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