Flemming Torp wrote:

"Larry" skrev i en meddelelse
...

The discharge-charge cycle is a ratio of 1:5. It takes 5 times as long
to CHARGE a lead acid battery as it does to DISCHARGE it. That ratio
hasn't changed in my lifetime. It's chemistry.....a slow chemical
reaction.

SNIP ...

Hi Larry, I've seen this rule of thumb before. But it cannot - in my
experience - be a valid general statement.

The 1:5 ratio has absolutely no meaning for cruisers. Its true that
the last 15% takes a long time to to charge, but this need not be done
on a daily basis. Over the range that most cruisers discharge and
charge, the charge rate, assuming a large source and quality
regulator, will at the 25% of capacity rate, tapering down to about
half that.

It is true that a 400 Ah bank that can accept 100 Amps in the "sweet
spot" can probably put out 500 Amps just before it melts something,
but this is of little concern.


Today, my battery bank consists of two 70Ah batteries + a start battery
of 60Ah. If I spend - let's say - eight hours at sea using my
instruments, chartploter and autopilot, and the cooling compressor
running for 24 hours, I will have used something like 70Ah i.e. roughly
50% af the capacity of the bank ...

I'd say you need more capacity if you want to stay out for extended
periods. I've found that 3 times the daily use is better, because
that allows you to cycle between 50% and 85% daily, with a run time of
about 90 minutes. More, of course, is better, ignoring cost, weight,
and space issues.

There is no easy way to do better than this, not counting wind and
solar. Each cruiser is in a different situation. I like to find a
nice harbor, and "squat" for a week or two, perhaps traveling a few
miles to the next island, so I'm faced with daily charging. More
solar panels (I have 150 Watts) would ease the situation - if I was
out full time I'd double or triple the solar, and add wind generation.

For some cruisers, running a genset for extended periods is an option,
but in many areas that I cruise that would be anti-social. I do,
however, carry a 2K Honda as backup so that a vacation isn't ruined by
mechanical problems. Also, boats that spend more time sailing then
hanging out can use a shaft driven alternator.



When I connect the land charger (in my case 220V) charging the 12V
batteries with 35A it does not take five times as long to "fill" the
battery bank back to close to 100% ...

Well, its a little hard to measure the last few percent. At what
point do you declare that it is now "fully charged" and you're now
just trickle charging to make up for self discharge?

It is true that chronic undercharging can be a problem, but that is
minimized if you fully charge the bank periodically, either on shore
power or with an extended motor sail.


What is the problem with the rule og thumb? Is there some kind of
"hidden assumption"? ... Or under what circumstances is the ratio 1:5
valid for charging the battery bank?

It might work well for submarines.


If I decide to increase the capacity of the bank to - say - 600Ah - will
I have to install a larger charger - i.e. giving more than 35A - in
order to give the batteries a full recharge - or is it just a matter of
time until the bank is "full" again?

It depends on your usage. I tend to go out for 1-3 weeks and never
plug in to shore power. Then the boat stays at the slip for a week,
so the charge rate is not a big issue. A 35 Amp charger would put
out the full 35 Amps for about 6 hours if I came in 50% charged, and
then spend several hours tapering off, so this would probably be big
enough even you wanted to travel the next day with a full battery.


I have decided to add an alternator
to my Volvo Penta 2002. It will give 60A. This one - in combination with
the existing alternator - the total charge current will be around 100+A
... with a bank of 600Ah, that should be no problem - right? I mean: No
harm to the batteries?

If you have a large bank and a large alternator, the quality of the
regulator, monitor, combiner (or equivalent), fuses and general wiring
become important. You'll spend as much, or more for these components
as for the alternator and batteries. With proper regulation, a large
alternator should effectively shut down as the bank gets charged.

A particular problem that you will have with this setup is that if you
use two regulators, one on each alternator, they will confuse each
other and there's a fair chance that only one will turn on. It is
possible to control them with one regulator, and there are special
devices to balance two engines, but you should consider this issue
carefully.

BTW, many small "stock alternators" (such as the Hitachi's on a
Yanmar) have an internal regulator and are "N-type," and those
designed for external regulators are usually P-type. While they can
be used together, you can't have a single regulator controlling both
types.

"Flemming Torp" fletopkanelbolle2rp.danmark wrote in news:45c0691b$0
:

When I connect the land charger (in my case 220V) charging the 12V
batteries with 35A it does not take five times as long to "fill" the
battery bank back to close to 100% ...

