VK2ATZ Lead-Acid Battery De-sulfator

SCHEMATIC DIAGRAM and OPERATION

This circuit shown at below is essentially a switching DC-to-DC converter that steps a DC voltage up to a higher level. It takes power from the battery and pulses it back into the battery. The pulse rate is set by the 555 timer chip,U1 which switches the MOSFET at a 1 kHz rate. When Q1 is in the non-conducting state, current is drawn from the battery through L2 so it charges capacitor C4 slowly. Q1 is then switched on for 50 microseconds, causing C4 to discharge through L1. When Q1 is switched off again, the stored inductive energy in L1 pulses back into the battery through diode D1.
This pulse of current can be as high as 6 amps. The use of an inductor to supply this high voltage pulse is what makes it possible to restore a badly sulfated battery with a high internal resistance. The peak voltage applied across the battery can be as high as 50 volts. This voltage will decrease as the battery’s internal resistance declines or it’s function is restored to normal.

NOTES
There is no reverse polarity protection for this circuit so label the leads well. Connect them backwards and you will blow components. Connect positive of the pulse charger to positive of the battery!
There is an issue with electrical equipment connected across the battery; lights, radio, etc. Depending on the impedance of this equipment, it may absorb some of the pulse energy, thereby minimizing the effect on the battery. To solve this problem, slip a ferrite toroid core over each positive battery lead (right at the battery) going to the other equipment.
Exclude the pulse charger lead. The ferrite core will increase the high frequency resistance without affecting the DC performance of the circuitry. Hence all the pulse energy will enter the battery and not be consumed by the electrical loads connected to it.

Keep the lead length from the pulse charger to the battery as short as possible to minimize RF radiation and power loss in the wires. A faint audio tone might be heard when the circuit is in operation.
Pulse energy happens at less than 100% efficiency. The circuit draws about 40 MA from the battery so some additional charging must be applied to offset this. A solar panel would be perfect.

Parts List:

Q1 IRF9540 P channel MOSFET
IC1 LM555CN Timer IC
D1 FR607 Fast recovery diode, >6 A, 100 V
C1 30 ?F, 16 V Electrolytic
C2 0.0022 ?F Disk ceramic
C3 0.047 ?F Disk ceramic
C4 100 ?F, 16 V Electrolytic, low impedance type
R1 470 k. 1/4 W
R2 22 k. 1/4 W
R3 330 . 1/4 W
R4 330 . 1/4 W
L1 220 ?H (nominal) Ferrite inductor, 6+ A peak
L2 1000 ?H Ferrite choke, 100 mA
Case Aluminum project box
Clip leads Alligator type, insulated (RS)
Board material 0.1" spaced copper pads