whatever holds your batteries 
in place is strong enough to keep them in place in rough weather and, 
very worst case, in a knockdown or capsize. The hold-downs that came 
with our boat were unbelieveably inadequate and were about the very first 
thing I changed on the boat.

Alan

re .22:

One more thought about Prevailers: They are expensive! An 8G4D (180 A-hr) 
Prevailer is about $400. Our 8G27 (85 A-hr) batteries are about $200
each. At these prices, installing an automatic, does-it-right charging
system makes considerable sense as it will maximize battery life and
minimize the chances of disaster. 

An 8G4D weighs about 135 lbs, while an 8G27 weighs only about 64 lbs. 
Something to consider when planning installation/removal and hold-downs.

Alan

The more I read in this string, the better I feel about the $59 marine battery
I purchased to replace the old diehard marine that lasted "only" 4 years.

--RS

    Although i'd love to upgrade the whole DC storage/charging system
    completely, i have to do it a few components at a time. I am aware of
    the different charging characteristics of gel cell batteries, and know
    i can't use gel cells if the charging settings of the AC charger or the
    regulater cannot be adjusted. One can adjust the kickout voltage of the
    t-MAC at which time it "turns over control" to the normal regulator
    which is not the OEM one, though i can't remember which one it is. The
    T-MAC is not fully automatic, but it will have to do for a season.

    The existing battery box is well designed and has a couple of stout
    tiedowns for the existing 8D batteries. Even the surveyer liked them.
    They are not acid proof though (although epoxied glass/wood), but
    that's another item that will have to wait.

    Defender '93 catalog prevailer group 8D is $349. I'll bet shiping is a
    bit extra though :-) The battery box is accessible, but moving
    anything that weighs more than 150lbs around is a pain. 

    I'm going to run a few more tests, but am not optimistic about the
    outcome.

    	Something worth considering if you have to buy anew battery. A few
    years ago I decided I needed at least one new battery, but I wasn't
    really excited about a battery price. At one point I decided that a
    battery distributer was probably a lot better source than ANY retail 
    outlet I could hope to find. I found 2 distributers in Worcester by 
    looking in the phone book and ended up with 2 blemmed group 24s for 
    50 bucks. Not exactly the battery scale were talking here, but I got my
    $50 worth, have had the batteries for three year. I want a at least one 
    new battery now, I stole one to run my truck over a year and it's been
    crankin through this very cold winter. 
    
    	The idea really paid off for me and since I live just outside of
    Worcester it was closer than any marine outlet, less Gouge Bros. 
    
    Geoff

I've been the expensive battery route twice with Surretts and never 
again! The delta increase in performance is just not worth the 
$$$$ for me. Think SAM's or BJ's!

Joe

re.28:

For batteries used with an OEM charging system, you are likely right. 
However, all the test data I've seen indicates that with proper
(re)charging and care, high-quality batteries do indeed have better
performance and longer life. See, for example, the discussion of
batteries in the 1994 West Marine master catalog. 

Much depends, too, I think on how one's batteries are used. If you keep 
your boat at a slip so that the batteries can be recharged using 
shorepower and you only daysail, then lower-quality batteries and an OEM 
charging system make sense. 

However, if you keep your boat on a mooring (as we do) and/or do 
extensive cruising away from shore power (as we do), then I think that 
high-quality batteries with an improved charging system would be 
preferable and even necessary. Fully recharging our batteries with the
original OEM alternator was basically impossible without many, many
hours of engine running. With our better system, nearly full recharging 
can be done with a reasonable engine running time.

Alan

    On our previous boat we used Sears Diehard's and would get 2-3 seasons
    out of them; more if I kept solar cells hooked up. We also have a wind
    generator that we kept for the new boat. We have stayed at a dock for
    about 10 days over the past 10 years, so you can see that our batteries
    get mistreated. Before the wind generator, we had to take the dam
    things ashore and charge them. AArrrgghhhh...

    With the new boat our plan is to end up with a top notch high quality
    DC system that can take occasional abuse. We will go for either
    Prevailers or Dynastys. Over the next 2 years we will get a monster
    alternator (currently at 90a) and charge indicator/regulator.

