Conference unifix::sailing

There are, I think, many standard battery (physical) sizes. What goes 
into the battery varies tremendously. What you want is a marine deep 
cycle battery -- for two reasons standard automotive batteries will die 
a very early death in marine applications. First, they aren't physically 
strong enough to endure the vibration and shock loads encountered 
sailing in rough weather. Second, the plates won't survive more than a 
few deep discharges. 

Though seemingly simple devices, batteries and battery charging are
quite complex. The usual automotive-type alternator is a far from ideal 
battery charger. The more sophisticated systems (eg, Ample Power and 
Cruising Equipment) cost several hundred to a few thousand dollars, but 
they will keep batteries properly charged and extend their life from 
perhaps four years to as much as twenty years. The optimum discharge 
level is 50% of the battery's capacity.

One of the best marine batteries are Surrettes (available at Boat/US 
among other places). A 105 A-hr Surrette is about $100 (we have three). 
A 85 A-hr is also available. The readers of Practical Sailor weren't too 
happy (as I recall) with Sears Die-Hard marine batteries (the one I was 
given was died in infancy). 

    I am not familiar with your boat, or the complexity of the circuits
    on your boat, but the advice I got was this:
    
     I have very simple electrical needs - running lights, and a bilge
    pump. I intend to have a separate batery for each. I was told that
    the greater the number of amp-hours, the longer you can power these
    things (seems reasonable!).
    
     So given that, you buy the biggest amp-hour you can fit. 
    
     To determine the time it would take to drain the battery, measure
    the resistance in the circuit, using a Volt ohm meter, then calculate:
    
     		I = V / R where:
    
    I = the current in amps of your circuit,
    V = the voltage (12 volts)
    R = the measured resistance in the circuit
    
    If you calculate an I of 4, then a 100 amp-hour batery will
    (theoretically) run for 25 straight hours.
    
    
    			Gregg

re .2:

Yes, but ..... the Amp-Hr ratings of batteries are usually for an ending 
battery voltage of 10.6 volts (or thereabouts). At this voltage, the 
battery is essentially fully discharged and its voltage is so low that 
most electronics won't work. Moreover, most batteries won't withstand 
many complete discharges (perhaps fewer than 100) before failing. As a 
practical guideline, use about half the capacity of the battery before 
recharging. This will extend its life very significantly. 

    I'm curious about something.  All the descriptions of battery life
    I've seen suggest that battery storage has a bucket of water analogy:
    you "fill it" with so many amp-hours, and then you can "pour out"
    that many amps as you need them.
    
    My curiosity is that batteries don't always behave like that;  if
    your car battery is run, you can often wait a few minutes for it
    to 'recharge' slightly.  Or if you have a flashlight that's going
    dim, shutting it off for a few minutes can give you another few
    seconds worth of good light again when you turn it back on.
    
    Is this effect only significant when the battery is nearly discharged,
    or is the water analogy really only a first approximation to the
    real capacity of the battery, which might depend on frequency of
    use, temperature, amount of current drawn per time period, etc?
    
       - Jim
    

re -.1:

Batteries produce electricity via various chemical reactions. In a 
lead-acid battery the electolyte (sulfuric acid) reacts with the lead 
plates to produce electricity. As the battery discharges, the sulfuric 
acid is converted to lead sulfate (I think), and the specific gravity of
the electrolyte decreases. The chemical reaction occurs at the surface
of the plates, with the result that the acid near the plates is
consumed. Due to the construction of the battery, a significant time is
required for more acid to diffuse through the electrolyte to the plates. 
This is why removing the load from a battery for a time will appear to 
'recharge' the battery, at least somewhat. Maximum battery capacity is
achieved at low discharge rates (note the Amp-hr capacities are often
specified for a load that will discharge the battery in 20 hours). The 
best way to determine the state of charge is to measure the voltage of 
the battery. For a lead-acid battery, the voltage should be measured 
after there has been no load on the battery for 24 hours (which isn't 
always practical, of course). By the way, the current drawn by a diesel 
starter motor is typically 150 A for a small diesel. 15 minutes of 
cranking the engine could well appear to discharge the battery. But 
150 A times 0.25 hour is only 37.5 Amp-hrs, about one-third the capacity 
of a 105 Amp-hr battery. 

