Guide to Parallel Welding Machines & Underwater Cutting/Welding

Posted on Aug 30, 2024 in Technology

How to Put Two Welding Machines in Parallel

When using two welding machines in parallel, a parallel switch with a minimum capacity of 300 amperes is required. This necessitates the use of a double-pole safety switch. Adjusting two variable power machines for parallel operation involves two phases:

Phase 1: Current Adjustment

Each machine should be configured to deliver the same current when operating in parallel, with each machine providing half of the total current.

Phase 2: Voltage Adjustment

The open circuit voltage of both machines must be identical to prevent one machine from feeding into the other, which could result in polarity reversal.

Procedures for Paralleling Welding Machines

  1. Determine Polarity: Identify the polarity of leads 3-4 on each machine (Direct Polarity).
  2. Temporary Setup: Connect a voltmeter and a temporary switch (any small lever switch will suffice) across the terminals of each machine.
  3. Connect to Parallel Switch: Connect the terminals of each machine to a 300-ampere double-pole parallel switch. Use cables with a minimum size of 105,000 mil (1/0 50 mm2) for each machine.
  4. Connect Leads: Connect the electrode holder lead and the ground lead to the parallel switch. Isolate both conductors.
  5. Match Machines: Use machines with similar power ratings and set them to approximately the same current. The combined current from both machines should equal the desired welding current.
  6. Check Open Circuit Voltage: Disconnect the temporary switch and start both generators. Verify that the open circuit voltage is the same for both machines; adjust if necessary. Note: When using motor-driven welding equipment with clutches, ensure the clutches are disengaged during the paralleling process.
  7. Verify Zero Voltage: Close the temporary switch. The voltmeter should read zero if the generators are properly paralleled. If not, the machines are not set correctly in parallel.
  8. Remove Temporary Setup: Once the zero voltage reading is confirmed, remove the voltmeter and temporary switch.

Final Test

  1. Close Parallel Switch: Close the parallel switch and observe the following:
    • If the open circuit voltage remains unchanged after closing the switch, the machines are correctly paralleled. The ammeter should read approximately zero under no-load conditions.
    • If the ammeter reads above 25 amps without the electrode in use, the generators are not properly paralleled. Re-check the circuits and voltages.
  2. Test the Arc: With the electrode holder away from the workpiece, connect the ground lead. There should be minimal change in the arc whether using one or two machines.
  3. Welding/Cutting Operation: Proceed with welding or cutting, ensuring that the current from each machine does not exceed its rated output.

Determining Generator Polarity

If the polarity is not marked on the device, it can be determined as follows:

  1. Disconnect Power: Ensure the power supply is off.
  2. Connect Cables: Connect the ground cable and electrode holder cable to the machine terminals.
  3. Prepare Electrodes: Place one electrode against the machine body and the other against the clamp.
  4. Saltwater Test: Immerse the tips of both electrodes in a container of saltwater, ensuring the operator is insulated from the power source.
  5. Apply Current: With the electrodes approximately 5 cm apart, apply current. Bubbles will form on the negative electrode.
  6. Verify Polarity: If the bubbles rise from the electrode towards the electrode holder, the polarity is correct. If not, reverse the cables. Note: Underwater cutting and welding are typically performed with direct polarity (electrode connected to the negative terminal).

Ammeter

Ammeters measure the current flowing through a circuit. Clamp-on ammeters are particularly useful for underwater cutting and welding as they measure current without requiring direct connections. They help in setting the correct current for the job, preventing hull damage from excessive current or inefficient electrode usage due to insufficient current.

Electrical Cables for Underwater Cutting and Welding

Underwater cutting and welding require copper conductors insulated with rubber coating. Common sizes include 1/0 (50 mm2), 2/0 (70 mm2), and 3/0 (95 mm2) with lengths of 50, 100, 200, and 300 feet. The cable size selection depends on the specific task:

  • 1/0: Extra-flexible, recommended for connecting to the torch or electrode holder.
  • 2/0: Used for longer distances due to its low resistance. Recommended when the total cable length exceeds 300 feet (91 meters).
  • 3/0: Used for distances over 120 meters or when multiple parallel cables (1/0 or 2/0) are required to reduce resistance.

Cutting and Welding Electrodes for Underwater Use

Various electrode types are available for underwater cutting and welding:

  • Ceramic Tubular Electrodes: Primarily used for cutting and are being replaced by more modern options.
  • Steel Tubular Electrodes: Consist of a steel tube filled with flux and a hole for cutting oxygen.
  • Exothermic Electrodes: Used for cutting non-conductive materials by generating high temperatures.
  • Underwater Welding Electrodes: While initially the same as those used for surface welding but with waterproof coatings, specialized underwater welding electrodes are now available, offering improved performance.