LEAD ACID BATTERY

It looks as though these batteries are good for at least

12 AH in the current range you're looking at:

The discharge rate curves show them staying above 6.0V for over 12 hours at a discharge rate of 650mA.

So you should be okay.

--- The capacity of most lead acid batteries is defined by how long they can deliver current into a load, at a particular rate, until the voltage across the battery terminals falls to a particular value, usually about 5.25V for a 6V battery.

the battery you've chosen has a capacity of 13 ampere hours at a 20 hour rate, which means that if you start off with a freshly charged battery, the voltage across the battery's terminals will fall to about 5.25V in 20 hours if you discharge the battery at 13 AH/20H =

0.65A.

Since you have six batteries in series, that corresponds to 31.5V, and since you're using the center tap of the string as common, you can expect that the voltages on the ends will decay to 15.75V after

20 hours.

Since I don't have the discharge curves for the batteries in front of me, I can't say what the battery voltage will be after 12 hours of discharge, but I'd guess that you're cutting it kind of thin.

-- John Fields Professional Circuit Designer

Why dont you use 2 12 volt batteries, or rather 4 12 instead of 6 6volt. Then use regulators to set your output to 18 + & -. If then your batt volts drop a little, you still have some to spare. Would be cheaper that way also. Use the ldo still regulator or low power switching regulators to improve efficiancy. Jim..

Hi,

The charts for the battery is available at the following website

Please advice!

John

You'd have to either ask the battery manufacturer for their discharge curves, or get one and try it with a 700 mA load - about 8.5V ohms, at least 10 watts, a meter, and a clock. :-)

Good Luck! Rich

You won't have much fun with lead batteries, if you repeatedly discharge them all the way down. Even if you choose deep cycle or gel cells. If you have to depend on this kind of cheap technology, choose them to have at least double the capacity needed, so you discharge never more than 50%. Then you also don't need to worry about the voltage drop. Well maintained they will then last for 10yrs instead of 10 months. The charger will be another challenge for you, I doubt you will find one for

36V. So you have to take them apart each time and charge them in parallel or better one at a time, because otherwise you won't get them full. If you have 50% left, this will take 7h each, so you can set your alarm clock every night. :-( Ian suggested the right thing, take a single 12V battery with sufficient capacity(60-70Ah) and operate a switching dual supply from that.

--
ciao Ban
Apricale, Italy

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-- John Fields Professional Circuit Designer