    So discharging marine batteries completely is bad for battery life.
    Is this true for all batteries? I have some of those cordless power
    tools, I don't recharge the battery until the thing stops working.

    George

    re .6 
    
    Don't know if that's true for all batteries.  "Gel"
    batteries are supposed to tolerate some pretty deep cycling.
    Anyone have any experience with them?  The only name I've
    heard of is "Dry Fit," (DriFit?) made in W.Germany.
    
    Pound for pound, gel batteries are supposed to have more power,
    better charge holding ability, better shock absorbing ability,
    better shelf life, longer service life, and better recovery from 
    deep discharge.  They are also maintenance free and sealed, allowing 
    you to mount them anywhere and in any position.  The biggest drawback 
    I've heard of is they require a special type of charger, but I'm not 
    at all certain about what that entails.

    The bucket of water analogy is a good first approximation - but
    it is non-linear as Alan mentions. If you want to get the rated
    number of amp-hours out (of a healthy battery) you must discharge
    it at the "standard" rate - something like capacity in amp hours
    / 10 or is it capacity / 20. If you discharge more slowly, you can
    get significantly more amp hours out before it is "flat". In a high
    current situation, (like starting) you will get much less than the
    capacity (in amp hours out) before it is flat. That is why the
    predominant rating for auto (starting) batteries is now cold-cranking
    amps rather than amp-hours, and why starting batterries have a 
    significantly different construction than deep-cycle batteries.
    
    Cordless power tools may be a horse of a different color. Many of
    the smaller tools use Ni-Cad batteries, which have significantly
    different characteristics than lead acis. Ni-Cads tend to remember
    how they have been used, and their capacity changes accordingly.
    Therefore it is good to cycle a Ni-Cad to near exhaustion and then
    fully charge it. If, however, you leave a Ni-Cad lying around in
    a discharged state, it may die (suffer cell polarity reversals)
    so be sure to recharge them immediately when they reach the rapid
    voltage drop exhibited at the end of their discharge curve.

>< Note 843.7 by DELNI::FACHON >
>                             -< Gel batteries... >-
>
>    Pound for pound, gel batteries are supposed to have more power,
>    better charge holding ability, better shock absorbing ability,
>    better shelf life, longer service life, and better recovery from 
>    deep discharge.  They are also maintenance free and sealed, allowing 
>    you to mount them anywhere and in any position.  The biggest drawback 
>    I've heard of is they require a special type of charger, but I'm not 
>    at all certain about what that entails.
>

    The only  problem  with  gel batteries is their cost. In the solar
    powered  car  race across Australia only one heavily sponsored car
    used  gel  batteries  (it  won  by  a huge margin). The other cars
    couldn't afford them.

    I don't know exactly how expensive they are. If you have to ask...

--David

    re .8 on Ni-Cads
    
    Strange things NiCads, with memories and all that - but it's true.
    However .....  you can kick old nicads back into life very simply
    by belting them with a reverse charge when they are apparently dead.
    I had this explained to me once - it was something to do with whiskers
    growing across the poles due to constant recharging, and the reverse
    charge broke the whisker and gave many more useable charges.  And
    if it didn't work, you'd lost nothing anyway ...
    
    Brian

re NiCad batteries:

Apparently the latest designs do not have the 'memory' problems of early 
designs. Recharging is recommended prior to complete discharge.

    I once saw the price-list for Dryfit gel batteries,
    and I was not particularly alarmed.  On the contrary,
    if they really do what the manufacturer claims, they're a bargain. 
    
