SLA = Sealed Lead Acid


Schematic of the charger

Schematic for the SLA Charger

 

 

Single Cell SLA Charger

This charger is only meant for single cells of the lead/acid variety.
It can be used for cells with a capacity of up to around 10Ah if R1 is changed accordingly. SLAs should be charged with a current of from 10% to 30% of their rated capacity (in Ah or mAh)

The circuit should never be left connected to a cell while the (mains) power is off, as this will drain the battery and could possibly damage the charger.
Wrong cell polarity will damage the charger.
These two issues could be solved by adding some bits 'n' bobs, but it is my understanding, that most people tends to go for the simpler/cheaper circuit, so I left that out.


Set the charging voltage, without a cell connected, for 2V35.

Charge only at or around room temperature (20-25C).

 

 

PCB Lay Out

PCB for the SLA Charger

 

Component Overlay

PCB overlay for the SLA Charger

 

How to heat sink

Mounting the Heat Sink

 




Bill of materials


R1

1R2 0.5W*

R2

220R

R3

150R

VR1

47R

C1

100nF

D1-D4

1N4001*

Q1

BC547B*

IC1

LM317T




* Notes
D1-D4 can be any diode capable of 1A+ and Q1 can be just about any small signal NPN transistor

R1 could be selected for other charge currents:


Charge

Cell Capacity

R1

Current mA

to charge (aH)

4R7

1/4W

130-150

380-1,500

3R9

1/4W

150-180

460-1,800

3R3

1/4W

180-210

550-2,100

2R7

1/4W

220-260

670-2,600

2R2

1/4W

270-320

820-3,200

1R8

1/3W

330-390

1,000-3,900

1R5

1/3W

400-470

1,200-4,700

1R2

1/2W

500-580

1,500-5,800

1R0

1/2W

600-700

1,800-7,000

0R82

1W

700-900

2,200-8,500

0R68

1W

900-1,000

2,600-10,300




2004-10-27, by Søren.