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

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?

A dead battery with 6 working cells will show over 12V with no load.
Voltage is not an indication of charge unless you have a standard
load, like the 50A "battery tester" used by mechanics to test
batteries and alternators. Mine cost $19 from Harbor Freight made by
Chinese slaves.

Lead-acid batteries' charge status is shown by a temperature
compensated specific gravity, usually a float inside a glass "baster"
with a thermometer to measure the electrolyte temperature and a
compensating graph to correct the reading on the float. Of course, in
our haste, we sealed up, or at least made it too inconvenient to
measure in most modern batteries. The specific gravity of a fully
charged lead-acid battery cell is 1.270 at 72F. As the battery is
discharged, the heavy acid is converted into lead sulphate as it eats
the plates. The acid is used up, we hope, before it eats
irreplaceable holes in the lead plates we cannot recharge. As the
acid is used up, the resistance of the electrolyte increases, causing
the voltage drop under load you see on your voltmeter. A "discharged"
battery is never discharged fully. If it were, the electrolyte would
be a near insulator preventing us from recharging it! We consider a
specific gravity of 1.150 at 72F to be "discharged" as far as is
prudent. You'll notice the voltmeter drops awful as you load a
battery in this condition, trying to pull electrons through this much
resistance, so you recharge it, IMMEDIATELY if you know what's good
for you and your battery. Lead acid batteries should NEVER be left in
a discharged condition. The lead sulphate in solution in the diluted
acid can be "charged" apart and redeposited on the lead plates
bringing us back to life. IF we let the lead sulphate sit, quietly,
without agitation, it CRYSTALIZES into lead sulphate solids, which
falls out of the solution into the bottom of the battery. This is
BAD. It's very stable this way and won't dissolve so we can charge
it, ever again. Because the acid was used up to create it, when you
charge the battery, there's little acid recovered and little metallic
lead deposited back on the plates. When the acid is mostly used up,
everyone says you have a "dead cell" which won't charge much, and we
trade in the battery for a new one. Recharging immediately reduces
this crystalizing to a minimum and your battery may last for many more
years.

The only real way to measure "charge" is with a hydrometer calibrated
to measure the specific gravity. Even the little float balls
hydrometer is better than a voltmeter as the voltage depends on load
current. By the time the voltmeter drops with no load, it's too late.

The best other way is with an ampere-hour meter you can buy at marine
stores like Waste Marine. It had a counter that multiplies amps times
hours as you charge the battery, then measures amps times hours when
you discharge the battery. It reads out directly in ampere-hours
remaining from the little computer inside or has lights to show E to
F. Of course, it says BOAT on it so the price is tripled, as usual.

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?

The less far you discharge lead acid batteries, the longer they will
last but the less power you get to use out of them before recharging.
It's a tradeoff. As the voltage measured is load dependent, it's very
hard to come up with a readable voltage as your load changes. If
there's no load on the discharged battery, it'll read 12.7V, even
though it's discharged as far as it should go. As you add load, this
voltage drops rapidly. So, the best way to judge is to watch the
voltmeter as the load is increased. You'll soon learn to judge when
it's dropping too far for comfort.

The other problem is the way the stupid voltmeters are
connected......at the panel on the other end of the wires carrying all
that current. The voltmeter DOESN'T measure the battery voltage. It
measures the voltage at the breaker panel its mounted in, which is
stupid. As the boat ages, its connections naturally become corroded.
Corroded terminals have increased resistance. When you pull current
through corroded terminals, the connections, ANY connections, cause
the voltage to drop back at the panel where the meter is....even
though the poor battery is fully charged! This worsens as time goes
by, so you think, from the reading, the battery is toast. When you
buy a new battery, the terminals all get cleaned so the voltmeter
problem goes away. You credit the new battery. I, on the other hand,
am standing at the battery boneyard with my 50A test load meter
picking up some real bargains (free!) before the salvors get
there....(c; Thanks!

The voltmeter should be connected by separate, small wires, directly
to the battery under test. Put a 1A fuse in series with the small
wires in case there's a short that would melt them and start a fire.
Without the load current going through the connections the meter is
reading from, you can read the battery voltage, not the panel voltage.
They do it their way because, as usual, it's CHEAP. It's called
"remote sensing" in the power management biz....

I like the "asymptotically decreasing charging current" charger. So
don't boat supply places! Boat is the only place I know where you can
buy a 10A charger for $200....OUCH! Another bad idea is a charger
that's TOO BIG, whether it's "asymptotically decreasing charging
current" or not! You should not charge a lead acid battery over about
25% of its capacity rating....i.e. 25A on a 100AH battery. Even that
is too much as it charges. Regular battery chargers, the cheap ones,
taper off the charge by simply running from a 15V power supply. As
the battery charges, it's voltage rises rapidly at specific gravity
about 1.250, so the battery voltage comes up to the charger's natural
voltage and the current drops a lot. But there's a real problem
charging lead-acid batteries....HEAT.

