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SLA battery charging voltage?

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CMOS

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What will be the side-effect if I charge 12V/7Ah SLA battery through unregulatd power supply which has 0-15V transformer, bridge rectifier and filter capacitor. There is also 10R/5W current limiting resistor in series with the battery.
And finally I have used a cut-off circuit to stop charging when battery voltage reaches 13.8V.

Now my question is will the battery get damaged because my unregulated DC charging voltage is 17V after rectification and filtering?
 

rauol

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8) Ya,
the battery life will be degraded. if you want maximum life limit the current to C/10 rate ant the maximum voltage to 13.8volt, and never deep discharge it.
with resistive limiting it is difficult to control current with wide voltage variation.
you can use some standard circuit designed using LM317.
 

meax98

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Wrong,wrong! To charge SLA (Sealed Lead Acid) battery you need constant voltage, not constant current. So, dont't care about C/10, all you need is regulated and constant voltage source.

best regards

meax98
 

Alexg

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meax98 said:
Wrong,wrong! To charge SLA (Sealed Lead Acid) battery you need constant voltage, not constant current. So, dont't care about C/10, all you need is regulated and constant voltage source.

best regards

meax98

WRONG...... The SLA batteries will not tolerate too fast charging.... You have to control current also or they will last much less time.... It is important to read the specs from the battery manufacturer.

Best regards,
Alexg
 

CMOS

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I've used 10 Ohm/5W current limiting resistor and I have observed that charging current does not exceed 300mA.

I'll try using LM338 voltage regulator.
 

Ante

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Hi Guys,

Constant current is good, but don’t forget to check which final voltage the manufacturer recommends. This is very important for the life span of the battery, to high voltage and it will dry out the cells through the vent valves.

Ante :roll:
 

flatulent

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One manufacturer specifies for fast charging to use 14.7V and to monitor the current. When the current is down to 1% of the initial value the battery is charged. They also specify an alternate method of using 13.8V which allows the charger to be permanently attached to the battery.

Slower charging methods will also work. The chargers sold by some battery manufacturers are 13.8V with current limiting to keep the charger from being damaged. These are advertised as being usable on all of their batteries no matter the rating.
 

CMOS

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So will the charger circuit published in JANUARY 2004 issue of Elektor Electronics work effeciently?
It uses constant voltage (12V), low current continuous charging method without any cut-off circuitry. The circuit is a part of "Burglar Alarm" project.
 

rauol

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8) Dear meax98,
the impedence of a battery is very low , when the battery is discharged and you try to charge it without a current limit it will draw heavy current and burn your charger etc.. Every manufacturer will specify the maximum charging current of the battery.
as a rule of thumb C/10 charge rate is advisable for small battery.

If a Float/Boost mode charger is used then the Initial charging voltage can be 14.5 Volt and after full charge a trickle charge can be maintained. this type of charging is recommended for higher capacity battery.
 

Ante

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CMOS,

Where can I find the circuit “published in JANUARY 2004 issue of Elektor Electronics” so I can have a look at it? I have no access to the magazine so I need a link or a site.
Thanks!

Ante :roll:
 

CMOS

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Ante said:
CMOS,

Where can I find the circuit “published in JANUARY 2004 issue of Elektor Electronics” so I can have a look at it? I have no access to the magazine so I need a link or a site.
Thanks!

Ante :roll:
I am sorry, it is not available for online viewing. You need to subscribe it. I'll try posting the power supply schematic as soon as possible.
Thanks.
 

T

tong

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gcellchg.gif


charger_sch_2.gif



These work well..
 

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