    I've noticed battery shops advertising deals on batteries. Has anyone
    tried any?

    I can't seem to find Dynastys in the catalogs. Anyone know who sells
    them?

    Any comments on Prevailers vs Dynasty? I've seen some in other, older
    notes, but i was wondering what real experience people had.

    tnx,
    paul

Re: .29

My boat has an OEM charging system but I charge the batteries via
a CVT  with shore power at the dock. Because the OME system is
inadequate, I use a gasoline generator when cruising. The
generator is located on deck and I run the power cord directly to
the vessel's AC input connection just as I would use shore power.
We use the boat every weekend in the summer plus for vacations
and the batteries take a lot of abuse. 

We have refrigeration on board and that causes  3+ hours of
generator run time  to replenish the battery charge. But note
that whether I had $500 batteries or $50 batteries, the run time
for the generator is the same.  I could reduce the time if I had
a larger charger but that's independent of the battery.  It comes
down to energy in verses energy out and battery life verses
battery cost. High output alternators reduce charging time but
because of efficiencies, it would still be over an hour of
charging for me if the alternator had a constant output of 70
amperes. Charging at 70 amperes has problems because the 
batteries and the alternator get HOT. Just no free lunch.

Incidentally, I am one of the first to cringe when I see another 
boat dropping  anchor near me with an on deck generator or for 
that matter, even an internal generator;  I have been next 
to boats that have ran internal generators all night and they are 
loud enough to disturb/prevent sleeping. 

I am tired of the noise so this is the year of the wind
generator. My design is complete and my first prototype is almost
ready to test with my $50 batteries. It should quietly take care
of all of my electrical power requirements. I will still carry a
gasoline generator but it will get little use. 

Joe

    Try Sam's in Westboro.  They have two types of 8D batteries.  Meant for
    farm use.  One is for starting the other is for electric log splitters
    and milking machines.  The prices are $88 for the starting and $90 for
    the other.  
    
    The biggest draw back is the name "Agri Boss".
    
    KC
    

    re. -2
    
    Could you please go further into your "design" for a wind generator ? 
    I am interested in a small wind generator as an option to keep my
    batteries topped up during the week but most things I have seen would
    be overkill.

As should be amply clear, battery charging is not nearly as simple as 
one might think.

Assume your battery bank is nearly completely discharged and you want to 
fully recharge it as quickly as possible without damage to the 
batteries.

The first requirement is that the charging voltage be limited to some 
safe value, usually 14.4 volts for flooded-cell (conventional) batteries
and 14.1 volts for gel-cell batteries. This requirement is easily met by 
the usual alternator voltage regulator or shore power battery charger.

The next requirement is to get as much charging current into the battery 
as possible. At any state of (dis)charge, a battery will accept only so
much charging current for a fixed charging voltage. This so-called
acceptance current depends on the type of battery, its amp-hr capacity,
and its internal construction. Gel batteries typically have a higher
acceptance current than conventional batteries. 

When charging (at a fixed voltage) a deeply discharged battery first
begins, one of two things happen. If the charging source can supply
enough current, the charging current will equal the battery's acceptance
current (as high as 40 to 50 amps for a group 27 size gel battery and
well over 100 amps for a large gel battery bank). If the charging source
can only supply less than the acceptance current, then the charging
current will be whatever the charging source can supply. Shore power
battery chargers can rarely if ever provide a charging current equal to
the acceptance current. From this it should be evident that a critical
requirement for rapid recharging is a charging source capable of
supplying a very large charging current. Supplying anything less than
acceptance current lengthens the recharging time. For example, our Ample
Power alternator is capable of supplying a bit more than 100 amps at
14.1 volts. This is enough to supply acceptance current for two of our
three batteries if they are deeply discharged. Yes, the alternator gets
hot, but it is designed to. And a proper alternator regulator (eg, Ample 
Power) senses battery temperature and reduces the charging voltage (and
hence charging current) enough to prevent damage. 

