I have just bought a couple of Delphi Freedom marine deep cycle batteries
for my service bank. Is there a recommended minimum voltage below which one
should not discharge? Also, if the nominal capacity is (say) 100Ah, is that
measured between standard voltages or is it measured from a nominal full
charge (with full charge voltage dependent on the charging system) until
totally discharged - ie 0v? Or is there a standard "never go below" voltage
which manufacturers use?

I have an intelligent battery charging system on my boat that charges up to
a threshold 14v with an asymptotically decreasing charging current, and a
battery controller with which I can set alarms to warn me of impending doom
on the discharge cycle. At what level should I set the alarm to get best use
out of my batteries?

On Sat, 20 Dec 2003 19:39:04 +0100, "Ric" wrote:

I have just bought a couple of Delphi Freedom marine deep cycle batteries
for my service bank. Is there a recommended minimum voltage below which one
should not discharge? Also, if the nominal capacity is (say) 100Ah, is that
measured between standard voltages or is it measured from a nominal full
charge (with full charge voltage dependent on the charging system) until
totally discharged - ie 0v? Or is there a standard "never go below" voltage
which manufacturers use?

10.5 volts is considered "fully discharged".

For best results, it is generally recommended that you should only
discharge a battery to 50%, so you should only take 50 AH from a 100
AH battery.




--
Peter Bennett, VE7CEI
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

Or to state it another way if you don't have an amp-hour
meter (which you should), 12.2 volts is a good lowest
voltage.

DOug
s/v Callista

"Peter Bennett" wrote in message
news.com...
On Sat, 20 Dec 2003 19:39:04 +0100, "Ric" wrote:

I have just bought a couple of Delphi Freedom marine deep cycle batteries
for my service bank. Is there a recommended minimum voltage below which
one
should not discharge? Also, if the nominal capacity is (say) 100Ah, is
that
measured between standard voltages or is it measured from a nominal full
charge (with full charge voltage dependent on the charging system) until
totally discharged - ie 0v? Or is there a standard "never go below"
voltage
which manufacturers use?

10.5 volts is considered "fully discharged".

For best results, it is generally recommended that you should only
discharge a battery to 50%, so you should only take 50 AH from a 100
AH battery.




--
Peter Bennett, VE7CEI
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

12.2 is rather high if the load is large. Also, different batteries have
different characteristics.

I use an Amp-Hour meter, but also watch the voltage. If my fridge is running -
a 30 Amp load - the Voltage can go to 11.9 even if the batteries are down only
25%. Anything lower than 11.8 is getting pretty low on most batteries.

The fully charged, no load Voltage is only of minor interest, since it isn't a
very reliable measure of anything. Once even a load is put on, it drop down to
about 12.6. If all you have is a Volt meter, its a bit difficult determining
what's really going on - too much depends the load and the recent history.


"Doug Dotson" wrote in message
...
Or to state it another way if you don't have an amp-hour
meter (which you should), 12.2 volts is a good lowest
voltage.

DOug
s/v Callista

"Peter Bennett" wrote in message
news.com...
On Sat, 20 Dec 2003 19:39:04 +0100, "Ric" wrote:

I have just bought a couple of Delphi Freedom marine deep cycle batteries
for my service bank. Is there a recommended minimum voltage below which
one
should not discharge? Also, if the nominal capacity is (say) 100Ah, is
that
measured between standard voltages or is it measured from a nominal full
charge (with full charge voltage dependent on the charging system) until
totally discharged - ie 0v? Or is there a standard "never go below"
voltage
which manufacturers use?

10.5 volts is considered "fully discharged".

For best results, it is generally recommended that you should only
discharge a battery to 50%, so you should only take 50 AH from a 100
AH battery.




--
Peter Bennett, VE7CEI
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

That's why I said you really should have an AH meter.
The 12.2V is a resting voltage which is the only way to
determine level of discharge by measuring voltage. Also,
the 12.2V is for liquid electrolyte batteries (obsolete
technology IMHO) but cheap in the short term.

Doug
s/v Callista

"Jeff Morris" wrote in message
...
12.2 is rather high if the load is large. Also, different batteries have
different characteristics.

I use an Amp-Hour meter, but also watch the voltage. If my fridge is
running -
a 30 Amp load - the Voltage can go to 11.9 even if the batteries are down
only
25%. Anything lower than 11.8 is getting pretty low on most batteries.

The fully charged, no load Voltage is only of minor interest, since it
isn't a
very reliable measure of anything. Once even a load is put on, it drop
down to
about 12.6. If all you have is a Volt meter, its a bit difficult
determining
what's really going on - too much depends the load and the recent history.


"Doug Dotson" wrote in message
...
Or to state it another way if you don't have an amp-hour
meter (which you should), 12.2 volts is a good lowest
voltage.

DOug
s/v Callista

"Peter Bennett" wrote in message
news.com...
On Sat, 20 Dec 2003 19:39:04 +0100, "Ric" wrote:

I have just bought a couple of Delphi Freedom marine deep cycle
batteries
for my service bank. Is there a recommended minimum voltage below
which
one
should not discharge? Also, if the nominal capacity is (say) 100Ah,
is
that
measured between standard voltages or is it measured from a nominal
full
charge (with full charge voltage dependent on the charging system)
until
totally discharged - ie 0v? Or is there a standard "never go below"
voltage
which manufacturers use?

10.5 volts is considered "fully discharged".

For best results, it is generally recommended that you should only
discharge a battery to 50%, so you should only take 50 AH from a 100
AH battery.




--
Peter Bennett, VE7CEI
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

"Jeff Morris" wrote in message ...
12.2 is rather high if the load is large. Also, different batteries have
different characteristics.