    I'm not sure, but I think RigRite in Warwick, R.I.
    stocks them.  They should at least have price info, as 
    that's where I first saw the brochure on them.

    Dean

    Since I'm in the process of outfitting my boat for the Bermuda 1-2
    next year I decided to upgrade my batteries this year.  I had to
    consider the storage space available on my boat (I have three built
    in battery boxes), and the number of amp hours I'll use in a 24
    hour period.  I got some spec sheets from Surrette and called my
    local boat builder about specs on Rolls (new company by John Surrette)
    and found that I could fit some real high amp hour batteries in
    the existing boxes.  I spent a lot of time reading various books
    on the subject of batteries and alternators, talking to battery
    manufacturers and looking at the internals of deep cycle batteries
    at the boat show.  Adding up the opinions I decided to go with pairs
    of 6 volt batteries wired in series.  I have a total of 5 batteries
    on board, each fit in a space less than 7.5 x 11.5 inches (about
    13.5 inches tall).  Two pairs of two batteries are 225 amp hours
    each and the third bank is a single 12 volt starting battery.  I
    basically got the biggest battery I could fit in the space available
    and batteries that could be discharged to 50% of capacity and provide
    all the power I needed for 24 hours (I estimated high due to the
    possibility of 24 hours in a roaring gale with the autopilot groaning
    and eating up maximum power).  I decided that I'd rather not have
    to run the engine very often.  
    
    I also decided that i didn't want to run the engine very long, putting 
    back those little amps takes a long time and I still don't understand
    it entirely.  Some of the formulas used indicate that the alternator
    will put back about 85% of the total amp hours of the battery quickly.
    To get the remaining 15% can take a very long time and is a good
    job for dockside tickle charging.  I noted the following formula
    to determine size/amphours of batteries:
    
    #amp hours total * 85% * 50%  (where 50% is the amount the battery
    should be discharged before recharging)
    
    So, in one bank I have 225 amp hours * 85% * 50% = 95.6 amp hours.
    If my estimate for usage is 95.6 amps/day then I can switch banks
    on a daily basis and recharge the bank I'm not using (with the use
    of an isolator).
    
    Another formula uses 2/3 as the maximum continuous output current
    of an alternator.  2/3*x=95.6  Solving this gives me 143.4 amp
    alternator.  So, I bought a 9115 dual output Balmar Alternator with
    internal isolators.  I have one output going to my house batteries
    which consist of two banks of 225 amps each made up of dual 6 volt
    batteries, and the second output goes to my starting battery.  A
    factor that the Balmar person figured for me with tables I didn't
    have available was whether my engine could drive the alternator
    and still have power, if I had it in gear, to get through possible
    rough weather.  I lost track of the calculation which he went through
    over the phone, but he decided that my 22.5 hp Yanmar could drive
    that size alternator.  Time will tell as I only got it installed
    last weekend.  I bought the Balmar through Coast Navigation at an
    excellent price, if anyone is interested.
    
    Some other good to know facts is that a 100% charged battery at
    rest has a voltage of 12.63 volts.  a 50% discharged battery
    at rest has a voltage of 12.2 volts.
    
    The specific gravity of the batteries should be checked periodically
    1.265 is typical
    1.300 is fully charged
    1.100 is fully discharged
    1.000 is water
    These readings are at 77 degrees F.  add .001 for each 3 degress
    above 77F and subtract .001 for each 3 degrees below 77.
    
    Most of the above is from the 12Volt Doctor Handbook.

    People think I've really gone off the deep end and maybe I have
    but I can probably make it most of the way to Bermuda without even
    having to turn on the engine!!!!
    
    Oh yes, one last lesson I learned, don't charge your batteries unless
    they need it.  For the past four years I was afraid that I'd run
    my batteries dead so I was constantly running the engine to recharge
    them without even checking the voltage level.  That is a sure way
    of shortening the life of a good deep cycle battery.  I hope that
    I've learned enough to take care of my new very expensive batteries,
    because they can last many years when properly cared for.
    
