Hi:

I cant remember the rule of thumb for sizing an AC shore power charger
to the house bank size. Maybe 10% that is, 40 Ah charger for a 400 Ah
house bank????
Thanks,
Chris

wrote:

I cant remember the rule of thumb for sizing an AC shore power
charger
to the house bank size. Maybe 10% that is, 40 Ah charger for a 400
Ah
house bank????

A wet cell battery can accept an average of 15% of it's AH capacity as
a recharge rate over the charging cycle.

Thus, a 400AH bank will accept 60A recharge average over the recharge
cycle.

Lew

On Tue, 2 Oct 2007 13:37:52 -0700, "Lew Hodgett"
wrote:

Thus, a 400AH bank will accept 60A recharge average over the recharge
cycle.

That doesn't answer the question. Chargers are not rated by some
average [that is determained how? ], The rating is the maximum the
charger will put out.

Casady

On Tue, 2 Oct 2007 13:37:52 -0700, "Lew Hodgett"
wrote:

A wet cell battery can accept an average of 15% of it's AH capacity as
a recharge rate over the charging cycle.

Thus, a 400AH bank will accept 60A recharge average over the recharge
cycle.

Yes but it will accept 25% during the bulk charge phase which is where
most of the amp-hours are replaced.

I think it depends on how you use the boat and how you use the
batteries. If your only objective for the charger is to keep the
batteries topped up at dockside and supply house power, 30 to 40 amps
of charging capacity should be plenty. On the other hand, if you have
a generator and want to top the batteries up quickly while anchored or
underway, you need a charger that can put out 20 to 25% of your house
bank capacity.

On Oct 2, 1:37 pm, "Lew Hodgett" wrote:
wrote:

A wet cell battery can accept an average of 15% of it's AH capacity as
a recharge rate over the charging cycle.

Thus, a 400AH bank will accept 60A recharge average over the recharge
cycle.

Lew

Hi Lew:

Thanks for the info. I forgot to mention,, yes I have four wet cell 6v
T-105s.

Another question...... is there a minimum Ah charge rate for a 3 step
charger? That is if I increase my house bank up to 600-800 Ah would it
freak out a 30 amp charger if the bank was down to 30% of capacity??
Some where I heard the charger may sense the " emptyness" and consider
it a short......

Any truth to this or just more dock talk?

Chris

wrote

Thanks for the info. I forgot to mention,, yes I have four wet cell
6v
T-105s.

Another question...... is there a minimum Ah charge rate for a 3
step
charger? That is if I increase my house bank up to 600-800 Ah would
it
freak out a 30 amp charger if the bank was down to 30% of capacity??
Some where I heard the charger may sense the " emptyness" and
consider
it a short......

Basic rules of battery life straight from an old time Trojan
application engineer who had forgotten more about wet cell batteries
than the rest of us will ever learn.

T105s are happy when kept between 60%-65% and 90%.

For every AH hour you consume from a battery, you must replace it with
1.25AH.

A bank accepts recharge at an average of 15% of the AH capacity yes
the instantaneous can exceed 15%.

If you consume 100AH from your 400AH bank, you must replace it with
125AH at a 15% rate or about 60A which will require about 2 hours.

The above are the rules you live by with wet cells.

You can try all kinds of regulator hookus-pookus, but in the end, you
will live within the rules above.

Want to increase the time between recharge cycles or reduce recharge
time, increase the size of the battery bank.

A bigger bank with accept a higher recharge rate.

SFWIW, my boat is designed to have a house bank with 16, T105
batteries recharged from both solar and a Leece-Neville 4800.

As far as the regulator is concerned, it's only job it to control the
field current of the alternator which in turn controls the output of
the alternator.

Any decent regulator will have field current limit built into it to
protect both the regulator and the alternator.

I wouldn't sweat it if you have quality equipment.

Have fun.

Lew

wrote in news:1191352626.147744.9520
@o80g2000hse.googlegroups.com:

Hi:

I cant remember the rule of thumb for sizing an AC shore power
charger
to the house bank size. Maybe 10% that is, 40 Ah charger for a
400 Ah
house bank????
Thanks,
Chris



Yep...you can go as high as 25%, but that's a waste of money
becuase even if the batteries are down 60%, it won't drain at 10%
of AH for more than a few minutes because of REALITY. You cannot
charge lead acid batteries in minutes. You need 10-14 hours to
recharge them....er, ah...unless you're a yachtie who can
recharge them in minutes as if they were big capacitors!



Larry
--
Please - Turn OFF cruise control when
you turn on windshield wipers!

wrote in news:1191374548.703118.153360
@r29g2000hsg.googlegroups.com:

Thanks for the info. I forgot to mention,, yes I have four wet
cell 6v
T-105s.