Are you measuring this "charge" with a hydrometer, or just watching the
charged light on the charger wink into the green? There's a big
difference. Lionheart only has a dual 10A Guest charger charging the
twin 330AH golf cart beasts that is our house bank. Charging is rated in
days, not hours, but that is great because the boat is not going back to
sea for a week or two, anyways. The slower you charge, the better. On
the way into the marina, the engine provides her an initial 80A charge
for 30-60 minutes after the sails come down, then the 10A AC charger
provides the very long finishing charge. 1.270 specific gravity happens
in a day or two, depending on how deeply it was discharged.

What is the problem with the rule og thumb? Is there some kind of
"hidden assumption"? ... Or under what circumstances is the ratio 1:5
valid for charging the battery bank?

The ratio isn't really so important, other than to point out that
charging should be MUCH slower than discharging. If you discharge it
quickly, you can recharge it quicker (if you have the capacity). This is
what your car does in a couple of miles after sucking 200A out of it for
10 seconds to crank its engine. Your car has a big alternator that can
recharge the starting battery very quickly, quite successfully. But, our
discussion here is charging house batteries that were SLOWLY discharged
over many, many hours powering light loads like boat electronics, some
lighting, the bilge pump cycling, not 200A for 10 seconds. The
recharging time to recover gravity to 1.270 is much longer because the
depth of the discharge into the lead plates is much deeper than a
cranking charge. Failure to complete the recharging results in sulfation
of the unrecovered lead. The ratio isn't cast in concrete, but I hope
this gives you the picture. If you discharge it slowly, you need to
recharge it slowly.


If I decide to increase the capacity of the bank to - say - 600Ah -
will
I have to install a larger charger - i.e. giving more than 35A - in
order to give the batteries a full recharge - or is it just a matter of
time until the bank is "full" again?

I'd say that more depends on your cruising condition. If you use the
house batteries daily, when you are at a marina, you'd want to have
enough charging capacity to recharge 300AH overnight. (Remember, you're
discharging to 50% of capacity, right, not dangerously fully discharged
which destroys lead acid batteries in short order.) With 35A on a 300AH
discharge, watch your ammeter to see how long the charger takes to reach
the finishing stage (when the voltage regulator takes over as battery
voltage rises to its setting around 14.2VDC). If that length of time is
acceptable to your cruising condition, I see no reason to waste money on
more charging capacity. If you sail to a marina and stay a few days, for
instance, before sailing on, normally, you'll fully recharge the 600AH
bank by tomorrow, safely, and she'll be ready-to-go when you are. 35A is
well within the safe initial charging current on a 600AH bank. It'll
hardly use any cell water and never threaten plate warpage, which I like.

It's just a matter of time to "full"....longer is better.


I have decided to add an alternator
to my Volvo Penta 2002. It will give 60A. This one - in combination
with
the existing alternator - the total charge current will be around 100+A
... with a bank of 600Ah, that should be no problem - right? I mean: No
harm to the batteries?


600AH should start an initial charge at 25%....150A + your running loads.
Your charging at 100A is quite safe for the initial charge. Do not be
alarmed, however, when, after a few minutes, the ammeter starts to drop
which always, for some reason I've never figured out, causes the "captain
alarm" to go off. When the current tapers, the battery is saying, "Hey,
I'm cutting back to a safer level as my plates already have a nice
surface charge on them which has used up the available ions in their
close electrolyte...which is what made the voltage rise at high charge
rates. Charging continues as ions move into position at plate surfaces
to be replated deeper into the plates.

The battery sets the charging rate....unless some complete idiot has
jacked up the foldover voltage above 14.5V, so proud of himself he can
recharge in an hour at full current and 16VDC...which I've seen many
times. At 16V, by the way, we are not charging any faster. We have used
up the available lead sulfate ions near the plates and are now converting
water into hydrogen and oxygen (lots of bubbling going on). Charging a
battery releases no gas, if done right, slowly. Overcharging a battery
gasses like mad as the water is consumed. Oh, if there are lead sulfate
ions available, they soon become lead OXIDE from all the available OXYGEN
from the gassing and heat generated by the overcharging. Hydrogen loves
hydrogen so becomes H2 gas. Oxygen loves METAL...ask any iron plate. It
would much rather combine with Lead ions as Lead Oxide than make Oxygen
gas. Any Lead Oxide created is lost. It's very stable and will form
crystals that precipitate to the bottom of the battery....unless it's not
a wetcell where they become a little current block in gelcells and AGMs.



With a 35A charger and 100A of engine charging, you have enough capacity
to easily run the boat and recharge quite quickly...probably as fast as
the batteries will allow at 14.2-14.4VDC...(c;

Use your hydrometer, temperature compensated of course, and watch the
charging curve for yourself. It's the ONLY way.

Larry
--
Democracy is when two wolves and a sheep vote on who's for dinner.
Liberty is when the sheep has his own gun.