    Pam
    

    
       FWIW, the Sears Catalog lists the rating of their Die-Hard and
    Enercell (?, you know, the sealed ones) batteries in Amp/Hours and
    Cold-Cranking Amps.
    
       So far I haven't had reason to replace the batteries on my boat
    (they're only 2 seasons old), however when the time comes I expect
    I'll do what I've done with my cars in the past -- go to Sears and
    buy the strongest battery they have that will fit the space. I've
    never had any problems with a Sears battery, so why break tradition?
    
    
    Frank
    

    Why break the tradition?  Because cold cranking ability doesn't
    mean a thing in most marine applications.  The ability to deep cycle
    and repeatedly recharge does.  A car battery won't last the season
    no matter how good it is.  It always surprises me how people will
    spend a lot on their boat and not on the batteries.  A dead battery
    takes a good percentage of the fun out of your day.  Buy a good
    marine battery and bypass the Diehard.
    
    Dave

    
    Re .15
    
       It appears you've made a number of assumptions about my note
    and my level of intelligence. You're wrong on both:
    
       First, while I indicated that I would purchase a Sears Die-Hard
    battery, I in no way indicated that it would be one of their better
    automotive batteries. You made that assumption. In fact, Sears
    sells a number of marine batteries under the Die-Hard label. Based
    on my past experiences with their automotive batteries, I would
    replace my current marine battery with a Sears marine battery. In
    addition, putting an automotive battery in my boat (and I imagine
    most other boats as well) would require changing all of the cable
    terminators (or using some sort of adapter) as the poles on the marine
    battery have wing-nut screws, whereas the automotive battery doesn't.
    
       Secondly, although this is the SAILING conference, not every
    one who reads this conference or writes to it owns a sailboat. You
    made that assumption. I own a power boat so the CCA ability of a
    battery certainly does play a deciding role in the battery I would
    choose. The engine oil recommended by the manufacturer is straight
    40 weight. This can be pretty thick in a cold engine, so the starter
    will need a good kick from the battery to turn the engine over.
    
       Finally, in my particular case, though I would use a marine battery
    as a replacement, an automotive battery probably would work well.
    When my boat is at its mooring, the only thing running is the bilge
    pump, and that only runs when it needs to. Thus the battery will
    only see a heavy load when I go out on weekends, and it will be
    recharged relatively quickly once the engine is spinning (there's
    an alternator on the boat, ya know). So, the service demands on
    my current batteries are similar to what an automotive battery
    would experience. (Last season, I was at a slip with the battery
    charger plugged in while I was away. So here again, with the trickle
    charge present, an automotive battery would certainly work well.)
    
       One last thing. While I'm always happen to listen to another
    person's advice, I don't appreciate the condescending tone which
    I sensed in your reply. This is supposed to be a friendly forum
    for exchange of information, so let's try to keep it that way.
    

    Frank
    

re .15 and .16:

Since this is a SAILING notes conference, .15 may be pardoned for 
assuming that .16 owns a sailboat (and .16 did not previously indicate 
otherwise). It might be helpful if everyone were a little more careful 
to indicate on what their advice, comments, etc, are based.

re .16: Sears Die-Hard batteries

I have not shared your good experiences. This and the unpleasant, rather 
arrogant service at many Sears stores have made me an ex-customer of 
Sears.

    Re: .15, my apologies.  Did not mean to offend.  True I did assume
    you had a sailboat which does indeed have far different requirements
    than, er, power vessels.  It was also easy to assume from the note
    that you did mean auto battery.  My less than stellar partner did
    just that.  You can jury rig them to work in marine applications.

    Dave

    I have two marine Diehards aboard; one is four years old the other
    two.  They have stayed aboard over the winter with the charger
    connected and are still going strong.  
    
    These replaced OEM marine battries one of which lasted 6 months
    the other 2 years.  The first failed at the same time as one bank
    of my charger.  I do not know which was the culprit.
    

