DIY-Welder - Build your own Arc, MIG and TIG welder

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Description

This is similar to the "Weldernator" designs with some improvements for reliability.

The alternator has any regulator removed and the field brush connection brought out externally. The '-' terminal may be left connected to the case if it already is.

A series of resistors sets the field current. Depending on the speed and alternator, the values may need to be adjusted. If you can find a 10-Ohm rheostat that is at least 20 watt, that will work. You would want to add series resistor for the maximum settin.

All resistors should be 5 watt or higher.The single 1 ohm settng (top right resistor) may need to be 10 watt.

The MOV will suppress the spike when the arc is broken. Without it, the voltage will spike up until the diodes break down. This will reduce the life of them. It should be about 100V. An example can be found on Digikey, search for part # ERZ-V07D101.

The Motor run capacitor also helps reduce surges. These are common on motors and are usually 4.7UF at 300VAC. An electrolytic could be used, but the large voltage changes will reduce the life. The big metal-can motor run caps are much more durable.

The field wires should be #16 gauge wire. The output should be #4 or larger.

+12V is from the starter battery on the engine. It should have a 5 amp fuse.

Operation

The rotary switch selects the current. Another position can be used with no connection to turn the alternator off. Note: when the engine is not running, it should be turned off or it will drain the battery and add wasted heat to the field. A separate switch can be added to the +12V for power on/off.

Switch to one of the lower resistance settings (rightmost position.) Run the engine and measure the output voltage. You would want a no-load voltage of 50 to 70 volts. You may need to adjust the pulley ratio. You don't want more than about 70V or you may damage the alternator diodes.

Try the welder and choose the best switch position. you can fine tune the output by adjusting the throttle.

Improvements

If more output is needed, you can parallel two alternators. Just connect the fields and outputs together. You might try a lower resistance value.

For more arc stability, a reactor can be added in series with the welder lead. 20 to 30 windings of heavy wire around an iron pipe can make a considerable difference.