Capacitor charge and discharge circuit for fastener welding

1. A capacitor discharge (CD) fastener welding circuit comprising:

an input voltage source;

a rectifier bridge of diodes receiving the input voltage source;

at least two capacitor charge switches linked with the rectifier bridge;

at least one capacitor linked with the at least two capacitor charge switches;

at least two capacitor discharge switches linked with the capacitor and to welding output terminals; and

a voltage sensor detecting a voltage at the at least two capacitor charge switches, a voltage sensor detecting a voltage at the at least one capacitor and a voltage sensor at the welding output terminals detecting a voltage supplied to the terminals.

2. The capacitor discharge fastener welding circuit of claim 1 including a current sensor at the at least one capacitor sensing a current provided to the capacitor.

3. The capacitor discharge fastener welding circuit of claim 1 including a control system linked with the capacitor discharge fastener welding circuit for monitoring voltage and current sensors and actuating the at least two capacitor charge and discharge switches.

4. The capacitor discharge fastener welding circuit of claim 1 , wherein the at least two capacitor charge switches comprise relay contacts.

5. The capacitor discharge fastener welding circuit of claim 1 , wherein the at least two capacitor charge switches comprise solid state switches.

6. The capacitor discharge fastener welding circuit of claim 5 , wherein the solid state switches comprise IGBTs.

7. The capacitor discharge fastener welding circuit of claim 1 including a switch-mode DC-DC converter between the at least one capacitor and the rectifier bridge.

8. The capacitor discharge fastener welding circuit of claim 7 , wherein the DC-DC converter is selected from: a buck boost converter, a SEPIC converter and a Cuk converter.

9. The capacitor discharge fastener welding circuit of claim 1 , wherein the at least one capacitor comprises a plurality of capacitors.

10. The capacitor discharge fastener welding circuit of claim 1 including a resistor connected to one charge switch on a DC side of the rectifier bridge.

11. The capacitor discharge fastener welding circuit of claim 1 including a current controlling device for controlling a capacitor charge current, the current controlling device selected from: resistors, switches or buck boost convertors.

12. The capacitor discharge fastener welding circuit of claim 1 , wherein the at least two capacitor charge switches are positioned before the rectifier bridge of diodes.

13. The capacitor discharge fastener welding circuit of claim 1 , wherein the at least two capacitor charge switches are positioned after the rectifier bridge of diodes.

14. A process for capacitor discharge fastener welding including the steps of:

a) providing an input voltage source, a rectifier bridge receiving the input voltage source, at least two capacitor charge switches linked with the rectifier bridge, at least one capacitor linked with the at least two capacitor charge switches, at least two capacitor discharge switches linked with the capacitor and to welding output terminals;

b) charging the at least one capacitor including closing the at least two capacitor charge switches when the at least two capacitor discharge switches are open;

c) opening the at least two capacitor charge switches disconnecting the capacitor from the input voltage source;

d) closing the at least two capacitor discharge switches allowing current from the capacitor to discharge through the output terminals;

e) opening the at least two capacitor discharge switches cutting off a current path to the output terminals.

15. The process for capacitor discharge fastener welding of claim 14 including the step of providing a voltage sensor detecting a voltage at the at least two capacitor charge switches, a voltage sensor detecting a voltage at the at least one capacitor and a voltage sensor at the welding output terminals detecting a voltage supplied to the terminals.

16. The process for capacitor discharge fastener welding of claim 15 including the step of monitoring the voltage sensor at the at least two capacitor charge switches and the voltage sensor at the at least one capacitor and the voltage sensor at the welding output terminals in any of steps b)-e) alone or in combination for a value that is not equal to an expected value.

17. The process for capacitor discharge fastener welding of claim 16 including the step of aborting steps b)-e) wherein at least one action selected from: opening the at least two capacitor charge switches and at least two capacitor discharge switches, dumping the charge in the capacitor through a capacitor discharge circuit, disabling a welder and sending an error message is performed.

18. The process for capacitor discharge fastener welding of claim 14 including the step of providing a current sensor at the at least one capacitor sensing a current provided to the capacitor.

19. The process for capacitor discharge fastener welding of claim 18 including the step of monitoring the current sensor at the at least one capacitor in any of steps b)-e) for a value that is not equal to an expected value.

20. The process for capacitor discharge fastener welding of claim 19 including the step of controlling the at least two capacitor charge switches using pulse width modulation.

21. The process for capacitor discharge fastener welding of claim 14 including the step of providing a DC-DC converter between the at least one capacitor and the rectifier bridge adjusting a capacitor voltage to a desired value.

22. The process for capacitor discharge fastener welding of claim 14 , wherein the welding process utilizes contact CD mode.

23. The process for capacitor discharge fastener welding of claim 14 , wherein the process utilizes gap CD mode.

24. A capacitor discharge (CD) fastener welding circuit comprising:

an input voltage source;

a rectifier bridge of diodes receiving the input voltage source;

at least two capacitor charge switches linked with the rectifier bridge;

at least one capacitor linked with the at least two capacitor charge switches;

at least two capacitor discharge switches linked with the capacitor and to welding output terminals; and

a current sensor at the at least one capacitor sensing a current provided to the capacitor.