Damage to a .8 amp Sla battery by overcharging

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kawa
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Damage to a .8 amp Sla battery by overcharging

I have a buisness application that I'm using a .8 amp Sla battery as the power source. The application operates a 12 volt motor and small receiver/transmitter. The standard 500Ma float charger will charge the battery up to 12.6v to 12.8v prox. This charge will only operate the system for about 1/2 the time I need.

For the proper "operating time" and "immediate power" requirements I need the beginning voltage of the .8 amp battery to start at a full 13.4 Volts prox.. When voltage drops below 11.5v the unit stops working and the battery is recharged to a full 13.4v prox..

In the summer this is done 2 to 3 times a week. During winter the system is idle.

My question is this.

In the long haul (expecting a 2 to 3 year battery life) will it damage a Sla Battery to charge it to a full 13.4v rather than the lower voltage (12.6 to 12.8v recommended)?

Many thanks

fisher727
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Re: Damage to a .8 amp Sla battery by overcharging

Your charger should float charge the battery to about 13.4 volts which will not hurt the battery. The 12.6 to 12.8 volt is to low and will reduce the life of the battery do to possible sulfation of the battery. These voltages I gave you are for a temperature of 77 degrees.

Eric Fisher
www.SiliconeBatteriesUSA.com

LinkOfHyrule
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Re: Damage to a .8 amp Sla battery by overcharging

I know an SLA is supposed to last many years (like 20 max) if kept fully charged and rarely deeply discharged. Float voltage is 2.25V/cell or 13.5V for that battery.

What are you using this for, anyway? For a tiny 10Wh battery, you might just try a LiFe if you can replace the charger.

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kawa
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Re: Damage to a .8 amp Sla battery by overcharging

Many thanks for the replies.

After your answers I did some more checking and have discovered the chargers I'm using in my kits may "float" the charging voltage @ 13.4 volts but upon the batteries cooling and resting the voltage settles to 12.9 to 13.1. Both brands are 500mah floating.

I can use a 1 amp unregulated charger to get the full 13.4v or higher (after settling), but I'm concerned about damaging the batteries. I also need to sell a charger with my unit that is "fool proof" so far as charging the SLA to a settled 13.4V or higher.

Would a 1A or 2A float charger raise the total (settled) voltage to say 13.4V or more after settling.

The SLA powers a small 12 volt water pump motor that runs for 2 to 4 seconds and then rests for 5 to 10 minutes. It is then started again. The motor is turned on and off by a "key fob" transmitter and mini receiver. The receiver and motor are powered by the same SLA battery. This unit is worn "on the body" so weight is very critical. I've tried a AA and a AAA battery pack which are actually slightly lighter than the .8A SLA battery. They also didn't have as much run time.

Being electronically challenged, all I can say is the running motor draws about 1.2 amps. When the receiver is connected it drops the battery voltage by 1.1V.

With real (no load at all) beginning voltage at 13.4 volts everything operates fine for as long as I need to i.e. 8 to 10 hours of operation and will pump 8 to 10 liters of water. Obviously the extra .3V to .5V beginning voltage is critical for my application.

What can I do to get a economical charger that will charge the 12V SLA battery to a real beginning voltage of 13.4V??

Thanks for the input!

LinkOfHyrule
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Re: Damage to a .8 amp Sla battery by overcharging

Unfortunately, that's the normal resting voltage for SLA batts. It's not chemically possible to get them any higher for any usable duration (save for it being really cold out), nor would that garner longer runtime. In fact, forcing them higher would damage them and lessen their capacity.

The only thing I can think of is a more advanced (or larger) battery. NiCD cells might be your best bet if they're charged relatively regularly (Ni-based chemistries are notorious for self-discharge). NiMHs offer more runtime and are smaller for a given amount of stored energy, but are a little more expensive (though that's not really an issue for a battery this small, I think?) and somewhat heavier. Either kind should get you significantly better runtime than the SLA, though. Not sure why the AA/AAA packs didn't work as well unless they were alkaline or very low-quality Ni cells.

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mf70
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Re: Damage to a .8 amp Sla battery by overcharging

To amplify, a battery's voltage depends on its chemistry. If you have an application that requires 13.4V minimum, any lead-acid chemistry battery will Not do it, unless the charger is attached and active, bringing it up to 13.4V.

All lead acid types (floodie, gel, SLA) have a fully charged resting voltage very close to 13.0. In order to get them to that point, a float charger will have to pump electrons in at 13.4V.

Other chemistries, such as LIon will have different resting voltages, as well as different charge requirements. LIon also will have the best energy density per pound (obviously, a LEAD-acid chemistry will not be very light!), which may make the trouble to set up the needed charge cycle worth the trouble. You may be able to find a computer laptop battery pack that matches your needs. (They tend to be surprisingly expensive, since they include a cell-by-cell battery management system in the pack.)

One other question: When you say .8 amp SLA, do you mean it's rated at .8A-HOUR capacity? That's pretty small! Most scoot batteries are about 18AH. (This means that they will supply .9A for 20 hours.)

Mark

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