    So what is the difference between the marine batteries and the auto
    batteries? Specifically how are they different in terms of there
    construction?
    
    
    George

    I installed 2 Sears deep cycle batteries on my last boat about 7-8
    years ago.  I was very pleased with both the price and performance.
    
    I am about to replace one of the batteries on my current boat. I
    have found quality batteries at much lower prices than Sear's this
    time around, and will go with the lower price.
    
    Walt

    
    Re .20
    
       Physically, from the outside the only difference is the connection
    poles. The automobile battery has either side-mount threaded poles
    or top-mount stub poles. The marine battery will have stub poles
    with wing-nuts for securing the cables.
    
        Internally, the plates for the battery - I believe - are made
    of the same material. However, from what I remember, the plates
    are coated differently. What happens in a battery is that as it
    is discharged the plates get covered with some sort of by-product
    caused by the chemical reaction. As this covering gets thicker, the
    battery loses its ability to provide its maximum amount of current.
    
       In a marine deep-cycle battery, the plates are initially coated
    with some sort of material that will inhibit the formation of the
    destructive coating, allowing the battery to be discharged to a
    greater level, more often.
    
       I know I just read something about the process that goes on inside
    the battery. If I remember, and can find it, I'll post it here.
    
    
    Frank
    

A recent entry in SAILING made the comment:

  And the second advantage [of automobile batteries] is: they are designed 
  to start an engine.

The implication of this statement is that deep-cycle marine batteries 
are not suitable for engine starting. I disagree. I think deep-cycle 
marine batteries are quite suitable for engine starting in the sailboats 
most of us can afford to own. 

Automotive batteries must be capable of supplying sufficient current to 
start an engine in very cold weather (eg, at least 0 deg F). As we all 
know, the current that a battery can supply decreases rapidly with 
decreasing temperature and the power required to turn an engine 
increases with decreasing temperature. Thus an automotive battery is 
designed to produce a large current even at low temperatures. Some of 
the design features that enable large currents to be drawn (eg, thin
plates) are features that are not desirable in deep-cycle batteries. 

A standard specification of batteries is cold-cranking amperes, ie, the 
number of amperes a battery can supply for 30 seconds at 0 deg F without 
the battery voltage falling below 7.2 volts. A typical 105 amp-hr 
conventional deep-cycle battery has a cold-cranking ampere (CCA) output 
of 530 amperes. A similar-sized Prevailer deep-cycle gel battery has a 
CCA output of 700 amperes. Both of these batteries will certainly supply 
more amperes at higher temperatures. (I've never had to start our diesel 
at a temperature below 40 deg F while sailing.) 

How much current does a starter motor draw? Most engine service manuals 
don't say, but it appears that (from a Ford heavy-duty truck manual and 
a VW Golf manual) the typical starter motor running current is 200 to 
300 amperes and that stall current is perhaps 500 amperes. These numbers
are for engines ranging from a 1600 cc diesel to a 9200 cc heavy-duty
truck gasoline engine. Thus is would seem that, at least at temperatures
above freezing, a deep-cycle battery would be more than capable of
starting a small marine diesel engine. In fact, we've been starting our
1600 cc diesel with only deep-cycle batteries for eleven years. If the
batteries are rather discharged, it has been necessary to use two in
parallel, but this would be true of automotive batteries as well.
Interestingly enough, by the way, the intermittant maximum current
rating (ie, for engine starting) of battery selector switches is in the
range of 325 (Cole Hersee) to 360 (Perko) amperes. 

While it is true that battery manufacturers would like us to buy 
expensive deep-cycle batteries, the fact that every published reference 
I have seen (including Practical Sailor) recommends against automotive 
batteries persuades me that deep-cycle batteries are the only ones to 
have on my boat. 

Of course, your opinions and choice may be different.

Alan

Hello Alan,

nice topic to disagree.(we could fill a RA90 with the different opinions).