As the battery recharges, the acceptance current (at a fixed charging 
voltage) decreases, falling to, say, 5 to 20 amps. This current is 
easily supplied by an OEM alternator or a shore power charger. It might 
take an hour or more of charging for the current to fall this far 
(depending on alternator output, battery bank capacity, and how 
discharged the batteries were). In this phase, there is no added value 
to having a high-output alternator. 

After some more time (as much as hours), the charging current will fall 
to a low value, say a couple of amps. Now the charging can be done by a 
wind generator or large solar panel. The acceptance current for a 
fully-charged group 27 Prevailer battery is about 0.3 amp or less at
13.8 volts. 

The total amp-hrs that must go into the battery somewhat exceeds the 
total used (inefficiency and all that). If you use, say, 100 amp-hrs per 
day, you'll have to put at least that much back into the batteries. This 
much from only solar panels or a wind generator is unlikely. A big solar 
panel might provide maybe 10 to 20 amp-hrs on a sunny day and it would
take an unusually windy day (in New England) to get 100 amp-hours from a
wind generator. 

Our liveaboard friends (who use ice for refrigeration) had both a large 
solar panel and a small wind generator. These weren't quite enough to 
supply all their electrical needs. And the wind generator was noisier
than a small gasoline generator in winds over 10 to 15 knots. Other 
brands of wind generators may be quieter, but I'd be surprised if 
they're not somewhat noisy.

There are a couple of interesting consequences of having a large battery
bank rather than a small one. First, for any given daily usage, the
percentage discharge of the batteries will be lower, which will increase
battery life. Second, the acceptance current will be higher, which will
decrease total recharging time (assuming a high-output alternator or
other charger). 

Finally, battery life is again increased by using two or more charging 
voltages. Our older design Ample Power regulator initially charges at a 
high voltage (variable, we use 14.1 volts) to maximize the acceptance
current. After a while, the charging voltage is reduces to a lower value
(variable, we use 13.8 volts) to fully charge the batteries without 
damaging them if the charging continues indefinitely. (In hotter climates 
than New England these voltages should be reduced.)

    This discussion is really interesting.  Enough to go to the manuals and
    check what you've got.  In my case, I'm not sure.  My boat has an OEM
    alternator that is rated at 35amps (seems pretty low) and a factory
    installed Guest 2515 "charger/converter" that is rated at 15amp
    continously and 20amp "limited duty".  
    
    For batteries, I have two group 30 (I think) 70# beasts that are rated
    with a 195min reserve (25amps for 195min?).  They could also be group
    27 but I've never seen that size with 195min reverve rating. 
    Dimensionally they are 7.5"w x 13"l x about 10"h.
    
    The voltmeter typically shows 13.6v while charging them (they might be
    fully charged now as they are just installed and brand new).  When I
    turn on everything (especially cabin lights) the voltmeter (LCD readout
    from my NKE MFD chartable display) droops to about 12.6v.  Everything
    means 8amps for cabin lights, 2amps for nav lights, 1/4amp for
    instruments, "?" for stereo (could be a lot with four speakers by is
    probably less than 2amp at low volume and the rest for the batteries.  
    
    With charger off and no load, batteries show 12.3v.  With all the above
    up and running, this drops to 12.1v.   When I fire up the diesel
    (haven't done this since last October and then on the old battery) the
    voltage takes a big jump to 14.4v.  But that battery was somewhat
    discharged and has since found a new home in my buddies camper.
    
    It seems to me from this discussion, that I should focus first on
    upgrading the diesel alternator to 75 or 100amp unit (maybe more?). 
    The Yanmar 1GM10 is small but has more than I need to drive the boat. 
    Will a 100amp alternator represent much more load on the diesel than a
    35amp would?  Or is simple a matter of cost (why Yanmar put such a low
    power unit on)?
    
    None of the current shorepower chargers seem to have much more than
    15-20amp capacity so maybe not much needed here, with the possible
    exception of how smart is this Quest unit.
    

re .35:

Engine manufacturers use low-output alternators because they are less 
expensive than high-output alternators and because they are quite 
adequate for battery charging when the engine is run for a long time, eg 
as in a powerboat.

