Stupid question time...
If I have a 100ah battery how much power can I expect to get out of it... is
100ah the total battery capacity or it's useable/available capacity. My
understanding is that a normal lead acid battery shouldn't be run too flat,
so when is flat too flat? If I should only let my battery drain down to say
a 90% charge, have I only got 10ah before I need to recharge?

"Nigel" wrote in message
...
Stupid question time...
If I have a 100ah battery how much power can I expect to get out of
it... is
100ah the total battery capacity or it's useable/available capacity.
My
understanding is that a normal lead acid battery shouldn't be run
too flat,
so when is flat too flat? If I should only let my battery drain down
to say
a 90% charge, have I only got 10ah before I need to recharge?

If it is a "leisure" or deep discharge battery, then conventional
wisdom is that it shouldn't drop below 50% of charge. This sort
of battery would normally be used for the "domestic" stuff on
your boat.

A "normal" or engine-starting battery is designed to give high
current for short periods of time, then be charged straight away,
so it is more difficult to give a value.

I don't suppose that has helped much.

--
Steve Brassett

100AH is its total capacity. Normal rule of thumb is to only
discharge it down to 50%. So, you have 50AH of useful
capacity.

Doug
s/v Callista

"Nigel" wrote in message
...
Stupid question time...
If I have a 100ah battery how much power can I expect to get out of it...
is
100ah the total battery capacity or it's useable/available capacity. My
understanding is that a normal lead acid battery shouldn't be run too
flat,
so when is flat too flat? If I should only let my battery drain down to
say
a 90% charge, have I only got 10ah before I need to recharge?

In article ,
says...
100AH is its total capacity. Normal rule of thumb is to only
discharge it down to 50%. So, you have 50AH of useful
capacity.

The advice for NiCad batteries for mobiles etc. is that it is good for
them to go through complete discharge-recharge cycles. Anyone able to
explain why lead/acid batteries are different - if indeed they are?

"Stefan" wrote in message
...
In article ,
says...
100AH is its total capacity. Normal rule of thumb is to only
discharge it down to 50%. So, you have 50AH of useful
capacity.

The advice for NiCad batteries for mobiles etc. is that it is good for
them to go through complete discharge-recharge cycles. Anyone able to
explain why lead/acid batteries are different - if indeed they are?

I think - and it is only think, that it is to do with how the plates are
constructed and move when they afre accepting or delivering high current
flows.

A lead acid battery has its plates made of a grid of lead latice upon which
lead oxide powder is compressed, a bit like plastering a wall.

When high currents are passed the plates actuall flex, the higher the
current the greater the flex. Domestic batteries tend to have thick plates
to give capacity, this means that when they flex the outer particles of the
oxide are compressed or streached so tend to fall off. When they build up in
the bottom of the cell and short a pos. & neg. plate the battery has failed.

The flatter the battery the higher the charging current it will accept for
any given charging voltage, so the more teh plates flex and the more they
shed oxide.

This explanation does for me, although there may be chemical one as well.
This also explains why tubular plates (being curved so resisting flexing)
tend to have a longer life than "normal" flat plate batteries.

Tony Brooks

NiCads develop a memory over time and can't be fully recharged unless
they are fully discharged occasionally. Lead acid batteries don't
develop a memory but do start to shed lead from the plates when they get
very low.

As a practical matter you really can't get more than about 35-40% of a
wet cell's capacity out of a normal cycle while cruising. They should
not be discharged more than 50 to 60% and when recharging that last
10-15% takes a long time. Up to about 80% you can safely push 25% of
the capacity per hour back in but above that the rate of charge drops
quickly.

Stefan wrote:
In article ,
says...

100AH is its total capacity. Normal rule of thumb is to only
discharge it down to 50%. So, you have 50AH of useful
capacity.


The advice for NiCad batteries for mobiles etc. is that it is good for
them to go through complete discharge-recharge cycles. Anyone able to
explain why lead/acid batteries are different - if indeed they are?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

On Wed, 16 Jun 2004 10:34:33 -0400, Glenn Ashmore
wrote:

NiCads develop a memory over time and can't be fully recharged unless
they are fully discharged occasionally.

This is (almost) a myth. The Ni-Cad memory phenomenon
does exist, but I can almost promise that no-one
reading this has ever experienced it. It requires
that the partial discharge/charge cycle be repeated
*****EXACTLY***** many, many times. It was discovered
in a satellite (and eventually duplicated) where the
battery discharged for a precise length of time into
a precise load, and then was recharged for a precise
length of time at a precise rate. When the program
of the satellite was changed later, it was found that
the battery could not continue providing power after
passing the previous discharge point.

It simply won't happen just because you don't run
a Ni-Cad down to zero before recharging it. In
fact if you DO run it to zero, there is a very good
chance that (because of slight differences in cell
capacity) that you will reverse-charge one or more
of the cells, which WILL ruin that cell quickly.
Better to get it onto the recharger as soon as
you experience a significant drop in output
under load. At the point where your battery drill
stalls at no load or very light load, you may well
be pumping up one of the cells backwards as the
other cells push the last few electrons through
the load.

The commonest way to damage Ni-cads, however, is to
leave them on the charger too long, or to charge
them too fast at some point in the recharge cycle.
Every time this happens, the battery will lose
some of it's capacity.

"Peter W. Meek" wrote in message
...
On Wed, 16 Jun 2004 10:34:33 -0400, Glenn Ashmore
wrote:

NiCads develop a memory over time and can't be fully recharged unless
they are fully discharged occasionally.

This is (almost) a myth. The Ni-Cad memory phenomenon
does exist, but I can almost promise that no-one
reading this has ever experienced it. It requires
that the partial discharge/charge cycle be repeated
*****EXACTLY***** many, many times. It was discovered
in a satellite (and eventually duplicated) where the
battery discharged for a precise length of time into
a precise load, and then was recharged for a precise


I Beg to differ with you.
I have on occasions, and know friends who have damaged
Ni-Cad batteries. They were damaged by partial depletion
then recharging. They were in sealed waterproof torches
and over a period of time the batteries were damaged by
that method of charging. I now always run my batteries from
full to empty no mater what type.
taz.

"Peter W. Meek" wrote in message
...
On Wed, 16 Jun 2004 10:34:33 -0400, Glenn Ashmore
wrote:

NiCads develop a memory over time and can't be fully recharged unless
they are fully discharged occasionally.

This is (almost) a myth. The Ni-Cad memory phenomenon
does exist, but I can almost promise that no-one
reading this has ever experienced it.

I am sorry but you are not entirly correct.

Proven many many times and easy to repeat.
Take two brand new and identical radio controlled racing cars.
FULLY charge and discharge the nicads of one of the cars ten times.
Randomly and gently cycle the nicads of the other car ten times.
Race the cars.

Fully charged/discharged car WILL win.
Not only will the car win a short sprint race... It will also win an
endurance race.

In message , Stefan
writes
In article ,
says...
100AH is its total capacity. Normal rule of thumb is to only
discharge it down to 50%. So, you have 50AH of useful
capacity.

The advice for NiCad batteries for mobiles etc. is that it is good for
them to go through complete discharge-recharge cycles.

Only applies where a critical cut-off voltage is involved for the
equipment. Otherwise "memory" is an urban myth

Anyone able to
explain why lead/acid batteries are different - if indeed they are?

Tend to have steeper discharge curves and be used in non voltage
critical applications

--
Keith Lewis