Another consideration, Chris, is COOLING the charging batteries
noone likes to consider. Yachites like things really neat, so
put the batteries in this sealed up wooden box that acts just
like a hot box for the poor batteries charging.

Heat is generated the old fashioned way during the chemical
change:

Power = Volts X Amps.

If you're charging at 14V at 40A that equals over a half a
kilowatt of electric power that is converted into heat by the
charging process. You can imagine how hot this could get in a
hot engine room where some idiot put the batteries to hide them
which starts out at 130F. The batteries are already hot when you
start charging them.

If you keep shoving AMPS, AMPS, AMPS into them, not matter what,
trying to "Yachtie Charge" them in minutes, and leave them
charging like this as the temperature rises, you can warp the
plates, boil the electrolyte, etc., etc. It's not rocket science
to see this isn't good for the batteries in the neatly-painted
wooden box that has 3 holes drilled in the top of it for the
wires to come out. Proper battery installations are always
VENTED, to let BOTH heat and hydrogen gas escape. Your car has
its battery located so plenty of cooling air gets to it, for
instance.

Please consider this when buying more AMPS to shove into them.

Larry
--
Please - Turn OFF cruise control when
you turn on windshield wipers!

On Wed, 03 Oct 2007 03:51:38 +0000, Larry wrote:

If you're charging at 14V at 40A that equals over a half a
kilowatt of electric power that is converted into heat by the
charging process.

Not true.

Are you saying that all of the charging power is converted into heat?

What about the portion that is turned into chemical energy? Heat
represents *wasted* energy in the charging process and should be about
20% of the total, not 100%.

I know you swear by these recommendations, but they are somewhat
conservative in my experience.

BTW, these comments relate more to alternator charging than shore power.
For those that are on the move, shore power chargers should be sized
to give a complete charge overnight, since there is little benefit to
"filling up" in less time. A 40 Amp charger is fine for most, assuming
it has the appropriate smarts to handle special cases like equalizing
and float. Weekend warriors can get by with smaller chargers, but
trickle chargers might leave the bank chronically undercharged, which is
bad.

more comments interspersed ...


Basic rules of battery life straight from an old time Trojan
application engineer who had forgotten more about wet cell batteries
than the rest of us will ever learn.

T105s are happy when kept between 60%-65% and 90%.

This is true, but they should be fully charged whenever possible.


For every AH hour you consume from a battery, you must replace it with
1.25AH.

The Charge Efficiency Rating that Trojan advertises for their wet cells
is 89%. I use 87% on my AH meter, and it generally proves to be too
conservative, that is, after several days on the hook my batteries are
more charged than the meter says.

This is a complex issue, since high discharge rates will discharge the
battery faster, a thus make the CEF appear lower (Peukert's Law at
work). In practical terms, if the discharge rate is higher than 5% of
the capacity per hour (that is, if a 400 Ah bank uses more than 20 Amps)
you will notice this effect more. This is one advantage of the new DC
"constant cycle" or Danfoss fridges are over the traditional holding
plate systems. I often force my fridge (which draws up to 35 Amps) to
cycle while the engine or generator is running in order to avoid this issue.


A bank accepts recharge at an average of 15% of the AH capacity yes
the instantaneous can exceed 15%.

I have used a "smart regulator" for the 16 years on two boats. In both
cases the charge rate started at 25% and did the bulk of the charging at
around 20%. When it drops below 15%, I figure its diminishing returns
and stop charging.

Of course, this only gets then up to about 80-85%, and if you require
going to 90 or 95%, that will require long charging at lower rates. My
solution is to equalize after a trip that involved many "incomplete
recharges" so as to remove any sulphation before it hardens.

In practice this means that my 4 T105's (450 Ah when new) are accepting
85 to 90 Amps for a considerable period. Its actually higher than this,
because the Ah meter (Xantrex Link 2000R) is factoring in the 87% CEF so
the Amps out of the alternator are somewhat higher.

This summer, the regulator started acting up, so I swapped in the old
stock alternator with a built in "dumb" regulator. It ran much closer
to the numbers Lew mentions. Fortunately we were in Maine, so the load
from the fridge was greatly reduced; had it been in the tropics this
would have been a real annoyance.


If you consume 100AH from your 400AH bank, you must replace it with
125AH at a 15% rate or about 60A which will require about 2 hours.

The above are the rules you live by with wet cells.

Unless of course you get an assist from modern technology and reduce the
charge time to about 90 minutes. I'm not quoting from books, I'm using
my real experience over the last 16 years. Our normal summer routine is
to spend a week or more at each anchorage, relying mostly on engine and
occasional genset time to recharge daily. The batteries have been
mostly Trojan T105's which have lasted about 6 years.

....


Want to increase the time between recharge cycles or reduce recharge
time, increase the size of the battery bank.

absolutely true

A bigger bank with accept a higher recharge rate.

In addition, it suffers less at high discharge rates and probably
overheats less.