A high-output alternator does require considerable power to drive. As an 
example, 100 amps at 14.4 volts is 1440 watts, which is 1.93 hp. Add a 
bit for mechanical losses and the required drive power is maybe 2.5 hp. 
For a more typical alternator output the required drive power is 
probably 1 to 1.5 hp. V-belt life may be short, too. 

This drive power may or may not be significant. A small diesel uses
roughly 0.055 US gal/hp/hour of diesel fuel. If you know your fuel
consumption, you can estimate how much power your engine is producing to
move the boat, which in turn allows you to estimate how much power is
left to run accessories such as an alternator. 

The run-of-the-mill shore power battery chargers are set to a (too) low 
voltage to minimize the battery water consumption. The result is 
chronically undercharged batteries. The voltages you quote sound very 
much like undercharged batteries. The state of charge is not 
particularly related to the age of the batteries. A fully charged 
battery has a no-load voltage of about 12.8 to 13.0 volts (depending on 
type). Under load the voltage will drop maybe a quarter of a volt fairly 
quickly (again depending on the battery -- more for small batteries, 
less for large ones) and then decrease slowly.
    
Your battery voltage increasing to 14.4 volts with the engine running 
simply says that the alternator is charging the batteries at 14.4 volts 
and that the load current from the alternator is (most likely) less than 
the alternator rated output. This too is not related to battery age or 
condition. A battery with serious defects (eg, shorted cells) may look 
like it is charging normally.

Another bit of complication is that alternator output is rated (usually) 
by some SAE method, ie, the output with the alternator case at ambient 
temperature. Since rated output drops with increasing temperature, a 
more realistic rating is that for a case temperature of 200 deg F. A 
large battery bank with a large acceptance current can take enough 
current from a small alternator to destroy it. 

The best way to test a battery is to fully charge it (very difficult 
without a good shore power charger), wait a day, put a constant load on 
the battery (I use 3.0 amps because that is about our average load over 
a day when sailing), and measure how long it takes the battery voltage 
to fall to 10.5 volts. Amps times hours for a new battery should equal 
or exceed its rated amp-hr capacity. As the battery ages, the amp-hr 
capacity declines, rather drastically if the battery is mistreated or 
poorly made. Our used-two-summers Prevailer batteries appear to have a
capacity of 85% to 90% of rated capacity. 

    Thanks Alan for that last.....
    
    While I am underpropped (by a small ammount) I can reach hull speed
    with the Yanmar set at 3200rpm.  Full throttle yields 3700rpm and the
    Yanmar is rated at 3600rpm for 1hr or 3400rpm cont.  So I might have a
    couple (of h.p.) to spare.   My usage of engine to recharge would
    likely be under sail in any regard, with the sails to drive the boat.
    Fuel useage on a 1GM10 is very difficult to measure, it just doesnt use
    enough in typical usage to measure (in and out of harbor, etc.). 
    Although one time, I did use almost exactly 1/2 tank when making an
    11hr run upriver to haulout for damaged keel.  That was 4.5 gal or
    thereabouts so: 4.5gal divided by .055 = 81.8 divided by 11 (hrs) = 
    7.4hp.  Pretty close.
    
    If I understand your reply correctly, I might have endangered my
    current alternator by upgrading my battery capacity.  Especially if I
    allow one or both banks to become deeply discharged.  The answer would
    certainly be to go to 75amps (a 215% increase) or perhaps to 100amps. 
    How do the regulators that come with the alternators moniter battery 
    temperature (according to the ad they do anyway)? I don't know where
    the current (no pun intended) regulator is, guess I have to chase the
    alternator's output wire about to find it.  This just became a much
    higher priority in my 1994 work plan.
    
    I think you nailed the problem with the installed charger.  I've always
    wondered why not 12.8v (as in auto's for instance).  I think I'll call
    Quest and see if there is a way of adjusting the charging voltage
    upward internally.  I do not let the shore charger run while I'm away,
    but always run it when on board for work/tasks/etc.  So no danger of
    overcharging the banks dry.  Perhaps another year for a "modern"
    charger. 
                         

    I am not sure, Alan if your previous answers were aimed at my question
    in .33 or not.  My question though was more around the design of the
    wind generator itself Vs. the electrical system.
    
