"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.

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 ...

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% ...

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?

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 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?

--
Flemming Torp
Gimle - DEN61

PS - I have seen som statements as to the power consumption of adding
another or larger alternator.
Some Danish friends have helped me defining the exact formula:

If we charge with 14V and 60A, and the efficiency factor is - say 50% -
the formula will be the following:

((14V * 60A)/50%) / 746 W/HP = 2,25HP.

A rule of thumb is given from
http://www.balmar.net/Page46-faq.html :

"What horsepower load will I put on my engine with a new alternator?

Typically, when an alternator is working at full output, it will
require approximately one horsepower for every 25 amps it produces. As
such, a 100-amp high-output alternator will demand up to four horsepower
to operate."

In this case, the rule of thumb seems to be quite accurate ...