How to solve problems with EMI caused by Welding Machines in Speed Controlles and Drives

High-frequency (HF) noise from Welding Machines is notorious for disrupting motor Drives (DC Drives & VFDs) and sensitive electronics like Computers, , CNC machines, PLC’s, etc. Since input power & output filters and shielded wire do not generally solved it, the noise is likely entering through the control signals wires, Armature & Field wires output side, or improper grounding.

Here are some suggestions to solve the problem:

1. Protect Control and Signal Lines Control signals like Forward/Reverse inputs. Those wires are highly susceptible to radiated noise. Twisted-Pair Shielded Cables.

2. Ensure all control and signal wires use twisted-pair shielded cables.

3. Single-Point Grounding: For low-frequency signals, ground the shield at only one end (usually the drive/panel end) to prevent ground loops.

4. Spatial Separation: Keep control wiring at least 8 to 12 inches away from power and motor cables. If they must cross, do so at a 90-degree angle.

5. Address the Output Side (Drive to Motor) the noise may be radiating from the cable between the drive and the motor.

6. Load Reactor + Ferrite Rings: Install ferrite rings or a load reactor at the output of the drive. This increases impedance for HF noise and filters out common-mode currents.

7. Both-End Grounding for HF: Unlike signal wires, motor cable shields should often be grounded at both ends to provide a continuous path for high-frequency common-mode noise.

8. Improve Grounding Infrastructure. A poor ground path forces noise to travel through your drive's electronics instead of to the earth.

 

9. Use Grounding Rods: The ground rod should be installed as close as possible to the machine ideally within 20 feet (6 meters) to minimize the wire's length.

 

10. Braided Ground Straps: Use flat, braided ground straps instead of round wires for grounding the drive and the welding machine. High-frequency noise travels on the surface of conductors (skin effect), and braids provide more surface area and lower impedance.

 

11. Dedicated Ground Rod: If possible, provide a separate, deep earth ground (Physical Grounding Rod) for the welder to isolate its HF return path from the rest of the shop's power system and use cable 4 AWG stranded copper wire for connecting the welder chassis or work table to a dedicated supplemental ground rod.

12. Distance: Increasing the distance between the Drive and other electronic equipment can also help reduce EMI. If possible, locate the Drive in a separate enclosure or room.

 

13. Power Input (AC or DC Supply) Install a large ferrite ring as close to the Drive's power terminals as possible.

 

14. The Technique: Pass all supply wires (L1, L2 & L3 or +/- DC Wires) through the center of the ring together.

 

15. The Secret: Loop the wires through a minimum of three times (turns). Each "turn" through the core increases the noise-blocking ability exponentially.

 

16. Motor Output Cables (Armature and Field) Since the welder is likely "back-feeding" noise through the motor frame, you must choke the output. Armature (A1, A2): Pass both armature wires through a single ferrite ring. Do not include the ground wire in the ring; the goal is to cancel common-mode noise traveling on the power lines.

 

17. Field (F1, F2): If your DC motor has a separate field supply, repeat the process with a smaller ferrite ring for these wires.

 

18. Control and Feedback Wires (Speed Pot, Forward/Reverse) these are the most sensitive. Even if they are shielded, HF noise can "jump" the shield. Placement: Place a small "snap-on" ferrite bead on the control wires right where they enter the Drive's terminal block.

19. Looping: If you have extra length, wrap the signal wires 3 times through the bead. This is often the fix for drives that "trip" for no apparent reason when the welder arcs.

20. Tightness: Ensure the wires are wound tightly against the core. Use cable ties to keep the ferrite from sliding down the wire.

21. Proximity: The ferrite must be within 2–4 inches of the drive. If it's too far away, the wire between the Drive and the ferrite acts like an antenna and picks the noise back up.

22. Material: For welding noise (which is usually lower frequency but very high energy), use Manganese-Zinc (MnZn) ferrites if available, as they handle lower-frequency spikes better than Nickel-Zinc.

The problem is the EMI generated by the Welder machine itself when is operating that is causing a lot of radiation, the HARMONICS WAVES are the ones who create that "NOISE" in the power lines and because of the high current & frequency they use for welding, and they flood the area with harmonic waves that penetrate any cable that is not adequately shielded to prevent such electromagnetic interference. Just like LIGHTING, when it is rains, they create a huge amount of radiation which affects everything around it, you can even hear it in the AM and FM radios receivers.