    For the majority of the sailing season, my boat sits patiently waiting
    for me to come to visit.  As she sits there, the batteries discharge
    and (given that I have a dynastart which is not a good charger in the
    first place) I am usually dealing with significantly discharged
    batteries.
    
    I fantasize about either a small wind generator or even a solar panel
    whose job it is to top up the batteries and balance out any discharge. 
    In this scenario, I would charge the batteries at the start of the
    season and would then hopefully keep enough charge to stay full except
    in times of heavy use (such as my annual vacation).
    
    Even with the present situation on a weekend, I am fine with power if
    I ensure that the batteries are topped up before I go, however leaving
    a charger in all week is not the solution.  Another solution would be
    to put in an alternator, however the dynastart takes up all of the
    space that I have and if I changed that, then I would need a starting
    motor as well.
    
    My electrical budget is pretty low, so I don't need ongoing amounts of
    power for operation, rather my need is the ongoing trickle charge
    during the week.

re .37:

In most (virually all) modern alternators, the regulator is internal or 
integral with the alternator and the output voltage is not adjustable. 
There is no separate wiring for the regulator.

The Ample Power regulator we have is a separate box from the alternator 
(I've mounted the regulator well away from the engine and its heat, in 
fact.) The temperature sensing is done by a component (probably a 
thermistor) attached to the positive battery terminal. The installation 
and wiring was quite time-consuming but not difficult.

It would be nice if alternator outputs were current-limited. In a sense 
they are -- as the load current rises, the output voltage drops, which 
reduces the battery acceptance current. I would suspect that a deeply 
discharged large battery bank could damage a small alternator from 
over-heating. Some of the more sophisticated non-OEM regulators do in fact 
provide an adjustable current limit so that they can be used with small 
OEM alternators with undue risk. 


re .38:

Hmmmmm. Prevailer batteries have a very low discharge rate, something
like 1% a month. Conventional batteries are somewhat higher, but still
only a few percent per month. Are you sure that there are no stray
currents from the battery? Dirt on the top of the battery can do it. Or
perhaps something is being left on that draws current. (Our shore power
battery charger draws about .007 amp from the battery when the charger
is off. That is over an amp-hr per week.) If your batteries are
significantly discharging, something may be wrong. Old and/or defective
batteries (the ones I've had) seemed to self-discharge quickly, or maybe
it was that they simply had no usable capacity left. 

The problem with wind generators is that they are (in general) not leave 
'em and forget 'em devices unless they have high wind over-speed 
controls. Such generators tend to be expensive. The one wind generator 
I've met was noisy enough that I would complain to the owner if it were 
near my boat. A small solar panel (eg, 10W) is about $160 US (wind 
generators are $500 and up) and should be enough to keep batteries
charged if they start at or near full charge. A 10W panel might provide
2 to 5 amp-hrs per day in clear weather (see Note 1514.63 if you want
gory details or the West Marine catalog if you don't). 

By dynastart do you mean one of those combined starter motor/generator 
devices? We had one on our first boat. Dreadful thing. If we'd kept that
boat another year I would have added an alternator no matter what. 

Alan

    Unfortunately that is what I mean ... I should replace it but space is
    the problem ..... I am pretty sure that there are no stray currents
    etc.
    
    One does need something to worry about though !

    After really (I mean really) digging into the wiring diagram supplied
    by Tartan and the West marine catalog and these last few replies, it is
    clear that a complete re-engineering job is in order.  Sad to say it
    will be outside my budget to even start.  There is no isolation, no
    regulator field protection, insufficient alternator capacity,
    insufficient charging voltage from the shore power charger and damn
    little useful of all the stuff on board (except the batteries).   
    
    The least I can do (and probably the first best step is to get the
    shore power charging up to snuff.  At least if the batteries start at
    100%, they will probably last until I can budget the complete rework
    this fall.  I don't want to install a $380 alternator with out
    protection, not too many models fit on a Yanmar anyway.  There is a
    a Balmar that will deliver 75amps @200deg @2400rpm (its or the engines?)
    and 115amp maximum.  That unit needs a regulator for another $134.00.
    