In your previous reply the last sentence may have the key to this discussion.
In Europe,I have seen no push from the manufacturers,to sell deep cycle 
batteries.My boat was delivered from the yard with "normal" batteries.
And the size of the battery is given as well.We use over here a plastic box
(white bottom/red top)in two different sizes.A small one for car size batteries
and a larger one for delivery van sized batteries.This boxes are sold in
every yacht chandlery in Switzerland,Germany and UK. From Thomas Foulkes
catalog: Battery box with hold down strap 16 1/2" x 9" x 10" .1
My boat was delivered with this boxes installed.Installing larger batteries
would be a major undertaking.This boxes just fit in at the right place.

Regarding the cranking ability of deep cycle batteries.Over here,the few
deep cycle batteries on the market are advertised as "marine grade"
batteries with no further data.

Peter

(I'm alergic to 3000VA inverters, 150A alternators,computer controlled
battery charger with no temperatur sensor,no fuses-only resetable breakers,
marine electronic with no diode in serie ,IP65 yacht connectors...) 

Well, deep-cycle batteries are standard equipment in the US. (Good 100 
amp-hr ones are about $100.) Given what you said about the cost of
deep-cycle batteries in Europe, perhaps the reason your boat was
delivered with automotive batteries was cost-cutting by the
yard/builder. 

Those red/white plastic boxes are common here, too. The two that came on
our boat are gathering dust in our basement. They look so fragile I cannot
imagine them keeping a 70 pound battery in place in a rough sea. One to
the first things I did after taking delivery of our boat (then new) was
to build heavy plywood battery boxes that will keep the batteries in
place even if the boat goes upside down. Doing so was a semi-major 
project, but it is very nice not to worry about batteries coming loose. 
(One of the causes of the loss of a Nicholson 70 a couple of years ago
was inadequately secured batteries.) 

Alan

PS SAILING had better not fill up a RA90 -- I'd have trouble explaining 
to my management why I'm requesting yet another big disk drive! Let's 
limit it to an RA81, which still leaves room for much more discussion. 

    I musta missed something in this discussion - why would you need "deep
    cycle" type batteries for a powerboat?  Isn't the usage exactly like
    a car?  (Battery used to start and then alternator keeps it charged)?
    

Automotive batteries may well be acceptable for a powerboat, as long as 
you never use the batteries except when the engine is running. My 
powerboat friend has a huge deep-cycle battery to keep his fridge 
running when anchored out and smaller deep-cycle batteries for lights, 
stereo, etc. When the engine(s) is/are not running, the electrical 
needs are those of sailboat. 

A bit more on battery electrical capacity. Amp-hrs is the usual measure 
of how much energy is taken from a battery. Everyday experience shows 
that high load currents (eg, for a starter motor) discharge a battery 
more quickly than low currents. But how much more quickly?

(What follows is roughly from the 1991 Ample Power catalog.) 

About a hundred years ago someone named Peukert described a simple 
formula (not surprisingly called Peukert's Law) to quantify how much of 
a battery's capacity has been used. 

Simply, C = T * I**N

where C is the amp-hours used
      T is the time the load current is drawn
      I is the load current
and   N is a constant.

N depends on the internal construction of the battery and varies from 
battery to battery and during a battery's life. A typical value is 1.2.

It is interesting to look at the effect of N. For N=1.2:

    I     I**N      time to use 100 amp-hrs
 (amps)             (hours)

    1     1         100
    2     2.3        43.6
    5     6.9        14.5
   10    15.85        6.3
   20    36.41        2.7    (eg, large bilge pump)
  250   754.27        0.13   (eg, starter motor)

At a load of 250 amps this implies that a 100 amp-hr battery will be
discharged in about 8 minutes, which is about what I'd guess from those
unpleasant times when our engine refused to start. It also implies that
minimizing current drawn will maximize the time before the battery is 
discharged. It is claimed that once N is determined (by experiment) the 
formula is accurate to about 1% or less.