I use an Amp-Hour meter, but also watch the voltage. If my fridge is running -
a 30 Amp load - the Voltage can go to 11.9 even if the batteries are down only
25%. Anything lower than 11.8 is getting pretty low on most batteries.

The fully charged, no load Voltage is only of minor interest, since it isn't a
very reliable measure of anything. Once even a load is put on, it drop down to
about 12.6. If all you have is a Volt meter, its a bit difficult determining
what's really going on - too much depends the load and the recent history.


No load voltage is a good indicator, if you know how to use it. You
shouldn't read the voltage after charging without load and never with
a high load. With a small load (0.1 - 2 A, for 60 Ah) the no load
voltage is very constant and reliable. Fully charged will give 12,6x V
and 11.7 is very close to empty. You should not let this voltage drop
below 12 V, which is ~30% capacity. For reading the voltage you need
an accurate meter, since an error of 0.1 V is significant.

How can you accurately use an Ah-meter? How do you know what is the
starting point (after few hours loading capacity could be anywhere
between 70 and 100%)? How do you know how many Ah you battery can
really deliver? The real capasity depends on load and the rated
capasity is unlikely to be accurate.

Joakim

"Joakim Majander" wrote in message
m...

How can you accurately use an Ah-meter? How do you know what is the
starting point (after few hours loading capacity could be anywhere
between 70 and 100%)?

The smarter Ah meters detect when the battery is fully recharged, then reset
themselves to zero automatically. They also use the ratio of
Ah-out/Ah-recharge to give an indication of the state of your batteries and
charging system. If the percentage is low, you are having to put back in a
lot more Ah than you took out, meaning your batteries are old (alternatively
it could mean you have a bad charging system which is boiling your
batteries).

The Rolls-Royce of Ah counters is the Victron model which is very
sophisticated and expensive. I have one by Thira which automatically resets
itself and gives a charging coefficient which is all I need.

Joakim Majander" wrote in message


No load voltage is a good indicator, if you know how to use it. You
shouldn't read the voltage after charging without load and never with
a high load.

So its reliable except when charging or discharging. And for a while afterwards.

With a small load (0.1 - 2 A, for 60 Ah) the no load
voltage is very constant and reliable. Fully charged will give 12,6x V
and 11.7 is very close to empty. You should not let this voltage drop
below 12 V, which is ~30% capacity. For reading the voltage you need
an accurate meter, since an error of 0.1 V is significant.

How do you use a voltmeter when there's a solar panel charging at 6 Amps, or the fridge is drawing
25 Amps?


How can you accurately use an Ah-meter?

Been doing it for years. Just follow the instructions.

How do you know what is the
starting point (after few hours loading capacity could be anywhere
between 70 and 100%)?

Being on shore power for a day, or running the engine for several hours generally puts you at a
reliable starting point. After sitting at anchor for a week or so, running down to about 50% and
charging up to 85% daily, there is a certain drift. Mine will start too read a bit optimistic,
perhaps 2% a day. That's still a lot more reliable than a volt-meter alone, especially since it can
be used regardless of the load or charge rate.

How do you know how many Ah you battery can
really deliver?

By using the A-H meter, plus a volt meter (which every A-H meter has), and checking the cells for
specific gravity every month or so.


The real capasity depends on load and the rated
capasity is unlikely to be accurate.

So? Life is full of inaccuracies. If you use a battery the same way every day, the capacity is not
going to vary that much. A good A-H meter compensates for the differing discharge rate with
different loads.

Having had A-h meters on two boats over the last 12 years, I can attest the their reliable nature.
They work as advertised.

BTW, I currently have a dual AH meter, with one leg on the house bank, and the other on the fridge.
This gives me an accurate readout of the fridge usage. While traveling, I kept of daily log so I
could correlate with air tamp and sea temp. Usage varied between 60 Amp-Hours a day (Maine) and 110
(S FL) for a Crosby 1/2 hp holding plate system with separate fridge and freezer.

"Joakim Majander" wrote in message
m...
"Jeff Morris" wrote in message
...
No load voltage is a good indicator, if you know how to use it. You
shouldn't read the voltage after charging without load and never with
a high load. With a small load (0.1 - 2 A, for 60 Ah) the no load
voltage is very constant and reliable. Fully charged will give 12,6x V
and 11.7 is very close to empty. You should not let this voltage drop
below 12 V, which is ~30% capacity. For reading the voltage you need
an accurate meter, since an error of 0.1 V is significant.

You'll get good (and convenient) readings if you leave the battery rest for
20min to 1 hour before taking the voltage reading. By rest, I mean detach
the terminal so there's no charge and no discharge at all. See my yesterday
post. Your light load probably accounts for the small differences you quote
for various charging states. Or perhaps your battery lives in a hotter part
of the world!
--
Jim B, Yacht RAPAZ,
Sadly, for sale:
http://homepage.ntlworld.com/jim.bae...cification.htm
jim[dot]baerselman[at]ntlworld[dot]com

How can you accurately use an Ah-meter? How do you know what is the
starting point (after few hours loading capacity could be anywhere
between 70 and 100%)? How do you know how many Ah you battery can
really deliver? The real capasity depends on load and the rated
capasity is unlikely to be accurate.

Joakim

You initially charge up they batteries and set the starting point to zero.
Then all changing and discharging will be accurately accumulated. Battery
capacity is a spec given by the manufacturer or you can detrmine it
yourself if you have the patience. Capacity vs load is taken care of by
the use of Peukert's Equation which compensates for capacity vs
load. No, nothing is perfectly accurate, but it is way better than trying
top use voltage to determine level of charge. Technically, to get an
accurate reading you have to disconnect all loads and charging sources
and let the battery rest for 24 hours. Not really very practical.

Doug
s/v Callista