    Then there is the isolator or perhaps the West Marine Combiner. And
    finally the West Marine multi-stage 20amp two bank charger.  That unit
    will do all three stages and equilization for my flooded batteries.  
    
    All in all, a cool $1k.
    
    phew 

    I must pipe in here to defend wind generators as a viable source of
    battery food.

    Our Hamiltom Ferris WG produces from 70-120 amp-hours per day when we
    are at anchor at Cuttyhunk in typical Buzzards' Bay conditions.
    Sometimes less, sometimes more. Its noise level is comperable to wind
    in the rigging and has aout the same anoyance level as clanking
    halyards. Even though it was right over our bunk on our 26' Ariel, i
    was always able to sleep. Your mileage may differ. I much prefer it to
    the throb of an engine, and the thought of making ice cubes from wind
    is much more appealing to me than from diesel fuel. It can;t be left
    alone w/o both a regulator and governor. I'd like to try leaving the
    fridge on in place of a regulator, but if there were no wind for a
    while, it would kill the battery.

    In the tradewinds a wind generator like ours (or a Windbugger, etc)
    plus a 40+ watt panel would provide more than enough juice without ever
    running the motor. Our's peaks out at 15 amps in about 20kts of wind.
    Even at 15kts it produces about 8a. which is about 120 a-h/day. Add in
    15 a-h from the panel and you certainly have enough power for a fridge
    and other misc stuff.    

    A 20 watt solar panel will on the average product 7 a-h/day. That's
    about 35 a-h between weekend uses. If you didn;t fully charge the
    battery last Sunday (and you probably didn't), a solar panel will go a
    long way towards floating a battery that was only brought back to
    70-80% full charge. For the ~$250 cost i think it's a good investment,
    and your batteries will like you for it.

    Wind and sub do not replace the need for a high output alternator and
    matching regulator, but they are a quite valuable addition; and in my
    opinion increase the serenity coeficient by decreasing motoring, and by
    almost always having at least something going into the batteries.

    paul

    We just got six 6v 220amp hour golf-cart batteries direct from Trojan
    at only $57 each. These are seriously heavy-duty batteries, and six of
    them fit in the same space as two 8Ds, for 660 ah instead of only
    400ah.
    Including delivery, this only cost us about $370.

Re: .33

The wind generator that I have designed is capable of over 15 
amperes. It is an alternator with a state of the art neodymium-
iron-boron permanent magnet field. The unit is completely sealed 
to the weather and consists of stainless steel and aluminum for 
construction. Both ends of the rotating field are supported by 
sealed ball bearings. There are no slip rings to contend with 
except for the rings that are part of the mount design so that 
the unit can point to the wind without winding the power 
transmission line. The propeller is most likely going to be made 
from ash rather than spruce as is commonly found in other units. 
I have built several props to date and they have a diameter of 5 
feet. Note that an earlier reply by Alan claimed that wind 
generators are noisy; I don't know what machines he was 
listening to but there is one h--- of a difference between a wind 
generator and a gasoline powered generator that I was using up to 
this year.

I just ran a test on the unit the other night. I rotated the 
field on my lathe to 560 RPM and it outputted slightly over 9 
amperes at 14.5 volts or about 130 watts. There was too much slip 
in the flat belt used by my South Bend  lathe to turn it over at
higher RPM's but I will do this later on my drill press. 

There are many advantages to an alternator over a generator for 
wind mills. A generator has a commutator that is noisy (
electrical noise) that can affect AM radios and possibly, lorans. 
A generator also has high RPM problems; my design will have the 
RPM's limited by the propeller design. 

If you don't have refrigeration problems, maybe you should 
consider a solar charger. In any case, my unit will be mounted on 
the back of my boat Mary Ellen, and it can be seen this season in 
places like Cutty Hunk, Hadley's Harbor, Vineyard Haven and 
Nantucket. 

Joe

    If you'd like to share schematics or anything else, I'd love to
    duplicate your design to see how it would work on my boat.
    
    Do you need to worry much about those windless days that the alternator
    just sits there, happily chewing up 12 volts in it's windings or do you
    diode the the device in some way?
    
