Solar-powered battery charger circuit

1. An interface circuit for charging a rechargeable battery from a power source, comprising:

first and second input terminals adapted to be coupled to said power source;

third and fourth output terminals adapted to be coupled to said rechargeable battery;

a normally-closed relay having normally-closed switch contacts and a coil having a first end and a second end, wherein said normally-closed switch contacts and said coil are connected in series between said first and second input terminals; and

an EMF conduction diode coupled between said fourth output terminal and a junction between said normally-closed switch contacts and said first end of said coil;

wherein said second end of said coil is coupled to said third output terminal, wherein current supplied from said power source through said normally-closed switch contacts energizes said coil to generate an electromagnetic field that causes said normally-closed switch contacts to open and thus remove said supplied current from said coil so that said normally-closed switch contacts continue to oscillate between an open condition and a closed condition, and wherein energy transferred from said power source to said electromagnetic field of said coil when said normally-closed switch contacts are in said closed condition is transferred by discharging said electromagnetic field in response to current through said EMF conduction diode when said normally-closed switch contacts are in said open condition.

2. The interface circuit of claim 1 further comprising:

a charge storage device coupled between said third and fourth output terminals.

3. The interface circuit of claim 2 wherein said charge storage device is comprised of a capacitor.

4. The interface circuit of claim 1 further comprising:

a voltage limiting device coupled between said third and fourth output terminals.

5. The interface circuit of claim 4 wherein said voltage limiting device is comprised of a zener diode.

6. The interface circuit of claim 1 further comprising:

a high battery voltage protection diode coupled to said third output terminal.

7. The interface circuit of claim 6 further comprising:

a fuse in series with said high battery voltage protection diode.

8. The interface circuit of claim 1 further comprising:

a step-down resistor coupled between said first input terminal and said normally-closed relay.

9. A method of recharging a rechargeable battery from a power source, said method comprising the steps of:

connected said power source across a series combination of the normally-closed contacts of a normally-closed relay with a coil of said normally-closed relay so that said normally-closed contacts oscillate between a closed condition and an open condition, wherein said coil stores energy from said power source in an electromagnetic field when said normally-closed contacts are in said closed condition; and

when said normally-closed contacts switch to said open condition, transferring said energy from said coil as said electromagnetic field discharges to said rechargeable battery via a unidirectional conducting device.

10. The method of claim 9 further comprising the step of:

storing said energy transferred from said coil as said electromagnetic field discharges in a charge storage device coupled across said rechargeable battery.

11. The method of claim 9 further comprising the step of:

clamping a voltage across said coil during discharge of said electromagnetic field to a predetermined voltage.

12. The method of claim 9 further comprising the step of:

stepping down a voltage from said power source provided to said normally-closed relay by providing a step-down resistor therebetween.

13. The method of claim 9 wherein said unidirectional conducting device comprises a diode.

14. The method of claim 9 wherein said power source is comprised of a solar panel.

15. The method of claim 9 wherein said rechargeable battery is comprised of a battery bank.