If I shove 50A through any device with 14V of voltage drop, battery or
load, heat is generated....50 X 14 = 700 watts! When the battery is
charging, from dead, notice how it doesn't get warm until the charge
is nearly full. The energy you're shoving in is being converted to a
chemical change, pulling lead sulphate apart into lead ions and
creating sulfuric acid by a reaction with the hydrogen in water. This
takes up the power. But, as it reaches full charge, we've converted
all the lead sulphates into lead and acid and there's nothing else to
convert, so the current ends up causing HEAT in the cells. If we kept
charging it at 50A, a constant current charger like you use to charge
NiCd or Ni-Metal Hydride batteries, 700 watts would MELT THE PLATES,
which are lead and soft anyways! That's why we want the charge to
taper off, not remain constant. If melting plates EVER touch, the
cell, of course, shorts and you get sprayed with acid in the ensuing
explosion! If you ever see a battery not properly encased explode in
a boat, you'll not soon forget what it does to EVERYTHING in the boat.

The best charger for lead acid batteries is the simply tapering
charger that has automatic shutoff from a voltage measuring circuit.
The charger turns off at 14.2V and back on again at 13.2-13.5V to
replace what you use. Car chargers aren't any good because they are
open to corrosion and flooding. A lot of the mumbo-jumbo in $600 boat
chargers is simply to justify charging $600 for a charger that costs
$60 to make. What I DON'T like about the fancy chargers is all the
NOISE they transmit at the dock to tear up the radios, cellphones,
stereo and TV. Lionheart has a dual 10A charger that just TEARS UP
the HF radio spectrum so bad our HF SSB is totally useless when it's
on. The old saturable reactor charger monsters, like the one my
captain gave me out of Lionheart, a 40A simple 3-step manual French
charger from Amel, makes no noise at all in my shop-stepvan...(c;

Well, hope this did you some good. We have dual 700AH banks of tall
golf cart batteries for house batteries on Lionheart. POWER is our
friend...(c;

Larry
Chief Engineer
S/V Lionheart
Charleston

Sitting under my ham radio & computer desk are 7 special cells in
series, giving me about 16 VDC when the float charger is off. They
are 900 AH "Edison" cells made of Nickel and Iron plates suspended in
Calcium Hydroxide, a base not acid. Ni-Fe cells, properly cared for,
last a lifetime as the reverse chemical process of charging them is
complete. The oldest cell, taken out of a very old Holiday Inn when
their antiquated manual-switchboard telephone system was replaced is
stamped July 8, 1936! The newest cell is 1948. This powers my
station in time of emergency, long enough to get the generators fired
up, even my computer's UPS. I've had them since the mid 1960s when an
old friend, long dead now, gave them to me. He was the Innkeeper, and
a ham.

Too bad we can't have Ni-Fe batteries any more. The nickel is BAD for
the environment as the battery companies that made them (Exide) just
dumped the electrolyte into the ground in many places, like Sumter,
SC, for instance, and the government busted 'em. Going from no load
to 100 amps, drops the stack's voltage about .8V if the terminals are
clean.....amazing power source from the turn-of-the-century.....(c;


Larry W4CSC

NNNN

"Ric" wrote in message
...
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?

snip

I'll assume at first that whenever you leave the battery idle it's fully
charged. Otherwise you're shortening its life through 'sulphation' -
hardening of the arteries as far as I'm concerned. I'll also assume you
don't use very high discharge currents (50a) for periods of time that would
cause the battery to overheat.

The life of your battery will then depend on how many, and how deep, your
discharge cycles are. Typically, you'll manage about 1000 cycles if you
discharge to 50% capacity. If you discharge to only 25%, you can expect
nearly four times the number of discharge cycles. Take it down to 75%
regularly and you'll only manage a few hundred cycles at best. These figures
vary a lot between different batteries depending on how they're built
(number of plates, support structures for the plates) but the pattern is
typical of deep cycle cells. Starter batteries are much more tolerant of
high amperages, but less tolerant of deep discharges (they have many more
plates and typically a less robust support frame).

Discharge percentage is most conveniently measured with an AH meter, though
if you allow the battery to rest with no loads or charges for an hour you'll
get a pretty good idea from voltage alone how far you've discharged. Varies
a bit with temperature, but 100% is typically 12.75v, 50% is 12.25v and 10%
(may you never see it!) is 11.75v. More precise is a hydrometer - not
convenient for frequent monitoring!

My vessel has a bigger battery capacity than I need (600AH), but I rarely
allow more than 25% discharge - 150AH a day. They were fitted in 1992, and
still work fine, though checking specific gravity against AH consumed shows
that they have probably lost about 20% of their capacity.

Hope that helps.
--
Jim B, Yacht RAPAZ,
Sadly, for sale:
http://homepage.ntlworld.com/jim.bae...cification.htm
jim[dot]baerselman[at]ntlworld[dot]com

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.

"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.