    Robert

Though my newly aquired boat does not have a large power demand, I do intend
to add a solar panel to act as a trickle charge during the week.  

I too am interested in the wind generator design -.2.  I think a similar design
including how to make the prop was in a CRUISING WORLD ARTICLE about a year 
ago.  COASTAL CRUISING may have been the location of the do it your self unit.
In any event I remeber is using a car alternator.  As per the rest of this 
discussion, not high enough rating, not resistant to enviorment (NaCL), not
high enough voltage etc, BUT the price would be hard to beat.

Other things that I have wondered about, what if you made a prop to turn slower,
and then geared into the alternater/generater.  Would this lower the wind noise?
What about to smaller props each driving  their own alternater?  CMOS
electronics draw far less than typical bettery leakage.  Smaller props = less
translational velocity at the blade tips = less noise.

Since I am most likely to try to use my engine to motor out and back into harbor
and then live with whatever wind exists, some form of secondary charging eg
solar is going to be need.

Doug
dtn 244 -7042

Please discuss wind generators in Note 2115. Thank you.

The Moderator

     A new battery technology enters the marketplace.   A small company
    here in Troy, Michigan has developed a new battery based on the metallic
    state of hydrogen.  Called a "metallic Hydride" battery, it is
    characterized by its ability to accept 60% of its capacity in a
    recharge of only 15min.  It is the first battery technology that makes
    the electric automobile feasible.  Much greater capacity (almost 100%
    greater) and unlimited cycles (yes it is supposed to outlast the auto
    in which is installed make this real exciting to General Motors who has
    invested heavily and is now going full speed ahead with its plans for
    electric powered autos.
    
    Expect very big bucks for one of these, but think of the advantages. 
    All you need is a 500amp alternator (which would take the entire output
    of my Yanmar at full throttle to deliver) and about 20 min time to get
    back to 100%, or have I got my numbers wrong again.
    
    

There is a 500 amp alternator on the market, i had the literature

this past summer, i believe it weighed about 50#. Forget how many

hp it needed to crank it.  cost was approx. 3K


JIm

    I imagine 500A alternator would suck up about 10 to 15 horsepower.

I had the spec's last summer for the wazoo alternator, for the money

i wasn't interested. I do remember a few things. One was the weight,

the other was a 3 belt pulley, also included was the rpm and output

at an rpm chart. Low rpm generated a fair amont of amps. 

I also thought 5 hp was required to push this beast, but it does

seem low.  In speaking with the co. they asked if i would be interested

in helping them develop a bracket for my engine, (none was available as 

yet) they would pay for the machining and give me the bracket, i declined.

There was more to this than just an alternator, also included was a 

"black box" and cabling.

JIm

    Let's see... 13.8V * 500A = 6900 Watts.
    
    1 Horsepower ~ 746 (?) Watts
    
    6900/746 = 9.25 H.P.
    
    THAT's with 100% mechanical to electrical efficiency (read
    superconducting alternator).
    
    I guess > 15 H.P., which would pretty well suck up my little Volvo!!
    
    	Electro_Boy

This estimate is based on a fairly crude set of assumptions.

Bear in mind, most are just pulled out of the thin air.

100% efficent. ie no power loss.

P(watts) = V(volts)*I(amps)

V(volts) from the battery = 16v

1hp(horse power) = 753W (watts)

I(max amps) = 500A (given)

Thus the horsepower consumption of this beast is at least:

P = VI
  = 16 v * 500 a
  = 8,000 w

hp = Watts
     ------
     753 watts/hp

   = 10.6 hp

Now of course there are all sorts of inefficentcies, these are probably at
least 40%.  This implies to get the full 500 A you need 14+ horse power.

To balance things out, you probably have to generate a fair amount of current
before you even approach the efficencies of a smaller alternator/generator.

Doug Claflin
dtn 244-7042

    Now that the efficiency is accounted for, where does the heat
    go? If this pig isn't water cooled, sure looks like a 
    potential thermal runaway condition when operated in a boat
    with no forced air cooling.
    
