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?

"Doug Dotson" wrote in message
...
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


Not quiet. Lets assume lead acid batteries and only engine charging.

Yes the 50% of discharge is a generally acceptable figure, but you are
unlikley to get them much above 80% of fully charged because we tend to use
automotive alternator regulator designs that are built down to a price and
not up to a duty (they do the job very well on a car).

This means that you can only reliably assume 30% of usable capacity. The
problem is that over the winter that 20% between 80% and 100% of fully
charged will sulphate, which further reduces the capacity of the battery.

To overcome this either charge with a mains charger that can charge to 100%
or fit an advanced regulator that may reach 98% of fully charged.

Tony Brooks


"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?

Hi Nigel,

it depends on the type of battery, you are using:

automotive batteries are made for short high current during starting, they
should not been discharged more than 60...80%. In your case 80 AH
discharging will be critical.

marine batteries are made for slow and long discharging and they should not
been discharged too much. Gel batteries should not been discharged more than
60 %, wet batteries not mote than 80 %.

Take a look at the voltage, if you have a digital meter: battery voltage
lower than 10.8 V will damage the battery (deep discharging).

regards

Juergen

"Nigel" schrieb im Newsbeitrag
...
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?

"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

Nigel wrote:

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?

batteries are USUALLY rated on a 10 hour cycle, so a brand new and fully
charged 100Ah battery with put out 10 A for 10 hours, a 60 Ah battery will
put out 6 A for 10 hours, and so on.

The vast majority of batteries, eg car / domestic type, eg NOT deep cycle
type as fitted to fork lifts and milk floats, will die VERY quickly if you
deep cycle them, losing as much as 5% of their total capacity every time
they are deep cycled, so a 2 year old 100 Ah battery that has not been deep
cycled but has been used for engine starting may only have 75 Ah capacity
left, given this I personally rate a 100 Ah battery as a 50 Ah battery to
take this into account.

Others are sure to disagree.
--
Liquid Cooled PC? -- http://www.surfbaud.co.uk/

E-mail (rot-13) qnirahyy NG oyhrlbaqre QBG pb QBG hx
EoF

On Wed, 16 Jun 2004 11:09:23 -0400, Guy Fawkes wrote:

Nigel wrote:

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?

batteries are USUALLY rated on a 10 hour cycle, so a brand new and fully
charged 100Ah battery with put out 10 A for 10 hours, a 60 Ah battery will
put out 6 A for 10 hours, and so on.

snip

Also worth mentioning that discharge at a higher current (ie over
shorter time) will produce less amphours - doubling current drain
might take 10percent off amphours. For this reason, batteries are
often quoted at 20 hour rate (C20).

Ian