12V Battery Charger for Sealed Lead Acid

This battery charger is for 12V Seales Lead Acid (SLA) battery. It is actually a half-wave rectifier. It only charges the battery on every half cycle. The plug pack doesn't like this as it leaves residual flux in the core of the transformer and causes it to overheat.

There are a number of points we need to cover about the care and use of Sealed Lead Acid batteries.
Firstly, these batteries must be charged, discharged and stored very carefully.
We normally think batteries can be stored for months (if not years) and they will be available for immediate use.

This is not the case with SLA batteries.
If you store a NEW, full charged SLA battery for 6 months or more, you will find it may be fully discharged.
You may also find you cannot charge it!! It may be worthless.
That's how delicate SLA batteries are.

They must be charged on a regular basis to prevent them discharging to a very low voltage level.
If the terminal voltage of a SLA battery is allowed to go below 8v, a process called SULPHATION starts to cover the surface of the plates and prevents the battery being re-charged. The internal resistance of the battery increases and it becomes useless. See products Sealed Lead Acid Battery Charger on Amazon

Parts List of SLA Battery Charger

2 - 1R8 0.5watt resistors
1 - 150R 0.25 watt resistor
1 - 180R
1 - 560R
1 - 1k5
3 - 2k2
1 - 3k3
1 - 4k7
1 - 8k2
1 - 1k mini trim pot

1 - 1n ceramic
2 - 47u 25v electrolytics

1 - 5mm red LED

4 - 1N4148 signal diodes
1 - 10v 0.25watt zener
1 - BC 547 transistor
2 - BC557 transistors
1 - MCR100-6 SCR
1 - 1m red lead
1 - 1m black lead
2 - alligator clips
1 - 2m very fine solder

1 - SLA Battery Charger PCB

Also required:
1 - 12v AC transformer (500mA AC)
1 - power lead
1 - case

Available on Amazon Sealed Lead-Acid Battery Charger
Source : Battery Charger for 12v SLA (Sealed Lead-Acid) Batteries

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Lead-Acid Batteries Charger with Solar Panel

This Batteries Charger is intended for charging sealed lead-acid batteries with a solar panel in small and portable applications. The customary diode that prevents the battery from discharging through the solar panel has been replaced by a FET-comparator combination.

The batteries charger will stop charging once a pre-set voltage (temperature compensated) has been reached, and recommence charging when the voltage has dropped off sufficiently. The load is disconnected when the battery voltage drops below 11V and reconnected when it gets back to 12.5V.

Solar Batteries Charger Schematic

The batteries charger circuit has the following features:

• Charges until Vbat = 13.8V (adjustable), then float charges;
• Shuts down load when Vbat < 11V (adjustable), resets at 12.5V; 
• Temperature compensation; 
• Will work with cheap and readily available components like LM393 comparators and BUZ11 FETs; 
• Uses less than 0.5mA when using TLC393 comparators; 
• Burns less than 20mW in FETs when charging at 0,5A. (More expensive FETs with a lower RDSON will yield even better results). Note that the charging current is limited only by the solar panel used.

Solar Batteries Charger PCB

Note that I added three DC/DC-converters (for 9, 6 and 3V) on the PCB, the actual charger is less than half of the PCB. I don't have a silk screen, so if you want to build this, you'll have to figure out the PCB for yourself.

With all the components into place, some additional electronics to get the DC/DC-converters in and out of standby, two small SLA-batteries (2.2Ah each), some odd parts and wiring, a fuse, a front plate and housing.

A final word: you build everything at your own risk, no functionality is implied, the resulting apparatus might not work, be unfit for drying pet dogs, and contain small parts that could suffocate children when swallowed or inhaled.

Source: Solar charger for lead-acid batteries

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