    Joe

Main places where efficiency is lost:

belt drive
bearings
diodes (huge, I presume!)
wires (500A continuous. Maybe these are buss bars, not "wires")
battery internal resistance (0.001 Ohms times 500A = .5V => 250W)
alternator internal resistance

Basically, if you have 80% efficiency, at 500A this puppy will provide
1200 watts of heat to your engine compartment and batteries, and that's
IN ADDITION to the heat your motor throws off when running at 15HP!

Good for those winter days. If you get one of these, add a 6KW resistance
heater, and warm up your boat FAST on those cold mornings.

--RS

    A while back I had stated that my vintage 1988 Guest chager was putting
    out about 13.2 volts and the batteries were only showing about 12.3
    under load for any length of time.  
    
    Contacting Guest to ask them if there was an adjustment to get this up
    to the 14.3 that my Yanmar puts out yielded some interesting
    information.  Seems that the Guest is supposed put out 13.9vdc.  With
    my NKE able to read voltage in digital fashion and the fact that both
    batteries are brand new and show equal charge conditions, the technical
    rep was able to deduce over the phone that only component would cause
    this to happen.  He said the large can electrolytic capacitor has
    degraded.  Apparently, the life of the beast is expected to be about
    seven years (1988-1994 is getting close) and that the effect would be
    lower RMS voltage from the bridge rectifier.
    
    He recommended that I change it, it is easy to do and a standard part
    that any electronics supply house would have.  Of course they would do
    it as well if I wanted to send the thing in with money.  
    
    BTW on launch day, I ran my diesel on #1 battery for about 4 hrs.  The
    chargin voltage was 14.3vdc and after the period was over my #1 battery
    would hold 13.6vdc under load.  Sound more like it?  Unfortunately, the
    #2 battery doesn't get any help when the selector is on #1.  ( I never
    knew that before.)  Given the paltry size of my alternator (35amp) this
    is probably good news.  Hooking both batterys in might just cook it.
    
    yet another interesting fact.  the crank pully on the Yanmar is 4.25in
    across.  the altenator pully is 3.75in across.  not much multiplying
    there.  prompts a question, if the battery selected can accept more
    current than the alternator can supply at the selected rpm, will the
    indicated voltage drop to the point that matches the given battery
    load?   ohms law stuff?
    
    i.e.: at 1200rpm, the alternator output is 15amps at 14.3vdc
    (hypothetical), but the battery can accept 30amps.  Will the voltage
    output of the alternator then be limited to whatever it takes to drive
    the available current (15A) into the battery?  If so, I could measure
    battery condition by slowly increasing rpm until I reach 14.3vdc and
    then taking into account at what rpm this occurs.
    
     

re -.1

You are correct:

If the alternator can't supply the needed current at the intended charging
voltage, the actual charging voltage will be lower. This is typical
charging behavior when initially charging a fully discharged battery.

--RS

    Re: .56
    
    I'm surprised that your alternator is capable of 15 amperes 
    @1200 rpm with the pully ratios you described. Most alternators
    require about 1600 rpms to begin charge.
    
    Joe

    Well, I don't know if it is putting out 15A, only that it is putting
    out 14.3vdc.  I never tried watching the voltage vs. rpm to see where
    the curve begins.  I'll try that tonight, before ripping apart my fuel
    system.  But West Marine does say that most alternators have a 2.5in or
    sonething like that sized pulley.  Mine definately looks to be almost
    as large as the drive pulley.
    
    Wonder why?  My Yanmar idles at about 700rpm and there is quite a bit
    more racket and vibration at that speed.  When advancing the throttle a 
    bit to 1200rpm things smooth out and get quieter.  So that is the rpm I
    usually use to charge batteries.
    
    
    the 

re .59:

The alternator voltage-rpm curve will depend on how (dis)charged the 
batteries are. The only way to know how much current is going into the 
battery is to measure it. Cruising Equipment (among others) sells 1 mV/A 
ammeter shunts, so if you have a voltmeter that reads to 1 or 0.1 mV, it 
is easy to measure alternator output current, current to/from a battery, 
etc. 

The shunts aren't all that expensive. Under $50 for the 200A max one, as 
I recall. 

Alan