Battery Life

100AH is the estimate.

100AH is the nominal rated current

In theory this means that a fully charged battery can supply 100A for 1 hour, or 10A for 10 hours, or 5A for 20Hours.

In practice this is never be the case, on a continuous straight discharge the available current will drop below 100A towards the end of the hour.

A battery has no impedance because it is a pure DC source which is not affected by capacitance or inductance. It does have a DC resistance across the cells which varies according to the charge. The resistance is difficult to measure directly as most batteries will have some degree of charge and there will have a terminal voltage which opposes any voltage used to measure the resistance of the cell, unless the battery is totally and utterly discharged in which case the resistance at the terminals will be very low resulting in a high initial charging current. As the terminal voltage rises this opposes the charging voltage and restricts the amount and rate of charge.

Here's the way I understood it ...

100A/H means that the: Battery will supply, under the same load conditions, 100Amp. for one continues hour (or multiples thereof,) without a voltage drop of more than a certain %. (The % depends on Battery type and quality.)

Obviously, an internal voltage drop, caused by increasing of the battery internal Resistance ("R" And not "Z" as someone has wrongly indicated,) will cause drop in the amperage through the load circuit.

Wangito.

It is not at all difficult to measure the internal resistance of a battery!

Assume the battery is modeled by a pure DC voltage source in series with an unknown resistance -the battery's internal resistance. Measure the no-load voltage at the battery's terminals. Now, connect a known resistance to the battery and measure the terminal voltage again. It will be less, with the difference being due to the ratio of the internal and external resistances, which form a voltage divider. As you now know the voltage in the second case, and since you know the value of the external resistance, you can calculate the current through the external resistance, which is the same current as that flowing through the internal resistance. Knowing the current, the voltage in each case, and the value of the external resistance, you can calculate the value of the internal resistance. This value is the difference between the load and no-voltages, divided by the current.

And yes, this internal resistance will vary depending on the battery's charge level, age, temperature - and discharge rate! Batteries are non-linear little devils.

A minor detail: A battery does indeed have an impedance! That impedance is simply its internal resistance. The fact that we're dealing with a DC source does not ban the battery from consideration of having an impedance simply because the frequency is zero. By no means!

Some battery makers provide internal resistance in their spcs. And also I have read in some of docs on web, which states that we can go up to 1.3 times of that. By trending can we decide on approx life?

Also we get battery tester - Battery Tester HiTester 3554 from HIOKI.

http://www.hioki.co.jp/

And also how about connecting capacitor acorss battery bank in order to limit the current to increase the life.

Regards

If the battery manufacturer gives you a single value for the internal resistance, they're deceiving you. The internal resistance of a battery varies as the battery discharges. Not only that, it varies with temperature, the discharge rate, battery age, electrode geometry, and host of other factors. Better that they give you curves which plot internal resistance against different important parameters.

But beware of this kind of "specsmanship." If they give you one value for the internal resistance, call them on it.

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Guest #2 Re: 04/11/2007 5:50 PM

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100AH is the nominal rated current

In theory this means that a fully charged battery can supply 100A for 1 hour, or 10A for 10 hours, or 5A for 20Hours.

In practice this is never be the case, on a continuous straight discharge the available current will drop below 100A towards the end of the hour.

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A battery has no impedance because it is a pure DC source which is not affected by capacitance or inductance. It does have a DC resistance across the cells which varies according to the charge.

The resistance is difficult to measure directly as most batteries will have some degree of charge and there will have a terminal voltage which opposes any voltage used to measure the resistance of the cell, unless the battery is totally and utterly discharged in which case the resistance at the terminals will be very low resulting in a high initial charging current. As the terminal voltage rises this opposes the charging voltage and restricts the amount and rate of charge.

************** Quote Ends *************

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It is not the normal discharge current but the max value @ which it can be used for short periods & a good [new] battery should meet.

In battery testing, charging & discharging the values below are recommended:

Normal-Discharge: @ 1/10AH Amps = 10 hours

Quick-Discharge: @ 1/5AH Amps =5 hours

Normal Charge: @ 1/10AH Amps = 14 hours

Quick Charge: @ 1/5AH Amps = 7 hours

PS: Some types of batteries have the "Memory" effect which if not considered during starting at least 10 cycles of Discharge/Charge will not deliver more than the max current drawn in these 10 cycles.

Ni-Cd & Ni-Ion are the examples [you may have noticed the Warning on Laptop & Mobile-phone batteries]

Experts recommend it for all types.

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Every Elecrical/ electronic device has its internal Impedance denoteed by [Zo] or [ZIn], lower for larger units as the connections to different internal parts are made for a copromised value [you have to keep a max size, weight & cost]

This can be varified by disharging a battery @ 2 or 3 different values [1/10AH, 1/5AH & 1/3AH rates] and measure voltage across the load [just @ battery terminals] & you will get lower voltage across the load @ 1/3AH rate than 1/5AH rate and @1/5AH rate than @1/10AH rate.

this all due to voltage drop across the internal Zo of battery. It is normally jionts + connectors resistance, but due to aging [plates active material & area are decreased due to cyclic chemical actions]

Internal resistance of battery can be measured on the basi of "Max-Transfer-Theorom" which states that max energy can only be trasferred to the load if Zo of SOURCE [Supply] is equall to Zo of SINK [load means it should absob current indicated as Zo[source]= (-)Zin

Start to discharge a battery from minimum rate continuously increasing @ Controlled-variable load & observing Power-meter . A time will reach where Power will be minimum.

Battery Rin = V_terminal/Current

You can refer to this very useful site

http://www.mpoweruk.com/life.htm

Thanks for very useful site

http://www.mpoweruk.com/life.htm

Nic

There are so many variables, not the least being the type of battery (I assume it is some form of lead acid), standard car, leisure battery, sealed, gel etc etc etc.....

I would say that provided the charger does not overcharge ever, that the battery is never discharged beyound 12.6 volts, distilled water is replaced when levels drop (on a non gel, and non sealed battery of course), the battery is kept in a fairly steady good environment and you keep one of those small conditioner units permently attached, even a normal car battery will probably last 10 years or more....

If you were talking about its capacity, work with an aprox value of 60%, that is using a 100 AH battery, only plan for about 60% of that. Do not drain it down below 12.6 volts....that will extend its life considerably. Treat it well and it will last a long time.

You have right !

Of course I do, so would a lot of other people too, Lead acid batteries are a science that is well documented everywhere, especially on the internet. You just need to read all the infos that are available.

I have designed chargers for them as a hobby for some years now, nothing exotic, but my test battery is over 5 years old now with no signs of problems and gets used in our caravan everytime we are away somewhere.....

It started when the very simple charger in the caravan broke and the company wanted 75 pounds sterling for a transformer that should not have cost more than 15 pounds!!!

Scottish blood will not allow such spendthrift actions!!!!